Open Collections

UBC Undergraduate Research

A pilot study of increment cores from young defoliated western hemlock on Haida Gwaii Nethercut-Wells, Acacia 2012

You don't seem to have a PDF reader installed, try download the pdf

Item Metadata

Download

Media
Nethercut-Wells_Acacia_FRST_497_Graduating_Essay_2012.pdf [ 1011.41kB ]
Metadata
JSON: 1.0075539.json
JSON-LD: 1.0075539+ld.json
RDF/XML (Pretty): 1.0075539.xml
RDF/JSON: 1.0075539+rdf.json
Turtle: 1.0075539+rdf-turtle.txt
N-Triples: 1.0075539+rdf-ntriples.txt
Original Record: 1.0075539 +original-record.json
Full Text
1.0075539.txt
Citation
1.0075539.ris

Full Text

 A Pilot Study of Increment Cores from Young Defoliated Western Hemlock on Haida Gwaii  Acacia Nethercut-Wells 4/9/2012 University of British Columbia Vancouver  Faculty of Forestry Graduate Essay Frst 497          1  Abstract Increment cores from five stands on Haida Gwaii, British Columbia were measured to identify radial growth suppressions caused by western blackheaded budworm (Acleris gloverana) defoliation. Z-scores were calculated based on annual basal area to identify periods of suppression and to quantify the severity of the suppression. Comparisons between stands illustrated an association between certain stand characteristics (density and age) and indicators of defoliation severity (percent mortality of western hemlock, suppressions per tree, and length of time suppression lasted). Although this pilot study was not able to make conclusions about growth suppressions and their relation to defoliation, it played an integral role in the development of further studies that will be able to achieve this.                   KEYWORDS: defoliation, western blackheaded budworm, Haida Gwaii, tree rings, increment cores.  2  Contents Abstract ......................................................................................................................................................... 1 Introduction .................................................................................................................................................. 3 Western Blackheaded Budworm Defoliation Events on Haida Gwaii, BC ................................................ 3 Biology of Western Blackheaded Budworm ............................................................................................. 3 Dendrochronology and Defoliators .......................................................................................................... 4 Research Objectives .................................................................................................................................. 5 Methods ........................................................................................................................................................ 5 Field Protocol ............................................................................................................................................ 5 Lab Protocol .............................................................................................................................................. 6 Results ........................................................................................................................................................... 8 F29-001 ................................................................................................................................................. 9 103F030-3 ............................................................................................................................................. 9 F30-27 ................................................................................................................................................. 10 F030-37 ............................................................................................................................................... 10 F069-1194 ........................................................................................................................................... 10 Summary ............................................................................................................................................. 11 Discussion.................................................................................................................................................... 11 Limitations and Opportunities for Further Research .............................................................................. 13 Conclusion ................................................................................................................................................... 14 Works Cited ................................................................................................................................................. 16 Figures and Tables ...................................................................................................................................... 17       3  Introduction Defoliation is the loss of foliage from a plant, which can be caused by both biotic and abiotic agents. Defoliation caused by insect herbivory is a common form of biotic disturbance in most forests. Conifer defoliation is especially damaging because they generally lack the ability to refoliate and severe defoliations may cripple their ability to form buds and refoliate the next growing season (Defoliator Management Guidebook 1995). Defoliation causes radial and height incremental growth loss, top-kill, and if severe enough, mortality (Defoliator Management Guidebook 1995). Top-kill also causes overall height loss and deformities. Stagnation of height growth may also occur in mature stands as a result of defoliation (Defoliator Management Guidebook 1995). Defoliation also weakens the tree, making it more susceptible to other biotic and abiotic agents (Henigman et al. 2001).  Western Blackheaded Budworm Defoliation Events on Haida Gwaii, BC Western blackheaded budworm (Acleris gloverana) is a defoliator that commonly occurs over western North America. It prefers to feed on western hemlock and true firs and can be found nearly everywhere that these trees grow in British Columbia, but have caused the most damage on Haida Gwaii (Henigman et al. 2001). Defoliation on the islands was first recorded in 1931 and since then was recorded in 1943 to 1944, 1952 to 1955, 1972 to 1974, 1985 to 1988, and 1996 to 2001 (Wood and Garbutt 1989; Nealis and Turnquiest 2010). Most recently, defoliation events have been recorded from 2009 to the present (Zeglan 2012). The defoliation that occurred in the 1980s was especially severe. In 1986, 56,000 ha were defoliated on Haida Gwaii and nearby Kitimat on the mainland; by 1987 there was 25% mortality over 3,100 ha on Haida Gwaii due to damage caused by both western blackheaded budworm and hemlock sawfly (Neodiprion tsugae) (Koot 1991). Although in this case both defoliators caused damage, western blackheaded budworms are able to cause defoliation that is similar in severity (Henigman et al. 2001).  