Community assembly along a successional chronosequence in the northern tropical karst mountains, South China

Background and aimsInsight for vegetation restoration in karst mountains could come from understanding the methods by which communities are built along a successional chronosequence. We integrated species diversity, phylogenetic structure, and functional trait diversity to investigate the mechanisms governing community assembly along a successional chronosequence in the northern tropical karst mountains, South China.MethodsFive successional sequences, including grassland, shrubland, young forest, middle-aged forest, and primary forest, were selected in the northern tropical karst mountains using the space-for-time substitution method. The relationships between species diversity and environmental variables (elevation, slope degree and rock exposed rate) were investigated using redundancy analysis and variance partitioning methods.Results and discussionOur results showed that as succession progressed, species and phylogenetic diversity showed an increasing trend, then a decreasing trend, with the maximum value occurring in young forests, which displayed the optimum curves over the successional gradient. In terms of functional diversity, shrubland, and young forest had significantly higher functional richness than grassland and middle-aged forest, and grassland and young forest had significantly higher quadratic entropy coefficients than primary forest. The vegetative community changed in phylogenetic structure from clustering in the early stages of succession to diverging in the late stages.In contrast, the leaf thickness density decreased as succession progressed, suggesting that the young forest vegetation had the highest resource acquisition ability and utilization rate as the successional progressed. Additionally, the chlorophyll content, leaf thickness, and leaf area showed a first increased then decreased trend as successional progressed.ConclusionsOur results suggest that due to harsher soil conditions, the vegetation in early successional stage was dominated by environmental filtering (i.e., limitation of environmental resources), whereas the vegetation in late successional stage was governed by competitive exclusion (i.e., species competition). Our findings can guide plants conservation and ecological restoration in the tropical karst regions.

Automated summary

This study investigated the effects of species diversity, phylogenetic structure, and functional trait diversity on community assembly along a successional chronosequence in the northern tropical karst mountains in South China. The results showed that species and phylogenetic diversity increased initially and then decreased, with the highest value occurring in young forests. Shrubland and young forest had higher functional richness than grassland and middle-aged forest, and grassland and young forest had higher quadratic entropy coefficients than primary forest. The vegetation community structure shifted from clustering to diverging as succession progressed. Leaf thickness density decreased as succession progressed, indicating the higher resource acquisition ability and utilization rate of young forest vegetation. Chlorophyll content, leaf thickness, and leaf area increased initially and then decreased as succession progressed.