Spatial structures of different-sized tree species in a secondary forest in the early succession stage

Forest structures may be analyzed by considering both spatial and non-spatial aspects. These aspects are generally considered independently with little attention focusing on their association. However, the relationships between spatial and non-spatial structures may aid in explaining the characteristics of forests from various perspectives. In this paper, we analyzed the spatial structures of a mixed pine-oak forest with different-sized trees and the relationships among stand spatial structural parameters. This forest, located in the Nanpan River Basin in Southwest China, was in the early stage of succession. Our results showed that: (1) most species populations and trees of different sizes were nearly randomly distributed; (2) the degree of mixture gradually increased with an increase in individual plant size; (3) dominance increased with increasing individual size and could be well modeled by a negative exponential function; (4) there were no clear differences in mixture or distribution patterns among small-, medium- and large-sized trees in vertical layers, but large-sized trees were usually more dominant than small- and medium-sized trees; and (5) the distribution patterns of trees of different sizes had no association with species mixing or dominance, although there was a significant correlation between the degree of mixing and dominance. These findings indicate that tree size directly relates to the non-spatial structure of forests while also predicting their spatial structure characteristics accurately.