Growth Variations of Tree Saplings in Relation to Species Diversity and Functional Traits in a Tree Diversity Pot Experiment

Despite the accumulating evidence of the beneficial effects of diverse mixed species forests on ecosystem functioning and services, foresters in subtropical forest cultivation in China still prefer easily managed monocultures, which is also due to the complexity of mixed forests and the unknown underlying mechanisms related to relationships between biodiversity and forest growth. In a designed pot experiment, we selected two early-successional tree species (Pinus massoniana Lamb., Liquidambar formosana Hance.) and two late-successional tree species (Schima superba Champ., Elaeocarpus decipiens Hemsl.) and planted four saplings in one pot with regard to tree species diversity (monoculture, two species and four species mixtures), each combination replicated four times. In this three-year duration experiment, the effect of tree species diversity, tree identity, and functional traits on sapling growth (tree height, ground diameter, crown projection area), were analyzed. The results showed that the increments of ground diameter and crown projection area increased with tree species richness, whereas the mean tree height increment showed the opposite effect. This growth variation was species specific and related to functional traits (early or late succession), as the increments of the early successional tree species (P. massoniana Lamb. and L. formosana Hance.) had a positive correlation with tree species richness, while the late successional tree species (E. decipiens Hemsl. and S. superba Champ.) showed negative effects. In addition, our study provided evidence for the allometric differences between mixtures and monocultures, which have an important reference value on mixed-species forests.