Neighborhood effects and environmental variables drive sapling growth in a young subtropical tree plantation

We established a forest biodiversity and ecosystem functioning experiment in southern China by planting 20,480 saplings of eight subtropical tree species in 320 plots in monocultures and mixtures of two, four and eight species to explore the biodiversity-ecosystem functioning (BEF) relationships and the underlying coexistence determinants. In this study, we aimed to report the growth of these planted saplings and explore its abiotic and biotic driving factors. Specifically, we analyzed the relative importance of sapling species identity, initial size, neighborhood interactions, neighborhood diversity, and environmental factors to sapling growth in the early stage of our BEF experiment. We found that the species of Ilex rotunda, Pinus massoniana and Elaeocarpus sylvestris grew much faster than other five species, followed by Castanopsis carlesii, Cinnamomum camphora and Schima superba. Erythrophleum fordii and Castanopsis fissa had the lowest growth rates in ground diameter and height. In addition, the relative growth rates of saplings were positively related to the neighborhood interactions, neighborhood diversity and soil nutrients, but were negatively related to initial size. Our study stresses the importance of better understanding the effects of environmental and local neighborhood conditions on initial growth of subtropical forest tree species in a mixed plantation, and provides reference for other BEF experiments in China and elsewhere.