Identifiering av gallringsbehov med hjälp av flygburen laserskanning
Thinning is one of the most important silvicultural activities in middle aged forests, partly to minimize damages and partly because it leads to earlier harvesting revenues and increases the value of the remaining trees. There are many different indices used to describe stand density and thereby the need of thinning in forests today. Studies have shown that forest variables can be estimated with high accuracy using airborne laser scanning and it is likely that the method could also be used to estimate forest density indices. In this study, the possibility of using the forest density index ?H² to determine and map priorities for thinning operations for a forest area was examined. The objective was to test how different variables derived from airborne laser scanning data can be used to estimate the index ?H². Tests were performed with low and high density laser data (densities of 0.8 and 10 measurements/m²). In field, ?H² was measured on 30 field plots with a size of 30x30m. The field plots were allocated in forests with a variety in structure, height, age, and tree species mixture. Different thinning indices that correlated to field measured ?H² were examined. These indices were computed directly from raw laser data, from raw laser data converted to a raster with different cell sizes, and using single tree detection. The results show that ?H² describes the need of thinning in a relatively good way for forests with a variety in structure, height, age and tree species mixture even though there are some exceptions. The method to convert raw laser data to a raster with 6m cell size gave a thinning index with the highest correlation to ?H². The method worked well for both low density (0.8 measurements/m2) and high density (10 measurements/m2) laser data with adjusted R² values of 89.7% and 90.8%, respectively. The relative RMSE was 14.3% and 13.5% for low and high resolution laser data, respectively.