SEASONAL PATTERNS AND REMOTE SPECTRAL ESTIMATION OF CANOPY CHEMISTRY ACROSS THE OREGON TRANSECT

We examined seasonal changes in canopy chemical concentrations and con tent in conifer forests growing along a climate gradient in western Or egon, as part of the Oregon Transect Ecosystem Research (OTTER) study. The chemical variables were related to seasonal patterns of growth an d production. Statistical comparisons of chemical variables with data collected from two different airborne remote-sensing platforms were al so carried out. Total nitrogen (N) concentrations in foliage varied si gnificantly both seasonally and among sites; when expressed as content in the forest canopy, nitrogen varied to a much greater extent and wa s significantly related to aboveground net primary production (r = 0.9 9). Chlorophyll and free amino acid concentrations varied more strongl y than did total N and may have reflected changes in physiological dem ands for N. Large variations in starch concentrations were measured fr om pre- to post-budbreak in all conifer sites. Examination of remote-s ensing data from two different airborne instruments suggests the poten tial for remote measurement of some canopy chemicals. Multivariate ana lysis of high-resolution spectral data in the near infrared region ind icated significant correlations between spectral signals and N concent ration and canopy N content; the correlation with canopy N content was stronger and was probably associated in part with water absorption fe atures of the forest canopy. The spectral bands that were significantl y correlated with lignin concentration and content were similar to ban ds selected in the other laboratory and airborne studies; starch conce ntrations were not significantly related to spectral reflectance data. Strong relationships between the spectral position of specific reflec tance features in the visible region and chlorophyll were also found.