While forests across the world experience unprecedented rates of environmental change, our ability to monitor and react to these changes is also increasing rapidly. Airborne remote sensing offers the unique opportunity to observe every tree canopy within a research plot. Here we tested the ability of imaging spectroscopy data collected by the Airborne Observatory Platform of the National Ecological Observatory Network to detect the response of northern hardwood forests to experimental nutrient addition by comparing crown-level spectral profiles of tree tops in nine forested stands. Experimental nutrient addition involved 8 years of 30 kg N/ha/yr as NH4NO3, 10 kg P/ha/yr as NaH2PO4, and a combined N+P treatment at the same rates. We asses plot level reflectance in young, mid-aged, and mature hardwood stands for a total of 36 plots. We examined how nutrient addition alters canopy reflectance and whether this can be used to remotely sense tree nutrient status.
Results/Conclusions
Preliminary results suggest that canopy reflectance is sensitive to nutrient addition, with higher reflectance in the visible and near infrared region for trees that received P than those that did not. Reflectance values of all 347 spectral bands with 1-m spatial resolution were used to further explore spectral properties associated with nutrient addition. Trees that received N or P showed distinct spectral features that differed from trees that did not receive nutrient treatment. This research may improve aerial forest inventory and forest health monitoring, thereby increasing our ability to track individual trees in response to environmental changes. Future investigations will examine which portions of the spectral profile are indicative of nutrient treatment and assess relationships between tree growth and canopy reflectance.