Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Forest floor seed banks and their response to slashburning in some forest ecosystems in south central… Yearsley, Karen H. 1993

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata


831-ubc_1993_spring_yearsley_karen.pdf [ 5.45MB ]
JSON: 831-1.0075178.json
JSON-LD: 831-1.0075178-ld.json
RDF/XML (Pretty): 831-1.0075178-rdf.xml
RDF/JSON: 831-1.0075178-rdf.json
Turtle: 831-1.0075178-turtle.txt
N-Triples: 831-1.0075178-rdf-ntriples.txt
Original Record: 831-1.0075178-source.json
Full Text

Full Text

FOREST FLOOR SEED BANKS AND THEIR RESPONSE TO SLASHBURNINGIN SOME FOREST ECOSYSTEMS IN SOUTH CENTRAL BRITISH COLUMBIAByH. KAREN YEARSLEYB.Sc., The University of British Columbia, 1983THESIS SUBMITTED IN PARTIAL FULFILLMENT OFTHE REQUIREMENTS FOR THE DEGREE OFMASTER OF SCIENCEinTHE FACULTY OF GRADUATE STUDIES(Department of Forestry)We accept this thesis as conformingto the required standardThe University of British ColumbiaApril 1993© H. Karen Yearsley, 1993In presenting this thesis in partial fulfilment of the requirements for an advanceddegree at the University of British Columbia, I agree that the Library shall make itfreely available for reference and study. I further agree that permission for extensivecopying of this thesis for scholarly purposes may be granted by the head of mydepartment or by his or her representatives. It is understood that copying orpublication of this thesis for financial gain shall not be allowed without my writtenpermission.Department of  rbief.-5 7-,,e,vThe University of British ColumbiaVancouver, CanadaDate  A Re /L 277 / /.9)3(Signature) DE-6 (2/88)iiABSTRACTSoil seed banks are part of the flora of many ecosystems,but little is known about those of temperate coniferous forestsin B.C., or their response to different disturbances. As aresult, a study of forest floor seed banks and their response tothe common disturbances of clearcutting and slashburning, wasconducted in the Engelmann Spruce - Subalpine Fir (ESSF) andInterior Cedar - Hemlock (ICH) biogeoclimatic zones of southcentral B.C. Studies were carried out on the Devil's Club - Ladyfern sites series in the ESSFwc2 variant and on the Oak fern siteseries in the ICHwkl variant in the Clearwater Forest District.The species composition, numbers and distribution of seedswere determined through greenhouse germination of forest floorsamples split into 1 cm layers. Germinant density was 2591/m2 and689/m2 in the ESSF and ICH samples, respectively. Most germinants(82 and 92% in the ESSF and ICH, respectively) belonged to thefive most abundant taxa from each site and most (78 and 97% inthe ESSF and ICH, respectively) were present in the top 3 cm ofthe forest floor. Seeds were poorly dispersed among the samplesand highly clustered in the samples in which they occurred.Germinants of most taxa decreased with depth, but otherdistributions were found. Vertical distribution patterns variedwidely among samples.Germination from the seed bank in both unburned and burnedareas on the study sites showed that 1) germinant density wasmuch lower in the field than in the greenhouse samples, and 2)burned areas had many fewer germinants than did unburned areas onthe ESSF site, but the reverse was found on the ICH site.iiiSoil temperatures were measured during and afterslashburning on the study sites. Forest floor depth of burn wasalso measured, and no relationship could be demonstrated betweendepth of burn and soil temperatures during burning. Therefore,the effect of elevated temperatures on buried seeds could not bedetermined.Shading reduced post-burn soil temperatures on both sites,but the influence of these temperatures on germination was notclear due to inconsistent results and lack of replication.Burning significantly reduced germination, whereas shadingresulted in significantly more germinants in burned, but notunburned, areas of the ESSF site. The effect of shading andburning on germination on the ICH site could not be determineddue to a lack of germinants.ivTABLE OF CONTENTSAbstract^ iiTable of Contents^ ivList of Tables viList of Figures ixAcknowlegements^ xiChapter 1 GENERAL INTRODUCTION^ 1Chapter 2 THE SEED BANK^ 42.1 Introduction 42.2 Methods^ 62.2.1 Study design and layout^ 62.2.2 Greenhouse germination Data collection Data analysis^ 132.2.3 Field germination Data collection Data analysis^ 172.2.4 Existing vegetation Data collection Data analysis^ 182.3 Results and discussion 182.3.1 Greenhouse germination Numbers and species^ Horizontal distribution of germinants ^ Vertical distribution.of germinants^ 322.3.2 Field germination compared to greenhousegermination^ 442.3.2.1 Numbers, species and distribution^ 442.3.2.2 Field and greenhouse germinationcompared to field vegetation^ 532.3.2.3 Temperatures during germinationmonitoring in the greenhouse and field studysites^ 572.4 Conclusions 61Chapter3.13.23.33VTHE EFFECTS OF FIRE ON THE SEED BANK^Introduction^Methods3.2.1^Study areas^3.2.2^Field germination^^Data collection3.2.2.2^Data analysis3.2.3^Effects of fire^^Data collection^^Data analysis3.2.4^Post-burn soil temperatures and shading in theintensive study areas^^Data collection3.2.4.2^Data analysisResults and discussion^65656767696970707073767676783.3.1 Field germination after burning^ 783.3.1.1 Germination on the burned intensive sitesin comparison to the unburned seed bank andvegetation^ 783.3.1.2 Germination in the extensive andintensive study areas^ 883.3.2 Effects of temperature during the fire, anddepth of burn, on seed mortality and germinationin the field^ 933.3.3 Effects of burning and shade on post-burn soiltemperature and germination^ 1053.3.3.1 Temperature^ 1053.3.3.2 Germination 1163.4 Conclusions^ 123Chapter 4 CONCLUSIONS AND RECOMMENDATIONS^ 1264.1 Conclusions^ 1264.1.1 The seed bank^ 1264.1.2 The effects of fire on the seed bank^ 1284.2 Recommendations 130Literature Cited^ 132viLIST OF TABLES2.1 The number of germinants by depth class and taxon, and totaldensity of germinants + the standard error of the mean bytaxon, in the ESSF greenhouse samples. The proportions ofgerminants and layers per depth class are also given^ 212.2 The number of germinants by depth class and taxon, and totaldensity of germinants + the standard error of the mean bytaxon, in the ICH greenhouse samples. The proportions ofgerminants and layers per depth class are also given^ 222.3 Horizontal distribution of the five most abundant germinanttaxa from ESSF greenhouse samples^ 282.4 Horizontal distribution of the five most abundant germinanttaxa from ICH greenhouse samples^ 292.5 Proportion of total greenhouse samples and samples that hadgerminants of each thickness, from the ESSF and ICHsites^ 332.6 Number and total density (number/m 2 ) of germinants in theunburned ESSF field subplots and 0-1 cm depth class of thegreenhouse samples^ 462.7 Number and total density (number/m 2 ) of germinants in theunburned ICH field plots and 0-1 cm depth class of thegreenhouse samples^ 482.8 Horizontal distribution of the three most abundant germinanttaxa from ESSF field subplots^ 502.9 Percent presence of the ESSF taxa in field vegetation, andin greenhouse and field germinants^ 542.10 Percent presence of the ICH taxa in field vegetation, and ingreenhouse and field germinants^ 563.1 Identification of the extensive field study sites accordingto the Biogeoclimatic Ecosystem Classification system^ 683.2 Number and density (number/m2 ) of germinants in the burnedand unburned field plots and subplots and in the greenhousesamples from the ESSF intensive site^ 79vii3.3 Number and density (number/m 2 ) of germinants in the burnedand unburned field plots and subplots and in the greenhousesamples from the ICH intensive site^ 823.4 Density of germinants (number/m 2 ) in the extensive plots andintensive burned plots and subplots of the ESSFwc2 studysites^ 893.5 Table 3.5 Density of germinants (number/m 2 ) in the plots ofthe ICHmw3 and ICHwkl extensive study sites and in theburned plots and subplots of the intensive ICHwkl studysite^ 913.6 Spearman rank correlation coefficients (rs) for the numberof surviving germinants versus depth of burn in the plots ofthe ESSF intensive site, for the most abundant taxa andtotal germinants^ 973.7 Spearman rank correlation coefficients (rs) for the numberof germinants versus depth of burn in the plots of the ICHintensive site, for the most abundant taxa and totalgerminants^ 993.8 Correlation coefficients (r) for the number of minutestemperatures exceeded 60, 70, 80 and 100 °C during the 1990ESSF burn, versus mean depth of burn^ 1003.9 Correlation coefficients (r) for maximum temperatures ( °C)reached during the 1990 ESSF burn versus mean depth of burn,by location and depth^ 1013.10 Correlation coefficients (r) for the number of minutestemperatures exceeded 60, 70 and 100 °C during the 1989 ICHburn, versus mean depth of burn^ 1033.11 Maximum, mean and minimum temperatures ( °C) recorded fromJune 19 to August 26, 1990, in the four shade and burntreatments on the ESSF intensive site^ 1143.12 Maximum, mean and minimum temperatures ( °C) recorded fromJune 18, to August 25, 1990, recorded in the four shade andburn treatments on the ICH intensive site^ 1153.13 Frequency of subplots, and observed and expected frequenciesof germinants in the burned versus unburned subplots of theESSF intensive study site. Results of the 'goodness of fit'analysis are presented 117viii3.14 Frequency of subplots, and observed and expected frequenciesof germinants in shaded versus unshaded subplots withinburned and unburned areas of the intensive ESSF field studysite. Results of the 'goodness of fit' analysis arepresented^ 119Table 3.15 Density (number/m2 ) of germinants in the four shadeand burn treatments of the intensive ESSF and ICH fieldstudy sites^ 120Table 3.16 Frequency of subplots and germinants in the fourshade and burn treatments of the ICH intensive studysite^ 121ixLIST OF FIGURES2.1 Location of the intensive and extensive study sites^ 72.2 Schematic layout of plot, subplot and greenhouse samplelocations in the ESSF and ICH field sites^ 92.3 Example of the relationship between samples and layers, andbetween sample thickness, layer thickness and depth classesfor the greenhouse samples 112.4 Forest floor germinant density as a function of depth forthe 5 most abundant taxa in the ESSF greenhouse samples...352.5 Forest floor and total density of all ESSF greenhousegerminants as a function of depth^ 362.6 Total germinant density as a function of depth for the 5most abundant taxa in the ESSF greenhouse samples^ 372.7 Forest floor density as a function of depth for germinantsof the 5 most abundant taxa in the ICH greenhousesamples^ 392.8 Forest floor and total density of all ICH greenhousegerminants as a function of depth^ 402.9 Total germinant density as a function of depth for the 5most abundant taxa in the ICH greenhouse samples^ 412.10 Daily maximum and minimum air temperatures ( °C) recordedduring the germination monitoring periods on the ESSF andICH field sites, and in the greenhouse^ 592.11 Typical pattern of hourly mean air temperatures ( 00) over a4 day period in the greenhouse (Jan. 25-28, 1990) and at theICH field study site (July 7-10, 1990) ^  603.1 Placement of depth of burn pins over the subplots andmeasurement of forest floor consumption on the intensivestudy sites^ 723.2 Placement of depth of burn pins over the thermocouples onthe ESSF site burned in 1990^ 74x3.3 Number of subplots in 0.5 cm depth of burn classes from theESSF and ICH intensive sites^ 943.4 Typical pattern of hourly mean temperatures (°C) over fourdays (July 7-10, 1990) at 1 cm depth in the forest floor ofthe four shade and burn treatments on the ESSF intensivestudy site^ 1063.5 Typical pattern of hourly mean temperatures ( 0C) over fourdays (July 10 - 13, 1990) at 1 cm depth in the forest floorof the four shade and burn treatments on the ICH intensivestudy site 1073.6 Daily mean range (maximum - minimum) of temperatures ( °C) at1 cm depth in the forest floor of the four shade and burntreatments on the ESSF intensive site during the 1990growing season^ 1093.7 Daily mean range (maximum - minimum) of temperatures ( °C) at1 cm depth in the forest floor of the four shade and burntreatments on the ICH intensive site during the 1990 growingseason^ 1103.8 Daily mean temperatures ( °C) recorded at 1 cm depth in theforest floor of the four shade and burn treatments on theESSF intensive site during the 1990 growing season^ 1113.9 Daily mean temperatures ( °C) recorded at 1 cm depth in theforest floor of the four shade and burn treatments on theICH intensive site during the 1990 growing season^ 112x iACKNOWLEDGEMENTSI thank my advisor, Dr. M.C. Feller, and the members of mycommittee, E. Hamilton, Dr. K. Klinka and Dr. R. Turkington fortheir help and advice. I am particularly grateful to Dr. Fellerand E. Hamilton for their patience and support during thisresearch. Dr. J. Pojar also provided useful suggestions in theearly stages of the project. Dr. V. Lemay advised me onstatistics.D. Meehan and G. Bryan of Weyerhauser, Canada, provided mapsand carried out the operational slashburning on the researchsites. The successful retention of unburned control areas wouldnot have been possible without their efforts and cooperation. D.Anderson, P. Olanski, J. Olinek and P. Wycherley of theUniversity of B.C., helped collect and transport the forest floorsamples. G. Reynolds wrote the programmes for the dataloggers.B. Lanterman, of the Agriculture Canada Research Station inSaanich very kindly allowed me the use of greenhouse facilities.Staff at the station maintained the temperature environment inthe greenhouse and provided me with data on temperature andhumidity in the greenhouse. A. Ceska of the Royal B.C. Museumidentified the grass and sedge specimens.Funding for this project was provided through the Universityof B.C. and by the Clearwater Forest District.1CHAPTER 1 GENERAL INTRODUCTIONA soil seed bank consists of all viable seeds (dormant butcapable of germination) found within the soil profile includingthe surface organic horizons ('forest floor'). Soil seed bankshave been found in nearly all plant communities that have beenstudied. Buried seeds occur in arctic, tropical, grassland,desert and wetland ecosystems, and in cultivated land and soilundisturbed for hundreds of years. As such, seeds are animportant part of the species composition of plant communities,but one that is often overlooked when inventories of diversityare made. This oversight may be partly because some species arepresent only as buried seeds at certain stages of a plantcommunity's development. Therefore, geographical distribution ofspecies should also include seed banks to be complete.Germination of seeds from seed banks is an important sourceof new plants in many of these communities. In order forgermination to take place, however, some alteration in the seedenvironment is usually required. Disturbance can changetemperature, moisture, light or chemical conditions in the soilsuch that seeds overcome dormancy and germinate.Depending on the size and severity, disturbance can alsoinitiate secondary succession in plant communities. Thus,germination of buried seeds can be an important means ofrevegetation after disturbance. Understanding plant successionmust, therefore, include the study of seed banks and theirresponse to disturbance.Buried seeds are also present in forest soils including2those of northern temperate and boreal forests. As pressures onforest land increase, there is a need to learn about thebiodiversity (genetic, species, structural and temporal) of old-growth forests. Management activities for whatever purpose(forestry, wildlife, parks, mining) cause disturbances inforests. Information on the impact of such disturbances onsuccession and natural diversity is required in order to minimizedamage to forest ecosystems and to aid in reconstruction ofdamaged areas. Seed banks may be as important for conservinggenetic and species diversity over time as other sources of newplants. Maintaining biodiversity therefore includes anunderstanding of how to maintain seed banks.As one of the most important economic activities in B.C.,logging, and subsequent site preparation and stand tending, isprobably the single largest source of disturbance in B.C.'sforests. While vegetative regeneration and germination from off-site seeds (e.g. fireweed) are both commonly observed afterclearcutting, little is known about the composition of, orgermination from, seed banks of forest soils in British Columbiaor Canada. Neither the long-term contribution of seed banks toforest vegetation over time, nor the means by which seed banksare maintained, are well known for this province.In managed forests with a dense closed canopy, many of thenon-crop plant species that contributed to the natural diversityof the original forest, may die out over the rotation, leavingseed banks as possibly the only source of propagules on the site.Even in second growth stands that are spaced and thinned, theremay be few plants left to reproduce either vegetatively or by3seeds. However, without a knowledge of species-specific seedlongevity, the type and severity of disturbance required tostimulate germination or the means by which seed banks aremaintained in forests, it cannot be assumed that seed banks willsupply the wildlife forage, and species and structural diversitypresently lacking in some managed forest plantations.In south central B.C. forests have high economic andbiodiversity values for timber harvesting, recreationalactivities and wildlife habitat. Timber harvesting typicallyinvolves clearcutting followed by slashburning. In view of theimportance of these values and the lack of knowledge about seedbanks and their response to disturbances such as logging and sitepreparation, the present study was established with the objectiveof quantifying forest soil seed banks and their response toclearcutting and slashburning in important forest zones in thisarea. This information should also provide a basis for furtherstudies that specifically address long-term succession and thecharacterization and maintenance of biological diversity.4CHAPTER 2 THE SEED BANK2.1 IntroductionStudies of temperate forest soils in other areas of NorthAmerica and Europe have found varying numbers of seeds.Germination of seeds stored in the soil is an important mode ofrevegetation for some of these forest communities (Marks 1974;Bormann and Likens 1979; Heinselman 1981). Only two studiesconducted in B.C. have been published (Kellman 1970, 1974) andthese concern coastal forests. Another study of disturbed coastalforest soils was carried out as part of a PhD thesis (McGee1988). In the interior of the province, studies have been done inthe Sub-Boreal Spruce Zone (Hamilton & Yearsley unpublisheddata). When the present study was initiated, there was noinformation on seed banks in the Engelmann Spruce Subalpine Fir(ESSF) and Interior Cedar Hemlock (ICH) biogeoclimatic zones(Pojar et al. 1987) where timber harvesting is important.Before the role of seed banks in revegetation after eithernatural or human-caused disturbances can be determined, baselinedata on species composition, abundance and distribution of viableseeds in the soil is needed. Species composition of the seed bankmay provide information about vegetation history, and a basis forpredicting post-disturbance plant communities and distribution.Seed abundance might be related to species importance in the somepost-disturbance communities, and to species-specificproductivity. We know little or nothing about the relationshipbetween plant and seed distribution. The horizontal distributionof seeds may provide information about dispersal and seed burial5patterns and possibly the distribution of the source plants.Vertical seed distribution is important to predict the responseof seeds to depth-dependant disturbances such as fire.Few studies have attempted to determine the distribution ofseeds. In many studies variability among samples, which is abroad indication of horizontal distribution, has beendeliberately eliminated by mixing samples together and thenassessing subsamples. Where vertical distribution of seeds hasbeen reported, samples have been split into very few layersand/or layers that were too thick to allow for detailedresolution of vertical patterns.Most seed bank studies have either counted and identifiedgerminants that emerged from soil samples in a greenhouse, orextracted, identified and tested the viability of seeds from soilsamples (Roberts 1981). While both methods are useful, neitherprovide information about what species actually germinate fromsoil in the field. This is perhaps as significant to revegetationas determining the exact species composition and abundance ofburied seeds. None of the coniferous forest studies hasadequately examined germination in the field, attempted tomeasure field conditions that might influence germination fromseed banks or compared field with greenhouse germinationconditions.The specific objectives of this part of the study were toquantify the species composition, abundance and distribution ofseeds in some forest floors in the ICH and ESSF zones in southcentral British Columbia. Two approaches were taken to collectinginformation to describe the seed banks of the areas studied.6First, forest floor samples were collected from the site, splitinto layers and monitored for germinants in a greenhouse. Thesecond approach was to monitor germination on the same site inthe field. The greenhouse germination yielded information onvertical and horizontal seed distribution, while the fieldgermination provided a comparison with the artificial greenhouseenvironment, and between unburned and burned forest floor (seeChapter 3).2.2 Methods 2.2.1 Study design and layoutIntensive studies were carried out on two cutblocks