Response of Natural Regeneration of Pinus massoniana and Quercus variabilis Mixed Forest to Thinning Intensity and Environmental Factors

Abstract

Based on target tree management, the effects of different thinning intensities and environmental factors on the natural regeneration of a Pinus massoniana and Quercus variabilis mixed forest were explored in order to provide a theoretical basis for the natural regeneration and sustainable forest management of P. massoniana and Quercus L. mixed forests. Taking the mixed forest after thinning as the research object, three average thinning intensities of WT (7.6%) for weak thinning, LT (15.3%) for light thinning, and MT (24.3%) for moderate thinning were carried out in 5 m×5 m quadrats with 7–10 replicates for each intensity level and 3 replicates for the control. Three years after the thinning, the amount of natural regeneration, growth height, regeneration density, diversity of regenerated tree species and their influencing factors at different thinning intensities were measured and analyzed. The results indicated four main features of the subsequent regeneration. (1) There were 32 species of vascular plants in the 28 quadrats 3 years after thinning, belonging to 22 families and 30 genera, and the dominant species for regeneration were arbor species. The number of regeneration species increased with increasing thinning intensity. (2) As thinning intensity increased, the number of natural regeneration plants between various height classes rose; so, the increased thinning intensity promoted the density of different height classes during regeneration. (3) As thinning intensity increased, so did species abundance S and species evenness. The degree and intrinsic diversity increased, while the Shannon-Weiner and Simpson indices showed no discernible trends. (4) Slope, aspect, and slope position, as well as thinning intensity, all had significant impacts on species richness, species evenness, and regeneration density. MT has the most appropriate promoting effect on natural regeneration and species diversity, so increased thinning intensity can promote natural regeneration and species diversity in the P. massoniana and Q. variabilis mixed forest. In addition, aspect and slope position can increase the species richness S and diversity of natural regeneration, whereas slope has a clear inhibitory effect on the species richness S and diversity during natural regeneration.