Leaf Area Index (LAI) Change Detection on Loblolly Pine Forest Stands with Complete Understory Removal

摘要

The confounding effect of understory vegetation contributions to satellite derived estimates of leaf area index (LAI) was investigated on two loblolly pine forest stands located in the southeastern United States. Previous studies have shown that understory can account from 0.40% of the total LAI values. The primary factors influencing the near infrared (NIR) and visible (VI) spectral responses within forest stands are canopy closure, understory contribution, and soil types. The confounding issue in evaluating spectral vegetation indices is the near flat response of the NIR band occurring over a wide range of LAI values. Thus, forest stands with varying vertical profiles, i.e. differing understory contributions, could have similar LAI values due to horizontal homogeneity. The two 1.0 has study plots contained planted loblolly pine stands (ages 19 and 23) with similar crown closure estimates (70% and 71% respectively). Understory vegetation was removed from both stands via mechanical harvest and herbicide application in late July and early August 2002, Ikonos and Landsat ETM+data were collected both prior and subsequent to understory removal and were evaluated for NIR and VI wavelength response. Total Canopies (TR&C) instrument combined with hemispherical photography. Initial results of ground-based measurements indicate significant differences in LAI before and after harvesting treatment. Preliminary satellite derived LAI results from Ikonos and Landsat ETM+data are presented.