Based on these observations and defoliation events elsewhere in British Columbia, stand-level defoliation by western blackheaded budworm occurs for one or two years only, but at a landscape level it lasts from two to six years (Nealis et al. 2004). Outbreaks generally occur every 10 to 15 years (Henigman et al. 2001). Biology of Western Blackheaded Budworm  Patterns of defoliation and severity of damage caused by the western blackheaded budworm can be anticipated because of its lifecycle. Generally, populations build in mature stands and then spread to adjacent immature stands (Defoliator Management Guidebook 1995). Damage is caused only in the larval stage, which begins in May or June, after they hatch (Koot 1991). The needles of opening buds are generally partially eaten and some are webbed together on the twigs so that pupation can take place in late August to early September (Henigman et al. 2001). The feeding takes place in the upper crown of dominant and co-dominant trees (Classified as Layer 1 and 2 trees in the field data collection, see Table 1); the effects of which become visible from mid-July to mid-August (Henigman et al. 2001). 4  Outbreaks of western blackheaded budworm end with population collapse. Populations are naturally limited at low levels by factors such as disease, parasites, insect and bird predation, and adverse weather (Schmiege and Crosby 1970; Koot 1991). There are more than 70 species of parasites that affect the western blackheaded budworm, as well as viral and fungal diseases (Schmiege and Crosby 1970). Adverse weather that limits population growth includes: cold, wet summers; ice and snow sliding off foliage and removing overwintering eggs; warm weather during early larval stages; and heavy rains during the late larval feeding or during the adult stage (Schmiege and Crosby 1970; Koot 1991). When populations become large, the increase generally occurs rapidly until a rapid decline occurs (Wood and Garbutt 1989). This rapid decline is often the result of foliage depletion, which causes starvation to occur, limiting the population both directly and, by reducing fecundity, indirectly (Schmiege and Crosby 1970; Koot 1991).  Hemlock sawfly is a defoliator that is often associated with western blackheaded budworm. Of the recorded outbreaks on Haida Gwaii, it only significantly defoliated in the 1985 to 1988 outbreak, which is notable for its severity (Wood and Garbutt 1989). The combined attack of both insects increases the damage sustained by the tree and the likelihood of complete defoliation. This is because the western blackheaded budworm prefers new foliage, while the hemlock sawfly prefers old foliage, causing a more complete defoliation (Koot 1991). There are recordings of other damaging insects on Haida Gwaii, including green-striped forest looper (Melanolophia imitata), saddleback looper (Ectropis crepuscularia), and western hemlock looper (Lambdina fiscellaria lugubrosa) (Wood and Garbutt 1989). None of these insects caused notable damage during the lifetime of the trees in this study (Wood and Garbutt 1989)   Healthy mature western hemlock can generally sustain one year of severe defoliation without serious damage and will recover in less than two years with minimal top-kill and growth loss (Defoliator Management Guidebook 1995).  In recent and ongoing outbreaks, juvenile stands regenerating from harvests were disproportionately affected (Nealis et al. 2004). Currently, the impacts of defoliation on juvenile western hemlock are poorly known as most previous studies considered mature trees (Nealis and Turnquiest 2010).  Dendrochronology and Defoliators The analysis of tree rings is one method for determining the occurrence and severity of the damage caused by defoliation. Generally, the effects of defoliation are visual observations such as top-kill, red foliage or mortality. Measuring tree rings is the only way to quantify radial growth reduction (Swetnam et al. 1988). Tree rings can also be used to reconstruct outbreak history, prior to written history.   Analysis of growth rings has quantified incremental radial growth suppression of mature western hemlock attributed to the western blackheaded budworm in previous studies, although results are quite inconsistent and depend on many variables. One study measured radial increment growth 5  reductions of 50% for four years following the collapse of an outbreak (Henigman et al.2001). Another study of a 1989 defoliation event concluded that radial incremental growth averaged 30% less during the outbreak than during the five years prior to defoliation in 1985 (Wood and Garbutt 1989). Additionally, in this study seven of the nine plots’ radial growth continued to decline the year after the population collapse (Wood and Garbutt 1989).  To date, tree-ring analysis has not been used to quantify the impacts of defoliation on regenerating trees. Research Objectives In this pilot study I analysed increment cores collected from five sites on Haida Gwaii dominated by young regenerating western hemlock. The purpose of this study was to determine if defoliation events could be identified from the cores of young western hemlock trees. If this was the case, then the magnitude of growth suppressions could be quantified. In this test of analytical methods, annual basal area increment was calculated from ring widths and annual values were compared to the average basal area growth for each tree. The premise of this approach is as follows. After reaching a growth rate that is average for that tree, if growth becomes suppressed below that average, then it is possible that a defoliation event occurred.  Results will help to determine if growth suppressions from defoliation can be reliably measured so that forest managers can quantify the risk that they are facing and the volume loss that should be anticipated. Understanding the effects of defoliation is important because intensive forest management relies on the wood supply from rapidly regenerating trees and short rotations make these defoliation disturbances especially problematic because of the unexpected productivity decline that they cause (Nealis and Turnquiest 2010). Methods Field Protocol The field protocols were developed by Stefan Zeglan, BC Ministry of Natural Resource Operations, and are summarized in the following section (Zeglan 2011). After an aerial survey of defoliated areas on Haida Gwaii, 20 study stands (e.g., defoliated forest polygons) were identified, five of which were assessed in this pilot study. For each study stand, the locations of sample plots were determined using a 100m x 100m grid overlaid on a 1:5000 map. The grid intersection points became potential plot centers, with access to sites and stand features considered.  Of the potential plot locations, 10 were selected for measurement, as well as a backup plot center if one of the original plots was determined to not be suitable in the field. GPS coordinates of the plot centers were used to locate and establish sample plots in the field.  