UBC Faculty Research and Publications

Structure and regeneration of old-growth stands in the engelmann spruce - subalpine fir zone Klinka, Karel 1998-12-31

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Scientia Silvica Extension Series,  Number 11, 1998Structure and Regeneration of Old-growth Standsin the Engelmann Spruce - Subalpine Fir ZoneIntroductionOld-growth sftandsf  are  important  for  management,consfervation, wildlife, recreation, and maintaining biologicaldiversfity in foresfted landsfcapesf.   However,  we are lackingthe  information    needed to  adequately identify  andcharacterize old-growth sftandsf.   Thisf isf  esfpecially true  forhigh elevation, interior foresftsf.  The characterization of sftandsftructure  and  regeneration  pattern  will help  in  thedevelopment of sfite-sfpecific guidelinesf for identifying old-growth sftandsf  and resftoring  sfome  of the  old-growthcharacterisfticsf in managed sftandsf.Thisf pamphlet presfentsf a sfynopsfisf of a sftudy invesftigatingsftand sftructure and regeneration of old-growth sftandsf in theMoisft Cold Engelmann Spruce -  Subalpine Fir (ESSFmc)Subzone near Smithersf, B.C.  The three sftandsf sfelected forthe  sftudy  were located  on zonal sfitesf,  each in  differentwatersfhedsf, and the sftandsf were esftablisfhed after fire.  Thecriteria usfed  for  sfelection  were: i)  absfence of lodgepolepine, ii) presfence of advanced regeneration, and iii) abundantsfnagsf and coarsfe woody debrisf.  Thesfe sftandsf were presfumedto  represfent the old-growth sftage of sftand  development orthe final (climax) sftage of sfecondary sfuccesfsfion.Tree species compositionDepending on climate, either sfubalpine fir, Engelmann sfpruceor both can be presfent in old-growth sftandsf in the ESSF zone.In  the  sftudy sftandsf, sfubalpine fir  wasf clearly predominant(96%) while the treesf, sfaplingsf, and sfeedlingsf of Engelmannsfpruce  formed  only a minor component (<4%).    In  theabsfence of a large sfcale disfturbance, I expect sfubalpine firto be the dominant tree sfpeciesf in the old-growth sftage.Diameter distribution of subalpine firThe diameter (dbh) disftribution of sfubalpine fir in the sftudysftandsf wasf closfe to a balanced, or inversfe-J sfhape (Figure 1).Thisf type  of disftribution isf  characterisftic of a balanced orsfteady sftate, where the disftribution will not change over timeuntil the  occurrence of a large-sfcale  disfturbance.   Similardbh disftributionsf were found  in  high-elevation sfpruce-firsftandsf in Colorado.G36G57G44G51G47G3G16G13 G15G13G17G13G19G13G1bG13G13G15G13G17G13G19G13G1bG13G14G13G13G14G15G13G36G57G44G51G47G3G15G27G45G4bG3GbfG46._G50GcG13 G15G13G17G13G19G13G1bG13G13G15G13G17G13G19G13G1bG13G14G13G13G14G15G13G36G57G44G51G47G3G14G13 G15G13G17G13G19G13G1bG13G29G55G48G54G58G48G51G46._G5cG3GbG36G57fG48G50G56G12G4bG44GcG13G15G13G17G13G19G13G1bG13G14G13G13G14G15G13Figure 1. Dbh distributions.G36G57G44G51G47G3G14G13 G14G13G15G13G16G13G17G13G18G13G29G55G48G54G58G48G51G46._G5cG3GbG36G57fG48G50G56G12G4bG44GcG13G18G13G14G13G13G14G18G13G15G13G13G15G18G13G16G13G13G36G57G44G51G47G3G15G2bG48G4cG4aG4bG57G3GbfG50GcG13 G14G13G15G13G16G13G17G13G18G13G13G18G13G14G13G13G14G18G13G15G13G13G15G18G13G16G13G13G36G57G44G51G47G3G16G13 G14G13G15G13G16G13G17G13G18G13G13G18G13G14G13G13G14G18G13G15G13G13G15G18G13G16G13G13G14G15G3G50G14G1cG3G50 G14G16G3G50 G14G17G3G50Figure 2. Height distributions. Dashed lines indicate the boundary ofcanopy layers.Height distribution of subalpine firCompared  to  the  diameter  disftribution,  the  heightdisftributionsf were modal (Figure 2).   The absfence of treesfat certain heightsf (depresfsfionsf  in the  height frequencydisftribution) isf believed to indicate canopy boundariesf.  Treesfin the lower canopy layer have greatly reduced height growth(unlesfsf releasfed), sfo they  will remain in  the  lower  canopyfor a long time.  