Impact Four Years after Thinning on the Growth and Stand Structure of Taiwania Plantation in the Liukuei Experimental Forest

This paper examines the impact of thinning 4 yr after it took place on the growth and stand structure of Taiwania cryptomerioides plantations in Liukuei Experiment Forest in Southern Taiwan. Thinning to 3 residual levels in basal area were carried out in 1999, and three 0.09-ha plots were set up in each treatment for stand monitoring purposes. The results showed that partially due to the stand density, the enhancements in the increments of basal area and volume by heavy thinning were less than those by medium thinning. However, enhancement of the growth rate was in a reverse order. The contagion index, which measures the spatial structure of a stand indicated that the regular pattern of individual trees in spatial locations in plantations was shifted toward a random or clumped one through individual tree thinning. The diameter differentiation index describing the spatial distribution of tree sizes indicated that the range of the difference in size of neighboring trees in the plantation was reduced through the thinning operation, with an increase in the proportions of trees having DBH differentiation of a small level (0.83) and a decrease in the average level (0.17). Due to variations in growth probably caused by competition among residual trees, 4 yr after thinning, the proportions of trees with a small difference level and average difference level were reduced (0.81) and increased (0.19), respectively.