Huber value
Huber values, i.e., sapwood-to-leaf area ratios, were measured both at the beginning of June and the end of August. Five healthy adult trees were selected from each field sample point, and the new assimilating twigs of the current year were taken as the first-order branches. We collected one third-order branch from the southern upper part of the canopies of the selected trees at each site. The areas of the assimilating branches were scanned (Epson Perfection 2400 Photo, Seiko Epson Corp., Japan). The cross sections of the branches were dyed with 1% aqueous acid-fuchsin, and the stained sapwood areas were measured using digital calipers.