Using airborne LiDAR to determine total sapwood area for estimating stand transpiration in plantations

This study offers an unprecedented opportunity to estimate total sapwood area over an entire catchment (A(scat)/A(g)) using small-footprint light detection and ranging technology with a minimal amount of labour in field. Forty-two-year-old plantations of Japanese cypress (Hinoki; Chamaecyparis obtusa Sieb. et Zucc.) and Japanese cedar (Sugi; Cryptomeria japonica D. Don) vegetated the 2.98 ha experimental catchment. Field observations identified diameter at breast height (DBH) of all trees and produced the relationship between DBH and tree sapwood area (A(stre)). The sum of A(stre) generated actual values of A(scat)/A(g). For light detection and ranging data analyses, local maximum filtering revealed height of tree apices (H) and tree number (N) with 9% omission errors. A novel process was developed to identify tree species by their apices based on height of the apices and canopy roughness. Four methods were tested. In Methods A-C, H was converted to A(str)e directly or via DBH, then, the sum of A(stre) created A(scat)/A(g). H-A(stre) or H-DBH relationships were varied irrespective of labour-intensive measurements, and A(scat)/A(g) was underestimated up to 85% of actual value because of the smaller N. On the other hand, in Method D, ready-made stand density management diagrams (SDMDs) overestimated mean DBH. However, a product of overestimated mean A(stre) and the underestimated N was almost identical to the actual A(scat)/A(g). The estimates were 84% and 95% of the true A(scat)/A(g) in Hinoki and Sugi, respectively, and the former will be more precise if the SDMD is suitable for the site as indicated through sensitivity analysis. Copyright (C) 2015 John Wiley & Sons, Ltd.