Transformation of a Degraded Pinus massoniana Plantation into a Mixed-Species Irregular Forest: Impacts on Stand Structure and Growth in Southern China

We transformed a Pinus massoniana plantation, the most important conifer plantation in southern China, with four different transformation treatments, in which Pinus massoniana was thinned to a density of 70%, and then differing richness and compositions of enrichment plantings were added. In order to examine the effects of the transformation, we compared species composition, stand structure and growth pattern in transformed stands with those in control stands. The results suggested that in the transformed stands species composition was diverse with trees both from the enrichment plantings and from natural recruitment. The size structure was changed such that the diameter at breast height (DBH) distribution tended to shift from a nearly normal distribution to an irregular multi-modal distribution. Substantial new ingrowth was found in the small DBH classes. The residual trees in the transformed stands were significantly larger than in the control treatment. However, for all trees, the control stands had the largest mean size, even though the residual tree growth was significantly smaller in the control stands. Finally, transformation treatment A4, which had the smallest overall mortality rate and simultaneously the mortality rate of each tree species was smaller than the corresponding value in other transformation treatments, was identified as the optimal transformation.