Relationships between leaf chemistry and reflectance for plant species from Jasper Ridge Biological Reserve, California

The authors´ study examined the statistical relationships among a number of foliar biochemicals including carbon, cellulose, lignin, nitrogen, and water on a leaf area (content) and dry weight basis (concentration). Foliar reflectance measurements of 484 samples taken from 17 naturally occurring species from Stanford University´s Jasper Ridge Biological Preserve were made over five dates during 1992-1993. Chemical determinations of total carbon, nitrogen, lignin, cellulose, and water were made on a subset of the data (26-38 samples depending on chemical). The contents and concentrations of some of these biochemicals were highly correlated with one another, but the degree of correlation varied with the weight or area basis used. Stepwise multiple linear regression between 800 and 2498 nm with a maximum of six regressors explained at least 89% of the variance when the second derivative of log(1/R) was used as the independent variable, where R is reflectance at a given wavelength. However, the bands selected by the regressions did not correspond to known absorption features and were completely different if the chemical data were expressed on a dry weight or an area basis. In general, more of the variance was explained using an area basis than a weight basis. Principal components analysis separated individual species from one another. Stepwise multiple linear regression using the first five principal component scores explained lower proportions of the variance than did regression using log(1/R) and its derivatives. However, this approach may be preferred because it retains information from all spectral bands