| The central goal of this work was to develop new top-down and bottom-up strategies to scale plant biophysical attributes from leaf to regional levels so that remote sensing can best bridge the gap between ecosystem structure and function.; I explore how plant canopies interact with photosynthetically active radiation (PAR), which affects photosynthetic capacity, and thus maximum carbon assimilation and net primary production. Along a 900 km Texas savanna transect, I found that tissue-level PAR absorption among species, genera, functional groups, growthforms, and between climatologically diverse regions was statistically similar. Canopy-level analyses indicated that leaf optical variability explained only a small proportion of the variance in canopy PAR absorption, while non-photosynthetic vegetation (e.g. woody stems and litter) and leaf area contributed significantly to canopy variance. However, analyses also revealed that the extent and leaf area of canopies were the dominant controls on landscape PAR absorption, while variation in tissue properties played a very secondary role.; Based on the quantified scale-dependence of PAR absorption across landscapes, I developed a suite of methods to access plant canopy structural and biophysical attributes from remote sensing data. Canopy radiative transfer (RT) models, which mechanistically simulate the spectral and angular variation in vegetation reflectance, can be inverted to estimate plant characteristics from multi-view angle, remotely sensed data. I found relationships between tissue spectral properties using a diverse array of woody plant and grass species, which allow greater efficiency in canopy radiation modeling.; I then focus on the spatial heterogeneity of land cover, land use, vegetation structure, and carbon uptake in a Texas savanna rangeland region. I devised a multi-satellite/inverse modeling approach to quantify variation in woody plant and herbaceous canopy attributes. I found that by estimating a suite of scale-dependent canopy and landscape structural characteristics, variation in land cover, land use, and fractional PAR absorption could be detected, providing a better understanding of the ecological impacts of human activities in semi-arid regions.; A combination of field and modeling techniques are used to quantify the relative contribution of leaf, stem, and litter optical properties, foliar chemistry, and canopy structural attributes to vegetation reflectance data. I discovered wavelength-specific sensitivity to these factors, which was ecosystem dependent due to differences in the morphology of plant canopies. Finally, I use a combination of imaging spectrometry and radiative transfer techniques to quantify the biophysical attributes of plant canopies and land-cover types in a sub-tropical savanna. The analysis revealed the complexity of the biotic, abiotic, and anthropogenic factors involved in land-cover/land-use change in the region. (Abstract shortened by UMI.)... |