The first measurement that was recorded was at the point of commencement (POC), where a marker was left on flagging tape stating the purpose of the survey, the date, the bearing to the first plot, and the survey crew initials. A handheld GPS unit was used to determine the location 6  of plot center. Due to inaccuracies of the GPS, the plot center was established when the surveyor came within one meter of the waypoint coordinates. This location was marked and on the marker the plot number, purpose of survey, date, bearing to the next plot, and surveyor initials were recorded. The plot number was also recorded on the field data form at this time.  The first step of plot measurement was determining the appropriate plot radius. The plot radius depended on capturing an average of six to eight Layer 1 and 2 trees in each plot. Once a plot radius was determined, it had to remain the same for all 10 plots within a polygon (stand). The additional basic information to be recorded on the field data form included: identification information (mapsheet code, location, polygon, plot, and GPS coordinates), presence of defoliation, and plot radius. Then, using the plot radius deemed appropriate, the plot was swept to count the number of living and dead trees by species in Layer 1, 2, 3, and 4.  The tallies were recorded on the form. For definition of canopy layers see Table 1. Table 1: Description of tree layers, categorized by diameter at breast height and tree height  Description of trees in each layer Layer Diameter at breast height (cm) Tree height (m) 1  12.5 cm any, given DBH  12.5 cm 2 7.5 to 12.4 cm any, given DBH range of 7.5 to 12.4 cm 3 0 to 7.4 cm  1.3 m 4 any, given height restriction of  1.3 m  1.3 m  Next, for all Layer 1 and 2 trees within the plot the species, status (living or dead), DBH, height, and presence of pest damage was recorded. Impact of defoliation was estimated by recording the percent live crown, the amount of defoliation as a result of western blackheaded budworm, whether top-kill had occurred and at what height, and a rating of defoliation on the Fette scale. The site index was also calculated by recording the species, age, DBH, and height of the largest diameter tree within a 5.64m radius plot. Increment cores were sampled from up to three western hemlock trees in canopy Layers 1 and 2 in each plot and up to thirty in each polygon (stand). Beginning with the largest diameter tree, a core sample was taken at breast height aiming for the pith and then placed in a pre-numbered straw and sealed. Then, the tree was tagged with a numbered label that corresponded to the number of the straw. Lab Protocol The increment cores were processed in UBC’s Tree Ring Laboratory in Vancouver. Once there, the cores were taken out of the straws and set in a labeled wooden core support to air dry. The dried cores were glued, with the tracheids vertically aligned, onto the supports and sanded with 220, 320 and 400 grit sand paper to easily differentiate between the earlywood and latewood of each ring. 7  After sanding, the mounted cores were scanned and then converted from a TIFF file to a GIFF file. The width of annual rings was measured using the program CooRecorder by marking the latewood-earlywood boundaries of successive rings on the scanned image. The annotated images were converted to ring-width measurements and imported into the program CDendro to assign calendar years to the annual rings.  In this pilot study, I assumed that the outermost ring closest to the bark represented a complete ring (e.g. latewood formation was complete when the tree was cored in September 2011) and the last year of growth was 2011.The resulting output file from CDendro was then converted into a text file and imported into Excel.  The majority (102 out of 119) of cores did not intercept the pith, but were close to it so that the inner-most ring formed arcs. For these samples a correction had to be applied to estimate the distance to the pith and the number and width of rings missed. For cores that had arcing rings, the number of missed rings was estimated using geometry. This method required the length (L) and height (H) of the oldest ring to be measured, which was done using electronic calipers. The distance (d) to the pith was calculated using the equation: d= (L2/(8H))+H/2 Then, the widths of the three oldest complete rings were measured and their average width was calculated. The number of rings to the pith was calculated by dividing the distance to the pith by the mean width of the three oldest rings. Finally, the average ring width was assigned to each of the missing rings to estimate the incremental growth of the trees when they first established.  This resulted in a time series of ring-width measurements for each tree starting from the pith (year of establishment) through 2011, when the outer-most ring was formed. If the estimate of missing rings was greater than 25% of the measured number of rings (5 out of 119), the sample was removed from the data because they did not provide enough information to accurately represent the growth history of the tree. Excel was used to calculate the following attributes to represent tree growth rates through time: (a) Cumulative ring width (sum of ring widths from the pith to bark),  (b) Cumulative basal area or cross-sectional area of the tree bole (cumulative ring width as the radius in the equation area = πr2 ),  (c) Incremental basal area (basal area of a given year minus the basal area of the preceding year),  (d) Average and standard deviation of the incremental basal area for each core, and  (e) Z-scores (units = standard deviations) comparing the incremental basal area in a given year to the average basal area increment over the lifespan of the tree.  Z-scores that were negative indicated smaller incremental growth relative to the long-term average for each tree.  Z-scores for rings closest to the pith of each tree were negative, but 8  became generally positive as the tree grew.  After the Z-scores became positive for the tree all negative Z-scores were noted as “suppressions”, periods of abnormal or decreased growth rates.   The origin of each stand was defined by the pith date of the oldest living tree and the period of assessment for each tree was the time period that it had been growing at an above average incremental growth. These interpretations are based on the fact that the trees from which the cores were taken were Layer 1 and 2 trees that were the oldest in the stand. For each site, histograms were generated depicting the frequency of radial growth suppressions for each year the stand was in existence and the stand-level average frequency of the suppression events for those years. When the annual frequency of suppressions was greater than the average frequency of suppressions, it suggested a disturbance large enough to affect many trees in the stand indicating a potential defoliation event.  