The effects of forest vertical structural variables (crown index, tree height, and large and small tree proportions) and density variables (basal area, adult tree density, shrub density, shrub coverage, and Excentrodendron hsienmu proportion in the forest canopy) on the natural rege-neration of the typical E. hsienmu populations in the karst mountains of Southwest Guangxi, China were studied. The results showed that the average regeneration density of E. hsienmu populations was 1742-3861 trees·hm-2 and relatively low. Forest vertical structure and density variables did not significantly affect the number of E. hsienmu seedlings, but significantly affected seedling ground diameter and height to some extent. Among the vertical structure variables, a significant nega tive correlation was observed between crown index and seedling height, but the association between crown index and seedling ground diameter was not significant. The large tree proportion and tree height were significantly negatively correlated with both seedling ground diameter and height. However, the proportion of small trees was significantly positively related to both seedling ground diameter and height. Among the density variables, adult tree density showed a significant positive correlation with both seedling ground diameter and height. A significant negative association was observed between the proportion of E. hsienmu and seedling ground diameter. Multiple regression analysis indicated that the model based on stand structure factors showed a poor fitness with regard to the number of E. hsienmu seedlings (P>0.05), and the quantitative distribution of E. hsienmu seedlings was affected to some extent by vertical structural variables. The stand structure factor model fitted well for the diameter and height of the seedlings (P<0.01). Seedling ground diameter was mainly affected by adult tree density, and seedling height was mainly determined by the combined effects of adult tree density and basal area.
研究垂直结构(树冠指数、大树比例、小树比例和树高)及密度因素(基面积、乔木密度、灌木密度、灌木盖度和蚬木比例)对桂西南喀斯特山地典型蚬木种群天然更新的影响.结果表明： 群落平均更新密度为1742～3861株·hm-2，密度相对较低.垂直结构和密度因素对蚬木幼龄植株个体数影响不显著，对地径和株高生长有一定影响.在垂直结构变量中，树冠指数与蚬木幼苗株高呈显著负相关，与幼苗地径的相关性不显著；大树比例和树高与幼苗的地径和株高均呈显著负相关，小树比例与幼苗地径和株高呈显著正相关.在密度变量中，乔木密度与幼苗地径、株高呈显著正相关；蚬木比例与幼苗地径呈显著负相关.多元回归分析显示，林分结构因子与蚬木幼龄植株个体数的拟合较差(P>0.05)，蚬木幼苗的数量分布在一定程度上受到垂直结构的综合影响；林分结构因子模型对蚬木幼苗地径和株高的拟合较好(P<0.01)，幼苗地径生长主要受乔木密度影响，株高生长主要受乔木密度和基面积的共同影响.
Keywords: density factor; karst mountain; seedling regeneration; vertical structure.