Patterns in Foliar Isotopic Nitrogen, Percent Nitrogen, and Site Index for Managed Forest Systems in the United States

Patterns in foliar nitrogen (N) stable isotope ratios (δ15N) have been shown to reveal trends terrestrial N cycles, including the identification of ecosystems where deficiencies limit forest ecosystem productivity. However, there is a gap our understanding within-species variation and species-level response environmental gradients or management. Our objective examine relationship between site index, %N, δ15N spectral reflectance for managed Douglas-fir (Pseudotsuga menziesii) loblolly pine (Pinus taeda) plantations across their geographic ranges Pacific Northwest southeastern United States, respectively. Foliage was measured at 28 sites using handheld spectroradiometer, further analyzed concentration. Unlike prior work grasslands shrubland species, results show that %N are not well correlated these tree species. multiple linear regression models suggest strong predictive ability spectroscopy data quantify δ15N, with some explaining more than 65% variance δ15N. Additionally, moderate explanations were found index (R2 = 0.49) 0.84) set. The development relationships reflectance, measures productivity provides first step toward mapping canopy forests remote sensing.