Effect of woody plant canopies on species composition, diversity and distribution of vascular ground flora in karst mountains: A case study in Southwest China

The knowledge of the relationships among the forest overstory, environmental conditions, and plant communities in the understory is essential for predicting changes in the composition, diversity, and distribution of ground vascular flora through successional time. This information is also helpful for understanding ecosystem processes in an area. With the aim of this study to explore the relationships among canopy characteristics, soil properties, and ground vascular flora, seven environmental variables of three woody plant canopies in karst mountains in Guangxi Zhuang Autonomous Region located in Southwest China were measured. Multiple comparisons, correlation analysis, multivariate statistics, such as multi-response permutation procedures (MRPP), non-metric multidimensional scaling (NMS), and canonical correspondence analysis (CCA) were used to analyse data. The understory environment differed in terms of soil organic matter (SOM), leaf area index (LAI), stand density, and light level (TTot) between the three woody canopy types. MRPP showed a significant difference in the ground-flora species composition of the three canopies with Canopy1 significantly differing with both Canopy-2 and Canopy-3; however, there was no significant difference between the latter two. The ground flora variables of Canopy-1 were well separated from those of Canopy-2 and Canopy-3 in the NMS ordination, while the latter two did not significantly differ from each other due to similar ground flora species composition. The notable relationships found between NMS axis-1 and environmental variables indicate that these factors play a role in differentiating ground flora. The effect of canopy structure and understory environmental conditions on the composition and distribution of ground flora were confirmed by CCA. The tree structure (basal area at breast height and stand density) is the most dominant factor influencing ground flora communities, followed by SOM and understory light level (TTot).