The Impact of Forest on Snowpack Stability A presentation by Miles Daly 3/1/08 Winter Ecology Field Course Mountain Research Station, University of Colorado, Boulder

A Fine Line eForests as mechanisms of avalanche prevention or eDo trees lead to snowpack instability

e What effects do forest disturbances such as fire and logging have on avalanche activity? d Are mature forests the preventative factor on otherwise avalanche prone slopes? d Decrease snow drifting d Decrease in overall catch d Increase surface roughness

eThe impact of individual trees on local snowpack dIncrease surface roughness ePrevents wind deposition eIncreases slope stability (?) dIncreasing local T.G.’s eBiological activity as heat source eTrees as conductive transport of solar radiation and ground heat eDecrease in snow depth

Possible Implications eBackcountry enthusiasts dTrees as snowpack anchors or hazard zones eAvalanche Mitigation dCan Vegetation be used as avalanche prevention?

Avalanche Factors eFactors needed for Avalanches dShear stress must overcome shear strength  Shear stress = ( mass )*(gravity)*(sin θ ) eForests effects on snow deposition dPrevents added mass eCanopy catches snow eDecreases wind depostion d*Lowers shear stress value*

Study of Gaspe Peninsula eLooks at avalanche activity at sites of fire and logging disturbances eTree-ring reconstruction methods dDetermine time and severity of avalanches eRelate avalanches to time of disturbance

Site T-9 e1938 Fire dLarge-scale avalanches occurred for years eCoincides with recruitment time of Balsam firs dAllowed for greater accumulation of wind deposited snow e1988 Large Scale Avalanche dYear of extremely high snow fall and winds dEvidence of continued large scale avalanches until 1995

Site T-10 e1988 Logging Activity dExtends onto starting slopes of 44 degrees. dAllows for large accumulations of wind deposited snow on steep aspects dFive years of large scale avalanche activity

Same methods used as in Gaspe Peninsula study D.M. McClung study: Logging effects on Avalanche Activity in British Columbia

McClung Study Findings In British Columbia clear cut logging has led to significant environmental damage due to avalanche activity 10,000 sites affected by avalanches Types of environmental damage: Prevents regeneration of seedlings Threat to infrastructure Stripping away soil cover Deposition of debris into streams and lakes

Field Work Methods eSnow trench extending out from subalpine fir dMeasured Snowpack profiles next to tree and 1 m away from tree eTemperature gradient eHardness profile eSnow grain types eIdea is to look for differences created by proximity to tree

Hardness Profile Next to Tree: 4 fingers from surface to 10 cm Fist below 10 cm Hardness Profile Away from Tree: 4 fingers from surface to 40 cm Fist below 40 cm Snow Grain Profile Next to Tree: Evidence of faceting below 5 cm depth Depth hoar a ground 3-4 mm! Snow Grain Profile Away from Tree: Rounding to 30 cm depth Faceting below 30 cm Depth hoar at ground ~ 2 mm Data Findings: Hardness and Snow Grain Type

Discussion of Field Work Overall, more research should be conducted From my data: Snowpack depth will often be shallower next to trees Due to tree wells and extending tree trunks Can lead to stronger TG and faceted grains Future Research Horizontal temperature gradient extending out from trees Effects of low structural strength snow grains surrounding trees on overall snowpack stability

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

Literature cited eMcClung, D.M Characteristics of terrain, snow supply and forest cover for avalanche initiation caused by logging. Annals of Glaciology, 32: 223–229. eGermain Daniel, Filion Louise, Hetu Bernard Snow avalanche activity after fire and logging disturbances, northern Gaspe Peninsula, Quebec, Canada. Canadian Journal of Earth Sciences. 42, eMark Williams of INSTAAR, snow hydrology class website