Species Composition Of Karst Forest Community And Their Interrelationships With Soil, Geological And Other Environmental Factors In Longhushan Nature Reserve, Southwest China

The Karst Mountains of Southwest (SW) China are characterized by a cluster of distinctive mini-hotspots with high biodiversity and unique types of vegetation. However, karst areas are also recognized as one type of geo-environment that is particularly susceptible to environmental damage if inadequately managed. Yet, S W China karst forests have been faced with serious degradation sequences, as a result of the anthropogenic influences combined with the ecological fragility of karst system, leading to the loss of significant ecosystems and to rock desertification in some areas. Hence the need to establish much improved management, conservation, and restoration strategies, toward the preservation of plant communities in the region. Moreover, the ability to manage and restore plant communities with respect to human-induced landscape change may, obviously, rely on our understanding of how species respond to the environmental variables.The main purpose of the present research was to analyze the relationships between variations in plant species (diversity, abundance) and the environmental habitat factors in the karst forest of Longhushan Nature Reserve. The study examined the composition of plant communities, in addition to the patterns of species diversity (richness, diversity) and abundance (dominance, density) with their ecological correlates. The analysis concerned a representative sample of vegetation plots from a systematic sampling using 30 m × 30 m quadrats (17 quadrats) randomly located along 4 south-north transects lines. The sampling combined measurements of plant species (diversity and abundance), with extensive information on rock type, environmental and soil factors, allowing for the consideration of the interactions between the three groups of environmental habitat factors. Plant species were examined using the statistical methods of General Linear Models-GLM (ANOVA, ANCOVA, Multiple Linear Regressions-MLR) and Generalized Linear Models-GzLM (Poisson, Negative Binomial, and Gamma Regressions) at 95% confidence interval (a= 0.05), to test the single or combined effects of the three groups of factors.From both statistical analyses methods, the models generated better fits by predicting plant species as a function of the combination of predictors from soil, geological, and environmental factors. By combining variables from the three groups, the best fit to the observed values of richness produced in MLR an F-ratio of F=23.318 with p<0.001 (adjusted R2=87.5%) and in Poisson model a likelihood-ratio of LR X2= 91.423 with p<0.001. That to the observed values of diversity generated in MLR F=13.330 with P<0.001 (adjusted R2=79.4%) and in Gamma model LR^=26.497 with p<0.001. For species dominance the best fit produced in MLR an F-ratio of 4.814, p<0.05 (adjusted R2=54.4%) and for Gamma model a LR X2 value of 19.302,p<0.01. Likewise, the best fit to the observed values of density produced an F= 13.217 with p<0.001 (adjusted R2=84.2%) in MLR and a LR X2=28.828 with p<0.001 in Negative Binomial regression. The analyses thus established evidence of significant patterns in species diversity and abundance related to the interrelationships between the three groups of environmental parameters. Both species diversity and abundance responded positively with elevation, slope, moisture, and in high dolomite percentage areas. Species diversity further responded positively with ground temperature and negatively with canopy coverage, while abundance responded positively with canopy coverage, but negatively with ground temperature and soil organic matter content. The findings, thereby, suggest that the variations in plant species were dependent on complex relationships between soil, environmental, and geological factors of karst ecosystem. Within this complexity of relationships it appeared that the geological factor played an important role in the distribution and performance of plant species in the area.Moreover, among the recorded 59 plant species, Sterculia nobilis, Ficus sp., Albizia chinensis, Liquidambar formosana, Streblus tonkinensis, and Bischofia javanica were found as the most dominant. They represented together 43% of the total species importance value and Sterculia nobilis, by far, was the most abundant constituting alone 32% of the dominant species importance value, and 14% of the total importance value. Several species were also recorded as endangered with few endemic and some of them are included in IUCN red list. Although the dominant species responded differently to the significant environmental factors, a number of those species were found typically well adapted to the special karst environment. Among them Sterculia nobilis, and Albizia chinensis were susceptible to grow well in all environmental habitats conditions, suggesting they could be appropriate, for instance, for the restoration of degraded parts of the forest.It was demonstrated that the significant variation in species diversity and abundance was provided after combining variables from soil, geological, and environmental factors, inferring their interactions influence on plants. Evidence supports these degrees of interactions and no single context explained all the associations between plant species and rock type, soil, or environmental factors. The findings have implications for the understanding of these interactions and suggest that not only plant species can be affected by it, but also carbonate rock type may be an important factor influencing the overall relationships between plant species and their environment in karst area. Therefore, effective and efficient management of karst mountain ecosystems requires an elaborate data set and understanding of all the components and physical features, as well as the complex links and interactions between them and plant communities, if species and their habitats are to be managed in a way that can sustain their performance and diversity. This knowledge can provide a reference for assigning priority sites for conservation and restoration, the prevention of rock desertification, biodiversity conservation and the development of sustainable management, conservation, and restoration strategies of karst mountains resources in southwest China.