Ecological public welfare forests have provided many more ecological benefits to human beings than commercial woodlands, thus, planting trees for ecological public welfare forests has been a major component of ecological restoration in Zhejiang Province in the 21st Century. In this study, the main objective was investigating plants' interspecific and environmental relationships to further the assessment of plant species distribution changes in ecological welfare forests. We used inventory monitoring data from 80 permanent sample plots, based on a stratified sampling technique applied to 5.256 × 10⁴ hm² of ecological public welfare forests in Jiangshan city in Zhejiang province. We employed a niche theory conceptual model, interspecific relations, and Canonical Correspondence Analysis (CCA) to investigate the interspecific relationships among dominant species and the relationships between species and their environments. The results showed that Cunninghamia lanceolata, Eurya muricata, and Funaria hygrometrica were the dominant species of the tree layer, shrub layer, and herb layer, respectively. The largest niche overlap was observed between Cyclobalanopsis glauca and Lithocarpus glabra, between Eurya muricata and Litsea cubeba, and between Pteridium aquilinum and Lygodium japonicum for the tree layer, shrub layer, and herb layer, respectively. The relationships between species and their environmental factors indicated that elevation and slope were the most important environmental factors affecting plant species distribution, and the aspect and the thickness of humus also influenced species distribution in our study area.
The uniqueness of this study is introducing the species-environment relations (CCA) into the analyzing framework to solve the complex inter-species, intra-species, and plant-environment relationships to enrich niche theory. This study also demonstrated that importance values were directly correlated with the breadth of ecological niches. In general, the higher the niche overlap between two species, the more similar the environmental conditions in which they were found. In addition, the analysis showed that the distribution frequency was an important factor affecting the niche breadth and species niche overlap. We observed positive relationships between the distribution frequency and the niche overlap probabilities, namely, the higher the distribution frequency the higher the probability of species niche overlap. Furthermore, the interspecific relationships reflected the interconnectedness of different species in the spatial distribution and represented mutual attraction or repulsion between species and their environment. In our study area, most of the interspecific relationships between the dominant species showed a positive correlation. There were many factors, including local climate, soil types, topography, and landforms, that influenced the distribution of plant species in a given community.
In summary, this study found the following general patterns for interspecific relationships: if species have a narrow niche, they also have a narrower spatial distribution, and specialize on certain resources with less overlap with other species in the CCA sequencing diagram, characterized as a tendency of deviating from the high species distribution areas. However, if species have a wide niche, they also have a wider distribution range and greater overlaps with other species, and occupy a majority of the species distribution area on the CCA sequencing diagram. For a given species, if it does not have significant interactions with other species, the higher its niche overlap values are with another species, the closer the distances between the species on the CCA sequencing diagram. If there is a positive correlation, this correlation is significant and there are shorter distances among species on the CCA sequencing diagram; while if there is a negative correlation, this negative correlation is also significant and the distances are longer among species on the CCA sequencing diagram. Our study not only indicates the complex interspecific and species-environment relationships for constructing ecological public welfare forests in subtropical regions, especially in China, but also provides recommendations of how to use our research in practice, including providing feasible suggestions to protect species diversity and accelerate positive community succession.