Detecting and Measuring Individual Trees with Laser Scanning in Mixed Mountain Forest of Central Europe Using an Algorithm Developed for Swedish Boreal Forest Conditions

Airborne remote sensing data from different types of sensors are tested within the Bavarian Forest National Park for estimation of forest attributes using several analysis methodologies. In this study, one algorithm that earlier has been validated for Swedish conditions was applied. The algorithm estimates tree position, tree height, and crown diameter of individual trees. The Bavarian Forest National Park is located in southeastern Germany. Three major forest zones are found at different elevations: (1) sub alpine spruce forests with Norway spruce (Picea abies) and partly Mountain ash (Sorbus aucuparia) above 1100 m, (2) mixed forests with Norway spruce, White fir (Abies alba), European beech (Fagus sylvatica) and Sycamore maple (Acer pseudoplatanus) on slopes between 600 and 1100 m, and (3) spruce forests with Norway spruce, Mountain ash and birches (Betula pendula, Betula pubescens) that are found in valley bottoms. Twenty-eight sample plots were field measured in all forest zones of the National Park during May and September 2002. Laser data were acquired using the Toposys II airborne laser scanner system recording first and last pulse. The number of trees that were detected using laser data was compared with field measurements. The overall detection rate was 44.2 %. In the top layer 67.9 %, in the middle layer 5.9 % and in the lower layer 2.5 % of the trees were detected. The percentage of detected volume was 85.2 % of the total volume measured in the field. The best results were obtained for a pure spruce stands and the worst for dense beech and spruce stands. High correlations were found between laser and ground measured tree height, with RMSE values of 1.40 m for all trees, of 1.37 m for coniferous trees and 1.41 m for deciduous trees. The correlation was also high between laser measured and field measured crown radius. For trees within 20 stands, the RMSE was 0.93 m. The measurements for the coniferous trees (RMSE 0.53 m) were more accurate than for the deciduous trees (RMSE 0.94 m). The volume was calculated by regression models on a single tree level. Overall 96.7 % of the volume was estimated.