TREE WELLS: COMPARISON OF CONIFEROUS AND DECIDUOUS TREES Magali Weissgerber, Winter Ecology, Spring 2015, CU Mountain research Station

Tree wells Wells in snow that form around tree trunks Important for animals soil temperature skiers

Tree well formation Radiation: solar radiation absorption by the tree (Marchand, 2014) Canopy effect on (Sturm, 1992 ; Harding, 1994): Snowfall Radiation penetration Temperature Christopher White (2012 Winter Ecology Project, “Variables Affecting Tree Wells Formation”) tested relationship between tree wells formation and DBH, height, surrounding tree density and species. He found significant positive relationship between tree well volume and: Tree DBH Tree density

Coniferous and deciduous trees difference Sturm paper on tree well formation in Alaska: tree wells around spruces but not around aspens (snow cones). In the southern Rockies, there are tree wells around spruces and aspens. Why this difference? Potential explanations: 1) Climate effect 2) Tree well formation is different depending on trees, especially between coniferous (Spruce for example) trees and deciduous trees (Aspen for example). Question and hypothesis Q: Is tree well formation around deciduous and coniferous trees identically influenced by the same tree characteristics (DBH, height)? Hypothesis 1: tree well formation around deciduous and coniferous trees is not affected identically by the same tree characteristics. Hypothesis null: the same tree characteristics affect identically tree wells formation independently of the tree species.

Methods Tree selection Deciduous: Aspen Coniferous: Engelmann Spruce Measurements of tree characteristics: DBH (DBH tape) Height (50 tape and clinometer) Measurements of well volume with: Depth Radius Environment measures: Canopy cover (convex mirror) Snow depth

Results ENGELMANN SPRUCE (DBH and depth) (linear model analysis)  Significant relationship for both

Results ASPEN (DBH and depth) (linear model analysis)  Significant relationship for both

Results COMPARISION (t test) T-ratio = p-value = T-ratio = p-value =  Significantly different  Nearly significantly different

Discussion Significant relationships Tree DBH / tree well volume for both tree species Tree height / tree well volume for both tree species  Tree height and DBH influence tree well formation of both Spruce and Aspen. Comparison DBH / Tree well volume relationship  different for Aspen and Spruce Tree height / Tree well volume relationship nearly different for Aspen and Spruce  may become significantly different with change in methods. H1 accepted: the data indicate that tree well formation around deciduous and coniferous trees is not affected identically by the same tree characteristics.

Discussion Differences of tree well formation between Alaska and Colorado are, according to the data, not only due to climate and environmental differences. Why? Possibly: Canopy effect? Radiation? Influence of DBH and height: Causality or correlation?

Discussion SOURCE OF ERROR Selection of trees with a measurable well Tree wells assumed uniform for volume calculation Difference with 2012 Christopher White project: 2012: “first day of data collection followed precipitation event” 2015: week-end of data collection followed a period of at least one week without precipitation

Conclusion Tree well formation differs between regions Tree well formation differs between trees

Acknowledgments Tim Kittel for his advices and his help, especially concerning data analysis. Aurore Rimlinger without whom I would not have been able to measure all these trees in such a few hours.

Bibliography Sturm, Matthew, Snow Distribution and Heat Flow in the Taiga, Arctic and Alpine Research, Vol. 24, No. 2, Harding, R.J., The Energy Balance of the Winter Boreal Landscape, Journal of Climate, American Meteorological society, LaMalfa, Eric Martin, and Ryle, Ron, Differential Snowpack Accumulation and Water Dynamics in Aspen and Conifer Communities: Implications for Water Yield and Ecosystem Function, Ecosystems, Marchand, Peter, Life in the Cold. An Introduction to Winter Ecology, University Press of New England, 4th ed

Supplementary slides

Results Environment comparison: Snow depth difference: for large conifers “the snow depth at the trunk is about 20% of the total undisturbed snow depth away from the tree despite differences in size or branch structure” (Sturm 1992) Spruce: 20.46% of undisturbed snow Aspen: 25.00% of undisturbed snow  Similar snowpack differences Canopy cover Spruce = 80.29% cover Aspen = 43.93% cover  Spruce covered by twice more canopy than aspens