Does sublimation decline after a spruce beetle outbreak? The need to develop a realistic processed-based model

In the subalpine forests of southeastern Wyoming, sublimation can account for half of annual water vapor fluxes. Recent spruce beetle disturbances in these forests have caused significant mortality to the forested canopy, radically altering ecosystem composition and the processes that control energy and mass exchange. While the loss of canopy allows more radiant energy into the understory, it also decreases snow interception. At the GLEES, WY AmeriFlux site, observations of winter sublimation appear to decrease coincident with the loss of the canopy following a spruce beetle outbreak. We hypothesize that in this subalpine forest the decrease in canopy interception of snow is the dominant process that drives changes in sublimation rates as the ecosystem responds to this disturbance. Testing this hypothesis will require development of a physically based process model to explain the drivers of sublimation. We use measurements of energy and mass exchange from eddy-covariance plus observations of the stable isotopes of snow water and atmospheric water vapor as tools to develop this model.