Snow Compaction Variation Across a Subalpine Transect William Weaver EBIO 4100 April 15, 2017 CU Mountain Research Station

Introduction Winter sports common in Colorado Ski and snowshoe traffic compacts snow Lots of animals live under snow Difference between disturbed and undisturbed areas? The subnivean space is crucial for the survival of small mammals and invertebrates during harsh winter conditions. As the snowpack deepens, the subnivean space becomes more protected from temperature change. This property is known as the insulative capacity of snow. This project will measure the density of the snowpack, as well as the temperature, to determine how effective the snowpack is at maintaining constant temperatures below the snowpack. Snow depth, type, compaction, and disturbance are all factors that determine insulative capacity (Rixen, 2002). The presence of debris can also affect the quality and thickness of depth hoar (Corn, 1992). Debris may be different depending on the biota nearby, such as willows or lodgepole pine trees.

Introduction Question: Subnivean space Area above ground, beneath snowpack Provides critical habitat(Corn & Raphael, 1992) Snowpack Insulates against large temperature changes(Yan,2010) Determines habitability of subnivean space Martens, insects, squirrels, snowshoe hares, etc. Question: Do winter trails increase snow compaction in the subnivean space relative to undisturbed areas? The subnivean space is crucial for the survival of small mammals and invertebrates during harsh winter conditions. As the snowpack deepens, the subnivean space becomes more protected from temperature change. This property is known as the insulative capacity of snow. This project will measure the density of the snowpack, as well as the temperature, to determine how effective the snowpack is at maintaining constant temperatures below the snowpack. Snow depth, type, compaction, and disturbance are all factors that determine insulative capacity (Rixen, 2002). The presence of debris can also affect the quality and thickness of depth hoar (Corn, 1992). Debris may be different depending on the biota nearby, such as willows or lodgepole pine trees.

Hypothesis HO: Winter trails have no effect on snow compaction relative to other forest locations. HA1: Winter trails increase snow compaction relative to other forest locations. HA2: Winter trails decrease snow compaction relative to other forest locations. The null hypothesis is: winter trails have no effect on snow compaction relative to other forest locations. The alternate hypothesis is: winter trails increase snow compaction relative to other forest locations. The second alternate hypothesis is: winter trails increase snow compaction relative to other forest locations. These hypotheses cover all possibilities.

Methods Forest Site z = 53,55 cm. Trail Site z = 37 cm. Clearing Site z = 48,55 cm. Methods I began by locating an appropriate transect site. There needed to be a trail with a clearing on one side and a forested area on the other. The location I chose did not have an exceptionally large clearing, but the snow depths were different enough to create snowpack that was different than the forested area. The trail was not as heavily used as the main trail, but there was evidence of ski traffic within the previous snow storm. The map marks the five snow pit locations: the green triangles mark the forest sites, the blue star marks the trail site, and the yellow circles mark the clearing sites. The Marr lab is the building in the bottom left corner.

Methods Raw Data Net mass of snow Layer thickness Snowpack depth Crystal structure Layer hardness Calculations Density Insulative Capacity To analyze the effects of snow depth, compaction, and disturbance, I dug five snow pits across a fifty meter transect. The center point was in the middle of a trail that has been compacted from ski and snowshoe traffic. The other four pits radiate away from the trail into a sheltered forest area and an open meadow in the opposite direction. This provides data to elucidate the effects of compaction and shelter on the subnivean space. I took the following measurements at each snow pit. Snow density (net mass per 1000cm^3) Snow depth Thickness of each snow layer Hardness of snowpack in each layer Crystal structure These measurements are part or the snow insulative capacity formula, which requires a summation of snow density multiplied by the thickness of each layer, respectively. The qualitative assessment of the snowpack will help inform the results of the study. Limitations Only one transect, one trail site Lower elevation Warm day, snow melted quickly

Results Snow Insulative Capacity Sum of layer densities times thickness (Marchand, 2013) Most Insulative = Forest Least Insulative = Trail Top and bottom layers provide most insulation Insulative capacity is determined by multiplying the thickness of a layer by the density of that layer (Marchand, 2013). Summing up each layer gives a total insulative capacity for the snowpack. The graph above stacks each insulative layer visually. The forest provides the most insulation to air temperature changes and the trail provides the least.

