Competition and Facilitation Co-Regulate Spatial Patterns and Coexistence in a Coniferous and Broad-Leaved Mixed Forest Community in Zhejiang, China

Abstract

Plant interactions have long been the subject of intense research and debate in ecology. Competition and facilitation are known to be the basic drivers of community structure, species coexistence, and forest succession dynamics; however, there remains a lack of understanding of how spatial patterns affect these in the mixed forest community of coniferous and broad-leaved species. In the present study, we studied the roles of competition and facilitation in a mixed forest community in the Zhejiang Province, China. For this, we divided plants measured at a study site according to the size of the diameter at breast height (DBH) into three levels of saplings as follows: saplings (1 cm ≤ DBH < 5 cm), juveniles (5 cm ≤ DBH < 15 cm), and adults (DBH ≥ 15 cm). We used the spatial point pattern method to explore the raw number, spatial distribution, and both intra- and inter-specific correlations of coniferous and broad-leaved species at these different diameter levels. The corresponding findings were as follows. First, the DBH and structure of coniferous and broad-leaved species were similar, showing a distinct distribution in an inverted “J” shape as the number of individuals with a particular diameter declined as DBH increased. Second, when all individuals of a similar diameter range were pooled, coniferous species were clustered at all size scales; however, in this situation, broad-leaved species (evergreen and deciduous) showed a clumped distribution at small scales, and this decreased as spatial scale increased. Third, there were small, but significant positive correlations between large-diameter trees and small-diameter trees of coniferous species and between evergreen broad-leaved species at different diameter levels; however, as the scale increased, the correlation diminished. On any scale, individual deciduous broad-leaved species at different diameter ranges did not have any significant correlation. Fourth, coniferous species had a strong competitive effect on broad-leaved species, and there was a weak promoting effect between deciduous and evergreen broad-leaved species as well. In summary, different tree species occupy similar living spaces, and through competition and facilitation, regulate the spatial pattern and community stability of coniferous and broad-leaved species in mixed forest communities.