Vegetation Canopy and Radiation Controls on Permafrost Plateau Evolution within the Discontinuous Permafrost Zone, Northwest Territories, Canada

摘要

This study examines the links between the spatial distribution of three-dimensional vegetation structural characteristics and historical permafrost plateau area changes using airborne light detection and ranging and aerial photography. The results show that vegetation is prone to reduced canopy fractional cover (by up to 50%) and reduced canopy heights (by 16-30%) at the edges of plateaus. Reduced biomass may cause a positive feedback, whereby diminished within- and below-canopy shadowing (by 1 h of shadow time per day) results in increased radiation incident on the ground surface (16% greater at open- vs closed-canopy plateau sites) and increased longwave radiation losses (74% greater at open- vs closed-canopy plateau sites). Increased incident shortwave radiation may result in augmented thawing of permafrost and increased meltwater runoff, which further inhibits vegetation and permafrost persistence. Edge influences on ground thaw cause vegetation to die over several years (confirmed using historical aerial photography), thereby exacerbating thaw and plateau area reduction (plateau area reduction =-27% over 60 years). Permafrost degradation is also evidenced by the increasingly fragmented characteristics of the landscape. Copyright © 2011 John Wiley & Sons, Ltd.