PARENT SESSION
Oral Session #60: Remote Sensing and GIS. Presiding: A. Gallant.
Thursday, August 9, 2001. 8:00 AM to 12:00 PM. Hall of Ideas E.
Remote sensing of forest structure and biophysical properties indicating forest response to chronic nitrogen deposition .
Wessman, Carol1, Asner, Gregory1, Buchmann, Nina2, 1 2
ABSTRACT- Limited understanding of large-scale forest ecosystem response to N deposition results from difficulties in evaluating small-scale studies across heterogeneous regions, and technical challenges of large-scale measurements. This study examines the sensitivity of remotely sensed reflectance to structure and biophysical properties of canopies experiencing different levels of nitrogen deposition. Radiative transfer modeling was used to quantifiably recreate canopy reflectance as measured by remote sensors. Field measurements across sites subjected to several N deposition levels were made to set realistic ranges of leaf and canopy variables within the radiative transfer model. Measurements were made in Germany in two Norway spruce (Picea abies) stands in relatively high N deposition areas and two European beech (Fagus sylvatica) stands, one in high and one in moderate deposition areas. Measurements from low deposition sites were made in the Colorado Rocky Mountains in two stands each of lodgepole pine (Pinus contorta) and trembling aspen (Populus tremuloides.). At each stand, foliar C and N concentrations; leaf, stem and litter optical properties; canopy cover fraction; and LAI were measured. Perturbations of individual model parameters determined the relative contribution of these attributes to canopy reflectance data. Reflectance from both broadleaf and confer stands was sensitive to reductions in cover and LAI values, as seen in high deposition areas. Foliar chemistry was detectable with increasing cover. Hyperspectral information was necessary to distinguish these contributions, and will be needed to track large-scale response trends.
KEY WORDS: nitrogen deposition, remote sensing, forest ecosystems, Germany