THE IMPACT OF LODGEPOLE PINE SIZE ON HEAT-FORMED TREE WELLS Created by Philip Neumann Winter Ecology, Spring ‘08 Mountain Research Station – University of Colorado, Boulder

Objective  To further understand the relationship between coniferous trees and their surrounding snowpack.  To link the importance of tree well formation to the rest of the winter ecological community.

Two Methods of Tree Well Formation  Snow deflection:  Overhanging branches deflect snowfall  Creates pocket of low snow accumulation  Large affected areas  Melting and Sublimation:  Trees absorb solar radiation  Radiation is reemitted into snowpack  Small affected areas

Snow Deflection vs. Melting and Sublimation

Factors That Create Heat-Formed Tree Wells  Incoming solar radiation  % solar radiation absorbed by tree  Not due to tree-produced heat  Air Temperature  Sublimation or Melting  Metamorphosis over time  Wind loading/scouring  Additional snow

Importance  Trees are a major source of heterogeneity in the snowpack. Tree wells exists at the tree-snow interface.  Large geographic spread  Local modification of snowpack creates a functionally different environment.  Reduced soil insulation by snowpack  Increased melting and sublimation  Current lack of study on heat-formed tree wells

Question What is the relationship between trees and their snowmelt patterns?

Hypothesis An increase in diameter of tree wells will be directly proportional to the increase in diameter of trees in a 1:1 ratio. Why?  Increased tree diameter increases lowest possible value  Similar heat absorption per unit area from tree to tree  More tree surface area for absorption for larger trees  More snow surface area to heat for larger trees Similar effective warming range

Hypothesis

Methods  Measure tree well diameter for trees in a 35x50ft plot.  Plot: Sheltered, relatively even stand of planted Lodepole Pine. 35ft downhill from a road clearing, slope of 13*, aspect of 170*  Measurements: Diameter of affected snowpack taken in two directions and averaged for tree well #’s. Diameter of tree measured at snow surface.

Transect

Results: Tree vs. Tree Well Diameter

Results: Tree Diameter vs. Adjusted Tree Well Area (Total Tree Well-Tree Area)

Results  Data fits well to a linear equation:  y=2.0591x  R-Squared of.9477  P-value of 4.763E-33  Data exhibits positive slope of ~2cm tree well/1cm tree diameter.  Exponential growth in effected snowpack data.

Discussion  The hypothesis is rejected.  Strong, linear fit of the data implies a direct connection between increasing tree size and tree well size.  Slope of ~2 implies that an given increase in tree diameter effects tree well diameter twice as much. WHY? Volume = Height x π(½ Diameter)²

Discussion  A change in diameter will affect circumference, and therefore surface area, by the same multiplier.  Explains capture of solar radiation  Accounted for in hypothesis  A change in diameter will affect tree volume by its square  Additional, unaccounted for, factor  Increase in mass and thermal capacity  Increased daily duration of heat transfer

Discussion  Larger trees… more effected snow volume  Creates diurnal “thermal islands” in the snow  Dictates snowmelt & sublimation rates May impact available soil moisture in cold season May present easier internivean access May present area to avoid for some… predator access  Increased temperature variation may be important— good or bad—for some species Most likely creates habitat quality gradients May present low-competition niche for some

Discussion Future studies:  Heat flux in tree wells  Heat flux inside trees  Photosynthesis rates in large/small trees Determined by diurnal tree stem diameter variation  Microbial activity below tree wells  Burrow entrance/exit

Conclusion  Increases in tree diameter result in exponential increases in effected snowpack.  Caused by the thermal capacity of trees  Heat at tree-snow interface creates microclimate  Increased daytime temperatures  Decreased soil insulation  Future studies could focus on:  Soil heat flux below tree wells  Heat flux in trees  The effects of heat flux on tree health and surrounding plant and animal communities

Works Cited Hardy, JP, Albert, MR. Snow-induced thermal variations around a single conifer tree. Hydrological Processes, 9: Halfpenny, JC,, Ozanne, RD Winter: An Ecological Handbook. Boulder (CO): Johnson Publishing Company. p Sevanto, S, Suni, T, Pumpanen, J, et al. Wintertime photosynthesis and water uptake in a boreal forest. Tree Physiology, 26: 2006