A large-scale aerial photographic technique for measuring tree heights on long-term forest installations

Tree height is both one of the most important and most expensive measurements to collect in the periodic reassessment of older genetic test sites, growth and yield plots, and other long-term forest installations. The methodology described here provides a feasible alternative to the conventional clinometer and tape technology. The system uses large-scale aerial photographs (LSP) with permanent ground control points. Test results indicate that, by the second assessment in installations containing 456 trees or more, the cumulative cost of LSP-measured free heights will be less, and be as accurate as and more precise than clinometer-measured heights. By the 10th assessment in installations containing 3000 trees or more, the LSP system can offer 80 percent cumulative savings over the clinometer and tape method.