locatedin the Clearwater Forest District (Figure 2.1), that were loggedduring the winter of 1988/1989 and operationally slashburned inthe fall of 1989. Unburned control areas were retained in bothstudy blocks. The sites were selected for minimum forest floordisturbance and a relatively uniform topography.One site was located in the Northern Monashee Wet Coldvariant of the Engelmann Spruce-Subalpine Fir biogeoclimatic zone(ESSFwc2). This site was identified as the Devil's club - Ladyfern site series (07) (Lloyd et al. 1990), with a well-developedunderstory of herbs such as Valeriana sitchensis, Athyrium filix-femina, Gymnocarpium dryopteris and Tiarella unifoliata, shrubsdominated by Rhododendron albiflorum, Menziesia ferruginea,Vaccinium membranaceum and V. ovalifolium, and a sparse mosslayer. Characteristics of the site also included a moderate slopegradient, southeast aspect, with a moist (subhygric) soilmoisture regime and a rich (permesotrophic) soil nutrient regime.7Figure 2.1 Location of the intensive and extensive study sites.Numbers beside symbols correspond to site numbers.8The site was located at km 30 on the Otter Ck. Forest ServiceRoad approximately 50 km north of Clearwater.The other site was in the Wells Gray Wet Cool variant of theInterior Cedar-Hemlock biogeoclimatic zone (ICHwkl) (Pojar et al.1987). This site was identified as the zonal Oak fern site series(01) (Pojar et al. 1987; Lloyd et al. 1990), and had a sparseunderstory of herbs, including Gymnocarpium dryopteris, Tiarellaunifoliata, Clintonia uniflora and Cornus canadensis, shrubs suchas Vaccinium membranaceum and V. ovalifolium, and a 1 - 2 cmthick layer of mosses. Characteristics of the site also includeda gentle slope, southwest aspect, and intermediate soil moisture(mesic) and nutrient (mesotrophic) regimes. The site waslocatedat km 7.5 on the South Foam Ck. Forest Service Road about 80 kmnorth of Clearwater. The humus forms found on both the ESSF andICH sites were hemimors and hemihumimors (Klinka et al. 1981,Lloyd et al. 1990).On each intensive site, 12 - 3 X 3 m plots were established.Nine plots were located in an area to be burned while the otherthree plots were located in an unburned control area. In eachplot, 25 - 10 X 10 cm subplots were established at grid pointsspaced 0.5 m apart each way (Figure 2.2). Subplots were offsetonly where there were stumps or large logs resting on the groundat the grid points. Forest floor samples were collected in theundisturbed forest floor close to the plots, using the same gridpattern as the subplots (Figure 2.2).Figure 2.2 Schematic layout of plot, subplot and greenhousesample locations in the ESSF and ICH field sites. (Not all plotsare shown.)1 02.2.2 Greenhouse germination2.2.2.1 Data collection Three-hundred and four - 10 X 10 cm forest floor (LFH)samples were collected from each intensive site before burning.Other studies of temperate coniferous forest seed banks havegenerally shown very few seeds in mineral soil (Moore and Wein1977; Graber and Thompson 1978; Granstrom 1982) so only theorganic layers were sampled. Samples were collected in July,1989.During the collection period, samples were kept outsidecovered with remay cloth to exclude seed rain. Once all samplesfrom a site had been collected, they were transported to theUniversity of B.C. and stored in a refrigerated room atapproximately 4°C. When stacking was necessary during transportand storage, layers of remay were placed between samples toprevent contamination, and inverted greenhouse trays were used asspacers to prevent compression of samples.In October 1989, the samples were removed from therefrigerated room and taken to the Saanich Peninsula where theywere covered and stored outside for about two weeks, then movedinto an unheated, plastic-covered greenhouse.Many of the ICH samples had a thick moss layer which wastrimmed off and discarded. Although seeds may have been lostalong with this moss, none were observed and any that were thereprobably originated from recent seed rain. The moss on the ESSFsamples was thin or absent and was therefore left intact. Eachsample was split parallel to the soil surface into 1 cm layers(Figure 2.3). Layers were placed in individual square containers,1 1Figure 2.3 Example of the relationship between samples andlayers, and between sample thickness, layer thickness and depthclasses for the greenhouse samples.12in standard greenhouse trays (eight per tray). Containers werelined with remay to prevent loss of soil through the drainageholes, Sample splitting was completed on November 21, 1989. A fewsamples from each site crumbled during splitting and weretherefore discarded. The total number of samples that were splitfor each site was 297 for the ESSF site and 301 for the ICH site.From December 6 to 13, 1989 the greenhouse was heated with akerosene heater but no temperatures were recorded. On December15, 1989, samples were moved into a heated glass greenhouse atthe Agriculture Canada Research Station on Saanich Peninsula, andthoroughly watered. Temperatures were maintained at 22 °C for 16hours per day and 15°C at night.A few seeds germinated while the samples were still in theplastic-covered greenhouse. These were recorded on December 9,1989. Data collection in the glass greenhouse started on December20, 1989, and was carried out once per week until April 3, 1990,except for weeks 1, 3 and 4 when data were collected twice.Samples were allowed to dry out from April 4 to 10, then turnedover and resoaked. Sampling resumed on April 17 and continueduntil April 24, 1990. The ESSF samples were moved outside ontobenches, covered with remay to exclude seed rain and monitoredfrom April 25 to May 29, 1990. Monitoring of the ICH samplesended on April 24 because very few seeds germinated after April10.Individual germinants were marked with coloured threadloops. A different colour was used each sampling date and loopswere removed when germinants died. Thus, it was possible todetermine which germinants were new each week, and to keep track13of them until they died, were identified, or were transplantedwhen further growth was necessary for identification.Germinants were allowed to grow in the soil from which theyoriginated until they were identifiable, and then were removed.Reference specimens for species that were not identified by April3 were transplanted before the samples were allowed to dry out.The reference specimens were grown for several weeks but diedbefore reaching maturity. Mature plants of some species werecollected in 1990 from the study sites and identified, toindicate potential identities for some germinants. Data analysis Horizontal distribution of germinants among samples wasexamined by two methods. First, dispersion of germinants amongsamples was calculated as the percent presence of germinants ofeach taxon in the maximum number of samples the taxon couldtheoretically occupy. For taxa that had more germinants thanthere were samples (i.e. > 297 for the ESSF or 301 for the ICHsites, respectively), the assumption was made that the maximumnumber of samples that could be occupied was equal to the totalnumber of samples. At maximum dispersion, these taxa would have >one germinant per sample. For taxa that had fewer germinants thanthere were samples, the maximum number of samples that could beoccupied was defined as being equal to the number of germinants.At maximum dispersion, these taxa would have one germinant persample. These calculations are therefore not influenced by therelative abundance of germinants in each taxon and thus allow14comparisons between taxa. The formula used for calculatingdispersion was:number of samples occupied by a taxon X 100 maximum number of samples the taxon could occupyThe lower this number was, the less dispersed (or moreconcentrated) the germinants were within the sampled area.Second, the coefficient of variation of mean germinants peroccupied sample was used as a measure of how evenly seeds weredistributed among the samples in which they occurred. Forexample, two species could occupy the same number of samples buthave very different distributions of seeds within those samples.The most uneven distribution would be a species with most of it'sseeds in one sample and only one seed in each of the remainingsamples. The other extreme would be a species with the samenumber of seeds in each sample occupied. The coefficient ofvariation allowed comparison among the taxa, which had differentnumbers of germinants occurring in different numbers of samples.The taxon with the highest coefficient of variation had the mostuneven distribution.The ranges of depths in the samples from which layersoriginated are referred to as depth classes. For example, all thelayers that came from 2-3 cm in the samples belong to the 2-3 cmdepth class, and so on. Samples varied considerably in thicknessbecause only forest floor was collected, so the number of layersper depth class decreased with increasing depth. Therefore, twodensities in germinants/m 2 were calculated for differentpurposes. These are referred to as total density and forest floordensity.Total density is the number of germinants in each depth15class divided by the total surface area sampled (2.97 m 2 for theESSF site and 3.01 m 2 for the ICH site). This was used to examinevertical patterns of seed distribution. Forest floor density isthe number of germinants divided by the actual area that wassampled in each depth class. This area decreased with increasingdepth so forest floor density is the actual density of germinantsin the forest floor only, for each depth class.The data were graphed to assess whether there werediscernable patterns with respect to depth. Large densities ofgerminants found in particular depth classes were examined todetermine how uniformly germinants were distributed among thelayers. This was important because a large clump of germinants inone sample could strongly skew the pattern of verticaldistribution, resulting in a misinterpretation of the data.2.2.3 Field germination2.2.3.1 Data collection Germination of seeds in the field was monitored in subplotsand plots over the spring and summer of 1990. (See Section 2.2.1for layout.) In the subplots, germination was recorded every twoweeks from June 4 to August 22 on the ICH site and from June 10to August 27 on the ESSF site. Individual germinants were markedwith coloured thread loops, and identities and mortality wererecorded.On the ICH site all germinants in the 3 X 3 m plots werecounted, marked and mapped at the same time as the subplots. Therelatively high numbers of germinants in the ESSF plots and thedensity of existing vegetation in the unburned plots made mapping16and recording plot germinants impractical. A single count of allgerminants surviving in the burned ESSF plots was made on thelast recording date (Aug. 26, 1990). The timing of seed dispersalof species on or near the sites was observed in order todetermine if any species of germinants originated from seed rain.On October 13 1989, one Campbell Scientific CR10 dataloggerper site was installed to record soil temperature over the next10 months. On the ICH site relative humidity (RH) and airtemperature were also recorded. On the ESSF site RH and airtemperature data were obtained from another datalogger locatedapproximately 100 m away. Each datalogger was located in an areaclose to both burned and unburned patches. Data loggers wereplaced in waterproof containers and temperatures were measuredwith thermocouples. After installation, thermocouple wires werecovered with forest floor and slash (except over the ends), andthe dataloggers were covered with plastic and logs to protectthem from animal damage and provide insulation.Thermocouples were placed at four locations, two in burnedand two in unburned forest floor. On the ICH site thermocoupleswere placed at 1 and 2 cm from the surface at all four locations.At one burned and one unburned location, thermocouples were alsoplaced at 4 cm depths. On the ESSF site, all four locations hadthermocouples at 1, 2 and 4 cm from the surface. Data wererecorded every five minutes, averaged and output once every 24hours. Winter data collection ended June 5, 1990 for the ICH siteand June 6, 1990 for the ESSF site.During the summer of 1990, the dataloggers and thermocoupleswere left in place but data were averaged on an hourly basis.17Soil that is shaded has a lower temperature than soil exposed tothe sun (Daubenmire 1968; Wells et al. 1979; Thompson and Grime1983), providing a cooler germination environment for buriedseeds. Therefore, starting June 18 (ICH site) and June 19 (ESSFsite), and for the rest of the temperature recording period, oneburned and one unburned location were shaded with slash. On theICH site the locations with 1, 2, and 4 cm deep thermocoupleswere shaded. Summer temperature data were collected until August24 on the ICH site and August 27 on the ESSF site. Data analysis Horizontal distribution of germinants was assessed by thesame methods as those used in the greenhouse germination analysis(Section Subplots were used in the analysis instead ofsamples. This analysis was carried out on ESSF data only, becausethere were no germinants in the ICH subplots.Density of field germinants was calculated as the number ofgerminants divided by the area sampled in m 2 (0.75 m2 for thesubplots and 27 m2 for the plots). Species composition and totaldensity from the 0-1 cm depth class of the greenhouse sampleswere compared to those of the field subplots. The assumption wasmade that field germinants did not originate from > 1 cm deep inthe forest floor. This provided the most conservative estimate ofpotential field germination, although it is possible that seedsdid emerge from deeper in the profile. For the ICH site, totaldensity in the plots was used because no germinants occurred inthe unburned subplots.Daily germination temperatures from field and greenhouse18were graphically compared. Air temperatures were used becausesoil temperature was not measured in the greenhouse. Hourlytemperature cycles were also graphed for a few selected daysusing the greenhouse and ICH data only. Hourly air temperaturesfrom the ESSF site were not available, but the soil dataindicated patterns similar to those from the ICH site.2.2.4 Existing vegetation2.2.4.1 Data collection Vegetation species presence and estimates of percent coverin the plots were recorded in 1989. These data providedinformation on possible sources of seed for some germinants,possible identity of germinants that could not be separated intospecies and divergence between the existing and former vegetationas represented by the seed bank. Data analysis Vegetation species composition and percent presence weretabulated with the taxa that germinated from the greenhousesamples and field plots and subplots. Percent presence wascalculated as the number of plots, subplots or samples eachspecies occurred in multiplied by 100 and divided by the totalnumber of plots, subplots or samples. The inability to identifymany of the germinants to species, however, made comparisonstentative.192.3 Results and discussion 2.3.1 Greenhouse germination2.3.1.1 Numbers and species Unidentified germinants were grouped into dicotyledons andgraminoids. The latter included Poaceae, Cyperaceae and Juncaceaegerminants that could not be identified even to family. Poaceaeprobably included more than one species. Vahlodea atropurpureaand Calamagrostis canadensis were collected on the ESSF site andCinna latifolia on the ICH site but it was not possible todetermine whether the germinant grasses were these or otherspecies. Both Vaccinium membranaceum and V. ovalifolium occurredon the sites but reference germinants were too small todistinguish between these species. An unknown Ericaceous speciescould have been Menziesia ferruginea on either site orRhododendron albiflorum on the ESSF site. Two species of Mitella(pentandra and breweri) grew on the ESSF site but referencegerminants died before the flowers essential for identificationdeveloped. The common sedge may have been either Carex mertensiior C. spectabilis; both were common in disturbed areas near theESSF site.Epilobium spp., other than E. angustifolium, may havedispersed some seed before samples were collected. However, noobservations of seed dispersal at either site, were made duringsampling. Mitella species were likely producing seed in an areaadjacent to the ESSF site at the time samples were collected butno observations of plants with seeds were made in the samplingarea. Mitella seeds, though very small, have no apparentadaptations for wind or animal dispersal and therefore were not20likely to have fallen on the sampling area. Hieracium spp. couldhave dispersed seeds onto the ICH site before sample collection.However, only one germinant (included in Asteraceae) wastentatively identified as Hieracium.There were 2591 germinants (872/m2 ) in total on the ESSFsite, representing 13 taxa and unidentified dicotyledons (Table2.1). The latter could have included several species, likely thesame taxa that were already identified. More than half of thegerminant taxa (excluding unidentified dicotyledons) wereherbaceous plants, including four out of the five most abundant.Herbaceous taxa accounted for the vast majority of the germinants(94%, excluding unidentified dicotyledons) for this site. Ninety-six percent of the germinants belonged to the five most abundanttaxa and unidentified dicotyledons. Mitella spp. accounted for46% of the germinants, followed by Luzula parviflora 21%),unidentified dicotyledons (14%), Carex mertensii (8%), Epilobiumciliatum (4%), and Vaccinium spp. (4%) (Table 2.1). The standarderror of total density among samples was relatively high fortotal germinants and for individual germinant taxa.There were 689 germinants (229/m 2 ) in total on the ICH site,representing 16 taxa and unidentified dicotyledons (Table 2.2).Ninety-six percent of all germinants belonged to the five mostcommon species and unidentified dicotyledons. Seven of thegerminant taxa (44%) were shrubs but most of the germinants (75%)were trees. Herbaceous taxa accounted for only 6% of thegerminants from this site. The most common species by far wasThuja plicata (72%), followed by Vaccinium sp. (9%), Sambucusracemosa (4%), Epilobium ciliatum (4%), unidentified dicotyledons21Table 2.1 The number of germinants by depth class and taxon, andtotal density of germinants + the standard error of the mean bytaxon, in the ESSF greenhouse samples. The proportions ofgerminants and layers per depth class are also given.Taxon 0-1 1-2Depth Class2-3^3-4^4-5(cm)5-6 6-7 7-8 TotalTotalDensityMitella spp. 363 312 279 171 35 20 3 1183 398^+^51_Luzula parviflora 79 242 156 35 31 4 547 184^+^31Dicotyledons 133 79 61 52 14 12 1 352 119 +^14_Carex spp. 1 6 27 39 73 68 214 72^+^43Epilobium ciliatum 58 36 6 100 34^+^17_Vaccinium spp. 60 29 9 1 99 33 +^6_Poaceae 29 7 1 8 45 15 +^4_Ericaceae 9 5 10 24 8 + 3_Sambucus racemosa 1 5 2 2 1 11 3+ 1Graminoids 1 5 6 2+ 1_Picea sp. 5 1 6 2 + 1_Galium sp. 2 2 <1Ribes laxiflorum 1 1 <1Valeriana sitchensis 1 1 <1Total Germinants 741 729 550 300 163 104 4 2591 872^+^82Total Layers 297 283 191 83 33 11 2 1 901Percent Germinants 28.6 28.1 21.2 11.6 6.3 4.0 0.2Percent Layers 33.0 31.4 21.2 9.2 3.7 1.2 0.2 0.122Table 2.2 The number of germinants by depth class and taxon, andtotal density of germinants + the standard error of the mean bytaxon, in the ICH greenhouse samples. The proportions ofgerminants and layers per depth class are also given.Taxon^ 0-1 1-2 2-3Depth Class3-4^4-5(cm)5-6 6-7 7-8 TotalTotalDensityThuja plicata^477 17 1 1 1 497 165 + 18_Vaccinium spp. 7 46 9 3 65 22 + 11_Sambucus racemosa^1 16 6 4 2 1 30 10 + 4_Epilobium ciliatum^10 8 5 2 2 27 9+ 2_Dicotyledons^4 12 5 2 1 24 8+ 2_Ericaceae 1 10 5 16 5 + 2_Rubus idaeus^1 4 1 6 2+ 1_Poaceae 2 2 1 5 2 + 1Asteraceae 2 2 4 1+ 1_Anaphalis margaritacea^2 1 3 1+ 1_Ribes laxiflorum^1 1 1 3 1+ 1_Picea sp.