Differential Snow Accumulation in Warm Edges Versus Cold Edges of Forest Gaps, and its Potential Implications for Tree Growth in a Sierra Nevada Conifer Forest

Abstract

Context Forest gaps affect snowmelt timing and amount because canopies are key controls over snowpack dynamics and interact with topography. Overlying canopy can decrease snowmelt by intercepting snowfall, but it can also reduce ablation rates from increasing shading. Changes in forest structure and canopy gaps, may therefore affect the amount, timing, and duration of snowmelt and potentially forest response to different water limitations. Objectives We test how the higher energy-input edges of gaps (‘warm edges’) differ from the lower energy-input edges of gaps (‘cool edges’) with respect to snow depth, snowmelt timing, and tree growth in a snow-dominated forest in the Western US. Methods We use multiple dates of LiDAR-based measurement to assess springtime snow depths in warm and cool gap edges in Sagehen Creek Basin, CA. Then we use paired tree sampling and ring width chronologies to ascertain moisture sensitivity of trees adjacent to warm and cool gap edges. Results Pre-ablation snow depths in cool gap edges exceeded those in warm gap edges by 9% to 18% (; the effect size depended on elevation and aspect. Snow also persisted longer in cool edges than in warm edges. Growth variations in warm-edge-adjacent trees were more correlated with interannual variations in snow depth those of cool edge trees, although neither had strong correlations. Conclusions These findings suggest that forest structures that maximize cool edge area may benefit snow depth and persistence leading to cool-edge trees that are less sensitive to interannual hydroclimatic variability than warm edge trees, despite this effect being small relative to other controls over growth.