A snowpack comparison between a limber pine site and a spruce site within a spruce forest Sam Sartwell, Winter Ecology, EBIO 4100, Spring 2014, CU Mountain Research Station, CU Boulder

Putting this question in a winter ecological perspective The purpose of the study is to understand the differences in the snowpack between these two areas. The snowpack structure itself is important for wildlife, as well as having avalanche implications. Avalanches have the ability to modify the landscape as a whole in large ways.

Existing state of knowledge “If a snow deposit…is subjected to a negative temperature gradient…it is metamorphosed to a "fragile" depth hoar with a hardness less than the original, which increases avalanche hazard” Akitaya, E “Temperature gradients in continental climates fluctuate and may remain greater than 10°C/m for months. As a result, weak layers of well developed faceted crystals form. After temperature gradients dissipate weak faceted layers are slow to gain strength because the crystals are large and they are under little load.” Greg Johnson, and Bruce Jamieson 2011 Following wildfire on the most xeric sites, limber pine is the principal pioneer species and dominates seedling establishment for 50 to 100 or more years. At most sites, however, Engelmann spruce and subalpine fir eventually establish and gradually replace limber pine.” Thomas Veblen 1986

Introduction Does snowpack structure vary in a group of limber pines (Pinus flexilis) within an Engelmann Spruce forest, compared to in the forest itself, on the Niwot Ridge? Hypothesis: The snowpack structure within a group of limber pines in the spruce forest will be different than in the spruce forest itself. Null Hypothesis: No change in snowpack.

Methods Two sites in the forest Random area selection (that fits parameters) Measure variables of Snowpack with Pit Kit (Provided by CU), as well as other variables Statistical method Possible limitations in methods: Not exactly the same placement between the three trees. Only one test site per grouping of trees. Only one grouping of trees per test variable.

Snowpack Comparison Spruce:Limber Pine (Pinus flexilis): Chi-Square test on hardness of layers: P-Value =.086

Results Hardness Tested with Chi-Square test: P-Value = Cannot reject Null Hypothesis. Not significant to the.05 level but still shows that there is some correlation.

Results More intense faceting under the limber pines (bigger crystal size on bottom layer). Less dense top layer in group of Limber pines. Overall more uniform snowpack in Spruce forest. Temperature profile more dramatic on bottom of snowpack underneath limber pines, and less dramatic directly above the depth hoar.

Discussion Findings agree with my Hypothesis, although hardness of snowpack statistically not significant to the P=.05 level. Differences in solar radiation could account for differences in snowpack – surface and depth hoar. Possible sources of error: only one test site per group of trees and one group of trees per test variable. Therefore testing more sites would further add to this research. Also testing on different angles would add depth to the research.

Discussion Research shows increased Depth Hoar can lead to increased avalanches. (Johnson et al.) This implies the more intense depth hoar within groups of limber pines could potentially trigger avalanches. Increased surface Hoar could also get buried. Groupings of Limber pines could be a good habitat for winter life (could also trigger avalanches). Research shows that early in the succession of the forest, there were more limber pines, and this could mean increased ease of transport for animals living in the subnivean environment.

Conclusions There is a difference in the snowpack. Decreased overall uniformity of snowpack in Limber Pine group, with much more depth hoar, as well as more surface hoar. Cannot reject null hypothesis but there is a correlation between hardness and the different groupings of trees.

Literature Cited Akitaya, E. 1974, Studies on depth hoar. Contributions from the Institute of Low Temperature Science, Series A, 26, Johnson, Greg, and Bruce Jamieson. "Strength Changes of Layers of Faceted Snow in the Columbia and Rocky Mountain Snowpack Climates in Southwestern Canada. U Calgary Web. Veblen, Thomas. "Age and Size Structure of Subalpine Forests in The Colorado Front Range." Torrey Botanical Club (1986). Web.

Acknowledgements CU Boulder for allowing use of Pit Kit Professor Tim Kittel Professor Derek Sweeney