The Impact of Forest on Snowpack Stability

1. The Impact of Forest on Snowpack Stability A presentation by Miles Daly 3/1/08 Winter Ecology Field Course See .doc file for notes [tk]See .doc file for notes [tk]

2. A Fine Line Forests as mechanisms of avalanche prevention or Do trees lead to snowpack instability

4. The impact of individual trees on local snowpack Increase surface roughness Prevents wind deposition Increases slope stability (?) Increasing local T.G.�s Biological activity as heat source Trees as conductive transport of solar radiation and ground heat Decrease in snow depth

5. Possible Implications Backcountry enthusiasts Trees as snowpack anchors or hazard zones Avalanche Mitigation Can Vegetation be used as avalanche prevention?

6. Avalanche Factors Factors needed for Avalanches Shear stress must overcome shear strength Shear stress = (mass)*(gravity)*(sin?) Forests effects on snow deposition Prevents added mass Canopy catches snow Decreases wind depostion *Lowers shear stress value*

7. Study of Gaspe Peninsula Looks at avalanche activity at sites of fire and logging disturbances Tree-ring reconstruction methods Determine time and severity of avalanches Relate avalanches to time of disturbance

8. Site T-9 1938 Fire Large-scale avalanches occurred for 15-20 years Coincides with recruitment time of Balsam firs Allowed for greater accumulation of wind deposited snow 1988 Large Scale Avalanche Year of extremely high snow fall and winds Evidence of continued large scale avalanches until 1995

9. Site T-10 1988 Logging Activity Extends onto starting slopes of 44 degrees. Allows for large accumulations of wind deposited snow on steep aspects Five years of large scale avalanche activity

11. McClung Study Findings

12. Field Work Methods Snow trench extending out from subalpine fir Measured Snowpack profiles next to tree and 1 m away from tree Temperature gradient Hardness profile Snow grain types Idea is to look for differences created by proximity to tree NE slope aspect 10 degree slope 43 cm DBH Snow Depth next to tree: 28 cm Snow Depth away from tree: 61 cm -differences in depth due to rise in ground level next to tree Tree well is present 9 cm on east side, 1 cm on west side Under snow- ground and tree bark are mossy Snow pit: -10 cm increments away from tree -5 cm increments next to tree Depth Hoar -Present at 10 cm depth next to tree -So unstable it was difficult to NE slope aspect 10 degree slope 43 cm DBH Snow Depth next to tree: 28 cm Snow Depth away from tree: 61 cm -differences in depth due to rise in ground level next to tree Tree well is present 9 cm on east side, 1 cm on west side Under snow- ground and tree bark are mossy Snow pit: -10 cm increments away from tree -5 cm increments next to tree Depth Hoar -Present at 10 cm depth next to tree -So unstable it was difficult to

14. Data Findings: Hardness and Snow Grain Type

15. Discussion of Field Work

16. Summary of Main Points Large scale forests prevent snow accumulation and avalanches on otherwise avalanche prone terrain. This should be taken into account when determining where to place infrastructure and where to conduct logging operations. More research is necessary to determine the impact of individual trees on snowpack stability

17. Literature cited McClung, D.M. 2001. Characteristics of terrain, snow supply and forest cover for avalanche initiation caused by logging. Annals of Glaciology, 32: 223�229. Germain Daniel, Filion Louise, He�tu Bernard. 2005. Snow avalanche activity after fire and logging disturbances, northern Gaspe� Peninsula, Quebec, Canada. Canadian Journal of Earth Sciences. 42, 2103-2116. Mark Williams of INSTAAR, snow hydrology class website