Numerous studies separately identified the contributions of the environment (niche process) and space (neutral process) to the species richness or composition at different scales, but few studies have investigated the contributions of both types of processes in the two types of data at the landscape scale. Using understory plant species data across Hainan Island, Dr. HU Yuehua of Xishuangbanna Tropical Botanical Harden (XTBG) and his colleagues found that the environment (biotic and abiotic factors) played a major role in the determination of both the richness and composition of understory plant species at the landscape scale.
In the study, the researchers disentangled the contributions of spatial structures and environmental variables to the richness and composition patterns of tropical understory plant species in three types of forests at the landscape scale across Hainan Island in southern China (108°37′ ~111°05′ E, 18°10′ ~ 20°10′ N). In the period from April to December in 2008, they established 134 plots in three types of tree communities, which included a rubber (Hevea brasiliensis) plantation (70 plots), a eucalyptus (Eucalyptus urophylla) plantation (50 plots), and a secondary forest (14 plots), in 10 counties spread throughout Hainan Island.
Their study found that the environmental heterogeneity dominantly structured the distribution patterns of the richness and composition of understory plant species at the landscape scale.
Of all the environmental factors and principal coordinates of neighbor matrices eigenfunctions (PCNMs) analyzed, the overstory composition (forest type) was found to always play the leading role in the determination of the richness and composition patterns of the understory plants. Among the spatial structures, broad scale ones outperformed medium and fine scale ones in shaping species richness and composition patterns. The multivariate regression tree (MRT) analysis of the species diversity revealed that the soil moisture might be the key to the maintenance of most of the native species diversity. The alpha and beta diversities of the secondary forest plots were remarkably higher than that of the two plantations. The researchers thus concluded that niche assembly was the key mechanism regulating understory plant species distributions in Hainan Island.