Results Top two layers vs. bottom two layers Larger temperature gradient lead to faceting in the clearing bottom and top layers. Forest bottom layers showed mostly rounding. My .csv data files have my temperature data, I did not have time to make graphs for the temperatures that I took. The temp gradient in the clearing had a 2 degree per 10 cm. gradient, supporting the observed faceting in the lower layers. Top two layers vs. bottom two layers Trail - only rounding and faceting

Results Trail had most consistent hardness The hardest snow was the trail and forest bottom layers. The trail bottom layers showed some faceting but was not that dense. This suggests that the trail may not have been used during early snowfalls, resulting in compaction due to upper layer compaction rather than direct compaction due to skis. Trail had most consistent hardness Bottom forest layers, rounding

Results Green = Forest Red = Clearing Blue = Trail Forest density increased linearly with depth Others had highest densities halfway down This linear regression plots density versus layer midpoint. The interesting thing is that the forest density does correlate with depth, suggesting uniform compaction over the season. The other layers are lass dense at the top and bottom, suggesting that compaction was not uniform and that faceting shifted water mass towards the middle of the pack. I also observed an ice layer around the 25cm. Depth in the clearing, supporting this theory.

Results Tukey test (using ANOVA) P-value = bar position If bars cross middle line, correlation is significant No significant difference between top layers This is a Tukey test based on ANOVA results. The charts plot differences in means between sites. If the bar crosses the center line, then the correlation is significant. There is no significant difference in the mean densities of the upper layers between sites.

Results Tukey test (using ANOVA) P-value = bar position If bars cross middle line, correlation is significant No significant difference between bottom layers, but the trial and forest are nearly there (p- value = 0.12) There is no significant difference between the bottom layer densities across sites, but the trail-forest comparison is very close to being significant. I ran these tests with density, effective water content, insulative capacity, and layer thickness, but density was the only test that even came close to being significant.

Discussion Bottom forest layer had highest densities No significant difference between forest, clearing, or trail Data show importance of temperature gradient Trail and clearing exposed to heat loss at night Bottom forest layer had highest densities Insulative capacity highest in forest: depth, density Chosen trail Moderate traffic Likely no early season compaction Future Research Earlier in the season More heavily used trail Three transects The trail I chose was moderately traveled, but it was likely not used during the first few snowstorms, so the bottom layer was not compacted relative to the forest. The temperature gradient difference between sites is best shown with density, since high temperature gradients lead to faceting and low gradients lead to rounding (1 degree per 10 cm.). The insulative capacity was highest in the forest, which makes sense because the forest had deeper snowpack but was also less dense overall. The additional Tukey tests show no significant difference in any of the other parameters I calculated.

Conclusion No significant difference between upper or lower layer densities Fail to reject the null hypothesis No significant difference between lower layer densities Likely a result of the chosen trail Lack of consistent compaction

Citations Corn, J. G., & Raphael, M. G. (1992). Habitat characteristics at marten subnivean access sites, 56(3), 442–448. https://doi.org/10.2307/3808856 Ge, Y., & Gong, G. (2010). Land surface insulation response to snow depth variability. Journal of Geophysical Research: Atmospheres, 115(D8), D08107. https://doi.org/10.1029/2009JD012798 Marchand, P. J. (2013). Life in the cold an introduction to winter ecology /. Rixen, C., Haeberli, W., & Stoeckli, V. (2004). Ground Temperatures under Ski Pistes with Artificial and Natural Snow. Arctic, Antarctic, and Alpine Research, 36(4), 419–427. https://doi.org/10.1657/1523-0430(2004)036[0419:GTUSPW]2.0.CO;2