Tables were created to summarize the growth suppressions each tree experienced. This summary included the  Pith date,   Number of suppressions that have occurred over the life of the tree,   Year the suppressions started,   Number of years they lasted,   Average Z-score for the suppression, and   Minimum Z-score for the suppression. The average Z-score describes the severity of the growth suppression throughout the growth suppression. Likewise, the minimum Z-score describes the severity of the growth suppression by quantifying the growth suppression in a single year. For suppressions in some trees, the average and minimum Z-scores were the same because the suppression only lasted one year. The lower the Z-score for both of these measurements, the more severe the growth suppression, relative to the average growth of the tree.  The data for individual trees were also summarized at the stand level.  For each stand, the average and minimum Z-scores for all suppressions were summarized by determining the grand average and range (minimum and maximum) Z-scores. These values provided the range of the extent of suppressions and standardize them to make the affects comparable among trees and stands.  Results In this pilot study, data were from five different stands. Each stand had 10 plots and each plot had between 6 and 54 trees in all four layers of the canopy.  There were 378 Layer 1 and 2 trees that were measured. Of those trees, cores were taken from up to 3 western hemlocks per plot, for a total of 119 cores.  9  The average proportion of living hemlock relative to all other trees recorded in all layers varied between 0.51 (F30-3) and 0.87 (F069-1194). The average proportion of living hemlock in Layers 1 and 2 relative to all other trees in Layers 1 and 2 varied between 0.28 (F30-37) and 0.94 (F069- 1194). The average densities of all trees ranged from 1930 st/ha (F30-3) to 4220 st/ha (F30-37). All stands had some active defoliation. 6 out of the 10 plots in F30-3 had some current defoliation and all other stands had 10 out of 10 plots showing signs of current defoliation. The proportion of dead western hemlock relative to all trees multiplied by a factor of 100 ranged from 0 (F29-001) to 10.07 (F30-3).  The stand with the greatest proportion of dead trees was also the least dense stand. The amount of defoliation damage per tree on average ranged from 0.14% (F069-1194) to 13.53% (F29-001) among stands. Each stand had some trees that had experienced top-kill.  The proportion of trees in a stand that experienced top-kill ranged from 0.02 (F29-001) to 0.05 (F30-27). The average DBH of Layer 1 and 2 trees in each stand ranged from 15.51 cm (F30-27) to 20.34 cm (F30-3). The average height of Layer 1 and 2 trees varied from 10.58 m (F30-27) to 18.5 m (F30-3).  F29-001 Stand F29-001 included 23 trees (Table 2). The year most trees began growing was 1986, with the average pith date of the trees in 1988. Each tree encountered between zero and five suppressions in its lifetime, averaging 1.5 suppressions for each tree. The year most suppressions started in the stand was 2011, which was also the year most suppressions occurred (Figure 1). Suppressions lasted between one and five years, averaging 1.6 years. The minimum average Z- score in the stand was -1.86 and the average Z-score in the stand was -0.44. There were 12 out of the 29 years of the stand’s existence that encountered above average frequencies of growth suppressions and 13 years that did not show any evidence of growth suppressions; one of these was in 2004, surrounded by years that show some degree of growth suppressions (Figure 1). The periods of above average frequencies of growth suppressions occurred over three years from 1996 to 1998, four years from 2000 to 2003, and five years from 2007 to 2011.  103F030-3 Stand 103F030-3 included 18 trees (Table 3). The year most trees began growing was 1981, with the average pith date of the trees in 1982.  Each tree encountered between one and four suppressions in its lifetime, averaging 1.7 suppressions for each tree. The year most suppressions started in the stand was 2001, but this was not the year most suppressions occurred; most suppressions occurred in 2003 (Figure 2). Suppressions lasted between 1 and 13 years, averaging 3.4 years. The minimum average Z-score in the stand was -1.02 and the average Z-score in the stand was -0.51. There were 13 out of the 34 years of the stand’s existence that encountered above average frequencies of growth suppressions and 12 years that did not show any evidence of growth suppressions; one of these was in 1997, surrounded by years that show some degree of growth 10  suppressions (Figure 2). The periods of above average frequencies of growth suppressions occurred over two years from 1998 to 1999, and 11 years from 2001 to 2011. F30-27 Stand F30-27 included 32 trees (Table 4). The year most trees began growing was 1990, with the average pith date of the trees in 1988. Each tree encountered between zero and four suppressions, averaging 1.6 suppressions for each tree. The year most suppressions started in the stand was 2002, which was also the year the most suppressions occurred (Figure 3). Suppressions lasted between 1 and 11 years, averaging 2.5 years. The minimum average Z-score in the stand was - 1.40 and the average Z-score in the stand was -0.38. There were 12 out of 31 years of the stand’s existence that encountered above average frequencies of growth suppressions and 12 years that did not show any evidence of growth suppressions; one of these was in 1993, surrounded by years that show some degree of growth suppressions (Figure 3). The periods of above average frequencies of growth suppressions occurred over two years from 1996 to 1997, eight years from 2001 to 2008, and two years from 2010 to 2011.  F030-37 Stand F030-37 included 17 trees (Table 5). The year most trees began growing was 1985, with the average pith date of the trees in 1985. Each tree encountered between zero and four suppressions, averaging 1.7 suppressions for each tree. The year most suppressions started in the stand was 2001, which was also the year the most suppressions occurred (Figure 4) (as well as 2011). Suppressions lasted between one and nine years, averaging 2.5 years. The minimum average Z-score in the stand was -0.81 and the average Z-score in the stand was -0.41. There were 14  out of 32 years of the stand’s existence that encountered above average frequencies of growth suppressions and seven years that did not show any evidence of growth suppressions; one of these was in 1994, surrounded by years that show some degree of growth suppressions (Figure 4). The periods of above average frequencies of growth suppressions occurred over one year in 1991, one year in 1993, two years from 1996 to 1997, four years from 2000 to 2003, and six years from 2006-2011.  