Species association of the dominant tree species in an old-growth forest and their implications for silvicultural practices in western Hunan Province, China

Mixed-species forest management has been receiving increasing attention due to the diverse ecological and economic benefits. Afforestation with multiple tree species, promoting mixed species through natural regeneration and the transformation of planted monocultures to mixed stands are the main focus of mixed-species forest management. The optimal species configuration, i.e., an appropriate spatial arrangement of young and adult trees of different species, is of great importance to such transformations, as well as to the restoration of degraded secondary natural forests. Species association refers to a recurring group of co-occurring species. Species pairs with positive association share the same habitat requirement and thus coexist well. The measurement of species association facilitates a comprehensive understanding of community structure, function, formation, maintenance and succession in the forest. In turn, the association of the tree species in a given area can be a measure for species configuration. Little is known about this species association in natural forests in the western Hunan Province, China. In this study, the species association between dominant tree species (including sapling and adult trees) was investigated in an old-growth forest. The overall species association was first determined using a variance ratio (VR) test and the pairwise species association was then determined using a chi-square (X-2) test, the association coefficient (AC), the Dice index (DI), and Spearman's rank correlation coefficient (SRCC). The VR test showed a significant overall positive species association, indicating a stable structure in the old-growth forest. We also determined the pairwise intra-and interspecific association between saplings and adult trees. The light requirements of the tree species were considered and the optimal species configuration was determined, important for the establishment of mixed-species plantations, the transformation of monocultures, and enrichment plantings in degraded secondary natural forests. Additionally, based on the findings of this study we provided suggestions for suitable silvicultural practices.