Abstract:

Objective: Detailed analysis of spatial dominance of individual tree species was carried out in order to provide a theoretical basis for the protection of key species and the maintenance of species diversity in forest communities. Method: In this study, based on the spatial dominance indices(tree size dominance and hyperbolic tangent indices), we constructed marked second-order characteristic functions to investigate the changes of spatial dominance of main tree species at different spatial scales. We simulated dependent, spatial marked point patterns to test the effectiveness of the constructed marked second-order functions and to analyze the influences of spatial aggregation of conspecifics on the spatial dominance of focused tree species. We investigated the changes of spatial dominance of the main tree species at different spatial scales in a 1.6 hm² forest plot in Yachang nature reserve and explored the relationships between tree dominance and species mingling. Result: 1) The studied forest community was an old-growth forest in which structural diversity was rich. A total of 86 species, 61 genera and 35 families were recorded, and the basal area of this stand was 49.81 m²·hm^-2. Different species in the community had different ranges of DBH distributions. Larger-sized tree species such as Rhododendron cavaleriei and Liquidambar formosana were the dominant tree species in the stand, and tree species of small-sized species, e.g. Ilex ficoidea and Eurya nitida, were also dominant in terms of their abundances. Size dominance and hyperbolic tangent index values of different tree species indicated that spatial dominance of tree species was associated with the population mean DBH. 2) All the tree species had a tendency to attract trees of similar sizes at small scales, and generally, spatial dominance of large-sized tree species was lower than the expected value or simulation envelopes constructed from the null model. However, spatial dominance for small-sized tree species was significantly greater than the expected, and its value tended to approach the expected value with the increasing spatial distance. 3) Spatial aggregation of conspecifics can increase or decrease the degree of species dominance. For large diameter tree species, such as L. formosana, conspecific aggregation resulted in the decrease of its spatial dominance; on the contrary, conspecific aggregation can increase species spatial dominance for small-sized tree species such as I. ficoidea. Conclusion: Our analysis of both simulated and experimental plot data showed that mark dominance second-order functions can effectively describe the spatial dominance of tree species at different scales. The species spatial segregation effects might reduce the competitive exclusion of inferior species by dominant species, and thus can maintain species coexistence and improve the species diversity in forest communities.

Key words: stand spatial structure, spatial dominance of species, second-order characteristic function, spatial segregation hypothesis, maintenance of species diversity