F069-1194 Stand F069-1194 included 25 trees (Table 6). The year most trees began growing was 1977, with the average pith date of the trees in 1975. Each tree encountered between zero and four suppressions, averaging two suppressions for each tree. The year most suppressions started in the stand was 2011, which was also the year the most suppressions occurred (Figure 5). Suppressions lasted between 1 and 14 years, averaging 3.7 years. The minimum average Z-score in the stand was -0.90 and the average Z-score in the stand was -0.40. There were 12 out of 56 years of the stand’s existence that encounter above average frequencies of growth suppressions and 23 years that did not show any evidence of growth suppressions; two 11  of these occurred between years that show some degree of growth suppressions in 1990 and 1994 (Figure 5). The periods of above average frequencies of growth suppressions occurred over 12 years from 2000 to 2011. Summary Table 7 allows for comparison among stands. The average pith dates (age) ranged from 1975 to 1988 among the stands, a 13 year difference. The modal pith date ranged from 1977 to 1990 among stands, also a 13 year difference. F069-1194 has the oldest average pith date and oldest modal pith date, making it the oldest stand.   In F30-3 each tree went through a suppression period at least once; all other stands had at least one tree that did not experience any suppressions. The average number of suppressions per tree between stands ranged from 1.5 to 2.  The stand with the greatest number of average suppressions was also the oldest, while the stand with the lowest number of average suppressions was one of the younger stands. The maximum number of suppressions per tree did not vary drastically between stands; F29-001 had a maximum of 5 and all the others had a maximum of 4. Comparison among stands reveals that most suppressions started in 2011 (F29-001, F30-37) and 2001 (F30-3, F30-37). In F30-27, most suppressions started in 2002. On average, suppressions lasted between 1.6 years (F29-001) and 3.7 years (F069-1194). The average number of years suppressions lasted was associated with the age of the stand; the younger the stands trees’ the shorter time on average the suppression lasted and the older the stands trees’ the longer the time on average the suppression lasted. There was a similar trend for the maximum number of years the suppression lasted. The younger stand’s (F29-001) suppression lasted a maximum of 5 years and the older stand’s (F069-1194) suppression lasted a maximum of 14 years. For both of these associations, all of the stands’ ages corresponded to the length of the suppression, not just the extremes. The lowest minimum average Z-score, -1.86, occurred in F29-001 (also the youngest stand). The highest minimum average Z-score, -0.81, was less of an extreme, but occurred in stand F30-37. The average Z-score ranged from -0.38 (F30-27) and -0.44 (F29-001), meaning the average growth suppression sustained by each tree in each stand was the same. Similarly, the maximum average Z-score ranged from -0.05 (F30-37) to 0.00 (F30-27). Discussion It appears as though some growth suppression indicators are associated with the age of the stand and some with the density of the stand.  As stated, F069-1194 is the oldest stand, by both average pith date and modal pith date. This stand had the highest average number of suppressions per tree and the greatest average number of years each suppression lasted. These indicators could mean that growth suppressions may be more extreme in older stands, but they may also just be a result of the stand being alive for more suppression periods.  12  F30-3 had the lowest stand density and the tallest trees with the greatest diameter. It also had a much larger proportion of dead western hemlock, which could be a definitive result of western blackheaded budworm defoliation. There are not many other indicators of the stand’s growth suppression that are as apparent, although the average number of years the suppression lasted is comparatively high (3.4), but not the highest, the average Z-score is the highest (-.051), but not remarkably different from the other stands. Though it should also be noted that relative to the other stands, F30-3 is the second oldest, so these indicators may once again be a result of the stand living through more suppressions, rather than an actual indication of a more severe suppression event.  It has been suggested that stand tending treatments such as spacing and fertilization are strategies to mitigate damage caused by western blackheaded budworm because they help to maintain a healthy, more resilient stand (Defoliator Management Guidebook 1995). Nealis and Turnquist explored this concept more with some significant conclusions (2010). First, severe impacts of defoliation, such as frequent top-kill, were the most common in the largest trees in the youngest stands which has been spaced just before the outbreak (Nealis and Turnquist 2010). The five stands of young western hemlock in this study do not exhibit varying top-kill occurrences, suggesting that density and tree diameter are not a cause of more severe top-kill . Second, in spaced stands that had been moderately defoliated, radial growth was reduced for two years, but mean annual ring width and basal area increment in surviving trees recovered quickly and was even enhanced after the defoliation (Nealis and Turnquist 2010). When this defoliation becomes severe though, which is more common in spaced stands, top-kill or mortality could occur, rather than increased growth (Nealis and Turnquist 2010). F069-1194 is a stand that is least dense, which may be a result of thinning. This is also a stand that shows more signs of a greater severity of defoliation. Based on Nealis and Turnquist’s findings this could be a result of severe defoliation in a spaced stand. The following details qualities of a high-risk stand, as defined by the Defoliator Management Guidebook (1995).  o Cool and wet Coastal Western Hemlock biogeoclimatic zone (CWH vh1, CWH wh1, and CWH wh2); o > 80% western hemlock or true firs; o Dense and overstocked o Dominant and co-dominant trees All stands in this study are in the cool and wet Coastal Western Hemlock biogeoclimatic zone (MFLNRO 2012). Stands F29-001 and F069-1194 have proportions of living western hemlock that are greater than 80%. Both of these stands also have a high proportion of western hemlock that are dominant and co-dominant (Layer 1 and 2). Although none of the stands are particularly overstocked, they meet many of the characteristics of high-risk stands, which should be considered when making management decisions.   13  Limitations and Opportunities for Further Research This study was able to compare suppression intensities and timing between stands, but these suppressions cannot be attributed to western blackheaded budworm defoliation at this time. To do so will require corroborating evidence, as follows. Attributing growth suppressions to defoliation would require using documentary records to determine when defoliation by the western blackheaded budworm occurred in each stand and assess whether the recorded defoliation occurred in a growth suppression period, as defined by the tree ring cores. This can be achieved in two ways.  