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Survival and growth of western larch seedlings in relation to light availability Klinka, Karel 1997-04-07

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Survival and Growth of Western Larch Seedlingsin Relation to Light AvailabilityIntroductionWestern larch  (Larix occidentalis  Nutt.) is  an importantcomponent of the  montane forest  in southeastern  BritishColumbia.   It  grows in  cool-temperate (IDF  and ICH  zones)and boreal climates (MS zone and, occasionally, ESSF zone).Larch is considered a very shade-intolerant species which cantolerate low light (partial shading) only during the seedling stage(the  first  5 growing seasons).    Typically,  it  regenerates  afterfire in the open on seedbeds exposed by burning.  However, towhat extent it  tolerates  low  light  and how various lightenvironments affect its survival and growth is not known. Theobjective of our study was to determine the variation in survivaland growth of western larch  seedlings  in  relation  to  lightavailability and site conditions.Materials and MethodsFive study sites were located on zonal sites in 4 biogeoclimaticsubzones: sites  1, 2,  and 3 were near Okanagan Falls, site 4near Castlegar, and site 5 near Cranbrook (Table 1). The maindifferences between the  sites  were climate (temperature  andprecipitation) and soil  moisture. Each study  site  included  aportion of a clearcut and an adjacent forest stand. Canopies ofthese stands had different sizes of gaps providing for a varietyof light environments in their understories. At each study site,approximately 500 one-year-old, container-grown seedlingswere planted in  mineral soil  approximately 1.5 m apart inirregularly  spaced  transects  extending from  60 m inside  theclearcut, through  the  stand  edge, to about 60 m inside  theadjacent stand.  Sites 1, 2, and 3 were planted in the spring of1993 and sites 4 and 5 were planted in the spring of 1994.Planted seedlings were monitored for three growing seasons.Light availability (percent  of above-canopy light,  PACL) foreach seedling was determined during the second growing seasonby the procedure described in Chen et al. (1996). Each August,seedlings were examined for survival and injuries. The seedlingswith a history of damage were excluded from  sampling  anddata analysis. During the third growing season before leaf fall,60 to 100 surviving seedlings on each study site were selectedfor random destructive sampling. The total height (H) and basediameter (D)  of the  sampled seedlings were measured in  thefield. After excavation, the seedlings were stored in a portablecooler,  and transported  to  a laboratory  to  determine totalbiomass.Table 1.  Study site characteristics.1 Biogeoclimatic subzones: IDFxh - Very Dry Hot InteriorDouglas-fir; IDFdm - Dry Mild Interior Douglas-fir; MSdm- Dry Mild Montane Spruce; and ICHmw - Moist WarmInterior  Cedar-Hemlock.2 SMR (actual soil moisture regime): VD - very dry; MD -moderately dry; SD - slightly dry, F - freshResultsHow survival varied with light availabilitySurvival of planted seedlings varied with light availability andstudy site (Figure 1). Survival significantly (p <0.05) decreasedwith decreasing light from intermediate to low light levels, butthere were no significant differences with increasing light fromintermediate to high light levels. However, this pattern variedgreatly among the  study sites. At the  end of the  1st  growingseason,  survival ranged from  10 to  100% and did not varysignificantly  among 10 light  classes  except for a  very lowsurvival in the 0.1 - 10.0% light class on site 4. At the end ofthe  2nd  growing season,  accumulated survival  significantlydecreased in most of the light classes across all the study sites.The accumulated survival at the end of the 3rd growing seasoncontinued to  decrease: it  ranged  from  0 to  60% at lightavailability <30% and from  30 to  100% at light  availability>30% across the study sites. Therefore, we conclude that duringthe seedling stage western larch may survive low light levelsas low as 10%.In relation to site quality, the accumulated survival at the end ofthe 3rd growing season at high light levels increased with in-) n 1 R21 5 x V2 5 d M3 2 d S4 2 m5 0 d MScientia Silvica Extension Series, Number  1, 1997Figure 1. Survival of study seedlings in relation to lightavailability at the end of  the first (           ), second (           ) andthird (           ) growing season.Implications for managementConsidering the constant decline in survival (faster in low thanhigh light) in the first 3 growing seasons, we expect that survival(1) will further decline across all the  study sites in  low lightenvironments (<30%) but (2) will stay more or less  constantbetween 40 and 100% of light availability.  