广西凭祥西南桦中幼林林木生长过程与造林密度的关系

Relationship between Planting Density and Tree Growth Process of Betula alnoides Mid-young Plantations in Pingxiang,Guangxi

造林密度决定着林分后期密度大小，是影响人工林生长的重要因素之一，与林木生长过程密切相关，决定着林分的健康状况及生产力，是林分合理结构的数量基础。

11-year-old Betula alnoides plantations for density trial with five planting spacing treatments were investi-gated through stem analysis at Pingxiang City, Guangxi, to assess the effects of initial density on tree growth process. The results showed that the initial density had no remarkable effects on tree height growth and stem shape index, while there were significant differences in diameter at breast height （DBH）, individual tree volume and stand volume among treatments of initial density, and the stand volume of treatment of 2 m × 3 m was significantly higher than that of other treatments. The fast growing period of DBH trended to increase with the decrease of initial density, the DBH growth commenced to decrease since the sixth year after planted under the 1.5 m × 2 m treat-ment, while it decreased mostly since the eighth year under other treatments, indicating that thinning should be con-ducted at the sixth year for 1.5 m × 2 m treatment, and at the eighth year for 2 m × 3 m and 3 m × 3 m treatments, while for other treatments, it was delayed with the decrease of density. All the current and mean annual increment curves of tree height crossed when 5 - 6 years old, and did not reach quantity mature until 11 years old for all densi- ty treatments, while remarkable differences of the current annual increment of individual tree volume were seen a-mong treatments. Taking factors such as growth performance, stand volume, and use efficiency of forest land, etc. into consideration, 2 m × 3 m was determined as the most optimum planting density in the present study.