First, the field notes on the health of individual trees can be linked to their ring-width series. For example, codes for pest damage were recorded for some trees in the stands. A better understanding of these codes and supporting information about the extent of the damage would help determine if the growth suppressions were a result of western blackheaded budworm or other undefined pest damage, but there is no way to determine the extent of this. Second, the tree-ring records could be cross-referenced with the Forest Insect and Disease Survey (FIDS) maps that show the location and timing of a defoliation event. These maps are derived from aerial surveys, making them a reliable record of defoliation. To verify a suppression is a result of western blackheaded budworm defoliation, the tree-ring record would show a growth suppression when the map has indicated a defoliation event. Additionally, climatic impact would have to be ruled out as a factor of the growth suppression.  Incremental growth reductions could be attributed to both climatic factors and defoliation events. If a suppression is climate related, then it would occur in the same year for all trees in all stands, but if it was defoliation related, it could occur in different years for trees within the same stand and among stands. Differentiating defoliations from climate effects would require detailed site level climate data and climate-growth analyses. Even with this information, it may be difficult to positively attribute growth suppressions to western blackheaded budworm defoliation because the individual trees and stands as a whole are so young. As a result of their young age and favourable growing conditions, the annual growth does not vary much from year to year within individual tree records, making the tree rings complacent and difficult to crossdate, a method for detecting false and missing rings due to environmental stress.  In spite of these limitations, suppressions were detected but were variable among trees in a stand and among stands. At the tree level, young western hemlock is variable in growth, depending on growing conditions and factors such as slope, aspect, soils, species composition and tree-level competition. Because stand-level factors may directly affect the growth of a single tree in a stand, or a whole stand, it is difficult to attribute differences of growth among trees and stands to a defoliation event.  In summary, determining if a suppression was definitively a result of defoliation is challenging and will require additional samples from more sites to then compare among trees and stands for more conclusive results. In this pilot study analysis among stands was limited because only five have been sampled to date. By comparing among the stands, important information may be gained.  For example, years 14  when suppressions are common among sites may indicate widespread defoliation.  Differences may indicate local defoliations due to variations in forest susceptibility.  If the observed growth suppressions were a result of defoliation and not some other agent, then trends and associations between stand characteristics and growth suppressions could be tested to assess cause and effect. Increasing the number of stands sampled and further statistical analysis could determine whether differences are statistically significant. Additional improvements can be made when sampling trees in the field. Specifically, many cores did not include the pith. Because of this, the Duncan method needed to be applied to estimate pith dates, ring widths, and number of rings missed. For some cores, the estimated number of missed rings was high, more than 25% of the measured rings were being estimated; when this was the case the cores could not be analyzed, possibly resulting in the loss of crucial information. Even when the estimations were not too great, the overall analyses was compromised because growth suppressions were identified by the calculation of a Z-score, which is based on the mean and standard deviations of incremental basal area growth for all years. Essentially, average growth increment measurements might have been affected by this estimation, resulting in the misidentification of a suppression or missing a suppression. As well, the estimated values close to the pith were averages and could not show any suppressions that may have occurred in the first years of the trees’ lives.  Thus, as additional trees and stands are sampled, up to three cores should be taken from the same tree if the first cores did not hit the pith. This simple change in field methods will significantly increase the likelihood of cores intersecting the pith, increasing the accuracy of the analysis. Improvements may be made to lab analyses as well.  First, the assumption that every outer ring was complete and formed in 2011 may be a source of error. When trees are stressed, due to defoliation or climate, they may not have sufficient carbon to allocate to radial growth, resulting in a missing ring. Young western hemlock may also have false rings, bands of latewood formed within an annual ring, which also result from stress.  Missing and false rings are normally detected by crossdating to ensure accurate calendar years are assigned to each ring. Without crossdating, an error could result. In this study, we had to assume the outer ring was 2011 because the trees were young and there were not very many rings to compare and the growth of young trees is so complacent that crossdating is not possible. For further analysis of cores it would be important to consider this. By specifically looking for false rings and narrow rings that would indicate stress, the mistake of deeming a false ring a true ring can be avoided. Some cores showed an irregular latewood boundary, making it difficult to measure the width of each ring. Because of this, the measurements of growth on these rings may not be representative of the tree’s true growth. Unfortunately, the asymmetrical or non-circular bole growth of young western hemlock is another limitation when representing tree growth from increment cores. This is an aspect of the pilot study that is a rare occurrence, but nevertheless present. It could be addressed by assessing cross-sectional disks instead of increment cores. By determining the 15  degree of asymmetry at breast height (where the cores were taken) of some disks, the average incremental ring growth can be determined as well as any evidence of partially missing rings, which may not be complete around the whole circumference of the tree and therefore potentially not present in the increment core sample. In this pilot study, Z-scores calculated over the lifespan of individual trees were used to detect periods of growth suppression.  However, these Z-scores cannot detect potential growth suppressions in the rings formed before the trees growth reaches a point that it is above average.  As a result, some suppressions may have been missed.  This limitation can be addressed by using moving averages to assess growth rates and detect suppressions.  This method separates the rings into five year increments, and compares the width of the middle ring (year 3 of 5) to the five- year average (e.g., the surrounding ring widths). This method would allow a longer period of analyses for most trees, including analysis of the rings closest to the pith. This method requires the presence of the pith in the core to accurately identify all suppressions.  