^2 2 <1Pinaceae 2 2 <1Ribes sp. 1 1 2 <1Graminoids 1 1 <1Juncus ensifolius 1 1 <1Rubus parviflorus 1 1 <1Total Germinants^512 121 35 14 3 4 689 229 + 21Total Layers^301 299 259 125 35 12 3 1 1035Percent Germinants^74.3 17.6 5.1 2.0 0.4 0.6Percent Layers^29.1 28.9 25.0 12.1 3.4 1.2 0.3 0.123(4%) and Ericaceae (2%) (Table 2.2). The standard errorsassociated with total densities were relatively high for totalgerminants and for individual germinant taxa.The proportion of unidentified germinants in other studieshas varied considerably. Only one (Ingersoll and Wilson 1990),however, had more unknowns than the ESSF samples in this study.The authors did not discuss reasons for the relatively highnumbers of unidentified germinants in their study. The proportionof unidentified germinants from the ICH samples was comparable tothose reported by Archibold (1979), Kellman (1970), Strickler andEdgerton (1976) and Scheiner (1988). Other studies did not listunidentified germinants.In this study germinants remained unidentified because theydied before producing true leaves. None of the species haddistinctive enough cotyledons to be able to assign identitieswith any confidence at that stage of development. The cause ofdeath could not be determined in most cases but may have includedfaulty development, lack of nutrients in the sample, dehydration,insect damage, and fungal attack. Of these, the first two aremore likely since samples were checked for moisture almost everyday and damage by insects and fungi was not observed.Germinants of genera such as Mitella, Vaccinium andEpilobium, that could not be separated into species, were likelyspecies that were growing in the existing vegetation. Mitellaspp. and Vaccinium spp. both grow in mature forests in the studyarea. Epilobium spp. were abundant in adjacent clearcuts andcould have seeded into the site.The number of taxa found on these sites was similar to other24comparable studies. Although taxa numbers from other studiesranged from 3 to 57, most had fewer than 20. Where both viableand non-viable seed content was determined, there were highernumbers of taxa. The high proportion of germinants that belongedto very few taxa in this study is typical of the distribution ofseeds among taxa reported by several other researchers (Kellman1970; Moore and Wein 1977; Granstrom 1982; Fyles 1989).Most of the more abundant germinant taxa from both sites, orat least congenerics, have been found in temperate forest soilseed banks by other researchers. These include: Sambucus racemosa(Kellman 1970; Bormann and Likens 1979; Kramer and Johnson 1987;Granstrom 1988), other Sambucus species (Strickler and Edgerton1976; Graber & Thompson 1978; Kramer and Johnson 1987; Morgan andNeuenschwander 1988a,b; Mladenhoff 1990), Rubus idaeus (Graber &Thompson 1978; Bormann and Likens 1979; Granstrom 1982, 1987,1988; Fyles 1989), other Rubus species (Olmsted and Curtis 1947;Moore and Wein 1977; Morgan and Neuenschwander 1988a,b; Scheiner1988), Epilobium ciliatum (formerly E. watsonii) (Kellman 1970,1974; Strickler and Edgerton 1976; McGee 1988; Ingersoll andWilson 1990), Luzula parviflora (Morin and Payette 1988), otherLuzula species (Granstrom 1982, 1988, Kramer and Johnson 1987),Carex mertensii (Kellman 1970), other Carex species (Olmsted andCurtis 1947; Moore and Wein 1977; Whipple 1978; Archibold 1979;Kramer and Johnson 1987; Fyles 1989; Pratt, et al. 1984; Morinand Payette 1988; Mladenhoff 1990), non-viable V. ovalifoliumseeds (Morin and Payette 1988), Vaccinium spp. other thanVaccinium membranaceum and V. ovalifolium (Kellman 1974;Granstrom 1982), Mitella spp. other than M. pentranda or M.25breweri (Strickler and Edgerton 1976; Kramer and Johnson 1987),and Menziesia ferruginea (Kellman 1974).Thuja plicata was the only major taxon not found in otherNorth American studies. The high number of Thuja plicatagerminants from the ICH site may have resulted from the factthat, following logging, branches and foliage of this specieswere left on the ground where they deposited a large number ofseeds.The proportion of herbaceous to shrubby taxa among otherstudies shows no consistent pattern, similar to the results fromthis study. Most or all of the germinants from sites studied byIngersoll and Wilson (1990), Kramer and Johnson (1987), Olmstedand Curtis (1947), Strickler and Edgerton (1976), and Whipple(1978) were herbaceous taxa. Shrub taxa were in the majority instudies by Kellman (1970) and Granstrom (1982).Total density of greenhouse germinants in this study fallswithin the range found by comparable studies of mature forestsoil seed banks. Densities of germinants in other studies rangefrom approximately 100 germinants/m 2 to 1100 germinants/m2 .Comparison among studies is difficult, however, because of a widevariation in methodology. Densities from different studies arebased on samples of different thicknesses and size, on samples ofmineral soil as well as forest floor and on different samplingintensities.The high variation in germinant density among samples inthis study appears to be similar to or greater than that reportedby a few previous studies. However, many researchers have eithernot included measures of variation or have obscured variation by26pooling samples. In addition, the measures of variation used areinconsistent from one study to another. Nevertheless, high sampleto sample variation in germinant numbers has been recognized as acharacteristic of soil seed banks, representing the uneven natureof seed distribution (Champness 1949; Major and Pyott 1966;Bigwood and Inouye 1988) and probably of burial forces (Garwood1989).Johnson (1975) proposed that seed bank densities decreasewith increasing altitude and latitude. The high numbers ofgerminants in the ESSF site relative to the ICH site suggest thatthis is not the case. Overall site productivity related tomoisture and nutrients may have resulted in a larger seed bank onthe ESSF site, possibly through a higher rate of input andconditions more conducive to maintaining dormancy. This wassuggested by (Fox 1983) as an explanation for the presence of,and variation among, arctic soil seed banks. Fyles (1989) hasspeculated that the vegetation history and species composition ofsites are more likely causes of between-site variation in seedbank density than is latitude. Whipple (1978) and McGee (1988)both found that moister sites had more germinants than driersites at subalpine and near sea-level elevations, respectively,while Morin and Payette (1988) observed a shift in speciescomposition but no decrease in seed abundance with increasingaltitude. Horizontal distribution of germinants The order of the five most abundant taxa from the ESSF sitefrom least to most dispersed was: Carex spp. < Epilobium ciliatum27< Luzula parviflora < Vaccinium spp. < Mitella spp. (Table 2.3).Carex spp. germinants were much more concentrated than those ofany other taxa. Luzula parviflora had a similar dispersion toEpilobium ciliatum, while Vaccinium spp. germinants. were almostas highly dispersed as those of Mitella spp.For the ICH site, the order of the five most abundantgerminant taxa from least to most dispersed was: Vaccinium spp. >Ericaceae > Thuja plicata > Sambucus racemosa > Epilobiumciliatum (Table 2.4). Ericaceae, Thuja plicata and Sambucusracemosa had similar dispersions, while Epilobium ciliatum washighly dispersed relative to the other taxa.Most of the ICH taxa were more dispersed than the ESSFgreenhouse germinants, although none of the more abundant taxafrom either site occupied the maximum number of samples. Intotal, 18% of the ESSF samples and 32% of the ICH samples had nogerminants at all. Germinant taxa from both sites showed norelationship between the degree of dispersion and number ofgerminants. For example, Vaccinium spp. (ESSF) was almost asdispersed as Mitella spp. but the latter was over 10 times asabundant. Similarly, Thuja plicata, from the ICH samples, hadabout the same dispersion as Ericaceae, but over 30 times thenumber of germinants.Most of the more abundant germinant taxa from both sites hadhigh coefficients of variation (C.V.), indicating relativelyuneven, or clustered, distributions, among the samples in whicheach taxon occurred. Of the ESSF taxa, Epilobium ciliatum andCarex spp. had the highest C.V. Mitella spp. and Luzulaparviflora had somewhat more even distributions that were28Table 2.3 Horizontal distribution of the five most abundantgerminant taxa from ESSF greenhouse samples. Dispersion is thenumber of samples with germinants expressed as a percentage ofthe theoretical maximum number of samples. The coefficient ofvariation is a measure of how evenly germinants were distributedamong the samples in which they occurred.TaxonDispersion of Germinants Evenness of Distribution'MaximumSamplesSamplesOccupiedPercentPresence MeanStandardDeviationCoefficientof VariationCarex spp. 214 16 7.5 13.4 30.1 224.9Epilobium ciliatum 100 27 27.0 3.7 9.3 252.3Luzula parviflora 297 90 30.3 6.1 8.2 134.4Vaccinium spp. 99 47 47.5 2.1 1.9 89.8Mitella spp. 297 146 49.2 8.1 11.0 135.91 Based on the mean number of germinants per occupied sample.29Table 2.4 Horizontal distribution of the five most abundantgerminant taxa from ICH greenhouse samples. Dispersion is thenumber of samples with germinants expressed as a percentage ofthe theoretical maximum number of samples. The coefficient ofvariation is a measure of how evenly germinants were distributedamong the samples in which they occurred.TaxonDispersion of Germinants Evenness of Distribution'MaximumSamplesSamplesOccupiedPercentPresence MeanStandardDeviationCoefficientof VariationVaccinium spp. 65 18 27.7 3.6 7.1 195.6Ericaceae 16 8 50.0 2.0 1.6 80.2Thuja plicate 301 158 52.5 3.1 3.6 116.0Sambucus racemosa 30 17 56.7 1.8 1.9 108.9Epilobium ciliatum 27 24 88.9 1.1 0.4 39.9Based on the mean number of germinants per occupied sample.30similar, while Vaccinium spp. had the most even distribution(Table 2.3). Among the ICH samples, Vaccinium spp. had the mostuneven, and Epilobium ciliatum the most even distribution. Thujaplicata, Sambucus racemosa and Ericaceae fell between theseextremes (Table 2.4). In general, the ICH taxa were more evenlydistributed than the ESSF taxa.Two germinant taxa common to samples from both sites, didnot have the same dispersion or C.V. on both sites. Vacciniumspp. had almost the highest dispersion among ESSF samples but thelowest among ICH samples. Conversely, Epilobium ciliatum had thesecond lowest dispersion among ESSF samples but the highest amongICH samples. C.V. for Vaccinium spp. was lowest among ESSFsamples and highest for ICH samples. Epilobium ciliatum had thehighest C.V. among ESSF samples but the lowest among the ICHsamples.Seeds in forest soils probably have distributions that arealways clumped to some degree because 1) source plants rarelyhave even distributions, 2) dispersal mechanisms tend to resultin clusters of seeds, 3) burial forces are heterogeneous and 4)mortality both on and in the soil is likely to be spatiallyheterogeneous. Seed distribution of different species in the soilof a mature coastal forest in New Jersey ranged from nearlyrandom to highly clustered (Matlack and Good 1990).Seed clustering probably occurs at different scalesdepending on the disturbance history of the site, dispersalmechanism and microtopographical variation. Bigwood and Inouye(1988) concluded that seeds are likely clustered at all scales.The general relationship between dispersion and clustering in the31present study supports this. However, because the location ofsamples relative to each other in the field was not recorded andgerminants were not mapped, conclusions can only be made aboutthe degree of clustering, and not about the size and distributionof seed clusters at scales larger than the samples.These data do show that each taxon had a range ofdistributions, from no seeds to single occurrences to largeclusters in some cases. Carex spp., for example, had onegerminant each in half the samples it occurred in, but 120germinants in another sample. In contrast, the maximum number ofseeds per sample for Vaccinium spp. (ESSF) was 10 and over 80% ofthe samples had three or fewer germinants of this taxon.Major and Pyott (1966) have suggested that the small samplesizes typical of many seed bank studies result in unacceptablyhigh variation among samples and therefore a poor estimate ofseed numbers. Increasing sample size will reduce the standarderror of the mean but will not decrease the variation in densityamong samples, given the inherently clustered distribution ofseeds. The value of increasing sample size is in providing abetter estimate of seed numbers by ensuring that the range ofseed densities is sampled for each species. Results of this studyand those of Bigwood and Inouye (1988) show that between-samplevariation is probably a poor measure of the precision of suchestimates. This study had a much larger number of samples persite than any other comparable project, but the S.E. of germinantdensity was still relatively high.The differences in distributions of Vaccinium spp. andEpilobium ciliatum between the two sites may be the result of32sampling error associated with relatively rare, sporadicallyoccurring large clusters interspersed with more evenlydistributed, but still rare, small clusters. Alternatively, thedifferent distributions may reflect differences between the sitessuch as seed input and dispersal.The high number of samples, amounting to a relatively hightotal surface area, obtained from these sites, probably gave areasonable estimate of the number of viable seeds for the moreabundant taxa at least. However, because sampling was confined toa relatively small portion of each cutblock, species clustered ata larger scale may have been missed. For example, Rubusparviflorus germinants were observed on the ICH site within a fewmeters of the sampling area but only one germinant was recordedfrom the greenhouse samples. Vertical distribution of germinants Table 2.5 summarizes the proportion of samples of eachthickness. The proportions by sample thickness of samples thathad germinants, were similar to those of the total samples forboth the ESSF and the ICH site. Samples from the ESSF site wereapproximately 3 cm thick on average, with the majority (84%)being 2 to 4 cm thick. Samples from the ICH site averaged 3.4 cmthick and most (88%) were from 2 to 4 cm thick.Ninety percent of the ESSF greenhouse germinants came fromthe top 4 cm of forest floor. Almost the same proportion ofgerminants came from the 0-1 and 1-2 cm depth classes (29 and20%, respectively), while the 2-3 cm and 3-4 cm depth classesaccounted for 21% and 12% of the germinants, respectively. There33Table 2.5 Proportion of total greenhouse samples and samplesthat had germinants of each thickness, from the ESSF and ICHsites.ESSF Samples^ICH SamplesSampleThickness(cm)% Samples% Total^WithSamples^Germinants% Samples% Total^WithSamples^Germinants1 4.7 4.1 0.7 0.52 31.0 28.5 13.3 13.73 36.4 34.6 44.5 41.74 16.8 18.3 29.9 31.95 7.4 8.9 7.6 8.36 3.0 3.7 3.0 2.97 0.3 0.4 0.7 0.58 0.3 0.4 0.3 0.5% Total SamplesWith Germinants 82.8 67.834were no germinants deeper than 7 cm (Table 2.1). A few Mitellaspp. and unidentified dicotyledon germinants were found in the 6-7 cm depth class. Luzula parviflora and Carex spp. emerged fromas deep as the 5-6 cm depth class, but Epilobium ciliatum andVaccinium spp. were almost entirely confined to the top 3 cm offorest floor.Of the five most abundant taxa of ESSF germinants, forestfloor density of Mitella spp. and Luzula parviflora showed nopattern with respect to depth. Carex spp. appeared to increasesharply with depth, while Epilobium ciliatum and Vaccinium spp.showed a very slight decrease with depth (Figure 2.4). Forestfloor density of all germinants summed increased with depth to 5-6 cm, then decreased sharply in the 6-7 cm depth class (Figure2.5).Total density of Mitella spp., Epilobium ciliatum andVaccinium spp. decreased with depth (Figure 2.6). Luzulaparviflora had the highest total density in the 1-2 cm layers,then decreased steadily with depth. Total density of Carex spp.germinants increased with depth to 4-5 cm, then decreasedslightly. For all taxa combined, total density was similar forthe top 2 cm, then decreased steadily with depth (Figure 2.5).Seventy-four percent of the ICH greenhouse germinants camefrom the 0-1 cm depth class. Thuja plicata accounted for themajority of these (93%). The top 3 cm of forest floor contained97% of all the germinants. All of the other more abundant taxa,except Epilobium ciliatum, had the highest proportion ofgerminants in the 1-2 cm depth class. There were no germinants inlayers > 6 cm below the surface (Table 2.2). Sambucus racemosa35Figure 2.4 Forest floor germinant density as a function of depthfor the 5 most abundant taxa in the ESSF greenhouse samples.36Figure 2.5 Forest floor and total density of all ESSF greenhousegerminants as a function of depth.375-6 6-70-1^1-2^2-3^3-4^4-5Depth Class (cm)12510075AMgr n0 doEI PM!AEVALisigizi F-1111 7/1•I40°A ,441--I.regge'r^Amor Carex sp.Epilobium ciliatumVaccinium spp.5025Mitella spp.Luzula parviflorusFigure 2.6 Total germinant density as a function of depth forthe 5 most abundant taxa in the ESSF greenhouse samples.38density decreased sharply with depth (Figure 2.8). This patternwas similar to the distribution of Thuja plicata germinantsbecause of the abundance of this species relative to other taxa(Figures 2.7, 2.9).The patterns for Carex spp. and Epilobium ciliatum in theESSF samples, and for Vaccinium spp. in the ICH samples, werestrongly skewed by large clusters of germinants in very fewsamples. Eighty-eight% and 97% of the Carex spp. germinants fromthe 4-5 and 5-6 cm depth classes, respectively, came from twosamples. Approximately 50% of the Epilobium ciliatum germinantsin the 0-1 and 1-2 cm depth classes also came from a singlesample. The relatively high forest floor density in the 1-2 cmICH depth class for Vaccinium spp. was mainly the result of 30germinants that emerged from one sample. These accounted foralmost half of the total number of germinants for the taxon and65% of the germinants in the 1-2 cm depth class. Therefore, thedistributions of these three taxa were not consistent withrespect to depth.Several studies have shown a decrease in seeds withincreasing depth (Kellman 1970; Strickler and Edgerton 1976;Moore and Wein 1977; Kramer and Johnson 1987; McGee 1988). Ingeneral, results from this study support these observations,although there is considerable variation in the patterns ofindividual taxa. Granstrom (1988) has pointed out, however, thatwas the only taxon to occur in all depth classes up to, andincluding, 5-6 cm. All Vaccinium spp. and most of the Epilobiumciliatum germinants occurred in the top 4 cm of forest floor.Ericaceae were not found deeper than the 2-3 cm depth class.39Figure 2.7 Forest floor germinant density as a function of depthfor the 5 most abundant taxa in the ICH greenhouse samples.40Figure 2.8 Forest floor and total density of all ICH greenhousegerminants as a function of depth.41Figure 2.9 Total germinant density as a function of depth forthe 5 most abundant taxa in the ICH greenhouse samples.42Forest floor density was generally low for all ICH taxa,other than Thuja plicata, at all depths, except for an increasein density of Vaccinium spp. germinants in the 1-2 cm depthclass. (Figure 2.7). What appears to be a slight increase inforest floor density at 5-6 cm for Epilobium ciliatum andSambucus racemosa was based on only three germinants in twosamples and therefore cannot be considered a trend. When allgerminants were summed, both forest floor density and totalbecause this apparent trend is based on the means of all samples,the differences in patterns among individual samples areobscured. He also notes that adequate sample size has beenaddressed in relation to horizontal distribution, but not forvariation in vertical distributions.Results from both Granstrom (1988) and this study indicatethat high variation exists in depth distributions among samples.Patterns that individual taxa exhibited in the present study weremade up primarily of 1 or 2 cm thick clusters situated atdifferent depths in different samples, rather than the samepattern of distribution within each sample. This means thatdifferences in seed density with depth were the result of eitherdifferences in the mean number of seeds per cluster ordifferences in the number of clusters.Another problem with previous determinations of depthdistribution is a lack of resolution, either because the layerswere relatively thick or because the sample was divided into onlytwo or three layers. Other researchers have generally used 2 to 5cm thick layers (Kellman 1970; Strickler and Edgerton 1976; Mooreand Wein 1977; Granstom 1982; Kramer and Johnson 1987). Samples43divided into two layers (Kellman 1970; Kramer and Johnson 1987)can only indicate linear trends in distribution. For example, ifthe samples from the present study had been divided into 2 - 3 cmthick depth classes, Luzula parviflora would have shown a simplereduction in seeds with depth and the high densities in the 1-2and 2-3 cm depth classes would have been missed.The difference between the patterns of total and forestfloor density can be explained by the fact that the proportion oflayers per depth class decreased more than the proportion ofgerminants per depth class (Tables 2.1, 2.2). The increase inforest floor germinant density with depth for the ESSF site,suggests that seeds may be more concentrated in the deeper partof the profile. What is not known is whether there were seeds inthe mineral layers corresponding in depth to the deeper forestfloor layers, that would have moderated this distribution. Ifthere were seeds in the mineral soil the pattern of distributionfor total density would not decrease as much with depth or mightnot decrease at all.The presence of Mitella spp. and Sambucus racemosagerminants throughout the ESSF and ICH profiles, respectively,could have been the result of continuous input over many yearssince both taxa grow in mature forests as well as earliersuccessional stages. Luzula parviflora and Carex spp. are morecharacteristic of disturbed habitats and are therefore morelikely to have been deposited in an early successional stage,several decades ago or through small localized disturbances.Epilobium ciliatum, which was most abundant at 0-1 and 1-2 cm,may have been more recently deposited. Plants growing on44roadsides and older cutblocks in the vicinity of both sites couldhave been a source of wind-blown seed of this species in recentyears. The Thuja plicata germinants in the 2-3, 3-4 and 4-5 cmdepth classes probably originated from surface seeds that wereaccidentally dislodged during sample splitting.Definite conclusions about the age of seeds in relation tolocation in the forest floor profile cannot be made withoutknowing the means of seed burial, the rate at which seeds movethrough the soil, if at all, and the specific longevity of seeds.Mature forest species could, however, have a shorter period ofviability if they are able to contribute to the seed bankcontinuously. The fact that Vaccinium spp. germinants did notemerge from the deeper layers may mean that seeds of this taxonlose viability or are otherwise lost relatively quickly but arecontinually added to the seed bank.2.3.2 Field germination compared to greenhouse germination2.3.2.1 Numbers, species and distribution Epilobium spp. germinants could have been either Epilobiumangustifolium or E. ciliatum. Germinants that could not beidentified even to family were all dicotyledons. Like thegreenhouse germinants, (Section Poaceae, Vaccinium spp.and Mitella spp. field germinants may have been the same speciesthat grew on the sites. Viola glabella was