HIGH-SPECTRAL-RESOLUTION REFLECTANCE OF DOUGLAS-FIR GROWN UNDER DIFFERENT FERTILIZATION TREATMENTS - EXPERIMENT DESIGN AND TREATMENT EFFECTS

Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] seedlings were grow n with different fertilization treatments in an experiment designed to investigate the effects of foliar biochemistry on needle and canopy r eflectance measurements. Potentially confounding effects of the covari ance of canopy structure with foliar biochemical concentration were mi nimized by fertilizing after leaf expansion. Seedlings showed no signi ficant differences in specific leaf area, % needle moisture, biomass, or LAI, but showed significantly different total nitrogen concentratio ns, and some differences in chlorophyll concentrations. Measurements w ere made of needle optical properties, and bidirectional reflectance w as obtained of needles and of canopies. Canopy reflectance was acquire d under sky illumination using two field spectroradiometers. Needle an d canopy treatment differences were highly significant in the visible region. Some treatment differences were also found in broad-band regio ns in the infrared in the canopy reflectances. Narrow-band infrared di fferences were detected in needle first derivative spectra, and coinci ded with known protein absorption features. Needle and canopy bidirect ional reflectances were similar, but narrow-band features found in the needle infrared spectra were not found in the canopy data. Two possib ilities for the failure to detect these narrow features in the canopy data are a confounding effect from variability caused by illumination angle changes and/or the low signal-to-noise characteristics of the fi eld spectroradiometer relative to the laboratory instrument. The suite of optical and structural measurements taken from the same set of tre es should provide a useful data set for parameterizing canopy models a iming to predict high spectral resolution reflectance of canopies.