Interspecific relationship and canonical correspondence analysis within woody plant communities in the karst mountains of Southwest Guangxi, southern China

The interspectific associations of main woody plant species and the relationships between environmental factors and plant communities were investigated in the karst mountains of Southwest Guangxi, southern China. Eleven sampling plots (20 m×20 m in size each) were established in three forest communities (Quercus acutissima forest, Liquidambar formosana forest, and Excentrodendron hsienmu forest) in the study site, and statistic methods including niche theory, interspecific relation principle, two-way indicator species analysis and canonical correspondence analysis were used. The results showed that Quercus acutissima, Liquidambar formosana, and Excentrodendron hsienmu were dominant species in the study area. The largest niche overlap was observed between Ardisia quinquegona and Schefflera octophylla, between Psychotria rubra and Ficus pandurata, and between Orophea hainanensis and Canthium dicoccum for the Quercus acutissima natural secondary forest, Liquidambar formosana natural secondary forest and Excentrodendron hsienmu natural secondary forest, respectively. No significant positive correlations were found in terms of the overall interspecific associations among dominant woody plant species in Quercus acutissima natural secondary forest. The χ² test showed that the number of species pairs in positive association was 50, the number of species pairs in negative association was 52, and the number of species pairs in non-association was 3, the association ratio was 0.96, and the significance rate of test was 6.67%. The overall interspecific associations were negative correlations among dominant woody plant species in Liquidambar formosana natural secondary forest, but the correlations were not significant. The χ² test showed that the number of species pairs in positive association was 96, the number of species pairs in negative association was 113, the number of species pairs in non-association was 1, the association ratio was 0.85, and the significance rate of test was 8.10%. The overall interspecific associations were significantly positive correlations among dominant woody plant species in Excentrodendron hsienmu natural secondary forests. The χ² test showed that the number of species pairs in positive association was 19, the number of species pairs in negative association was 17, the association ratio was 1.12, and the significance rate of test was 8.33%. By CCA analysis, soil pH, total phosphorus, slope aspect, soil total potassium and elevation were the most important factors affecting species composition and distribution in plant communities in the study area, which accounted for about 76.95% of the variation. Our study indicates that the more significantly positive the associations between plant species are, the higher the degree of niche overlap is. In contrast, the more significantly negative the associations between plant species are, the lower the degree of niche overlap is.