common on both sites.On the ESSF site Ribes lacustre was the most common species ofRibes in the existing vegetation but R. laxiflorum was found aswell.Since seed rain was not excluded from the unburned areas, it45is possible that some germinants came from plants either on ornear the plots. On the ESSF site Poaceae, Epilobium spp.,Valeriana sitchensis, Vaccinium spp., Mitella spp. and Violaglabella could all have been dispersed onto the unburned plotsduring 1989. On the ICH site the unburned plots could havereceived seed rain from Vaccinium spp., Epilobium spp. andAnaphalis margaritacea in 1989. Thuja plicata may also havedispersed onto the plots from nearby trees or slash. Epilobiumangustifolium almost certainly seeded in from nearby plants onboth sites.There were a total of 128 germinants (171/m2 ) in the ESSFfield subplots (Table 2.6). Of these, 39% were Mitella spp., 16%unidentified dicotyledons, 16% Epilobium spp., 11% Poaceae, and5% Vaccinium spp. which together comprised 87% of the germinants.The 0-1 cm depth class of the ESSF greenhouse samples had ahigher density of germinants than the field subplots (Table 2.6).There were 11 taxa each (excluding unidentified dicotyledons) inboth the greenhouse and field subplot germinants. Four of thesetaxa, and possibly five (Epilobium spp. may have been E.ciliatum), germinated in both.In both the greenhouse samples and the field subplots,Mitella spp. had the highest density followed by unidentifieddicotyledons. Of the remaining taxa that were the most abundantin the greenhouse germinants, Epilobium spp., Poaceae andVaccinium spp. were also the next most abundant in the fieldsubplots. Luzula parviflora, third most numerous taxon in thegreenhouse was entirely absent from the field subplots.46Table 2.6 Number and total density (number/m 2 ) of germinants inthe ESSF field subplots and 0-1 cm depth class of the greenhousesamples.TaxonField Subplots Greenhouse 0-1 cmNumberTotalDensity NumberTotalDensityMitella spp. 50 67 363 122Dicotyledons 21 28 133 45Poaceae 14 19 29 10Vaccinium spp. 6 8 60 20Picea sp. 1 1 5 2Epilobium spp. 20 27Epilobium ciliatum 58 20Pinaceae 4 5Ribes spp. 4 5Valeriana sitchensis 4 5Viola spp. 2 3Abies lasiocarpa 1 1Rubus spp. 1 1Luzula parviflora 79 27Ericaceae 9 3Galium sp. 2 <1Carex spp. 1 <1Graminoids 1 <1Sambucus racemosa 1 <1Total 128 171 741 25047Ericaceae, Carex spp. and Sambucus racemosa all had moderatenumbers of germinants in deeper layers of the greenhouse samplesbut were not present in the field subplots. Ribes spp. occurredin the field subplots but not in the greenhouse germinants,although one Ribes laxiflorum germinant was found in the 1-2 cmdepth class of a greenhouse sample.No germinants were found in the ICH subplots. In the plots,however, there were a total of 22 germinants (0.81m2 ). One of thethree plots did not have any germinants. Out of the 10 taxa inthese plots only four had more than one germinant, and none hadmore than six. The four most abundant taxa were Ribes spp.,Epilobium spp., Sambucus racemosa and Thuja plicata whichtogether accounted for 73% of the germinants (Table 2.7).The ICH greenhouse samples had a much higher number ofgerminants than did the field plots (Table 2.7). This result isespecially striking because the field plots covered a 27 m2sampling area compared to only 3.01 m 2 for the greenhousesamples. Nine taxa (excluding unidentified dicotyledons)germinated in the field plots, compared to 12 from the greenhousesamples. Of these taxa, five were found among both greenhouse andfield germinants. For all germinant taxa in both the field andgreenhouse, germinant densities were higher in the greenhouse.Epilobium angustifolium, Epilobium spp. and Ribes spp.germinants were found in the ICH field plots but not in thegreenhouse samples. However, Ribes laxiflorum germinated fromgreenhouse samples and this may have been the species thatoccurred in the field. Similarly, the Epilobium germinants thatwere not identified to species in the field may have been E.48Table 2.7 Number and total density (number/m2 ) of germinants inthe ICH field plots and 0-1 cm depth class of the greenhousesamples.TaxonField Plots Greenhouse 0-1 cmNumberTotalDensity NumberTotalDensityThuja plicata 2 <1 477 159Sambucus racemosa 4 <1 1 <1Vaccinium spp. 1 <1 7 2Dicotyledons 1 <1 4 1Anaphalis margaritacea 1 <1 2 <1Picea sp. 1 <1 2 <1Rubus idaeus 1 <1 1 <1Ribes spp. 6 <1Ribes laxiflorum 1 <1Epilobium spp. 4 <1Epilobium angustifolium 1 <1Epilobium ciliatum 10 3Asteraceae 2 <1Pinaceae 2 <1Poaceae 2 <1Ericaceae 1 <1Total 22 <1 512 17049ciliatum, which was the second most abundant taxon in the 0-1 cmdepth class of the greenhouse samples. All other germinant taxafrom the field plots were also found among greenhouse germinants.The four remaining taxa from the greenhouse samples that were notfound in the field plots (excluding Epilobium ciliatum and Ribeslaxiflorum) had only one or two germinants each.In the ESSF field subplots, Mitella spp. had the lowestdispersion of the germinant taxa, followed by Poaceae, andEpilobium spp. (Table 2.8). The taxa ranked from most unevenly tomost evenly distributed among the subplots where they were foundwere: Epilobium spp. > Mitella spp. > Poaceae (Table 2.8). Thedispersion of Mitella spp. germinants was only slightly higher inthe greenhouse samples than in the field (Tables 2.3 and 2.8).Epilobium sp. had much a lower dispersion in the greenhousesamples than in the field subplots. Mitella spp. and Epilobiumspp. both had much more even distributions (i.e. lowercoefficients of variation) in the field subplots than in thegreenhouse samples.Most of the genera, and some species, represented in thefield germinants have been found in seed banks of other studies(see Section In addition, Ribes lacustre (Kramer andJohnson 1987), other Ribes species (Olmsted and Curtis 1947;Strickler and Edgerton 1976; Kramer and Johnson 1987), Violaglabella (Kramer and Johnson 1987), other Viola species (Olmstedand Curtis 1947; Strickler and Edgerton 1976; Graber and Thompson1978; Granstrom 1988; Morin and Payette 1988; Ingersoll andWilson 1990; Mladenoff 1990) and Anaphalis margaritacea (Kellman1970, Pratt et al. 1984), have also been recorded. There were no50Table 2.8 Horizontal distribution of the three most abundantgerminant taxa from ESSF field subplots. Dispersion is the numberof subplots with germinants expressed as a percentage of thetheoretical maximum number of subplots. The coefficient ofvariation is a measure of how evenly germinants were distributedamong the subplots in which they occurred.TaxonDispersion of Germinants Evenness of Distribution'MaximumSubplotsSubplotsOccupiedPercentPresence MeanStandardDeviationCoefficientof VariationMitella spp.PoaceaeEpilobium sp.50142026111652.078.680. on the mean number of germinants per occupied subplot.51references to Valeriana sitchensis. Granstrom (1987) has shownthat Epilobium angustifolium does not maintain dormancy for morethan a year so germinants of this species in the field probablycame from recently arrived seed.There are no comparable studies of field germination fromforest floor exposed to light in situ. Several researchers havesuggested that the results of greenhouse germination may bebiased because of an inability of this method to provide theconditions that all species need to break dormancy and germinate(reviewed by Roberts 1981). Results from this study indicate thatgermination from greenhouse samples provided a goodrepresentation of the major taxa that germinated under fieldconditions, although this does not mean that all seeds andspecies in the soil germinated. In a few cases, likelycongenerics were identified in the greenhouse germination. Theabsence in the field of some of the minor greenhouse germinanttaxa may have been the result of the low probability of samplingthese species, either because of extremely patchy distributionsor very low numbers of germinants. Alternatively, some of thesetaxa may not have been part of the seed bank at all butoriginated from recent seed rain instead.The greenhouse germinant taxa that were not found in thefield may, in the case of the ESSF, be the result of a smallersample area in the field. The absence of Luzula parviflora andCarex spp. germinants in the field may have been because theseeds of this taxon were not as abundant in the surface of theforest floor.The fact that the total density was higher in just the top52cm of the greenhouse samples suggests that the greenhouse mayhave provided better germination conditions than the field.Studies by McGee (1988) and Ingersoll and Wilson (1990) haveshown that samples germinated in a greenhouse environment hadsignificantly more germinants than samples that were keptoutside.In the present study, higher greenhouse germinant densitiesmay have been the result of a longer period of germination: 135(ICH) to 166 (ESSF) days compared to 80 days for fieldgermination. However, when greenhouse germinants that had emergedafter 80 days were tallied, there was a lower total density forthe ESSF greenhouse samples (127 germinants/m2 ) than for thefield germinants. ESSF greenhouse germinants did not reach thesame density as the field germinants until 124 days after thestart of monitoring. In addition, most of the field germinants(87%) had emerged by only 56 days from the start of monitoring.Despite the lower density of greenhouse germinants after 80 days,all but one taxon present at 166 days were already present after80 days.In contrast, the total density of ICH greenhouse germinantswas higher than the final field density only 14 days after thestart of monitoring, even when Thuja plicata was excluded. Allbut one minor greenhouse germinant taxa was present by the 80thday of monitoring. Thus, for the ICH site, greenhouse conditionsappear to have been more favourable to germination than fieldconditions. Field germinants may have been rare because seedswere unable to germinate in the thick moss cover of the unburnedarea, which may have insulated seeds from higher temperatures or53wider temperature fluctuations, or because there was insufficientmoisture.As with the greenhouse samples, the horizontal distributionof germinants in the ESSF field subplots was clustered at bothscales that were examined. The generally higher dispersion andmore even distributions of the field germinants may have been dueto the smaller number of samples, the fact that distribution ofgreenhouse germinants was based on germination from the wholeforest floor profile, of some other factor. Field and greenhouse germination compared to fieldvegetation Four taxa found in the original vegetation also occurred asgerminants in both the ESSF field subplots and greenhouse samples(Table 2.9). Mitella spp., which had the highest presence andabundance of the germinant taxa, was very common in thevegetation. Valeriana sitchensis, Vaccinium spp. and Poaceae alsooccurred in the field vegetation and as germinants.Luzula parviflora was the only species common to bothgerminants and field vegetation that had a higher percentpresence in the greenhouse samples than in the field plots. Thistaxon was not found among field germinants. Two taxa (Viola spp.and Abies lasiocarpa) were found as field germinants andvegetation but were not among greenhouse germinants. In addition,the Ribes spp. germinants found in the field subplots may havebeen R. lacustre which was present in the existing vegetation.Epilobium spp. and Epilobium ciliatum, which were relativelycommon and abundant as germinants, were absent from thevegetation. Carex spp. was an important greenhouse germinant taxa54Table 2.9 Percent presence of the ESSF taxa in field vegetation,and in greenhouse and field germinants.Percent PresenceFieldVegetationGreenhouseGerminantsFieldSubplotGerminantsTaxa in CommonMitella breweri 91.7Mitella spp. 49.2 34.7Vaccinium membranaceum 91.7Vaccinium ovalifolium 91.7Vaccinium spp. 15.8 6.7Valeriana sitchensis 100.0 0.3 4.0Menziesia ferruginea 83.3Rhododendron albiflorum 66.7Ericaceae 4.0Poaceae 33.3 8.4 14.7Luzula parviflora 8.3 30.3Viola spp. 91.7 2.7Abies lasiocarpa 8.3 1.3Ribes lacustre 41.7Ribes spp. 5.3Unique TaxaGymnocarpium dryopteris 100.0Streptopus roseus 100.0Tiarella unifoliata 100.0Veratrum viride 91.7Athyrium filix-femina 58.3Arnica sp. 50.0Dryopteris assimilis 33.3Rubus pedatus 16.7Clintonia uniflora 8.3Moneses uniflora 8.3Pyrola minor 8.3Picea sp. 1.3 1.3Epilobium ciliatum 9.1Carex spp. 5.4Sambucus racemosa 3.0Graminoid 1.3Galium sp. 0.7Ribes laxiflorum 0.3Epilobium spp. 21.3Pinaceae 2.7Dicotyledons 37.7 18.712 297 75Total Area^(m2 ) 108 2.97 0.75+ = Taxa present as trees before logging.55that was also missing from the field vegetation.The field vegetation had many more taxa than eithergreenhouse or field germinants. Percent presence of fieldvegetation was generally much higher than either field orgreenhouse germinants. Several species, including Streptopusroseus, Tiarella unifoliata, and Veratrum viride, had highpresence (> 90%) in the ESSF field vegetation but were entirelyabsent from the identified germinants.Vaccinium spp. and Thuja plicata occurred in the existing orpre-harvest ICH vegetation and as field and greenhouse germinants(Table 2.10). The unknown ericaceous species was the only othergerminant taxon that may have occurred in the existingvegetation, possibly as Menziesia ferruginea. This taxon was onlyfound as germinants in the greenhouse samples, not in the fieldplots.Clintonia uniflora, Cornus canadensis, Rubus pedatus,Streptopus roseus and Tiarella unifoliata all had > 90% presencein the existing vegetation but did not occur as germinants. Thegerminant taxa Epilobium (E. spp. in the field and E. ciliatum inthe greenhouse), Sambucus racemosa and Rubus idaeus were notfound in the existing vegetation but were found as germinants inboth the greenhouse and the field. The number of taxa present inthe vegetation was slightly higher than for the greenhousegerminants but much higher than for the field germinants.For both sites, the generally lower percent presence of taxaas germinants than as existing vegetation species probablyreflects the difference in sample unit size (0.01 m 2 vs 3 m2 forgerminants and existing vegetation, respectively). Vaccinium spp.56Table 2.10 Percent presence of the ICH taxa in field vegetation,and in greenhouse and field germinants.Percent PresenceFieldVegetationGreenhouseGerminantsField PlotGerminantsTaxa in CommonThuja plicata 52.5 33.3Vaccinium membranaceum 90.9Vaccinium ovalifolium 90.9Vaccinium spp. 6.0 33.3Menziesia ferruginea 36.4Ericaceae 2.7Unique TaxaClintonia uniflora 100.0Cornus canadensis 100.0Gymnocarpium dryopteris 100.0Rubus pedatus 100.0Streptopus roseus 100.0Tiarella unifoliata 90.9Lycopodium annotinum 72.7Orthilia secunda 54.5Goodyera oblongifolia 27.3Viola spp. 27.3Dryopteris assimilis 18.2Linnaea borealis 18.2Streptopus amplexifolius 18.2Oplopanax horridus 9.1Sorbus scopulina 9.1Veratrum viride 9.1Sambucus racemosa 5.6 66.7Rubus idaeus 2.0 33.3Anaphalis margaritacea 1.0 33.3Picea sp. 0.7 33.3Ribes sp. 0.7 33.3Epilobium ciliatum 8.0Asteraceae 1.3Poaceae 1.3Ribes laxiflorum 1.0Graminoids 0.3Juncus ensifolius 0.3Pinaceae 0.3Rubus parviflorus 0.3Epilobium angustifolium 33.3Epilobium sp. 66.7Dicotyledons 6.3 33.3n 12 301 3Total Area^(m2 ) 108 3.01 27+ = Taxa present as trees before logging.57and possibly Ericaceae were common to vegetation and germinantsin both the ESSF and ICH sites indicating some consistency ofresponse in these species.The relatively low similarity between the speciescomposition of vegetation and germinants on the ICH site has beenfound in other studies of forest soil seed banks (Roberts 1981;Archibold 1989). The ESSF site may have had more taxa in commonbecause the characteristics of the ecosystem favoured speciesthat bank seeds. For example, there may have been a more opencanopy or more frequent small disturbances resulting in smallgaps that allowed enough light into the understory for forestspecies to produce seeds. Other studies (Matlack and Good 1990;Mladenoff 1990) have indicated that such gaps may provide forreplenishment of the seed bank through local reproduction of someforests species that can only produce seeds in gaps.Of the six taxa possibly common to ESSF greenhousegerminants and vegetation, Mitella spp. and Vaccinium spp. areprobably most important. These two taxa account for almost 50% ofthe total greenhouse germinants from the ESSF site. Therefore,even though species composition was not very similar, asubstantial proportion of the seed bank originated from speciesthat grow in forests, rather than species characteristic only ofearly successional stages. Temperatures during germination monitoring in the greenhouse and field study sites Field and greenhouse daily and hourly temperature patternswere different even though actual temperature ranges overlapped.58Throughout the germination periods, temperatures ranged from 6.1to 31.5 °C for the greenhouse, 0.8 to 31.2°C on the ICH site and -1.3 to 29.9 °C on the ESSF site. Mean temperatures for therecording period were lower in the field than in the greenhouse(20.5, 12.0 and 15.1 °C for the greenhouse, ESSF site and ICH siterespectively).The greenhouse temperature stayed mainly between 15 and 25 °Cthroughout the recording period. In the field, temperaturesgenerally increased over the summer at both the sites (Figure2.10). Field temperatures showed greater fluctuation thangreenhouse temperatures, especially the maxima. The mean of thedaily ranges of temperatures for the germination monitoringperiods was highest in the ICH field site (13.7°C), but similarin the ESSF field site and the greenhouse (10.1 and 9.0 °C,respectively).Field temperatures showed a pattern of change over a daywith a rise toward afternoon followed by a drop at night.Variation in greenhouse temperatures occurred on an hourly basisand the main difference at night was that there was lessfluctuation in temperature (Figure 2.11).The differences in temperature fluctuation patterns couldhelp account for the differences between greenhouse and fieldgermination results in either species composition or numbers ofgerminants. Without specific tests, however, little can beconcluded about the influence of the temperature regimes ongermination since other factors, such as moisture, disturbance,monitoring frequency and shading, varied as well.ICH greenhouse samples probably received more moisture than59Figure 2.10 Daily maximum and minimum air temperatures recordedduring the germination monitoring periods on the ESSF and ICHfield sites, and in the greenhouse.6 0Figure 2.11 Typical pattern of hourly average air temperaturesover a 4 day period in the greenhouse (Jan. 25-28, 1990) and atthe ICH field study site (July 7-10, 1990).61did the ICH field plots, which could have explained greatergermination in the greenhouse. Lower soil moisture may also haveallowed soil temperature to rise higher, possibly to lethallevels for seeds. Shading in the field, especially in the ESSFsite, could have inhibited germination by lowering soiltemperatures. The fact that greenhouse samples were monitoredmore frequently and were split into layers, thus exposing more ofthe profile to air and light, may also have contributed to thehigher germinant densities observed in the greenhouse.2.4 Conclusions The density of germinants, number of taxa and variation ingerminant numbers among samples, appeared to be within the rangesencompassed by other comparable to other greenhouse germinationstudies of northern temperate forest soils. Almost all of themajor germinant taxa, or related species, from both greenhouseand field have been found in other comparable studies.The greenhouse germination appeared to provide a reasonablygood estimate of the numbers and species composition of the moreabundant seed bank taxa, although some relatively rare taxa thatgerminated in the field were not present in the greenhousesamples. The greenhouse germination overestimated the number offield germinants and included some taxa not found in the field.Therefore, while greenhouse germination may provide informationon the total seed bank, it will not always predict what willgerminate in the field.This study indicates that there is a significant number ofburied seeds in the forest floor of moist ESSF sites, and that62many of these will germinate after logging, even if the forestfloor is not further disturbed. The taxa that germinated in thefield tended to be those whose seeds were more abundant in the 0-1 cm depth class of the greenhouse samples.In contrast, a much smaller seed bank was present in thegreenhouse samples from the ICH site and very few seedsgerminated in the field. Therefore, germination from seed banksdoes not appear to be an important means of regeneration of anyspecies on mesic ICH sites. This result also shows that siteproductivity, along with vegetation history and stand structure,is probably more important than altitude in determining theextent of the buried seed population.Horizontal distribution of the most abundant greenhousegerminant taxa was clustered at both scales examined. Germinantswere concentrated into smaller areas than the maximum possibleand showed relatively uneven distributions within the samples inwhich they occurred. The relative abundance of germinants pertaxon was not related to the horizontal distribution ofgerminants. The degree of dispersion and clustering variedgreatly among the germinant taxa.Despite a very large number of samples compared to otherstudies, variation in germinant density among samples was high.This indicates that, while increasing sample size may increasethe precision with which seed numbers are estimated, between-sample variation is not a good measure of that precision.Vertical distribution of germinants was highly varied bothamong and within taxa. Although overall results showedincreasing, decreasing and centre-peak