Efficient measurements of basal area in short rotation forests based on terrestrial laser scanning under special consideration of shadowing

Terrestrial laser scanning has been used in forest research for about ten years and use-orientated applications are of increasing importance. The effect of shadowing in single location laser scanning, e.g., as used for biomass estimations, has not been quantified so far even though it affects the quality of information derived from the laser scans. In our study we quantified the effect of shadowing on automated basal area measurements in a densely stocked poplar short rotation forest and developed a method to correct unsampled areas. We found that on average about 5.0 +/- 2.5% of the plot area (12.56 m(2)) was not sampled by the laser scanner due to shadowing. Efficient basal area measurements based on terrestrial laser scanning were possible and if a correction factor was derived from the scan data, the effects of shadowing could be accounted for. The relative mean absolute error could then be lowered from 9.8% to 8.4%. This new method allows fast, fully objective, and precise plot-level measurements of basal area considering the effects of shadowing. It could be applied in the future to support monitoring growth developments in densely stocked stands such as short rotation forests.