Snow Redistribution by Wind and Interactions with Vegetation at Upper Treeline in the Medicine Bow Mountains, Wyoming, U.S.A.

High-elevation areas in the Rocky Mountain treeline ecotone exhibit heterogeneous snow distribution resulting from interactions among topography, vegetation, and wind. Our study area—Libby Flats—is a gently arched ridge at 3200 m a.s.l. in the Medicine Bow Mountains, Wyoming. The Libby Flats snow season (October-May) features sub-freezing temperatures, abundant snow, and strong westerly winds (averaging 10 m s–1). While relief is gentle on Libby Flats, it, together with islands of krummholz and flagged trees, produces snow depths ranging from 0 to 7 m. These variable snow depths have important feedbacks on the occurrence of trees and vegetation, as well as direct controls on ecosystem properties. To better understand the factors controlling these interactions, snow distribution patterns were measured and modeled over a 6.25 km2 area on Libby Flats during the 1997–98 snow season. Snow-depth observations during the snow season were compared with results from the SnowTran-3D model. These tests demonstrated that the model closely reproduces the observed snow distribution patterns and adequately represents snow depths at a 5 m spatial resolution on Libby Flats. Simulation experiments demonstrate the relative importance of wind speeds, precipitation, and vegetation in the natural system.

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