distributions with63increasing depth, closer examination of individual samplesrevealed two important facts. First, the observed patterns weremade up of individual relatively thin (1 to 2 cm) clusters ofseeds located at different depths in the profile, rather than aconsistent pattern found in each sample. Second, thedistributions of some taxa were highly skewed by one or two verylarge clusters of germinants in one or two samples. Theimplication of these findings for sampling is that relativelylarge numbers of samples are required not only to assess seednumbers and species but also to describe the three-dimensionaldistribution of buried seeds. In addition, samples must bedivided into many relatively thin layers to provided goodresolution of the patterns of vertical distribution ofgerminants.Some germinant taxa that grow in disturbed areas had moreseeds deeper in the forest floor profile, suggesting that inputmay have decreased over time. Another early successional taxon -Epilobium spp. - was located closer to the surface of the profileindicating more recent origin through wind-blown seed dispersal.However, nothing is known about the burial mechanisms at work onseeds in these sites and therefore it cannot be concluded thatthere is a relationship between vertical distribution and seedage.Taxa that grow in mature forests and those characteristic ofearly successional disturbed habitats were both present amongseed bank germinants from both sites. In the ESSF site a largeproportion of the germinants were of mature-forest taxa.Continuous seed input over many years may have been the means64through which these taxa maintained seed banks. The clusterednature of both the vertical and horizontal distribution ofgerminants, however, suggests that periodic, small disturbancescreated gaps in the forest which stimulated seed production. Ifforest plantations are managed for a dense canopy, species thatrely on these disturbances to maintain seed reserves, may be lostor severely reduced.Differences in the temperature regime between greenhouse andfield environments may help to explain differences in germinationbetween these locations. However, these differences may haveresulted from a number of other factors, such as reduceddaylength in the greenhouse, lack of moisture in the ICH fieldsite, and disturbance in the greenhouse in the form of samplesplitting. The latter may have stimulated higher seedgermination. Alternatively, the higher density of greenhousegerminants may be due to the longer period and greater frequencyof germination monitoring, particularly for the ICH samples.Given the wide variation in temperature conditions underwhich seeds germinated in both the greenhouse and the field, therequirements for germination do not appear to be very narrow forany taxon. While there may have been taxa that did not germinatebecause a narrow set of requirements was not met, this is notvery probable since such a strategy is unlikely to evolve in atemperature environment that is highly varied.65CHAPTER 3 THE EFFECTS OF FIRE ON THE SEED BANK3.1 IntroductionDormancy and germination in seeds are known to be influencedby temperature, light, moisture, and chemistry (Mayer andPoljakoff-Mayber 1982; Bewley and Black 1985). Of these, thechanges in the soil temperature environment, both during andafter burning, are likely to have a profound effect on buriedseeds. Burning elevates soil temperatures during the fire, andusually results in higher temperatures and more extreme diurnalfluctuations in temperature in the growing seasons after the burn(Wells et al. 1979; Feller 1982). Fire severity, which determinesa) soil temperature during (magnitude and duration), and after(magnitude and fluctuation) the fire, and b) quantity of surfaceorganic matter removed, and the characteristics and verticaldistribution of buried seeds, will determine how seeds areaffected by fire.Fire is an important source of disturbance in both unloggedforests and after logging in the south central interior of B.C.During the 1988/89 to 1990/91 fiscal years, wild fires burned3048 ha of forest, while slashburning was carried out on 31,748ha (36% of the area harvested during this period) in the KamloopsForest Region (B.C. Ministry of Forests 1989, 1990, 1991).Although such burning has been practiced for many years to managevegetation, reduce fire hazard and increase planter access,relatively few studies have attempted to determine whethervegetation management objectives are being met. In interior andnorthern B.C. no studies have specifically addressed the response6 6of seed banks to fire. It is particularly important to determinehow plants respond to fire in areas where fire is not a frequentevent, if the natural diversity of these communities is to bemaintained. However, the nature of post-burn conditions in thesoil has not been assessed in relation to the germinationrequirements of seeds.During forest fires and slashburns seed mortality may resultfrom direct combustion of seeds along with the forest floor, orfrom lethal temperatures being reached in the forest floorprofile. More moderate temperatures deeper in the profile maystimulate germination or have no effect on seeds. Germinationcould also be affected by the alteration in the post-firetemperature environment. The magnitude and duration of elevatedtemperatures can determine whether or not seed mortality occurs(Stone and Juhren 1951; Went et al. 1952; Floyd 1966). Hightemperatures for very short periods may do less damage, forexample, than prolonged exposure to more moderate temperatures.There is little information on the patterns of forest floorheating during actual fires. Data are relatively difficult tocollect with a sufficiently large sample size to adequatelycharacterize the considerable variation that occurs during mostfires. Forest floor consumption is another measure of fireseverity that is simple to collect and might provide anindication of heating during burns if a relationship could beestablished between depth of burn and heating in the remainingforest floor.67The specific objectives of this component of the study wereto:1) quantify the effects of slashburning on germination fromseed banks of burned forest soils in the ESSF and ICH zones insouth central British Columbia;2) quantify temperatures in the forest floor duringslashburning;3) determine if there is a relationship between forest floortemperature and depth of burn during a slashburn; and4) quantify the effects of shading and burning on post-burnsoil temperatures and on germination of buried seeds.3.2 Methods 3.2.1 Study areasIntensive studies were carried out on one ESSFwc2 and oneICHwkl site. These sites were both operationally slashburned inthe fall of 1989. The layout of plots and subplots on these sitesis described in detail in Chapter 2, Section 2.2.1.In 1990, six additional ICH and seven ESSF sites in theClearwater Forest District were surveyed for germinants (SeeChapter 2 Figure 2.1 for site locations). These sites had allbeen logged during the winter of 1988/89 and operationallyslashburned in the fall of 1989 and are hereafter referred to as'extensive sites'. Four of the ICH sites were located in theThompson Moist Warm variant (ICHmw3), the remaining two were inthe ICHwkl. All ESSF sites were in the ESSFwc2 variant (Table3.1).Identification of these sites was tentative because sampling68Table 3.1 Identification of the extensive field study sitesaccording to the Biogeoclimatic Ecosystem Classification system.SiteNumber LocationZone andVariantSiteSeriesMoistureRegime1 S. Foam Ck. ESSFwc2 07 to 08 Subhygric to Hygric2 Chalet Rd. ESSFwc2 01 Mesic3 Barriere Mt. ESSFwc2 01 Mesic4 Wallace Ck. ESSFwc2 (01) to 07 (Mesic)^to Subhygric5 Wallace Ck. ESSFwc2 07 Subhygric6 Fowler Ck. ESSFwc2 07 Subhygric7 Camp 6 Ck. ESSFwc2 01 Mesic1 Berry Ck. ICHmw3 07 to 08 Subhygric to Hygric2 Berry Ck. ICHmw3 05 Submesic3 Finn Ck. ICHmw3 04 & 08 Submesic and Hygric4 Otter Ck. ICHmw3 04 Submesic1 S. Foam Ck. ICHwkl 01 to 05 Mesic to Subhygric2 S. Foam Ck. ICHwkl 06 Subhygric69was carried out after slashburning and therefore many key plantspecies were missing. Nevertheless, a range of site series fromeach variant appeared to be represented (Lloyd et al. 1990). Someof the ESSF sites were identified before burning for anotherresearch project.The ESSFwc2 sites (Table 3.1) included Azalea - Feathermoss(05), Azalea - Oak fern (01), Devil's club - Lady fern (07), andHorsetail - Sphagnum (08) site series. ICHwkl site series wereOak fern (01), Devil's club - Lady fern (05) and Devil's club -Horsetail (06) (Table 3.1). ICHmw3 site series includedSoopolallie - Twinflower (04), Falsebox (05), Devil's club - Oakfern (07) and Skunk cabbage (08) (Table 3.1). Some sites includedmore than one site series because of varied small-scaletopography.3.2.2 Field germination3.2.2.1 Data collection Methods for collecting field germination data for bothburned and unburned areas of the intensive sites are outlined inChapter 2, Section each extensive site nine 0.5 X 0.5 m plots were located 5m apart along a transect. The total area sampled per site was2.25 m2 , equal to the area of the burned subplots on eachintensive site. Transects were subjectively located in areas thatwere representative of the cutblock in terms of speciescomposition and abundance. Sampling was carried out from July 21to 23, 1990. All germinants inside each plot were counted andidentified if possible.703.2.2.2 Data analysis Density was calculated for germinants of all taxa in theburned subplots and plots of the intensive sites and plots on theextensive sites. Germinant density was calculated on a per m2basis. Species composition of germinants in the extensive siteswas examined to assess the ecological distribution of seed banktaxa found in the intensive sites.3.2.3 Effects of fire3.2.3.1 Data collection During the 1989 burns, soil temperatures were recorded underfour subplots each in three of the burned plots. Temperature datawere collected with a Campbell Scientific CR10 data logger and 36channel multiplexer. At each location thermocouples were buriedat 1, 2 and 4 cm below the forest floor surface. Eleven of the 1cm thermocouples were coated Chromel-Alumel wire, connecteddirectly to the data logger. The remaining thermocouples werecoated Copper-Constantine wire connected to the multiplexer whichwas, in turn, connected to the data logger.The data logger and multiplexer were enclosed in metal boxesand wrapped in plastic garbage bags to exclude moisture and soil.They were buried in a hole under approximately 30 cm of mineralsoil. Thermocouple wires were buried in trenches underapproximately 10 cm of mineral soil. Temperatures were recordedevery 10 seconds, averaged, and output once per minute. In bothcases the datalogger was excavated and stopped as soon aspossible the day after the burn.The ESSF site was burned on September 14, 1989 and the ICH71site was burned on October 9, 1989. The codes and indices of theCanadian Fire Weather Index System (Canadian Forestry Service1984) at the time of burning for the ESSF site were: FFMC=86,DMC=11, DC=47, ISI=7, BUI=14 and FWI=9. When the ICH site wasburned, the codes and indices were: FFMC=82, DMC=29, DC=165,ISI=2, BUI=41 and FWI=5.As a result of technical problems, only temperatures lessthan 100°C were recorded during the 1989 ICH burn and data fromthe 1989 ESSF burn were unusable. Therefore, on September 20,1990, temperatures were recorded during operational slashburningof another ESSF cutblock near the intensive ESSF site. For thisburn, two Campbell Scientific CR10 data loggers and Chromel-Alumel thermocouple wire were used to record forest floortemperature at four locations. Thermocouples were installed at 1,2, 3, 4, and 6 cm below the surface at all four locations. Atthree locations an additional thermocouple was placed at 10 cmand at one of these locations there was also a thermocouple atthe forest floor surface. All other procedures were similar tothe 1989 burns.Depth of burn was measured using pins made of 2.4 mm steelwelding rod bent to a right angle with the measurement arm 12 cmlong. The pins were placed at each of the 25 subplots per plot inthe area to be burned (see Figure 2.2 for layout). Pins wereinstalled (Figure 3.1) and litter depth recorded in July andAugust of 1989. A single measurement of litter depth was madejust outside each subplot, to avoid disturbing the seed bank.Forest floor consumption (depth of burn) was recorded within twodays after the sites were burned. Depth of burn was measured at72Figure 3.1 Placement of depth of burn pins over the subplots andmeasurement of forest floor consumption on the intensive studysites.73the middle and 1 cm from each end of the arm of the pins (Figure3.1).On the 1990 burn three depth of burn pins were installedwith the arms parallel and five cm apart over each group ofthermocouples (Figure 3.2). Three measurements were taken alongeach pin for a total of nine per thermocouple location, the dayafter the burn. Data analysis The number of minutes that temperatures were > 60, 70 and100°C was determined for each location and depth in both the 1989ICH burn and the 1990 ESSF burn. Number of minutes > 80 °C wasalso determined for the 1990 ESSF burn. The duration oftemperatures over 60, 70 80 and 100°C was correlated with themean depth of burn of the subplots (SAS 1988). Correlationanalysis was also used to determine if there was a relationshipbetween mean depth of burn and maximum temperature reached duringthe 1990 ESSF burn for the 1, 2 and 4 cm depths.The mean depth of burn was calculated for each subplot andplot. Thirteen subplots were excluded from the ESSF analysisbecause the pin had been disturbed before sampling and depth ofburn could not be determined. However, all 225 subplots were usedfor germination analyses that did not involve depth of burn. Fourextra subplots were installed on the ICH site to accommodateavailable lengths of thermocouple wire, for a total of 229 burnedsubplots, all of which had reliable measurements.An estimate of seeds consumed along with the forest floorwas calculated as a partial determination of seed mortality. TheFigure 3.2 Placement of depth of burn pins over thethermocouples on the ESSF site burned in 1990.7475potential number of seeds in each subplot was based on the meannumber of greenhouse germinants per 1 cm thick layer in eachdepth class. Seed consumption was calculated as the percentage ofthe depth class consumed, for each subplot. Since depth of burnwas measured to the nearest 0.1 cm, consumption was calculated in10% increments. For example, a depth of burn of 0.3 cm wastranslated into consumption of 30% of the estimated seeds in the0-1 cm depth class.Estimations of seed consumption and remaining seeds arebased on the assumptions that a) the greenhouse germinationrepresented seed numbers and distribution in the field, and b)that the vertical distribution of seeds was uniform within depthclasses. Because both distribution and numbers of germinants werefound to be highly variable in the greenhouse samples, however,these estimates probably contain some error.The relationship between the total number of germinants andaverage depth of burn in the burned subplots and plots wasexamined using correlation analysis. The data on germinants anddepth of burn both deviated severely from normal distributions,thus violating one of the assumptions of correlation analysis.Since neither log nor square-root transformations resulted innormally distributed data, the non-parametric rank correlationprocedure of Spearman (Zar 1974) was employed (SAS 1988). Numbersof germinants of individual taxa in the plots were alsocorrelated to depth of burn, but there were too few germinants inthe subplots to be analysed by species.To further examine the effect of fire on germination, anestimate was made of the number of seeds remaining in the post-76burn 0-1 cm layer of each subplot. This estimate was thencompared to the number of germinants per subplot by depth ofburn. Statistical analysis of the difference between the numbersof germinants and remaining seeds was not appropriate, however,because the latter was estimated.As with seed consumption, estimates of remaining seeds werebased on the number of germinants/layer in each greenhouse depthclass. In subplots where the post-burn 0-1 cm of forest flooroverlapped two pre-burn depth classes, the proportion of eachdepth class occupied was used to calculate remaining seeds. Forexample, 0-1 cm in subplots with a 1.4 cm depth of burn wasequivalent to the pre-burn 1.4 to 2.4 cm depths, and therefore60% of the estimated remaining seeds came from the pre-burn 1-2cm depth class and 40% from the pre-burn 2-3 cm depth class.3.2.4 Post-burn soil temperatures and shading in the intensivestudy areas3.2.4.1 Data collection See Chapter 2, Section for details of fieldtemperature data collection. Percent shading was also estimatedfor each subplot, to determine whether germination was affected.The four combinations of 'treatment' conditions for bothtemperature and germination were: shaded/burned, shaded/unburned,unshaded/burned and unshaded/unburned. Data analysis Since there was no replication of the soil temperaturemeasurements on the sites, statistical analysis of the77differences between treatment means was not appropriate. Meantemperatures were based on repeated measurements at eachtreatment location and were therefore not independent of eachother. The first 13 days were excluded from calculation of themean temperatures because the thermocouples had not yet beenshaded. Due to malfunctions in the temperature recording systemssome data were unusable. Thirty-nine days of data were excludedfrom the shaded/unburned location of the ESSF site and 13 days ofdata were excluded from the shaded/burned location of the ICHsite.The effects of burning and shade on field germination in theESSF subplots were examined with 'goodness of fit' analysis totest the null hypothesis that the ratio of germinants pertreatment was the same as the ratio of subplots per treatment.The frequencies of subplots per treatment were considered theexpected ratios for this analysis. Germinants in all burnedversus all unburned subplots were tested first. Germinants inshaded versus unshaded subplots within the burned and unburnedtreatments were then tested. There were too few germinants in theICH subplots to be analysed statistically.In all three tests, the number of degrees of freedom was 1.Therefore the Yates correction for continuity was employed toreduce the possibility of rejecting a true null hypothesis (TypeI error) due to an inflated, calculated chi-square statistic (Zar1974). In this procedure, 0.5 is subtracted from the absolutevalue of each observed frequency - expected frequency value usedto calculated the chi-square statistic.783.3 Results and discussion 3.3.1 Field germination after burning3.3.1.1 Germination on the burned intensive sites in comparison to the unburned seed bank and pre-burn vegetation It is possible that some species were dispersed onto thesites after the fire, thus contaminating the seed bank of theburned plots. Nearby plants of Epilobium angustifolium wereobserved to have seeds which could have been blown onto bothsites after the fire. However, seeds of fruit-bearing speciessuch as Ribes spp., Vaccinium spp., and Sambucus racemosa, thatcould have been carried onto the burned plots by animals orbirds, had little or no fruit left by the time the site wasburned.A total of 49 germinants (22/m 2 ) in 36 (16%) of the 225burned ESSF subplots was recorded during the first post-burngrowing season (Table 3.2). On the last sampling date (Aug. 26,1990), 715 (9/m 2 ) germinants were recorded in the burned plots.The total density was much higher in the unburned subplots thanin the burned subplots and plots.There were eight germinant taxa plus unidentifieddicotyledons in the burned ESSF subplots. The most abundant wereunidentified dicotyledons and Epilobium spp. (27% each),Epilobium angustifolium (14%), and Ribes spp. (10%). Theseaccounted for 78% of the germinants (Table 3.2). In addition tomost of the taxa found in the burned subplots, Epilobiumciliatum, Carex spp., Ribes laxiflorum, Cirsium sp. and Hieraciumsp. germinants were found in the burned plots on the lastsampling date.79Table 3.2 Number and density (number/m 2 ) of germinants in theburned and unburned field plots and subplots and in thegreenhouse samples from the ESSF intensive site.TaxonBurned Seed Bank Germinants Unburned Seed Bank GerminantsField SubplotsNumber DensityField PlotsNumber DensityField SubplotsNumber DensityGreenhouseSamplesNumber DensityPoaceae 1 <1 5 <1 14 19 45 15Epilobium angustifolium 7 3 359 4Epilobium sp. 13 6 20 27Epilobium ciliatum 33 <1 100 34Ribes lacustre 3 1 89 1Ribes spp. 5 2 1 <1 4 5Ribes laxiflorum 2 <1 1 <1Viola spp. 3 1 53 <1 2 3Luzula parviflora 1 <1 8 <1 547 184Sambucus racemosa 3 1 136 2 11 4Carex spp. 24 <1 214 72Mitella spp. 50 67 1183 398Vaccinium sp. 6 8 99 33Picea sp. 1 1 6 2Valeriana sitchensis 4 5 1 <1Cirsium spp. 1 <1Hieracium spp. 1 <1Abies lasiocarpa 1 1Pinaceae 4 5Rubus sp. 1 1Ericaceae 24 8Graminoid 6 2Galium sp. 2 <1Dicotyledons 13 6 3 <1 21 28 352 119Total 49 22 715 9 128 171 2591 872n 225 9 75 297Area^(m2 ) 2.25 81 0.75 2.9780Poaceae was the only germinant taxon to be recorded in allburned and unburned ESSF seed banks assessments. Luzulaparviflora, Sambucus racemosa and Viola spp. also germinated fromboth burned and unburned forest floor but not from all unburnedseed banks. Carex spp. germinated only in the burned plots andgreenhouse samples. The highly clustered distribution of thistaxon may account for it's absence from the burned subplots.Viola spp. germinants were missing from the greenhouse samples,which may indicate that this taxon originated from recent seedrain, rather than from the seed bank. Both Luzula parviflora andSambucus