The Effects of Slope Aspect on Tree Density in the Subalpine Forest Alex SandbergBernard Winter Ecology 2018 Mountain Research Station University of Colorado Boulder BACKGROUND Subalpine forest Highest elevation forests ID: 763963
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The Effects of Slope Aspect on Tree Densityin the Subalpine Forest Alex Sandberg-Bernard Winter Ecology, 2018 Mountain Research Station, University of Colorado Boulder
BACKGROUNDSubalpine forest Highest elevation forests Subalpine fir – Abies lasiocarpa Engelmann spruce – Picea engelmanniiLimber pine – Pinus flexilis - (Peet 1981)
BACKGROUNDTopography can control abiotic factors Slope aspect N slopes – less solar radiation, deeper snow pack S slopes – more solar radiation, shallow snow pack - (Måren et. al. 2015) Vegetation & species distributionSpruce/fir stands on moist slopes Limber pine in drier areas - (Peet 1981) More moisture, higher tree density - (Måren et. al. 2015)
Does tree density depend on aspect?H0 = there is no relationship between tree density and aspect H 1 = there is a relationship between tree density and aspect
SITE SELECTION & SETUPNiwot Ridge – north and south slopesTwo plots just below tree line Three 50 m transects per plot Three observation points per transect Pseudoreplicates – no time for true replicationhttps://caltopo.com
METHODSBitterlich sampling methodBitterlich stick Rotation around fixed observation point Count “in” treesDensity measured as basal area (m2/ha)ID all “in” trees Snow depth measurement Proxy for moisture https://commons.wikimedia.org/wiki/File:WZP-8.png Yang, et. al. 2017
Results: Basal area and aspectTwo-tailed t-testp << 0.001 Higher density on N slope
Results: Basal area, aspect, tree species2 factor ANOVA with interactionp << 0.001 Species is important
Results: Basal area and snow depthRegressionsN slope: p = 0.087 S slope: p = 0.31 Opposite trends Deeper snow on S slope
DISCUSSIONGreater density on N slopeConfirms expectation and previous studies No moisture relationship found Tree species is important factor Spruce most important on N slopeLimber pine absent on N slopeBalanced ratio of spruce:fir on S slopeWhy more south slope snow?NW winds
FUTURE RESEARCHMore snow pack measurementsTrue replication needed
CONCLUSIONAspect good predictor of basal areaGreater density on north slopesTree species is important Moisture effects uncertain, warrant further study
REFERENCES Peet, R. 1981. Forest vegetation of the Colorado Front Range - Composition and dynamics. Vegetatio 45: 3-75. DOI: 10.1007/BF00240202 Måren, I.E., S. Karki, C. Prajapati, R.K. Yadav, and B.B. Shrestha. 2015. Facing north or south: Does slope aspect impact forest stand characteristics and soil properties in a semiarid trans-Himalayan valley? Journal of Arid Environments 121: 112-123. DOI: https://doi.org/10.1016/j.jaridenv.2015.06.004 Farrell, J. 2016. The Effects of Topography on Forest Cover in Subalpine Forest. http://culter.colorado.edu/~kittel/WEcol_Projects16/JasonFarrell_Topography&TreeDensity_16.pptx Mote, P.W., A.F. Hamlet, M.P. Clark, and D.P. Lettenmaier . 2005. DECLINING MOUNTAIN SNOWPACK IN WESTERN NORTH AMERICA*. Bull. Amer. Meteor. Soc. 86: 39–49. DOI: https://doi.org/10.1175/BAMS-86-1-39 Mote, P.W. 2006. Climate-Driven Variability and Trends in Mountain Snowpack in Western North America. J. Climate 19: 6209–6220. DOI: https://doi.org/10.1175/JCLI3971.1 Yang, W., H. Koba - yashi , K. N. Nasahara , R. Suzuki, and A. Kondoh . 2017. Quantitative Evaluation of Bitterlich Sampling for Estimating Basal Area in Sparse Boreal Forests and Dense Tropical Forests. Open Journal of Forestry 7: 143-156. DOI: https://doi.org/10.4236/ojf.2017.72009 Mueller- Dombois , D., Ellenberg , H. 1975. Aims and Methods of Vegetation Ecology. John Wiley & Sons Inc., New York