Treesf in the upper canopy will continue togrow, sfo almosft no treesf will remain at the canopy boundary.Modality wasf an unexpected characterisftic asf the  heightdisftribution in high-elevation sfpruce-fir sftandsf in Coloradowasf  reported  to  approximate  the  inversfe-J  sfhape.Consfidering that the oldesft sftand (Stand 2) sfhowed the mosftpronounced modal disftribution, I conclude that  thisf  heightsftructure  will not change with  time  and that  the  modaldisftribution isf  characterisftic of the  old-growth sftage.Age distribution of subalpine firEven though the dominant trees were old (close to 400 yearsat breast height) and approached the maximum life span ofsubalpine fir, the age distributions did not show an inverse-Jshape (Figure 3).  This was unexpected as the age structureof many high-elevation, old-growth stands was reported tobe close to  an inverse-J.    Because of weak relationshipsbetween size and age, and lack of information on mortality,it is difficult to predict the future age structure.Since trees were cored at 1.3 m, it is important to know howlong  it  takes  for  subalpine  fir  seedlings  to  reach  breastheight.  The data showed that seedlings growing under thecanopy reach 1.3 m in 11 to 140 years.  Nevertheless, even100-year old seedlings still respond  to  release.Factors influencing the regenerationpattern of subalpine firThe most important  environmental factor  influencing  theestablishment of  seedlings  was decaying wood. Althoughregeneration  also occurred on the  forest  floor,  there  wereat least  twice  as many seedlings  on decaying wood whencompared with substrate cover (Figure 4).Another factor  that  showed  significant  correlation withregeneration  was time  of snowmelt.  The zone withintermediate  snowmelt  time  had the  highest density ofseedlings.  Snowmelt progresses from around the tree stemsand on downed large  coarse woody debris to  canopy gapswhere the highest snow accumulation and the latest snowmeltoccur.Other factors such as understory vegetation, light, or canopygaps were weak predictors of the presence of regeneration.SummaryThe following conclusions can be made on old-growth standsin  the ESSFmc subzone:    (1) subalpine  fir  will be thedominant species; (2) the diameter distribution of subalpinefir will be balanced or inverse-J shaped; (3) height and agestructures of subalpine fir will feature a modal distribution;(4)  the  regeneration  pattern of subalpine  fir  will be moststrongly influenced  by the presence of decaying wood;  and(5) canopy gaps may not improve the abundance of subalpinefir  regeneration.Scientia Silvica  is published by the Forest Sciences Department,The University of British ColumbiaISSN 1209-952XEditor: Karel Klinka (klinka@interchange.ubc.ca)Research: P?l Varga (pvarga@interchange.ubc.ca)Production and design: Christine Chourmouzis (chourmou@interchange.ubc.ca)Financial support: G.F. Dodd Operational Research Chair, BC Ministry of ForestsCopies available from:  www.forestry.ubc.ca/klinka, orK.Klinka, Forest Sciences Department, UBC,3036-2424 Main Mall, Vancouver, BC, V6T 1Z4G36G57G44G51G47G3G15G24G4aG48G3GbG5cG48G44G55G56GcG13 G14G13G13 G15G13G13 G16G13G13 G17G13G13G13G18G14G13G14G18G15G13G15G18G16G13G36G57G44G51G47G3G16G13 G14G13G13 G15G13G13 G16G13G13 G17G13G13G13G18G14G13G14G18G15G13G15G18G16G13G36G57G44G51G47G3G14G13 G14G13G13 G15G13G13 G16G13G13 G17G13G13G29G55G48G54G58G48G51G46._G5cG3GbG56G57G48G50G56G12G53G4fG52G57GcG13G18G14G13G14G18G15G13G15G18G16G13Figure 3. Age (determined at 1.3m) distributions of trees.G8G3G26G52G59G48G55G3G52G49G3G36G58G45G56G57G55G44G57G48G56 G8G3G36G48G48G47G4fG4cG51G4aG56G3G52G51G3G36G58G45G56G57G55G44G57G48G56G29G29GbG1aG15G8GcG29G29GbG15G14G8GcG27G3aGbG15G1bG8GcG27G3aGbG1aG1cG8GcFigure 4.  Percent cover of substrates (FF = forest floor, DW =decaying wood) and the percent of subalpine fir seedlings on thesesubstrates in Stand 1.The relative  density of  regeneration  was the same in  gapsand under the  canopy.    This suggests that  gaps are not themajor factor  controlling the  regeneration.


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