racemosa were missing from the unburned subplots, whichcould have been a function of the much smaller sampling areainvolved compared to the burned seed bank or greenhouse samples.Epilobium spp. germinants were found in all four ESSF seedbank assessments but were not identified to species in theunburned field subplots. E. angustifolium was the most abundantspecies in the burned plots but was absent from the greenhousesamples, where only E. ciliatum was recorded. Similarly, Ribesspp. germinants were found in both burned and unburned seed banksbut were not identified to species in the unburned subplots.These germinants could have been either R. lacustre which wasonly found in the burned seed bank, or R. laxiflorum which wasidentified in both the burned plots and greenhouse samples.Because of these overlaps, it was not possible to determinewhether or not Epilobium angustifolium and Ribes lacustregerminated only from burned forest floor.Cirsium sp. and Hieracium sp. were identified only from theburned ESSF plots. Only one germinant of each was recorded,81however, and both have wind-dispersed seeds that could haveoriginated from off-site sources during the germinationmonitoring period. Two of the most abundant unburned seed banktaxa, Mitella spp. and Vaccinium spp., were missing from theburned plots and subplots. Valeriana sitchensis and Picea sp.were also found only in the unburned subplots and greenhousesamples. In addition, Ericaceae germinants were only found in thegreenhouse samples.Epilobium angustifolium was the most abundant taxon in fiveof the ESSF plots. Sambucus racemosa had the most germinants intwo plots, and Ribes lacustre and Viola spp. were most abundantin one plot each.During the first growing season 14 (6/m 2 ) germinants emergedin 13 (6%) of the 229 burned ICH subplots. Half these germinantswere unidentified dicotyledons. Of the remainder, three wereRibes laxiflorum, two were Ribes lacustre, and one each wereRubus idaeus and Ribes spp. (Table 3.3). In the burned ICH plots504 germinants (6/m 2 ) were recorded. Sambucus racemosa was themost abundant (35%) followed by Rubus idaeus (16%), unidentifieddicotyledons (14%), Ribes laxiflorum (10%), Paxistima myrsinites(8%) and Ribes spp. (7%). These accounted for 90% of thegerminants in the burned plots (Table 3.3). Burned plots andsubplots both had much higher germinant densities than did theunburned plots.Rubus idaeus was the only germinant species found in allfour ICH seed bank assessments. Sambucus racemosa, Anaphalismargaritacea and Poaceae germinants occurred in both burned andunburned seed banks, although all three were missing from the82Table 3.3 Number and density (number/m 2 ) of germinants in theburned and unburned field plots and subplots and in thegreenhouse samples from the ICH intensive site.TaxonBurned Seed Bank Germinants Unburned Seed Bank GerminantsField SubplotsNumber DensityField PlotsNumber DensityField PlotsNumber DensityGreenhouseSamplesNumber DensityRubus idaeus 1 <1 81 1 1 <1 6 2Ribes laxiflorum 3 1 50 <1 3 1Ribes spp. 1 <1 35 <1 6 <1 2 <1Ribes lacustre 2 <1 15 <1Epilobium angustifolium 9 <1 1 <1Epilobium spp. 1 <1 4 <1Epilobium ciliatum 27 9Sambucus racemosa 178 2 4 <1 30 10Anaphalis margaritacea 8 <1 1 <1 3 1Poaceae 1 <1 5 2Thuja plicata 2 <1 497 165Vaccinium sp. 1 <1 65 22Picea sp. 1 <1 2 <1Paxistima myrsinites 41 <1Rubus spp. 10 <1Abies lasiocarpa 2 <1Ericaceae 16 5Asteraceae 4 1Pinaceae 2 <1Juncus ensifolius 1 <1Graminoid 1 <1Rubus parviflorus 1 <1Dicotyledons 7 3 73 <1 1 <1 24 8Total 14 6 504 6 22 <1 689 229n 229 9 3 301Area^(m2 ) 2.29 81 27 3.0183burned subplots.Epilobium ciliatum germinants were only found in the ICHgreenhouse samples. However, some of the Epilobium spp.germinants in both burned and unburned field seed banks couldhave been this species. Similarly, Ribes lacustre germinantsappear to have been confined to the burned seed bank, but theRibes spp. germinants in the unburned plots and greenhousesamples may have been this species. In addition, the Rubus sp.germinants in the burned plots could have been R. idaeus.Paxistima myrsinites, a relatively abundant germinantspecies, was found only in the burned ICH plots. Conversely,Vaccinium spp., Thuja plicata and Picea sp. germinants were foundonly in the unburned plots and greenhouse samples, whileEricaceae germinants emerged only from the greenhouse samples.Sambucus racemosa had the highest number of germinants infive of the burned ICH plots and the same number as unidentifieddicotyledons in a sixth. Rubus idaeus was the most abundant taxonin two plots while Paxistima myrsinites was most common in oneplot.Viola spp., Poaceae, Ribes lacustre and Luzula parvifloraoccurred as germinants in the burned ESSF subplots and plots, andin the pre-burn vegetation. Of these taxa, Viola spp. and Poaceaewere also found in the unburned subplots. Luzula parvifloragerminated from the greenhouse samples but not the unburned ESSFsubplots. No taxa occurred in both the original vegetation andthe burned ICH plots and subplots. There were fewer species amonggerminants than in the pre-burn plant community on both ESSF andICH sites.84It was not possible to be absolutely certain that any taxon,with the possible exception of Paxistima myrsinites, wasexclusive to either the burned or the unburned seed banks becauseunidentified dicotyledons were present in all locations. However,it is unlikely that taxa as numerous as Mitella spp., Thujaplicata and Vaccinium spp. in the unburned seed bank, were absentby chance from the larger area of the burned plots. The fact thatVaccinium spp. germinants were found only in the unburned seedbanks of both the ICH and the ESSF sites strengthens the evidencethat seeds of this taxon did not tolerate burning. Archibold(1989) suggests that the seed coats of Vaccinium spp. are toothin and soft to protect seeds from injury during fire.Paxistima myrsinites germinants had distinctcharacteristics, even in the cotyledon stage, and therefore it iscertain that the species did not germinate from the unburned seedbank. This species may be dependent on fire to break dormancy, oron post-fire conditions for germination. Paxistima myrsinites hasbeen found in seed banks by other researchers (Strickler andEdgerton 1976; Kramer and Johnson 1987) but in very small numbers(2 out of 211 germinants and one out of 2406 seeds,respectively). In the former study, some samples were treatedwith heat, but the authors do not state whether the Paxistimamyrsinites germinants originated from these or from unheatedsamples.The lack of species that were clearly adapted to germinateafter fire may have been because, although fire is part of theecology in the study area, the frequency of natural fires isrelatively low. The mean number of years between fires is 150 to85500 years in the ESSF zone and 100 to 350 years in the ICH zone(Parminter 1992). However, the nothing is known about the effectof fire frequency on the evolution of germination requirements ofseed bank species in these forests.The impact of fire on the number of germinant taxa could notbe determined since the area involved for the burned and unburnedseed banks was different. Also the greenhouse germinantsrepresented the entire thickness of the forest floor whereasgerminants in the field plots and subplots probably originatedfrom a limited portion of the profile.Comparisons between burned and unburned seed banks in theliterature are not based on monitoring operational burns andgermination in the field. One study showed that artificiallyburned samples had fewer germinants than unburned control samplesbut this difference was not significant (Ingersoll and Wilson1990). Samples collected along a transect from unburned toseverely burned areas after a wildfire, yielded the highest meangerminant density from plots subjectively judged to be moderatelyburned, and the fewest from unburned plots (Archibold 1979).However, the sample size was not equal for each burn severity andthere was considerable overlap in germinant densities among plotsfrom different areas, and therefore, these results should beregarded with caution. Also, the criteria used to assign burnseverity were not defined.Two studies have recorded the origin of plant species thatgrew after logging and burning, including those that germinatedfrom seeds in the field. The density of shrub germinants twoyears after burning in a Thuja plicata/Clintonia uniflora habitat86type in northern Idaho was approximately 6/m2 (Morgan andNeuenschwander 1988b), slightly more than shrub density (5germinants/m2 ) for the ICH burned plots in the present study.Density values were not presented for germinants in a study of amixed forest site in southwestern Nova Scotia (Martin 1955).All of the more abundant germinant taxa from the burnedplots and subplots of both the ESSF and ICH sites have beenreported in other studies (see Chapter 2, Section ofunburned forest floor. Viola spp. and Carex spp. seed bankgerminants have also been observed in the field after logging andslashburning by Martin (1955). Both of these genera were alsofound in the burned areas of the present study. Three othergerminant genera (Ribes, Rubus and Sambucus) were found in boththe present study and that of Morgan and Neuenschwander (1988b),but there were no species in common.The general absence of Epilobium angustifolium on the ICHsite may have been because the burn was much later than the ESSFsite when most of the seeds would have already been dispersed.The ICH site may also have provided a less hospitable seedbedthan the ESSF site, due to lack of moisture or some other factor.Seed densities in temperate forest soils have been describedas low compared to the more widely studied seed banks ofagricultural weeds and other vegetation types (Roberts 1981).What is not known is how many germinants are needed to make asignificant contribution to post-burn vegetation. Nor is it clearin these ecosystems how many seeds must be in the soil to resultin enough germinants to replace the parent plants. In fact, thequantity of seeds may not be as important as survival of87germinants, which may depend on chance climatic variations. Inthe present study, germinants generally did not grow as much overthe season in the unburned areas as in the burned areas. This waswhy fewer germinants were identified to species among theunburned field germinants. It is possible, therefore, that lowergermination on the burned areas is compensated for by bettergrowth and survival.Studies of an arctic tundra site (Racine 1981) and a Thujaplicata site in northern Idaho (Morgan and Neuenschwander 1988a)have shown that regeneration from buried seeds is favoured byhigh severity burns. Morgan and Neuenschwander (1988a) suggestthat high severity burns provide a more favourable seedbed byexposing more mineral soil, and are more likely to kill roots andrhizomes thereby reducing vegetative regrowth. However, fire thatis severe enough to destroy root systems is not likely to favourregeneration from buried seeds which will be consumed along withthe forest floor, unless there is a large number of seeds in themineral soil.Several taxa that germinated from the seed bank alsoregenerate vegetatively after fire or other disturbances. Theseinclude Vaccinium spp., Sambucus racemosa, Ribes laxiflorum andR. lacustre, Mitella spp. and Rubus parviflorus. For thesespecies, the seed bank may be a means of diversifying survivaltechniques to accommodate different disturbances, or simply achance occurrence not relied upon for regeneration. In thepresent study, burning appears to have reduced the number ofspecies that regenerate both vegetatively and from seed.The unburned ESSF subplots may have had a higher germinant88density than the burned subplots because: 1) the temperaturereached during the fire was high enough to destroy the seeds nearthe surface but not high enough to stimulate germination fromdeeper layers, 2) the species present in the seed bank wereparticularly sensitive to heat, or 3) the unburned areas providedbetter germinating conditions (e.g. more moisture).The unburned ICH plots may have had a lower germinantdensity than the burned plots and subplots because: 1) the thickmoss layer inhibited germination by blocking light and/orbuffering temperature changes, 2) the area selected for theunburned plots had fewer seeds than the burned to start with, or3) the severity of the fire, while killing most of the surfaceseeds, penetrated deeply enough to stimulate germination of themore deeply buried seeds. Germination in the extensive and intensive study areas Twelve taxa of germinants occurred in the seven ESSFwc2extensive sites (Table 3.4). The most abundant germinant taxa onthese sites were Epilobium angustifolium (38%), Sambucus racemosa(21%), Carex spp. (17%), Rubus parviflorus (11%), Ribes spp.(4%), and Ribes lacustre (2%), accounting for 93% of thegerminants. Epilobium angustifolium was the only species thatoccurred in all seven sites while Sambucus racemosa occurred insix sites. Epilobium ciliatum and Anaphalis margaritacea werefound in three sites. All other species were found in only one ortwo sites. Rubus parviflorus, with the 4th highest number ofgerminants, occurred in only three plots of one site.Germinants belonging to six taxa and unidentified89Table 3.4 Density of germinants (number/m 2 ) in the extensiveplots and intensive burned plots and subplots of the ESSFwc2study sites.TaxonExtensive Sites Intensive Site1 2 3 4 5 6 7 Plots SubplotsEpilobium angustifolium 11 2 11 7 19 4 2 4 3Sambucus racemosa 2 2 23 4 <1 <1 2 1Anaphalis margazitacea <1 <1 <1Epilobium ciliatum <1 <1 2 <1Carex spp. 14 11 <1Ribes lacustre <1 3 1 1Luzula parviflora 3 <1Ribes spp. 6 <1Epilobium sp. <1 <1Rubus sp. <1 <1Rubus parviflorus 16Rubus idaeus <1Viola spp. <1 <1Poaceae <1 <1Dicotyledons <1Ribes laxiflorum <1Rieracium spp. <1Cirsium spp. <1Total 13 10 26 53 23 5 16 9 790dicotyledons were found in the two ICHwkl extensive sites (Table3.5). The most abundant germinant taxa were Sambucus racemosa(44%), Rubus idaeus (31%), Epilobium angustifolium (7%), Ribesspp. (7%), Anaphalis margaritacea (4%), and Ribes lacustre (4%)accounting for 97% of the germinants. Sambucus racemosa and Rubusidaeus were the only species of germinants found in both ICHwklsites. All other taxa were confined to one site each.Germinants of 13 taxa and unidentified dicotyledons occurredin the four ICHmw3 extensive sites (Table 3.5). The most abundantgerminant taxa were Rubus idaeus (34%), Sambucus racemosa (25%),Paxistima myrsinites (13%), Rubus parviflorus (9%), and Populustremuloides (6%) accounting for 87% of the germinants. No taxonoccurred in all the sites but Paxistima myrsinites, Rubusparviflorus, Populus tremuloides, Rubus spp. and Epilobiumangustifolium were found in three of the four sites. Both Rubusidaeus and Sambucus racemosa germinants were found in two out ofthe four sites. The remaining species occurred in only one site.Despite the variation in species composition andbiogeoclimatic identification of the extensive sites, severalgerminant taxa were broadly distributed. Sambucus racemosa andEpilobium angustifolium germinants occurred in all biogeoclimaticvariants and both extensive and intensive sites. Sambucusracemosa germinants occurred in most of the extensive sites andall plots of both intensive sites. Epilobium angustifoliumgerminants had the highest abundance and frequency in theintensive and extensive ESSFwc2 sites but relatively lowfrequency and abundance in both intensive and extensive ICHsites.91Table 3.5 Density of germinants (number/m 2 ) in the plots of theICHmw3 and ICHwkl extensive study sites and in the burned plotsand subplots of the intensive ICHwkl study site.Extensive Sites^Intensive SiteTaxonICHmw3 ICHwkl ICHwkl1 2 3 4 1^2 Plots SubplotsEpilobium angustifolium <1 2 <1 1 <1Sambucus racemosa 21 <1 7 2 2Rubus idaeus 25 5 2 4 <1 <1Paxistima myrsinites <1 <1 11 <1Anaphalis margaritacea <1 <1 <1Ribes lacustre <1 <1 <1 <1Populus tremuloides 2 3 <1Rubus sp. 2 1 <1Rubus parviflorus 8 <1 <1Asteraceae < 1Epilobium ciliatum <1Betula paperifera <1Carex spp. 1Ribes spp. 1Ribes 1axiflorum <1 1Abies lasiocarpa <1Epilobium spp. <1Poaceae <1Dicotyledons <1 <1 < 1 <1Total 59 9 8 12 12 8 4 392Ribes lacustre germinants occurred in all biogeoclimaticvariants and in the plots and subplots of both intensive sites.This species, however, had low presence and abundance among theextensive sites and among plots and subplots of the ICHwklintensive site. Only in the intensive ESSFwc2 plots were Ribeslacustre germinants relatively abundant with high presence (89%).The intermittent distribution of this species, both within andamong sites may reflect the distribution of mature plants.Rubus idaeus germinants were found almost entirely in ICHsites of both variants, and were abundant with high frequency inboth the intensive and extensive plots. Only one germinant ofRubus idaeus occurred in the ESSFwc2 extensive sites. Paxistimamyrsinites was not found in any ESSFwc2 sites. Carex spp.germinants were moderately abundant but with low frequency in theESSFwc2 extensive and intensive plots and sites, and had onlythree germinants in one ICHmw3 extensive plot. Luzula parvifloragerminants were found exclusively in the ESSFwc2 extensive andintensive plots, but with low abundance and frequency.Germinants of all other taxa were either rare or notconsistently associated with any of the variants sampled. Forexample, Rubus parviflorus germinants were relatively abundant inthe extensive ESSFwc2 and ICHmw3 plots, though with low frequencyin the former variant. Paxistima myrsinites germinants wererelatively frequent in the intensive ICHwkl and extensive ICHmw3plots but were not found in the extensive ICHwkl sites. Ribeslaxiflorum and Poaceae germinants were found only in the ESSFwc2and ICHwkl intensive sites, while Viola spp. germinants werefound only in the ESSFwc2 intensive plots and subplots. Apart93from Viola spp. and Ribes laxiflorum, most of the more abundantgerminant taxa that emerged in the intensive sites were found inthe extensive sites of one or both zones.3.3.2 Effects of temperature during the fire, and depth of burn,on seed mortality and germination in the fieldThe distribution of forest floor depth of burn (DOB) classesin the subplots of the ESSF and ICH intensive sites, is shown inFigure 3.3. Much more forest floor was consumed on the ICH sitethan on the ESSF site. For the ESSF site mean DOB was 0.3 cm(+ 0.04 S.E.) and maximum DOB was 2.7 cm, while for the ICH sitemean DOB was 1.5 cm (+ 0.07 S.E.) and maximum DOB was 5.9 cm.Over one-third (37%) of the ESSF subplots had 0 cm DOB, and 84%had less than 1 cm DOB. Only 3% of the ICH subplots had 0 cm DOB,while 67% had > 1 cm DOB. The number of subplots per DOB classdecreased sharply with increasing DOB on the ESSF site, whereason the ICH site the number of subplots with DOB between 1 and 2cm exceeded the number of subplots with < 1 cm DOB.In the ESSF plots, average DOB ranged from 0.2 to 0.8 cm.mean DOB was < 0.5 cm in all but one plot. Mean DOB for the ICHplots ranged from 0.6 to 2.7 cm. Six of the ICH plots had DOBbetween 1 and 2 cm, and only one plot had a mean DOB < 1 cm.Seed consumption was estimated to be much higher on the ICHsite even though the estimated total number of seeds in theforest floor of ESSF subplots was greater. Approximately 10% ofthe total seeds (1851) in the ESSF subplots were consumed alongwith the forest floor. Of the total seeds (525) estimated tooccur in the forest floor of the burned ICH subplots, 71% were94Figure 3.3 Number of subplots in 0.5 cm depth of burn classesfrom the ESSF and ICH intensive sites.95consumed. Most of the seeds consumed were from the 0-1 cm depthclass (84 and 87% in the ESSF and ICH, respectively).The fact that more seeds were consumed on the ICH site was afunction of both the vertical distribution of the seeds and theamount of forest floor consumed. A much greater proportion ofseeds occurred in the top 2 cm of the ICH forest floor comparedto that of the ESSF (92 and 55%, respectively) and a much highervolume of forest floor was consumed on the ICH site than on theESSF site.The number of seeds predicted to be present in the post-burn0-1 cm of forest floor in the burned subplots was much greaterthan the actual number of germinants in the subplots. Over allESSF subplots only 9% of the 522 predicted seeds germinated. Inthe ICH subplots 13% of the predicted 111 seeds germinated. Whenthese results were broken down by subplots within DOB classes,all ESSF subplots and most ICH subplots had many fewer germinantsthan were predicted. In ICH subplots with DOB of 1.7 and 1.8 cm,the number of germinants was equal to the number predicted, whilein subplots with a 1.9 cm DOB germinants were higher thanpredicted. These results for the ICH are, however, based on veryfew germinants (two, one and three, respectively) and thereforecould reflect a chance occurrence of seeds rather than a positiveresponse to DOB. In addition, three of the germinants were neveridentified so it was not possible to assess whether theseoriginated from buried seed or from seed blown onto the siteafter the burn.The comparison between remaining seeds and actual germinantsis tentative because germinants may actually have originated from96deeper than 1 cm from the post burn surface. Little is knownabout the depth from which seeds of any species can germinate(Parker et al. 1989) including the species found in this study.Results of the few existing studies indicate that maximumgermination depth varies widely among species and plantcommunities from 2-4 cm for desert herbs and shrubs (Kemp 1989),to 8 cm in tropical forest trees (Maun and Riach 1981), to 13.5cm for an agricultural weed (Colosi et al. 1988). Luzula pilosahas been reported to germinate from a 2 cm depth (Kujala 1926cited in Granstrom 1982) but there is no information on L.parviflora which germinated in this study.The low rate of germination compared to the predicted numberof seeds in the post-burn 0-1 cm of forest floor probablyindicates that seeds in the unconsumed forest floor were alsokilled by the fire. Whether additional seed mortality was causedby exposure to lethal heating during the fire or by other factorscannot be determined from the results of this study. Poorgermination may also have been the result of unfavourablegermination conditions after burning.Most burned ESSF subplots with germinants had DOB of < 0.7cm, although germinants were also found in two subplots with 1.8cm and 2.4 cm DOB. However, the germinants in these two subplotswere Epilobium spp., which could have germinated from seeds thatwere blown in after the burn, and not from the seed bank. Depthof burn was not significantly correlated with either the totalnumber of germinants in the subplots (rs = -0.04, p = 0.59), orthe total number of surviving germinants in the plots (Table3.6). None of the germinant taxa was significantly correlated97Table 3.6 Spearman rank correlation coefficients (r$) for thenumber of surviving germinants versus depth of burn in the plotsof the ESSF intensive site, for the most abundant taxa and totalgerminants.Taxon^ rsSambucus racemosa^0.36^nsRibes lacustre -0.43^nsViola spp.