Estimating Forest Structure Indices for Evaluation of Forest Bird Habitats by an Airborne Laser Scanner

Bird species diversity is affected by the vertical and horizontal diversity of forest structure; therefore, several indices of forest structure have been proposed for the evaluation of bird habitats. If these indices could be measured in a wide area by remote sensing, it would be very useful for wildlife habitat assessment. The indices that we evaluated based on whether they can be estimated from airborne laser scanning data, are as follows: the foliage height diversity calculated by five layers (FHD5) and four layers (FHD4), the sum of vegetation coverage in five layers (COVSUM5) and four layers (COVSUM4) and the crown patchness (CP). Only COVSUM5 by 1 m and 2 m width calculated from one and two flight lines of laser scanner data were correlated to those from ground truth data. The difficulty in the estimation of these indices by an airborne laser scanner that records the first and last pulses is derived from the low density of the return pulses in the middle layers. We propose a simple interpolation method to estimate the distribution of foliage in the middle layer using the information from return pulses. The indices FHD5 by 1 m and FHD4 by 2 m obtained from two flight lines data and those recalculated after the interpolation were correlated to those from ground truth data in the Pearson’s correlation coefficient. CP obtained before and after interpolation from one flight line data also had relatively high correlation coefficients. * Corresponding author