Reflections in bumpy terrain: implications of canopy surface variations for the radiation balance of vegetation

Data from an optical imaging sensor and a small-footprint lidar were used to examine the relation between canopy reflectance and outer surface complexity in forest stands in the southern Cascades of Washington state. Albedo was estimated from the Airborne Visible Infrared/Imaging Spectrometer; canopy surface variation (termed "rugosity") was estimated from small-footprint lidar; and stand ages were obtained through U.S. Forest Service records and global information system coverages. Results showed that albedo from Douglas-fir/western hemlock stands decreased, and variation in the outer surface of the canopy increased with age. Estimates of rugosity increased most rapidly in young stands and then more slowly after about 150 years. Albedo declined by 10% across the age sequence, suggesting that older stands of this forest type enjoy a substantial advantage in energy input. The results highlight the impacts of land-cover change on local energy balance and climate.