^ -0.12^nsEpilobium ciliatum^0.06^nsCarex spp. 0.12^nsTotal Germinants^-0.21^nsns = not significant at p=0.05n = 9 plots98with mean DOB in the plots (Table 3.6).Germinants were not present in any burned ICH subplots thathad DOB > 2 cm. The occurrence of germinants was not uniform asmany 0.1 DOB classes had no germinants and no more than 27% ofthe subplots in any one class had germinants. Except for one DOBclass (1.8 cm) most subplots with germinants occurred in classesthat had relatively high total numbers of subplots. However,several DOB classes with high numbers of subplots had nogerminants in them so the occurrence of germinants was not simplya function of the larger sample area. Depth of burn was notsignificantly correlated with the total number of germinants ineither subplots (rs = -0.10, p = 0.12) or plots (Table 3.7). MeanDOB was not significantly correlated with the number ofgerminants per plot for any of the taxa individually (Table 3.7).Temperatures at depths of 3 and 4 cm did not exceed 100 °Cduring the 1990 ESSF burn. There was a negative relationshipbetween the length of time temperatures at 1 cm exceeded 60, 70,80 and 100 °C and the mean depth of burn during the 1990 ESSFfire. This correlation was only significant for time exceeding70°C (Table 3.8). For other depths, correlation coefficients weregenerally positive but were not significant. Maximum temperaturesreached during the burn decreased with increasing forest floordepth at each measurement location (Table 3.9). The correlationbetween maximum temperature reached during the slashburn and meandepth of burn was not significant at any depth (Table 3.9).Temperatures exceeding 100 °C were recorded during the 1989ICH burn at 1 cm depth in all but one out of the 12 locations, at2 cm depth in nine locations, and at 4 cm depth in six locations.99Table 3.7 Spearman rank correlation coefficients (re) for thenumber of germinants versus depth of burn in the plots of the ICHintensive site, for the most abundant taxa and total germinants.Taxon^ rsSambucus racemosa^0.52^nsRubus idaeus 0.40^nsRibes laxiflorum -0.34^nsPaxistima myrsinites^-0.16^nsRibes spp.^ -0.49^nsRibes lacustre 0.33^nsTotal Germinants^-0.50^nsns = not significant at p=0.05n = 9 plots100Table 3.8 Correlation coefficients (r) for the number of minutestemperatures exceeded 60, 70, 80 and 100°C during the 1990 ESSFburn, versus mean depth of burn.Depth (cm)1^2^3^4>100°C -0.81 0.59>80 °C -0.87 0.43 0.11>70°C -0.96* 0.20 0.24 0.34>60 °C -0.87 0.10 -0.32 0.78* significant: p = 0.04All other values are not significant at p = 0.05.n = 4 locations101Table 3.9 Correlation coefficients (r) for maximum temperatures(°C) reached during the 1990 ESSF burn versus mean depth of burn,by location and depth.LocationDepth (cm)^1^2^3^4^Mean^r^P0 573.11 546.2 500.4 778.0 649.4 618.5 -0.72 0.282 503.6 270.0 102.1 232.0 276.9 0.78 0.223 85.0 76.8 68.7 86.9 79.4 0.09 0.914 63.8 72.1 44.3 52.8 58.3 0.74 0.266 27.6 31.2 28.1 28.1 28.8 0.23 0.7710 14.9 7.9 17.7 13.5Mean DOB 1.9 1.6 1.0 0.7 1.3102The length of time over 60, 70 or 100 °C was not significantlycorrelated with the mean depth of burn at any depth (Table 3.10).Correlation coefficients for the 1 cm depth were just slightlyless than the critical value of r (0.10 > p > 0.05) and all werepositive.No consistent relationship was demonstrated by theseresults, between either maximum temperatures or duration ofelevated temperatures during burning, and depth of burn. However,the forest floor of the ICH site was exposed to temperaturesexceeding 100 °C for longer periods of time at deeper locations inthe profile than was the ESSF site burned in 1990, and also had ahigher overall mean DOB. The intensive ESSF site (burned in 1989)had the lowest mean DOB of the three sites and may, therefore,have been exposed to lower temperatures than either the ICH siteor the ESSF site burned in 1990.The poor relationship between the number of germinants andDOB may have been because the range of DOB was too narrow to bebiologically significant, especially in the plots. Alternatively,variation in initial species composition, numbers anddistribution of seeds, combined with variation in DOB, may haveobscured species-specific sensitivity to fire. So few germinantsoccurred in the subplots, especially on the ICH site, that anyeffect of DOB would have been difficult to demonstrate. DOB wasuseful primarily as a means to estimate seed mortality throughforest floor consumption.The relative lack of correlation between DOB and eithergermination or the magnitude and duration of elevatedtemperatures during fire suggests that DOB may not be a reliable103Table 3.10 Correlation coefficients (r) for the number ofminutes temperatures exceeded 60, 70 and 100°C during the 1989ICH burn, versus mean depth of burn.Depth^(cm)1 2 4>100°C 0.56 0.36 0.09>70 oC 0.56 0.36 0.08>60°C 0.56 0.34 0.17None of the values were significant at p = 0.05n = 12 locations104indicator of soil heating. It is likely that the sample size usedin this study was too small to base a model of soil heating on.This does not mean, however, that temperature did not affectgermination. On both sites there appeared to be a level of DOBbeyond which no germination took place (0.6 cm and 1.9 cm in theESSF and ICH, respectively). This may indicate a threshold levelof heating for buried seeds, since the greenhouse germinationdemonstrated that seeds were present deeper in the profile.Although the specific heat tolerances of most species ofgerminants recorded by this study are not known, otherresearchers have demonstrated that seeds of many speciestolerate, and in some cases are stimulated to germinate by,exposure to a wide range of elevated temperature/time treatments(Stone and Juhren 1951; Went et al. 1952; Floyd 1966). Pratt etal. (1984) found that the germination of Epilobium ciliatum(formerly watsonii) seeds was the same from samples heated to 75and 100°C for 20 minutes. Seeds of various other species heatedto 100 °C for as little as five minutes (Stone and Juhren 1951;Went et al. 1952; Daubenmire 1968; Munoz and Fuentes 1989) and asmuch as 400 minutes (Floyd 1966) have germinated.Results from this and other studies (summarized in Wells etal. 1979) show that temperatures during burns can reach from 65 °Cto 545 °C at 1 cm depth and from a slight rise to > 100 °C at 5 cmdepth. Few studies, however, have determined the duration ofexposure to various temperatures or distinguished between forestfloor and mineral soil. For these reasons, direct comparison withthe present study cannot be made. Two studies in which forestfloor samples were heated for 20 minutes at 60, 80 and 100°C105(Strickler and Edgerton 1976), and 75 and 100°C (Pratt et al.1984) had the fewest germinants from the 100°C treatment althoughthe differences were not significant.The length of time seeds were heated in other studies wasgenerally 20 minutes or less. In the present study, theunconsumed forest floor was exposed to temperatures of > 100 °Cfor either similar or less time during the 1990 ESSF burn but formuch longer during the 1989 ICH burn. Experimental heattreatments also do not mimic the patterns of heating that arefound under natural conditions. In the field, buried seeds aresubjected to a continuum of temperature rise and fall. Thus seedsthat experience some minutes at 70 °C may also experiencetemperatures of 100 °C or more during the fire.3.3.3 Effects of burning and shade on post-burn soil temperatureand germination3.3.3.1 Temperature During most days the soil temperature was lowest from 5:00to 7:00 AM and reached a peak in the afternoon (usually betweennoon and 3:00 PM on the ESSF site and 3:00 to 5:00 PM on the ICHsite) (Figures 3.4, 3.5). On both sites, hourly temperaturesduring the hottest part of the day were generally higher atunshaded locations than at shaded locations, in both the burnedand the unburned areas at all depths. Burned areas had highertemperatures than unburned areas in both shaded and unshadedtreatments of the ESSF site (Figure 3.4). On the ICH site,however, the burned location had higher temperatures than theunburned location in the shaded area but lower temperatures in106Figure 3.4 Typical pattern of hourly mean temperatures ( 0C) overfour days (July 7 - 10, 1990) at 1 cm depth in the forest floorof the four shade and burn treatments in the ESSF intensive studysite. UB = unshaded/burned, UU = unshaded/unburned, SB = shaded/burned, SU = shaded/unburned.107Figure 3.5 Typical pattern of hourly mean temperatures ( °C) overfour days (July 10 - 13, 1990) at 1 cm depth in the forest floorof the four shade and burn treatments in the ICH intensive studysite. UU = unshaded/unburned, UB = unshaded/burned, SB = shaded/burned, SU = shaded/unburned.108the unshaded area (Figure 3.5). On the ESSF site, unshaded/unburned temperatures were often similar to shaded/burnedtemperatures, while on the ICH site shaded/unburned temperaturesoften overlapped unshaded/burned temperatures, especially at the2 cm depth.The difference between maximum and minimum temperatures (therange) varied considerably from day to day and from location tolocation (Figures 3.6, 3.7). The daily temperature range wasgenerally greater in unshaded than in shaded locations, and onhotter days. Day-to-day fluctuation of maximum temperatures wasalso greater in unshaded than in shaded locations.Minimum temperatures fluctuated from day-to-day much lessthan the daily maximum temperatures and the range of minima wasmuch narrower than the range of maxima for each location, overthe growing season. Minimum temperatures were also much moresimilar among locations and depths than maximum temperatures.Maximum temperatures were, therefore, largely responsible fordifferences in mean temperatures among locations and depths. Thiswas probably because the minima generally occurred duringdarkness or before sunrise, when shading and surface colour hadlittle or no influence on temperature.Over the season, the highest temperatures were reachedduring August 10th to 20th for the ESSF site (Figure 3.8) andAugust 5th to 15th for the ICH site (Figure 3.9). All locationson both sites showed a general increase in average temperaturesover the whole season but the trend was most pronounced at thelocations with the highest temperatures (unshaded/burned on theESSF and unshaded/unburned on the ICH site) (Figures 3.8, 3.9).109Figure 3.6 Daily mean range (maximum - minimum) of temperatures( °C) at 1 cm depth in the forest floor of the four shade and burntreatments in the ESSF intensive site during the 1990 growingseason. UB = unshaded/burned, UU = unshaded/unburned, SB =shaded/burned, SU = shaded/unburned.110Figure 3.7 Daily mean range (maximum - minimum) of temperatures( °C) at 1 cm depth in the forest floor of the four shade and burntreatments in the ICH intensive site during the 1990 growingseason. UU = unshaded/unburned, UB = unshaded/burned, SB =shaded/burned, SU = shaded/unburned.111Figure 3.8 Daily mean temperatures ( 0C) recorded at 1 cm depthin the forest floor of the four shade and burn treatments in theESSF intensive site during the 1990 growing season. UB =unshaded/burned, UU = unshaded/unburned, SB = shaded/burned, SU =shaded/unburned.112Figure 3.9 Daily mean temperatures ( °C) recorded at 1 cm depthin the forest floor of the four shade and burn treatments in theICH intensive site during the 1990 growing season. UU = unshaded/unburned, UB = unshaded/burned, SB = shaded/ burned, SU = shaded/unburned.113Mean temperatures for the whole season in the ESSF site werehighest for the unshaded/burned treatment, followed by theunshaded/unburned, shaded/burned and shaded/unburned treatments(Table 3.11). On the ICH site, the unshaded/unburned location hadthe highest mean temperatures over the whole season followed byunshaded/burned, shaded/burned and shaded/unburned treatments(Table 3.12).At both sites, hourly mean temperatures decreased withincreasing depth during the hottest part of the day but reversedduring the coolest period. For this reason, the range oftemperatures decreased with increasing depth. The daily patternof temperature at the 4 cm depth tended to lag behind that of the1 and 2 cm depths by one to two hours.The only exception to the above pattern occurred in theshaded/unburned location of the ESSF site, where the maximumtemperature was higher at the 2 cm depth than at the 1 cm depth.Although there is a slight possibility the leads were incorrectlyattached to the datalogger, it is more likely that thethermocouple was not working properly, since it appeared tomalfunction most of the summer.Higher temperatures were expected to occur in burned areasthan in unburned areas, in unshaded than in shaded areas, and atlocations closer to the surface compared to those deeper in theprofile (Smith and James 1978; Wells et al. 1979). The darksurface of burned forest floor can result in higher temperaturesthrough increased heat absorption. Shaded surfaces are coolerbecause they are protected from insolation (Wells et al. 1979).Unshaded soil can reach temperatures as high as 60 to 70 °C due to114Table 3.11 Maximum, mean and minimum temperatures (°C) recordedfrom June 19 to August 26, 1990, in the four shade and burntreatments on the ESSF intensive site.1 cm^ 2 cm^ 4 cmTreatment^max mean min^max mean^min^max mean minUB 43.9 16.1 2.4 39.7 15.4 4.3 27.0 14.6 5.1UU 34.0 14.3 4.7 26.6 13.8 5.7 25.7 13.7 5.9SB 24.8 14.0 4.9 21.8 13.8 5.5 19.6 13.5 6.0SU 18.5 11.8 6.3 22.6 12.9 6.0 19.1 12.3 6.4UB = unshaded/burned, UU = unshaded/unburned, SB = shaded/burned, SU = shaded/unburned115Table 3.12 Maximum, mean and minimum temperatures ( °C) recordedfrom June 18, to August 25, 1990, in the four shade and burntreatments on the ICH intensive site.1 cm^ 2 cm^ 4 cmTreatment^max mean min^max mean^min^max mean minUU 57.4 18.5 5.0 45.8 17.4 6.5Us 43.4 16.9 5.8 27.0 15.7 7.1SB 32.7 16.4 6.8 25.6 15.1 6.8 21.1 14.9 7.9SU 34.4 14.8 6.5 30.9 14.6 6.8 21.0 14.2 8.3UU = unshaded/unburned, UB = unshaded/burned, SB = shaded/burned, SU = shaded/unburned116insolation, which can cause mortality in weed seeds afterexposures of several days (Egley 1990). Once vegetation growsenough to shade the soil surface, the effects of burning ontemperature may be neutralized, even within the first growingseason (Daubenmire 1968; Smith and James 1978).Temperatures recorded on the ESSF site were consistent withthe expected patterns in the shade and burn treatments. The factthat the unburned/unshaded location had the highest temperatureson the ICH site is difficult to explain. This could have been ananomalous result, brought about by particular conditions wherethe thermocouple was located. Alternatively, the temperaturescould have been within the normal variation that would have beendetected with sufficient replication of the measurements.Mean seasonal temperatures were generally higher on the ICHsite than on the ESSF site, although there was some overlapbetween the ESSF location with the highest temperature(unshaded/burned) and the ICH location with the lowesttemperature (shaded/unburned). This may have been due, at leastin part, because of moister soils in the ESSF site and, on theunburned areas, more vegetation cover. GerminationThe ratio of observed germinants per treatment wassignificantly different from the expected ratio for burned versusunburned subplots in the intensive ESSF site (Table 3.13). Therewas a higher than expected frequency of germinants in theunburned subplots and a lower than expected frequency ofgerminants in the burned subplots (Table 3.13). In fact the117Table 3.13 Frequency of subplots, and observed and expectedfrequencies of germinants in the burned versus unburned subplotsof the ESSF intensive study site. Results of the 'goodness offit' analysis are presented.Burned Unburned^TotalNumber of Subplots 225 75^300Observed No. of Germinants 49 128 177Expected No. of Germinants 133 44Calculated chi-squared statistic 208.83***significant:^*** = p < 0.001118observed ratio was almost the reverse of that expected.Within both the burned and unburned areas on the intensiveESSF site, the frequency of germinants was higher than expectedin the shaded subplots and lower than expected in the unshadedsubplots (Table 3.14). There was a significant difference betweenthe observed and expected ratio of germinants in shaded versusunshaded subplots of the burned treatment but not in the unburnedtreatment.On the ESSF site, burning appears to have had a greaterinfluence on germinant density than did shading. The relativedifference between densities in the burned subplots versus thosein the unburned subplots was much greater than the differencebetween densities in shaded and unshaded subplots within theburned and unburned treatments (Table 3.15).Results from the ESSF site showed that the lowest germinantdensity was in the unshaded/burned subplots (Table 3.15) whichalso had the highest mean temperature. Conversely, the shaded/unburned subplots with the lowest mean temperature had thehighest density of germinants. Of the remaining treatments, theunshaded/unburned subplots had a much higher germinant densitythan the shaded/burned subplots, even though their meantemperatures were similar (Tables 3.11, 3.15).Neither the shaded/unburned nor the unshaded/unburned ICHsubplots had any germinants, even though these two treatments hadthe lowest and highest mean temperatures, respectively (Tables3.12, 3.16). The two burned treatments had similar meantemperatures and both had low densities of germinants. Theunshaded/burned subplots had a slightly higher temperature and119Table 3.14 Frequency of subplots, and observed and expectedfrequencies of germinants in shaded versus unshaded subplotswithin burned and unburned areas of the intensive ESSF fieldstudy site. Results of the 'goodness of fit' analysis arepresented.Shaded Unshaded TotalBurned^Number of Subplots^45^180^225Observed No. of Germinants^19 30 49Expected No. of Germinants 10^39Calculated chi-squared statistic 9.65*Unburned Number of Subplots^15^60^75Observed No. of Germinants^33 95 128Expected No. of Germinants 26^102Calculated chi-squared statistic 2.32nssignificance: ns = not significant (p > 0.05), * = 0.005 > p >0.001.120Table 3.15 Density (number/m2 ) of germinants in the four shadeand burn treatments of the intensive ESSF and ICH field studysites.Burned^UnburnedShaded Unshaded Shaded UnshadedESSF Site^42^17^220^158ICH Site 4^7121Table 3.16 Frequency of subplots and germinants in the fourshade and burn treatments of the ICH intensive study site.Burned^UnburnedShaded Unshaded Shaded UnshadedNumber of subplots 67 162 3 72Number of germinants 3 11 0 0122also a higher density of germinants (Table 3.15).Results from both these sites suggest that the differencesin germinant density were not directly related to differences inthe temperature environment of the forest floor among the shadeand burn treatments. Other factors, such as differences in soilmoisture or chemistry that resulted from burning and shading, mayhave affected germination, either alone or in combination.Temperature may still have been important but could have beeninteracting with other variables which were not measured in thisstudy.The actual differences between the mean temperatures werenot very great but that was because they were averaged over thewhole season. Since the optimal germination conditions for thegerminant species encountered in this study are not known, it isnot possible to assess whether these temperature differencescould have had a significant effect.Results from other studies that germinated soil samplesunder controlled conditions are, like this study, inconsistent.Ingersoll and Wilson (1990) found that neither shading norburning had a significant effect on germination from blocks offorest soil. Shade generally decreased germination from soilsamples but the effect was significant only at the highest shadelevels (Pratt et al. 1984). In another study, shade significantlyreduced germination of Epilobium ciliatum (watsonii), but Mitellasp. emerged almost exclusively from shaded samples (Strickler andEdgerton 1976). However, there were too few Mitella sp.germinants to test whether the latter result was significant.Seeds of some species that form soil seed banks are123stimulated to germinate in the dark by diurnal fluctuations intemperature (Thompson and Grime 1983). Fluctuations intemperature decrease with depth and shading, which could functionas a means to prevent seeds from germinating when they are toodeep to reach the surface, or where high shade levels would bedetrimental