The final, potential weakness to the pilot study analyses was the dependence on  averages to represent individual tree growth and to compare among trees and stands. Averages were used to determine the number and severity of growth suppressions within trees and stands. All comparisons between trees in a stand and between stands were based on calculated averages. Care was taken to display the minimum and maximum values, but comparisons were based on averages because they are more representative of the available information. Averages have the ability to mask trends, though. Because the growth of the young western hemlock is so variable among trees, it is possible that averaging limited the appearance of trends at the tree and stand levels. Conclusion The purpose of this pilot study was to determine if radial growth suppressions could be identified in defoliated regenerating western hemlock on Haida Gwaii. Growth suppressions were quantified within trees and compared among trees and stands. Based on the frequency of suppressions, associations were identified between specific stand characteristics, such as density or age, and severity of defoliation. Although these associations were identified, they could not be attributed solely to defoliation events. Nevertheless, this pilot study played a crucial role in informing data collection and for identifying potential analytical techniques. With this information, further analysis of this data set combined with data from additional sites, in combination with other lines of evidence such as documentary records of forest health and climate-growth analyses, more meaningful conclusions can be reached. This pilot study played an integral role in the development of a method to reliably measure growth suppressions resulting from defoliations of young, regenerating western hemlock trees growing on Haida Gwaii. With this, forest managers will be better informed to make management decisions regarding western blackheaded budworm defoliation. 16  Works Cited Defoliator Management Guidebook. 1995. MOF. http://www.for.gov.bc.ca/tasb/legsregs/fpc/fpcguide/defoliat/defoltoc.htm Henigman, J., Ebata, T., Allen, E., Westfall, J., and Pollard A. 2001. Field Guide to Forest Damage in British Columbia: Western Blackheaded Budworm. Second Edition. Number 17. MOF/CFS Joint Publication. http://www.for.gov.bc.ca/hfp/publications/00198/wbhbw.htm Koot, H.P., 1991. Western Blackheaded Budworm. Forest Pest Leaflet. Pacific Forestry Centre. http://cfs.nrcan.gc.ca/pubwarehouse/pdfs/3178.pdf Ministry of Forests, Lands, and Natural Resource Operations. 2012. Haida Gwaii Forest District Maps. http://www.for.gov.bc.ca/dqc/forms/DQC_wall_28july03.pdf. Nealis, V.G., Turnquist, R. 2010. Impact and Recovery of Western Hemlock Following Disturbances by Forestry and Insect Defoliation. Forest Ecology and Management 260, 699-706. http://dx.doi.org/10.1016/j.foreco.2010.05.025 Nealis, V.G., Turnquist, R., Garbutt R. 2004. Defoliation of Juvenile Western Hemlock by Blackheaded Budworm in Pacific Coast Forests. Forest Ecology and Management 198, 291-301. http://dx.doi.org/10.1016/j.foreco.2004.04.013 Schmiege, D.C. and Crosby, D. 1970. Black-Headed Budworm in Western United States. Forest Pest Leaflet. USDA Forest Service. http://www.fs.fed.us/r6/nr/fid/fidls/fidl-45.pdf. Swetnam, Thomas; Thompson, Marna Ares; and Sutherland, Elaine Kennedy. (1988). Spruce Budworms Handbook: Using Dendrochronology To Measure Radial Growth of Defoliated Trees. Agriculture Handbook No. 639. USDA Forest Service Wood, C. and Garbutt, R. 1989. Defoliator Damage Assessment And Detection and Mapping of Insect Epidemics, Queen Charlotte Islands and Mainland Coast 1989. Forest Insect and Disease Survey (FIDS). Forestry Canada. http://cfs.nrcan.gc.ca/pubwarehouse/pdfs/32995.pdf  Zeglan, S. 2012. BC Ministry of Forests, Lands, and Natural Resource Operations. Personal communication. Zeglan, S. 2012. Haida Gwaii Budworm Map. BC Ministry of Forests, Lands, and Natural Resource Operations.http://www.for.gov.bc.ca/ftp/RCO/external/outgoing/for%20Lori_D/Inventor yPSP_overview.pdf 17  Figures and Tables Table 2: Summary of Growth Suppressions in Stand F29-001  Tree Pith Date # Suppressions Start Year # Years Avg Z Min Z  HGF29003 1991 1 2011 1 -0.61 -0.61  HGF29004 1994 1 2007 2 -0.06 -0.08  HGF29005 1989 1 2005 5 -0.80 -0.96  HGF29006 1985 0          HGF29007 1986 2 2001 1 -0.46 -0.46        2010 2 -0.44 -0.77  HGF29008 1986 1 2001 1 -0.02 -0.02  HGF29009 1989 0          HGF29010 1988 0          HGF29011 1989 3 1998 1 -0.46 -0.46        2001 1 -0.38 -0.38        2010 2 -0.43 -0.76  HGF29012 1994 0          HGF29013 1985 1 2011 1 -0.35 -0.35  HGF29014 1986 1 1999 3 -0.32 -0.46  HGF29015 1987 3 1998 1 -1.39 -1.39        2001 2 -0.06 -0.07        2011 1 -0.06 -0.06  HGF29017 1991 2 1998 1 -1.86 -1.86        2002 2 -0.58 -0.70  HGF29018 1985 2 1994 5 -0.60 -0.93        2001 2 -0.04 -0.10  HGF29019 1983 3 1996 2 -0.62 -0.92        2002 1 -0.34 -0.34        2008 1 -0.02 -0.02  HGF29020 1982 5 1997 1 -0.16 -0.16        2003 1 -1.04 -1.04        2007 1 -0.11 -0.11        2009 1 -0.94 -0.94        2011 1 -0.33 -0.33  HGF29021 1986 2 1998 1 -0.55 -0.55        2011 1 -0.16 -0.16  HGF29022 1990 3 1997 1 -0.11 -0.11        2000 3 -0.21 -0.27        2009 3 -0.73 -1.25  HGF29023 1983 1 2011 1 -0.34 -0.34 18   HGF29025 1987 0          HGF29026 1988 2 1998 1 -0.22 -0.22        2001 1 -0.27 -0.27  HGF29027 1991 1 2009 1 -0.19 -0.19 Minimum     0   1 -1.86 -1.86 Average   1988 1.5   1.6 -0.44 -0.50 Maximum     5   5 -0.02 -0.02 Mode Year   1986   2011       19   Table 3: Summary of Growth Suppressions in Stand 103F030-3  Trees Pith Date # Suppressions Start Year # Years Avg Z Min Z   HGF30372 1985 3 2001 1 -0.04 -0.04         2003 2 -0.30 -0.37         2009 3 -0.75 -1.38   HGF30373 1982 2 1998 1 -0.38 -0.38         2009 3 -0.27 -0.36   HGF3O374 1980 1 2001 3 -0.48 -0.72   HGF30375 1981 2 2001 3 -0.35 -0.82         2011 1 -0.22 -0.22   HGF30376 1978 1 1999 13 -0.76 -1.35   HGF3O378 1981 1 2002 1 -0.59 -0.59   HGF30379 1984 1 1999 6 -0.80 -1.33   HGF30380 1988 1 2002 4 -0.53 -0.75   HGF30381 1981 1 2002 2 -0.75 -0.93   HGF3O382 1977 1 1998 2 -0.59 -0.59   HGF3O383 1987 4 1992 1 -0.41 -0.41         1994 3 -0.72 -1.41         2006 2 -0.30 -0.31         2009 3 -1.00 -1.27   HGF3O384 1979 1 2001 3 -0.61 -0.87   HGF3O385 1978 2 1998 1 -0.01 -0.01         2006 4 -0.21 -0.25   HGF30386 1981 2 2003 2 -0.16 -0.20         2011 1 -0.75 -0.75   HGF3O388 1982 4 1988 6 -0.80 -1.10         2001 6 -0.50 -0.75         2008 1 -0.20 -0.20         2011 1 -1.02 -1.02   HGF3O390 1981 1 2003 6 -0.50 -0.66   HGF30393 1982 1 2002 10 -0.86 -1.32   HGF30394 1987 1 2006 6 -0.60 -0.85 Minimum     1   1 -1.02 -1.41 Averages   1982 1.7   3.4 -0.51 -0.71 Maximum     4   13 -0.01 -0.01 Mode Year   1981   2001        20  Table 4: Summary of Growth Suppressions in Stand F0-30-27  Tree Pith Date # Suppressions Start Year # Years Avg Z Min Z   HF302703 1990 0           HF302704 1987 1 2006 1 -0.19 -0.19   HF302709 1987 1 2009 1 -0.22 -0.22   HF302742 1986 3 2002 1 -0.19 -0.19        2008 1 -0.33 -0.33         