In low light levelsthe growth potential of the surviving seedlings will not be real-ized,  resulting in low vigour and increased competition withvegetation present on the site.  This will postpone the time toreach the  free-to-grow stage.   We conclude that  regenerationcutting methods other than  clearcutting, seedtree  or patch-cutting should  not be considered if  the  objective is  toregenerate western larch as a major timber crop species.ReferenceChen, H.Y.H., Klinka, K., and Kayahara, G.J. 1996. Effects of light ongrowth, crown architecture, and specific leaf area for naturallyestablished Pinus contorta and Pseudotsuga menziesii var. glauca.saplings. Can. J. For. Res. 26: 1149-1157.Scientia Silvica  is published by the Forest Sciences Department,The University of British Columbia, ISSN 1209-952XEditor: Karel Klinka (klinka@interchange.ubc.ca)Research: Han Y. H. Chen (han.chen@mnr.gov.on.ca)Production and designed: Christine Chourmouzis (chourmou@interchange.ubc.ca)Financial support: National Science and Engineering Research Council, BC Ministry ofForests, Weyerhouser Canada, Ltd., and Cranbrook Forest Industries, Ltd.For more information contact: Han Chen (han.chen@mnr.gov.on.ca)Copies available from: www.forestry.ubc.ca/klinkaFigure 2. Growth of study seedlings in relation to light availability2550751002550751002550751002550751000255075100Site 1Site 2Site 3Site 4Site 50 - 1010 - 2020 - 3030 - 4040 - 5050 - 6060 - 7070 - 8080 - 9090 - 100Percent above canopy light (PACL)Survival (%)0510152055 5 5555555 5 5555555555 5555555555555555555555555555555555555544444 44 44444 444444444 4444 44444444444444 44444444444444444444444444444444444444443333333 33333333333 3 33 3 333333333333333333333 3333333333 33333333333 33322222222 222222222222222222222222222 222222 222222 22222222222222222222222222111111 1111 111111111 11 1 11 11111 111111 11111 1111111111111111111111111111020406080100555 5 55 55555 5 555555555555555555555555555555555555555555555555544444444 44444 4444444444444444444444444444444444444444444444444444444444444444444443333333333 333333333333333 3 3 333333333 333333333333 33333 33333 33333 333333333333332222222222222222222222222222222222222222222222222222222 22222222 2222222221 111111111111111111 11 1 11 11111 1111111 1111 1111111111111111111111111110 20406080100020406055 5 55 5555 5 5555555555555555555555555555555555555555555555444 4 44 4 4 44444 44 44444 4 4444444444444444444444444444444444444444444444444444443333333 33333333333333 3 33 3 3333333333333333333333 333 33 33333 333333333333322222222 22222222222222222222222222 222222222222 22222222222222222222222221 11111 1111 111111111 11 1 11 1111111111111111 111111111111111111111111111 1Diameter (mm)Height (cm)Total biomass (g)Percent above canopy light (PACL)TB =e 1.253+0.020xPACL n=371, r2=0.40, P<0.001D =e1.274+0.010xPACL n=371, r2=0.39, P<0.001H =e 3.545+0.006xPACL n=371, r2=0.20, P<0.001creasing precipitation, decreasing temperature, and increasingsoil moisture.  At low light levels, a similar pattern occurred,although the trend was less pronounced.How growth performance varied with light availabilityGrowth characters measured on surviving seedlings at the endof third growing season indicated that base diameter and totalbiomass drastically increased with increasing light availabilitybut the increase in height growth was less pronounced (Figure2).  While the  increases  in  diameter and total  biomass wereconsistent with increasing  light,  there  was no significantincrease  in  height growth  with increasing light  from  40 to100%. At the end of the 3rd growing season, the mean height,the mean base diameter, and the mean total biomass of plantedseedlings in full light was 1.7-, 2.3-, and 7- fold greater thanthose of seedlings grown in low light.The response of growth to light availability was not signifcantlyaffected by climate (subzone)  or soil  moisture regime.Therefore, we conclude that regardless of site, high light levelscan maximize the growth potential of western larch seedlings.

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