to growth and survival of germinants (Thompson andGrime 1983). This does not appear to be the case for the seedbank species encountered in the present study.3.4 Conclusions Burning did not have a consistent effect on fieldgermination. On the ESSF site burning resulted in fewergerminants while on the ICH site there were more field germinantsin the burned area than in the unburned area. Differences betweenthese two sites in burn severity, initial abundance anddistribution of seeds, moss cover on the unburned areas and soilmoisture regime, may have affected the germination response onburned versus unburned areas.Germinants grew faster and larger on the burned areas thanon the unburned areas of both the ESSF and ICH intensive studysites. This increased growth may result in better survival whichcould counteract the lower numbers of germinants in burned thanin unburned areas on, for example, the ESSF intensive site.Only one germinant species appeared to have been favoured byburning (Paxistima myrsinites in the ICH site). Several, however,were absent from the burned areas (e.g. Mitella spp., Vacciniumspp.). The fact that only one taxon may have depended on fire togerminate is consistent with the relatively low frequency of124natural fire in the study area.The occurrence of germinant species was inconsistent bothamong plots within sites and among sites within variants andzones. At the smaller scale this variation probably reflects thehighly clustered nature of buried seeds combined with variationin microtopography and fire severity. At the larger scale,differences in seed production, burn severity and vegetationhistory were likely responsible for between-site variation.Most of the abundant germinant taxa encountered in theintensive sites were also found in some of the extensive sites.However, only Epilobium angustifolium and Sambucus racemosa werefound on all sites and the former probably seeded in primarilyfrom off-site sources. Several other taxa were found in all threevariants sampled but in fewer sites. Few of the more abundanttaxa were confined to one variant or zone. Of these, Luzulaparviflora was found only in the ESSFwc2 sites, while Paxistimamyrsinites was confined to the ICH zone, mainly in the ICHmw3sites.The concentration of seeds in the upper 3 cm of the forestfloor probably resulted in high seed mortality through combustionof the forest floor, especially on the ICH site. However, thenumber of germinants that occurred in the burned area was arelatively small percentage of what was estimated to remain inthe post burn 0-1 cm of the forest floor, indicating that either1) seeds in the remaining forest floor were killed by the fire or2) post-burn conditions were unfavourable to germination.It was not possible to distinguish between these twopossibilities because no relationship was established between125depth of burn and either 1) the magnitude or duration of elevatedsoil temperatures during the burn, or 2) the number of germinantsafter the burn. A larger sample size and the inclusion of otherimportant factors, such as soil moisture and texture, would berequired to construct a model of soil heating.The fact that there appeared to be a threshold depth of burnbeyond which no germination occurred on both sites, suggests thatlethal temperatures during the fire could have been responsiblefor the lack of germination. The length of exposure to relativelyhigh temperatures in this study was within the range that otherresearch has shown to be lethal to seeds of some species, but notto others. Not enough is known about the heat tolerances of seedbank species found in this study to assess the potential for seedmortality.In the post-burn environment, burning appears to haveaffected germination more than did shading. It was not possibleto determine whether this difference was the result ofdifferences in soil temperatures or some other factor. The factthat shading had a much more important influence on soiltemperature than burning, suggests that temperature was not ofprimary importance to germination. However, since temperaturemeasurements were not replicated and not measured wheregermination was being monitored, there was no direct measurementof the relationship between these two factors. Knowledge of theeffect of different temperature regimes on germination of speciesin the seed bank would be necessary to determine whether thedifferences in temperature recorded in this study could haveaffected germination.126CHAPTER 4 CONCLUSIONS AND RECOMMENDATIONS4.1 Conclusions 4.1.1 The seed bankThe density of germinants, number of taxa and variation ingerminant numbers among samples, appeared to be similar to othergreenhouse germination studies of northern temperate forestsoils, despite a wide variation in sampling methodology. No genuswas unique to this study, although not all germinant species havebeen found in other studies.Greenhouse germination appeared to represent the totalnumbers and species composition of the more abundant seed banktaxa. Taxa that were unique to either the greenhouse samples orthe field were relatively rare. Germinant density was much higherin the 0-1 cm depth class of the greenhouse samples than in thefield plots and subplots. Therefore, greenhouse germination wasnot an accurate predictor of field germination.Results indicate that moist ESSF sites have a relativelylarge number of buried seeds in the forest floor, many of whichwill germinate after logging. Soil seed banks did not appear tobe an important source of new plants of any species on mesic ICHsites. Site productivity, vegetation history and stand structure,are probably more important than altitude in determining theextent of the buried seed population.Greenhouse germinants were generally poorly dispersed andwere unevenly distributed within the samples in which theyoccurred. The degree of dispersion and clustering varied greatlyamong the germinant taxa and was not related to germinantabundance.127Increasing sample size probably increases the precision withwhich seed numbers are estimated, but between-sample variation isnot a good measure of that precision. This is because seeddistribution is inherently clustered.Patterns of vertical distribution represents individualclusters of seeds located at different depths in differentsamples rather than the same pattern in each sample. Thesepatterns can be highly skewed by large clusters of germinants inone or two samples. Therefore, relatively large sample sizes arerequired to assess both vertical and horizontal distribution ofburied seeds. Layers must also be thin enough to provide goodresolution of vertical distribution patterns.The location of particular germinant species in the profilemay indicate when in the successional cycle a species wasdeposited. However, nothing is known about the seed-burialmechanisms on these sites and therefore it cannot be concludedthat there is a relationship between vertical distribution andseed age.Both mature-forest and early successional taxa were amongthe seed bank germinants from both sites. Seed banks of mature-forest species are likely maintained through periodic, smalldisturbances that create gaps in the forest which stimulate seedproduction. The dense, closed canopy of some forest plantationscould lead to a loss or reduction of species that rely on gaps tomaintain seed reserves.The higher densities of germinants found in the greenhousethan in the field may have been due to one or more of: 1)differences in the temperature regime between greenhouse and128field environments, 2) reduced daylength in the greenhouse, 3)lack of moisture in the ICH field site, 4) splitting ofgreenhouse samples or 5) the longer period and greater frequencyof germination monitoring in the greenhouse.Seeds germinated under a wide variety of temperatureconditions in both the greenhouse and the field. The evolution ofnarrow temperature requirements for germination is unlikely tooccur in an temperature environment that is highly unpredictable.Therefore, it is probable that temperature requirements were metfor most or all taxa present in the seed bank.4.1.2 Effects of fire on the seed bankBurned areas had fewer germinants than unburned areas on theESSF site but the reverse occurred on the ICH site. The differentgermination response on these two sites may have resulted fromdifferences in burn severity, initial abundance and distributionof seeds, moss cover on the unburned areas and soil moistureregime.Germinants appeared to grow larger during the summer on theburned areas than on the unburned areas, which may result inbetter survival and offset the lower numbers of germinantsobserved in burned versus unburned areas on the ESSF intensivesite.The apparent lack of species requiring fire to germinate(with the possible exception of Paxistima myrsinites) isconsistent with the relatively low frequency of natural fire inthe study area. In fact, the seeds of several taxa appeared to bedestroyed by fire (e.g. Mitella spp., Vaccinium spp.).129The distribution of most germinant species both within andamong sites was inconsistent. Within-site variation was probablydue to the clustered distribution of buried seeds, and variationsin microtopography and fire severity. Differences in siteproductivity, burn severity and vegetation history were probablyresponsible for between-site variation.Of the two germinant species found on all sites, one likelydid not originate from the seed bank. Most germinant taxa foundon the intensive sites were also found in some extensive sites,and were generally not confined to particular variants orecosystems.A large proportion of buried seeds were likely consumedduring fire because of their concentration in the top 3 cm of theforest floor. Only a small fraction of seeds remaining in theunconsumed forest floor germinated, possibly because: 1) seedswere also killed by elevated temperatures during the fire or 2)post-burn conditions were unfavourable to germination.The study could not distinguish between these twopossibilities because the temperatures seeds were exposed toduring the burn could not be determined and the heat tolerancesof seed bank species found in this study are unknown. A largersample size and the inclusion of other important factors, such assoil moisture and texture, would be required to construct a modelof soil heating.There appeared to be a threshold depth of burn beyond whichno germination occurred on both sites. This suggests thattemperatures reached during the fire were lethal to seeds in theremaining forest floor. The length of exposure to elevated130temperatures in this study has been shown to kill seeds of somespecies.In the post-burn environment, burning appears to haveaffected germination more than did shading, while shadingappeared to have had a greater influence on soil temperaturesthan did burning. These results suggest that forest floortemperature was not of primary importance to germination.However, without 1) replication of temperature measurements, 2)measurement of temperatures where germination was beingmonitored, and 3) information on the effect of differenttemperature regimes on germination of the seed bank species foundin this study, little can be concluded about the importance oftemperature regime to germination or about the factors affectingtemperature regime.4.2 Recommendations The species composition, numbers and distribution of buriedseeds should be further investigated in B.C. forest soils,especially in moister, richer ecosystems. Studies should bereplicated within ecosystems to determine between-site variation.This information would extend current knowledge of thegeographical and ecological distribution of seed bank species.Research is needed on the importance of seed banks torevegetation after fire and other disturbances. Determining therelative contribution of seed banks and other sources of plants(e.g. bud banks, seed rain and seedling banks) to post-disturbance vegetation would require long-term monitoring ofindividual plants of different origins. The effect of different131types and severities of disturbance on the mode of revegetationof individual species and plant communities, would be a usefulbasis for planning forest management activities.Research on seed banks should focus specifically on 1)measuring factors in the environment that could influence buriedseeds (e.g. soil moisture, temperature, light and chemistry), 2)measuring changes in the seed environment during and afterdisturbance, and 3) determining, through controlled experiments,how seeds respond to such changes. Experiments on seed bankspecies should determine: 1) the depth from which seeds cangerminate, 2) the magnitude and duration of temperature exposurethat is lethal, and 3) the optimal temperature, moisture andchemical environment for post-disturbance seed germination.In order to maintain the contribution that seed banks maketo the natural diversity of forest ecosystems, research is alsoneeded to determine : 1) the longevity of buried seeds in forestsoils, 2) the relationship between source plant abundance andburied seed abundance, 3) the relationship between foreststructure and production of seed in forest understory species, 4)the means by which seeds become buried, and 5) the relationshipbetween the distribution of seeds, the distribution of plants,and mode of seed dispersal.132LITERATURE CITEDArchibold, O.W. 1979. Buried viable propagules as a factor inpostfire regeneration in northern Saskatchewan. Can. J. Bot.57:54-58.Archibold, O.W. 1989. Seed banks and vegetation processes inconiferous forests. In: Leck, M.A., V.T. Parker and R.L.Simpson (eds.). The Ecology of Soil Seed Banks. AcademicPress.Bewley, J.D. and M. Black. 1985. Seeds: Physiology of Developmentand Germination. Plenum Press. New York.Bigwood, D.W. and D.W. Inouye. 1988. Spatial pattern analysis ofseed banks: an improved method and optimized sampling.Ecology. 69(2): 497-507.Bormann, F.H. and G.E, Likens. 1979. Pattern and Process in aForested Ecosystem. Springer-Verlag. New York. 253pp.B.C. Ministry of Forests. 1989. Annual Report.British Columbia. Victoria, B.C. 79pp.B.C. Ministry of Forests. 1990. Annual Report.British Columbia. Victoria, B.C. 120pp.B.C. Ministry of Forests. 1991. Annual Report.British Columbia. Victoria, B.C. 91pp.Province ofProvince ofProvince ofCanadian Forestry Service. 1984. Tables for the CanadianForestFire Weather Index System. Environ. Can., Can. For. Serv.,For. Tech. Rep. 25 (4th ed.)Champness, S.S. 1949. Notes on the technique of sampling soil todetermine the content of viable buried seeds. J. Br.Grassland Soc. 4:115-118.Colosi. J., P.B. Cavers and M.A. Bough. 1988. Dormancy andsurvival in buried seeds of proso millet (Panicummiliaceum). Can. J. Bot. 66:161-168.Daubenmire, R. 1968. Ecology of fire in grasslands. Adv. Ecol.Res. 5:209-266.Egley, G.H. 1990. High-temperature effects on germination andsurvival of weed seeds in soil. Weed Science. 38:429-435.Feller, M.C. 1982. The ecological effects of slashburning withparticular reference to British Columbia: A literaturereview. B.C. Min. For. Land Manag. Rep. 13.Floyd, A.G. 1966. Effect of fire upon weed seeds in the wetsclerophyll forests of northern New South Wales. Aust. J.Bot. 14:257-267.133Fox, J.F. 1983. Germinable seed banks of interior Alaskan tundra.Arctic Alpine Res. 15:405-411.Fyles, J.W. 1989. Seed bank populations in upland coniferousforests in central Alberta. Can. J. Bot. 67:274-278Garwood, N.C. 1989. Tropical seed banks: a review. In: Leck,M.A., V.T. Parker and R.L. Simpson (eds.). The Ecology ofSoil Seed Banks. Academic Press.Graber, R.E. and D.F. Thompson. 1978. Seeds in the organic layersand soil of four beech-birch-maple stands. USDA For. Serv.Res. Pap. NE-401.Granstrom, A. 1982. Seed banks in five boreal forest standsoriginating between 1810 and 1963. Can. J. Bot. 60:1815-1821.Granstrom, A. 1987. Seed viability of fourteen species duringfive years of storage in a forest soil. J. Ecol. 75:321-331.Granstrom, A. 1988. Seed banks at six open and afforestedheathland sites in southern Sweden. J. Appl. Ecol. 25:297-306.Heinselman, M.L. 1981. Fire and succession in conifer forests ofnorthern North America. In: D.C. West, H.H. Shugart and D.B.Botkin (eds.). Forest Succession: Concepts and Application.Springer-Verlag. New York.Ingersoll, C.A. and M.V. Wilson. 1990. Buried propagules in anold-growth forest and their response to experimentaldisturbances. Can. J. Bot. 68:1156-1162.Johnson, E.A. 1975. Buried seed populations in the subarcticforest east of Great Slave Lake, Northwest Territories. Can.J. Bot. 53(24):2933-2941.Kellman, M.C. 1970. The viable seed content of some forested soilin coastal British Columbia. Can. J. Bot. 48:1383-1385.Kellman, M.C. 1974. Preliminary seed budgets for two plantcommunities in coastal British Columbia. J. Biogeog. 1:123-133.Kemp, P.R. 1989. Seed banks and vegetation processes in deserts.In: Leck, M.A., V.T. Parker and R.L. Simpson (eds.). TheEcology of Soil Seed Banks. Academic Press.Klinka, K., R.N. Green, R.L. Trowbridge and L.E. Lowe. 1981.Taxonomic Classification of Humus Forms in Ecosystems ofBritish Columbia. First approx. B.C. Min. For., Land Manage.Rep. No. 8. Victoria, B.C.Kramer, N.B. and F.D. Johnson. 1987. Mature forest seed banks ofthree habitat types in central Idaho. Can. J. Bot. 65:1961-1966.134Lloyd, D., K. Angove, G. Hope, and C. Thompson. 1990. A Guide toSite Identification and Interpretation for the KamloopsForest Region. Land Management Handbook 23. B.C. Ministry ofForests, Victoria, B.C. 399 pp.Major, J. and W.T Pyott. 1966. Buried viable seed in twoCalifornia bunchgrass sites and their bearing on thedefinition of a flora. Vegetatio. 13:253-383.Marks, P.L. 1974. The role of pin cherry (Prunus pensylvanica L.)in the maintenance of stability in northern hardwoodecosystems. Ecol. Monog. 44:73-88.Martin, J.L. 1955. Observations on the origin and earlydevelopment of a plant community following a forest fire.For. Chron. 31:154-161.Matlack, G.R. and R.E. Good. 1990. Spatial heterogeneity in thesoil seed bank of a mature Coastal Plain forest. Bull. Tor.Bot. Club. 117:143-152.Maun, M.A. and S. Riach. 1981. Morphology of caryopses, seedlingsand seedling emergence of the grass Calamovilfa longifoliafrom various depths in sand. Oecologia. 49:139-142.Mayer, A.M. and A. Poljakoff-Mayber. 1982. The Germination ofSeeds. Pergamon Press. Oxford.McGee, A.B. 1988. Vegetation response to right-of-way clearingprocedures in coastal British Columbia. Ph.D. Thesis. Univ.of B.C.Mladenoff, D.J. 1990. The relationship of the soil seed banks andunderstory vegetation in old-growth northern hardwood-hemlock treefall gaps. Can. J. Bot. 68:2714-2721.Moore, J.M. and R.W. Wein. 1977. Viable seed populations by soildepth and potential site recolonization after disturbance.Can. J. Bot. 55:2408-2412.Morgan, P. and L.F. Neuenschwander. 1988a. Shrub response to highand low severity burns following clear-cutting in NorthernIdaho. West. J. Appl. For. 3:5-9.Morgan, P. and L.F. Neuenschwander. 1988b. Seed bankcontributions to regeneration of shrub species after clear-cutting and burning. Can. J. Bot. 66:169-172.Morin, H. and S. Payette. 1988. Buried seed populations in themontane, subalpine, and alpine belts of Mont Jaques-Cartier,Quebec. Can. J. Bot. 66:101-107.Munoz, M.R. and E.R. Fuentes. 1989. Does fire induce shrubgermination in the Chilean matorral? Oikos. 56:177-181.Olmsted, N.W. and J.D. Curtis. 1947. Seeds of the forest floor.Ecology. 28(1):49-52.135Parker, V.T, R.L. Simpson and M.A. Leck. 1989. Pattern andprocess in the dynamics of seed banks. In: Leck, M.A., V.T.Parker and R.L. Simpson (eds.). The Ecology of Soil SeedBanks. Academic Press.Parminter, J. 1992. Typical historic patterns of wildfiredisturbance by biogeoclimatic zone. B.C. Min. For. Chart.Victoria, B.C.Pojar, J., K. Klinka and D.V. Meidinger.classification in British Columbia.22:119-154.Pratt, D.W., R.A. Black and B.A. a ponderosa pine community. Can.Biogeoclimatic ecosystemForest Ecol. Manage.1984. Buried viable seedJ. Bot. 62:44-52.Racine, C.H. 1981. Tundra fire effects on soils and three plantcommunities along a hill slope gradient in the SewardPeninsula, Alaska. Arctic. 34:71-84.Roberts, H.A. 1981. Seed banks in soils. In: T.H. Coaker (ed.).Adv. Appl. Biol. 6:1-55. Academic Press.SAS Institute Inc. 1988. Sas Procedures Guide, Release 6.03 Ed.Cary, NC: SAS Institute Inc. 441 pp.Scheiner, S.M. 1988. The seed bank and above-ground vegetation inan upland pine-hardwood succession. Michigan Botanist.27:99-106.Smith, D.W. and T.D. James. 1978. Characteristics of prescribedburns and resultant short-term environmental changes inPopulus tremuloides woodlands in southern Ontario, Canada.Can. J. Bot. 56:1892-1791.Stone, E.C. and G. Juhren 1951. The effect of fire on thegermination of the seed of Rhus ovata Wats. Am J. Bot.38:368-372.Strickler, G.S. and P.J. Edgerton. 1976. Emergent seedlings fromconiferous litter and soil in eastern Oregon. Ecology.57:801-807.Thompson, K. and J.P. Grime. 1983. A comparative study ofgermination responses to diurnally-fluctuating temperatures.J. Appl. Ecol. 20(1):141-156.Wells, C.G., R.E. Campbell, L.F. Debano, C.E. Lewis, R.L.Frederickson, E.C. Franklin, R.C. Froelich and P.H. Dunn.1979. Effects of fire on soil. A state-of-knowledge review.USDA For. Serv. Gen. Tech. Rep. WO-7.Went, F.W., G. Juhren and M.C. Juhren. 1952. Fire and bioticfactors affecting germination. Ecology. 33:351-364.136Whipple, S.A. 1978. The relationship of buried germinating seedsto vegetation in an old-growth Colorado subalpine forest.Can. J. Bot. 56:1505-1509.Zar, J.H. 1974. Biostatistical analysis. Prentice-Hall, Inc.,Englewood Cliffs, NJ. 620 pp.


Citation Scheme:


Citations by CSL (citeproc-js)

Usage Statistics



Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            async >
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:


Related Items