Distribution of wet heartwood in stems of Populus xiaohei from a spacing trial

Abstract

The development of wet heartwood was studied in relation to different tree spacings (2×5 m, 4×5 m, 4×10 m) in a 28-year-old Populus xiaohei T.S. Hwang et Liang in China. Stem discs of 5 cm thickness were taken every 2 m from the stump to the top (including the 1.3 m height), and wet heartwood area was measured for each section. Results indicated that wet heartwood was present in all sample trees, and represented a substantial part of the stem, accounting for nearly 62.0%, 56.0% and 65.2% of tree stem volume, respectively, for spacings 2×5 m, 4×5 m and 4×10 m. Wet heartwood tapered towards the top of the tree, closely following the stem wood profile. This vertical distribution pattern of wet heartwood was scarcely influenced by spacing. However, wider spacing resulted in larger wet heartwood area and volume, and the production of wet heartwood was positively and significantly correlated with tree diameter. Estimation of wet heartwood volume from external tree characteristics was possible using various regression models with fairly high coefficients of determination ranging from 0.87 to 0.92.