Lidar-Derived Forest Metrics Predict Snow Accumulation and Ablation in
the Central Sierra Nevada, USA
Abstract
Snowmelt is a critical water resource in the Sierra Nevada impacting
populations in California and Nevada. In this region, forest managers
use treatments like selective thinning to encourage resilient ecosystems
but rarely prioritize snowpack retention due to a lack of simple
recommendations and the importance of other management objectives like
wildfire mitigation and wildlife habitat. We use light detection and
ranging (lidar) data collected over multiple snow accumulation seasons
in the Sagehen Creek Basin, central Sierra Nevada in California, USA, to
investigate how snowpack accumulation and ablation are affected by
forest structure metrics at coarse, stand-scales (e.g., fraction of
vegetation, or fVEG) and fine, tree-scales (e.g., a modified leaf area
index, and the ratio of gap-width to average tree height). Using a newly
developed lidar point cloud filtering method and an “open-area
reference” approach, we show that for each 10% decrease in fVEG there
is a ~30% increase in snow accumulation and a
~15% decrease in ablation rate at the Sagehen field
site. To understand variability around these relationships, we use a
random forest analysis to demonstrate that areas with fVEG greater than
~30% have the greatest potential increased accumulation
response after forest removal. This spatial information allows us to
assess the utility of completed and planned forest restoration
strategies in targeting areas with the highest potential snowpack
response. Our new lidar processing methods and reference-based approach
are easily transferrable to other areas where they could improve
decision support and increase water availability from landscape-scale
forest restoration projects.