Healthy, dense forests growing in avalanche terrain reduce the likelihood of avalanche release by inhibiting the formation of continuous weak layers and a homogenous snow stratigraphy. Associated with warming temperatures, bark beetle attacks have increased in higher elevations, which profoundly affects snowpack in mountain forests and may alter the effects of forests in protecting people, settlements and infrastructure against avalanches.

We examined the snowpack under canopies of Engelmann spruce forest stands in the Uinta Mountains in Utah using a snow micro penetrometer (SMP). Repeated SMP measurements were recorded in winters 2015 and 2016 in study plots beneath canopies of recently infested trees, trees 3+-years after spruce beetle infestation, a harvested forest stand, and a non-forested meadow. To quantify changes to snow stratigraphy at our study plots, we applied a new method to match and combine several SMP measurements.

Our results suggest that recently killed trees can still maintain avalanche protection, but the snowpack was consistently more homogeneous in the harvested stand despite small-diameter trees and woody debris being present.

As mountain forests become more prone to mass attacks associated with climate change, changes in snowpack properties needs to be considered for avalanche control, winter backcountry activities, and protection forest management.