Tree and stand characteristics associated with the occurrence of false heartwood in individual Japanese white birch trees

Abstract

New wood uses of Japanese white birch (<i>Betula platyphylla</i> var. japonica) have attracted much attention in recent years, but false heartwood has led to a decline in commercial value due to its irregular wood color. In this study, we assessed the occurrence of false heartwood and its proportion to stem cross-sectional area (PFH) in individual Japanese white birch (482 trees) in a ca. 70-year-old natural secondary forest. Specifically, we investigated the relative strength of the direct/indirect effects of individual size (BA), growth rate (GR), crown ratio (CR), number of branch scars (NBS), basal area sum of neighboring trees (BAS) and topographic wetness index (TWI) on PFH. In total, 80.3% of trees had false heartwood. CR was found to be the most important factor, acting through direct and indirect negative effects. BA and NBS had a positive effect, and TWI had a negative effect on PFH. BA had a positive correlation with tree age, indicating that PFH can be reduced in trees with faster growth. Simultaneously, BAS had an indirect positive effect on PFH. These results suggested that thinning, which reduces BAS and increases CR, can reduce false heartwood.