Effects of Thinning on Growth and Regeneration of Cyclobalanopsis glauca Secondary Forest

Abstract

Based on the problems of poor productivity and natural regeneration of Cyclobalanopsis glauca secondary forest in hilly areas in southeast Hunan Province, experiments of thinning were carried out to analyze the effects on stand growth and regeneration of different thinning intensities and to provide guidance for managing secondary forests. Cyclobalanopsis glauca secondary forest was selected for research object, then experimental design was arranged with a randomized block by thinning intensity such as control(un-thinning), light thinning (10%), moderate thinning (20%) and heavy thinning (30%). Tree measuring factor and number of naturally regenerated seedlings were investigated for researching the responses to thinning treatment. Results showed that there were significant differences of mean DBH and current annual increment of DBH in terms of the four thinning treatments, and the larger the thinning intensity, the higher the DHB increment. The maximum mean height (10.1m) happened in stand of heavy thinning. However, significant differences existed in the current annual increment of height among the four thinning treatments. Stand volume was 93.27, 91.49, and 91.90 m3 hm−2 respectively in stand of heavy thinning, moderate thinning, light thinning, and were all lower than that of the control, but current annual increment of volume was 5.65, 4.43 and 3.75 m3 hm−2 yr−1, respectively and higher than that of the control. The Simpson index of shrub layer and herb layer of heavy thinning stand was 0.45 and 0.80, Shannon-Wiener index was 1.03 and 2.03, respectively. There were significant differences of naturally regenerated seedlings according to four thinning treatments only for seedlings of 5∼30 cm level, but there were no significant differences for seedlings of 30∼50 and 50∼150 cm level. The growing space and nutritional condition of retained trees after thinning were effectively improved, stand DBH and height increased with the increasing thinning intensity. However, stand volume was not significantly different among four thinning treatments. Besides, thinning at appropriate intensities could increase the biodiversity in shrub layer and herb layer, quantities of naturally regenerated seedlings also increased with the increasing thinning intensity. Heavy thinning (30%) was the best one among four thinning treatments for silvicultural interventions on Cyclobalanopsis glauca secondary forest.