Three-year Patch Thinning Effects on the Stand Structure in Overstory Trees of a Japanese Cedar Plantation in Taiwan

Stand structure plays an important role in forest ecosystem management. In this study, we examined the immediate and 3-yr effects of patch thinning treatments on the stand structure of overstory trees in a 35-yr-old Japanese cedar (Cryptomeria japonica) plantation located in the Zenlen area, central Taiwan. Among twelve 1-ha plots, 4 plots were randomly assigned to 1 of 3 patch thinning intensities in a randomized complete block design: no removal (control), and 25 and 50% tree removal in the area. The stand structure of the residual overstory trees was examined immediately after thinning and again after 3 yr using non-spatial stand structural indices (vertical evenness and the diameter at breast height (DBH) distribution), a pair correlation function (G function), and spatial stand structural indices (diameter differentiation index and structural complexity index). The vertical evenness of the overstory tree canopy was reduced after thinning. Unlike the left-truncated Weibull DBH distribution commonly caused by thinning from below, no notable left-truncated Weibull distribution caused by patch thinning was detected. The change in the spatial point pattern expressed by the G function with scale-up at a distance scale was influenced by the intensity of the thinning. The stand structural complexity was affected by the spatial scale used and stand attributes surveyed, and it was reduced immediately after thinning but had varying impacts on the DBH and tree height.