Estimation of stem biomass of forest stands using orthorectified aerial photographs

Ground-based forest inventory surveys can provide highly accurate measurements of tree and stand characteristics, but these are expensive to carry out. Aerial photography has been used for several decades as a tool in forest management and inventory. However, conventional methods of interpretation are both time-consuming and costly, with results varying among interpreters. With continuing development of personal computer technology, aerial photographs have become more accessible for digital analysis. This paper presents the potential operational use of digitized aerial photographs for the estimation of tree and stand characteristics of two forest plantations of Sitka spruce (Picea sitchensis (Bong.) Carriere) in Scotland. The digitized aerial photographs were processed using softcopy photogrammetry, and image analysis techniques were used for individual tree crown delineation. For the first site the estimations of stand top height, basal area, volume, biomass, and density (-23.7%) were similar to the ground-measured stand characteristics (+/- 10%), whereas for the second site the estimations were less accurate mainly because of the nonoptimal illumination conditions during the acquisition of the aerial photographs.