ESTIMATING KEY FOREST ECOSYSTEM PARAMETERS THROUGH REMOTE SENSING (WISCONSIN).

摘要

This research is fundamentally concerned with estimating forest ecosystem processes at large scales through measurement of related canopy characteristics using remote sensing. Foliar lignin content, the primary rate-limiting factor of forest litter decomposition, is important in modulation of nutrient cycling rates within forest ecosystems. A strong relationship between canopy lignin concentration and nitrogen availability (through nitrogen mineralization) was demonstrated in seven undisturbed forest ecosystems on Blackhawk Island, Wisconsin.; Work with near infrared spectroscopy confirmed that foliar nitrogen and lignin of native tree species have absorption properties in the near-infrared region which can be used to determine foliar concentration in a rapid and economic fashion. Laboratory analytical methods were modified for the analysis of data from NASA's high spectral resolution Airborne Imaging Spectrometer (AIS).; The relationship of canopy chemistry and biomass to canopy reflectance was evaluated with two sensors of differing spectral resolution. Data from the AIS and the Thematic Mapper Simulator (TMS) were acquired August 6, 1985, over 18 Wisconsin forest ecosystems measured for foliar biomass and lignin and nitrogen content. Canopy lignin content was the only variable significantly related to the remote sensing data sets.; The AIS data, transformed using a difference operation, were highly linear with canopy lignin content for deciduous stands and with lignin concentration for the full set of sites (including conifers). Using a three-term prediction equation derived from AIS first difference data (R{dollar}sp{lcub}2{rcub}{dollar} =.85), spatial distributions of canopy lignin concentration and annual nitrogen mineralization were estimated from a six-flightline mosaic of the island. TMS data for all sites exhibited a strong relationship with lignin concentration. Linearity with total lignin content of deciduous forests was strong only within stands similar in canopy closure.; Lignin or a close associate appears to be influential in canopy reflectance. Broad-band reflectance measurements convolve environmental effects such as canopy structure with foliar optical properties. High spectral resolution imagery accesses subtle spectral features through narrow-band measurements which can be mathematically transformed to reduce environmental noise.