Forest Structure Controls on Snowpack Dynamics in Two Contrasting Forest Ecosystems

Forest canopies exert strong and complex controls over snow accumulation and melt dynamics, particularly in snow-dominated environments. Given the importance of snow for recharging soil and groundwater and for runoff generation, furthering the process-based understanding of the interplay between forests and snowpack is critical across a range of snow-dominated ecosystems. Here, we compare results from two complementary field-based studies at sites with contrasting forest and snow dynamics – the Marcell Experimental Forest in northern Minnesota, USA, and the Chicken Creek Snowtography Study in southern Colorado, USA. We found that forest canopies exerted significant control over snow depth and SWE at the two sites, but with differing directionality. Snow depth was measured at both field sites in water years 2023 and 2024, while measurements at Chicken Creek, which began in water year 2022, also included snow-water equivalent. Forest structure metrics varied for the sites, but included quantifications for typical two-dimensional measurements (e.g., basal area, tree height, leaf-area-index), and three-dimensional complexity (e.g., canopy overlap, structural diversity, canopy light attenuation, etc.). Results from both studies demonstrate that 3-D canopy metrics are better predictors of snow depth and SWE than 2-D metrics, which are typically measured by field practitioners. At the ponderosa pine-dominated Chicken Creek site, which typically has a warmer and ephemeral snowpack, snow depth and SWE decreased as the canopy vertical complexity increased. At the sub-boreal Marcell site, which is colder and has a seasonal snowpack, peak snow depth increased with increasing canopy overlap. Our results demonstrate the importance of incorporating canopy metrics over basal areas in understanding forest-snow dynamics. The contrasting directionality in canopy complexity over snow metrics further shows that forest-snow interactions vary across ecosystems and climate gradients. Field-based studies across a range of forests, elevations, topographies, and latitudes are needed to inform forest management practices to preserve snowpack water storage in snow-dominated ecosystems.