[Effects of forest structure on natural regeneration of Excentrodendron hsienmu population in Southwest Guangxi, China.] / 林分结构对桂西南蚬木种群天然更新的影响.

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.

[Effects of topography on the diversity and distribution pattern of ground plants in karst montane forests in Southwest Guangxi, China].

Covariance analysis, curve-fitting, and canonical correspondence analysis (CCA) were used to explore the effects of topographic factors on the plant diversity and distribution patterns of ground flora with different growth forms in the karst mountains of Southwest Guangxi, China. A total of 152 ground plants were recorded. Among them, 37 species were ferns, 44 species herbs, 9 species lianas, and 62 species shrubs. Covariance analysis revealed that altitude significantly correlated with the individual number and richness of ground plants, and slope aspect had a significant effect on richness. Statistical analyses showed a highly significant nonlinear correlation between the individual number or richness of ground plants and altitude. Results of CCA revealed that slope aspect had a significant effect on the distribution pattern of ferns, and slope had a significant effect on the distribution patterns of herbs, lianas and shrubs. Ferns were more sensitive than herbs, lianas and shrubs to changes in heat and soil water caused by aspect. The effect of slope was stronger than that of elevation on soil water and nutrients, and it was the most important topographic factor that affected the distribution patterns of herbs, lianas and shrubs in this region.

[Natural regeneration of young Excentrodendron hsienmu in karst mountainous region in Southwest Guangxi, China].

A field survey was conducted in the karst mountainous region in Pingguo County of Southwest Guangxi, China to explore the structural characteristics, spatial distribution pattern, and growth dynamics of young Excentrodendron hsienmu as well as the main environmental factors affecting the natural regeneration of the E. hsienmu population. In the study area, the population structure of the young E. hsienmu was stable, and exhibited a clumped spatial pattern for the seedlings and seedling sprouts. The ground diameter growth and height growth of the young E. hsienmu presented the same variation trend, i. e., the ground diameter increased with increasing height. The ground diameter growth and height growth of the E. hsienmu seedlings were limited by population density, i. e., decreased with increasing population density. The correlation analysis showed that the trees more than 2.5 m in height and the shrubs were the major stand factors affecting the natural regeneration of young E. hsienmu, while the herbs had no significant correlation with the regeneration. The percentage of covered rock also had no significant effects on the regeneration. Kruskal-Wallis ANOVA showed that there existed significant differences in the height and ground diameter of young E. hsienmu at different slope degrees and slope positions. The population density, height, and ground diameter had significant differences across slope aspects. The natural regeneration of young E. hsienmu was comprehensively affected by the species biological characteristics, intraspecific competition, interspecific competition, heterogeneous habitat, and anthropogenic disturbances.