2011 1 -0.73 -0.73   HF302743 1989 2 2002 2 -0.36 -0.65         2005 1 -0.11 -0.11   HF302744 1987 3 1996 1 -0.19 -0.19        2002 5 -0.40 -0.90         2011 1 -0.64 -0.64   HF302745 1992 1 2010 2 -0.12 -0.20   HF302746 1991 1 2003 3 -0.19 -0.37   HF302747 1991 2 2003 2 -0.02 -0.02         2006 1 -0.13 -0.13   HF302748 1990 1 2002 2 -0.79 -1.10   HF302749 1990 4 1997 1 -0.04 -0.04        2000 3 -0.38 -0.56        2005 4 -0.73 -1.57         2011 1 -1.40 -1.40   HF302750 1989 1 2001 11 -0.61 -0.92   HF302751 1990 2 2003 4 -0.26 -0.59         2011 1 -0.30 -0.30   HF302752 1989 1 2002 10 -0.60 -0.81   HF302753 1995 1 2005 3 -0.43 -0.68   HF302754 1996 0           HF302755 1990 1 2000 5 -0.44 -0.99   HF302756 1994 1 2001 5 -0.45 -0.84   HF302757 1983 4 1997 1 -0.11 -0.11        2001 2 -0.73 -0.90        2005 4 -0.28 -0.49         2011 1 -0.65 -0.65   HF302758 1985 1 1999 1 0.00 0.00   HF302759 1984 3 1994 4 -0.36 -0.47        2001 2 -0.55 -0.78         2010 1 -0.20 -0.20   HF302760 1987 3 1991 2 -0.07 -0.10 21         1994 7 -0.67 -1.13         2004 1 -0.20 -0.20   HF302761 1990 1 2011 1 -0.18 -0.18   HF302763 1981 1 2001 1 -0.60 -0.60   HF302764 1983 1 2002 1 -0.26 -0.26   HF302765 1983 1 2001 2 -0.36 -0.61   HF302766 1989 1 2002 5 -0.81 -1.71   HF302767 1980 2 1994 4 -0.52 -1.03        2002 1 -0.66 -0.66   HF302768 1986 1 1999 1 -0.09 -0.09   HF302769 1997 0           HF302770 1988 2 2002 2 -0.15 -0.29         2008 4 -0.30 -0.76   HF302771 1990 4 1996 1 -0.25 -0.25        1999 1 -0.02 -0.02        2001 4 -0.53 -1.04         2011 1 -0.76 -0.76 Minimum     0   1 -1.40 -1.71 Averages   1988 1.6   2.5 -0.38 -0.55 Maximum     4   11 0.00 0.00 Mode Year   1990   2002                   22  Table 5: Summary of Growth Suppressions in Stand F0-30-37  Tree Pith Date # Suppressions Start Year # Years Avg Z Min Z  HF303711 1981 0          HF303713 1984 0          HF303716 1983 0          HF303717 1988 1 1997 1 -0.41 -0.41  HF303719 1986 0          HF303728 1979 2 1985 9 -0.74 -1.47        2002 2 -0.71 -0.74  HF303729 1989 4 1997 2 -0.17 -0.32        2001 1 -0.11 -0.11        2008 1 -0.25 -0.25        2011 1 -0.24 -0.24  HF303730 1986 3 1995 3 -0.09 -0.18        2002 1 -0.38 -0.38        2006 1 -0.05 -0.05  HF303731 1991 2 1999 3 -0.37 -0.77        2011 1 -0.58 -0.58  HF303732 1988 1 2005 7 -0.81 -1.14  HF303733 1985 3 1996 2 -0.64 -0.99        2000 3 -0.31 -0.56        2006 1 -0.44 -0.44  HF303734 1985 2 2000 1 -0.63 -0.63        2007 5 -0.47 -0.79  HF303735 1983 2 1990 4 -0.41 -0.60        2000 4 -0.64 -0.99  HF303736 1984 5 1991 1 -0.12 -0.12        1993 1 -0.20 -0.20        1996 1 -0.69 -0.69        2001 7 -0.76 -1.30        2011 1 -0.66 -0.66  HF303737 1992 1 2004 1 -0.25 -0.25  HF303739 1981 2 2003 1 -0.20 -0.20        2007 5 -0.28 -0.48  HF303740 1985 1 2001 1 -0.43 -0.43 Minimum     0   1 -0.81 -1.47 Averages   1985 1.7   2.5 -0.41 -0.55 Maximum     4   9 -0.05 -0.05 Mode Year   1985   2001       23   Table 6: Summary of Growth Suppressions in Stand F0-30-37  Tree Pith Date # Suppressions Start Year # Years Avg Z Min Z   HF69098 1977 3 1988 1 -0.32 -0.32         2001 2 -0.27 -0.37         2004 8 -0.88 -1.33   HF69099 1979 2 1985 3 -0.25 -0.40         2002 8 -0.83 -1.19   HF69100 1979 2 2001 7 -0.49 -0.93         2011 1 -0.53 -0.53   HF69101 1982 2 1997 2 -0.10 -0.12         200 12 -0.77 -1.09   HF69102 1977 2 1984 2 -0.34 -0.65         1998 14 -0.68 -1.16   HF69103 1980 1 1999 12 -0.88 -1.64   HF69104 1979 3 2002 1 -0.31 -0.31         2004 2 -0.19 -0.23         2010 2 -0.40 -0.41   HF69106 1977 2 2001 4 -0.42 -0.68         2006 6 -0.42 -0.68   HF69107 1979 1 2011 1 -0.58 -0.58   HF69108 1977 2 2003 1 -0.08 -0.08         2005 1 -0.40 -0.40   HF69109 1977 4 1989 1 -0.23 -0.23         1991 1 -0.25 -0.25         2003 5 -0.58 -1.25         2009 3 -0.57 -1.00   HF69110 1974 1 2005 7 -0.67 -1.16   HF69111 1955 2 1976 9 -0.21 -0.60         2011 1 -0.05 -0.05   HF69112 1977 3 1992 2 -0.02 -0.04         1995 2 -0.50 -0.50         1999 12 -0.90 -1.64   HF69113 1981 0           HF69115 1978 2 2007 1 -0.19 -0.19         2009 3 -0.49 -0.76   HF69116 1978 3 2003 1 -0.33 -0.33         2007 3 -0.31 -0.35         2011 1 -0.73 -0.73 24    HF69117 1976 2 1987 2 -0.33 -0.48         2002 10 -0.89 -1.34   HF69118 1970 4 2002 2 -0.21 -0.31         2005 2 -0.14 -0.22         2009 1 -0.02 -0.02         2011 1 -0.23 -0.23   HF69119 1973 1 2005 7 -0.51 -0.94   HF69120 1963 2 2003 2 -0.23 -0.38         2011 1 -0.08 -0.08   HF69121 1970 1 2009 3 -0.69 -0.81   HF69122 1977 0           HF69123 1968 2 1989 1 -0.03 -0.03         2009 3 -0.20 -0.37   HF69124 1972 4 1986 1 -0.09 -0.09         1988 1 -0.20 -0.20         2002 2 -0.75 -0.76         2005 7 -0.70 -1.36 Minimum     0   1 -0.90 -1.64 Averages   1975 2.0   3.7 -0.40 -0.58 Maximum     4   14 -0.02 -0.02 Mode Year   1977   2011                           25  Table 7: Summary of Core Analysis Results and Stand Information  F29-001 F30-3 F30-27 F30-37 F069- 1194 Average Pith Date 1988 1982 1988 1985 1975 Modal Pith Date 1986 1981 1990 1985 1977 Minimum Number of Suppressions Per Tree 0 1 0 0 0 Average Number of Suppressions Per Tree 1.5 1.7 1.6 1.7 2 Maximum Number of Suppressions Per Tree 5 4 4 4 4 Year Most Suppressions Started 2011 2001 2002 2001 2011 Minimum Number of Years Suppression Lasted 1 1 1 1 1 Average Number of Years Suppression Lasted 1.6 3.4 2.5 2.5 3.7 Maximum Number of Years Suppression Lasted 5 13 11 9 14 Minimum Average Z-Score -1.86 -1.02 -1.40 -0.81 -0.90 Average Z-Score -0.44 -0.51 -0.38 -0.41 -0.40 Maximum Average Z-Score -0.02 -0.01 0.00 -0.05 -0.02       Average Proportion of Living Western Hemlock in Stand 0.81 0.51 0.76 0.54 0.87 Average Proportion of Level 1 and Level 2  Living Western Hemlock in Stand 0.72 0.48 0.55 0.28 0.94 Average Trees/Ha in Stand 3480 1930 3340 4220 2980 Proportion of Plots with Active Defoliation 1.00 0.60 1.00 1.00 1.00 Proportion Dead Western Hemlock relative to all trees (X100) 0.00 10.07 0.83 0.42 7.27 Defoliation (%) 13.53 4.26 0.27 0.85 0.14 Proportion of Trees in Plot with Top-Kill 0.02 0.04 0.05 0.04 0.03 Average DBH of Level 1 and Level 2 Trees (cm) 16.36 20.34 15.51 17.23 17.72 Average Ht of Level 1 and Level 2 Trees (m) 10.97 18.50 10.58 11.52 17.12  26   Figure 1: Yearly Frequency of Trees with Suppressed Radial Growth in Stand F29-001 27   Figure 2: Yearly Frequency of Trees with Suppressed Radial Growth in Stand 103F030-3 28   Figure 3: Yearly Frequency of Trees with Suppressed Radial Growth in Stand F030-27 29   Figure 4: Yearly Frequency of Trees with Suppressed Radial Growth in Stand F030-37 30   Figure 5: Yearly Frequency of Trees with Suppressed Radial Growth in Stand F069-1194  

Cite

Citation Scheme:

    

Usage Statistics

Country Views Downloads
China 22 15
United States 7 0
Japan 5 0
City Views Downloads
Beijing 22 0
Tokyo 5 0
Unknown 4 0
Ashburn 2 0
Mountain View 1 0

{[{ mDataHeader[type] }]} {[{ month[type] }]} {[{ tData[type] }]}
Download Stats

Share

Embed

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"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.1037.1-0075539/manifest

Comment

Related Items