The effects of nucleation and species functional traits on tree seedling performance in the early stage of ecological restoration

The initiation of a new plant community in a restoration area hinges on the performance of seedlings post-planting. This study aimed to evaluate the impact of species functional traits—specific leaf area (SLA), wood density (WD), seed dry mass (SDM), and potential height (H)—on the seedling performance 25 months after planting, comparing two planting designs (rows and clusters) and the influence of fertilization addition in clusters. The restoration area is a riparian tropical forest located on the coastal plain at Caraguatatuba municipality, São Paulo, Brazil. We monitored 3017 tree seedlings and estimated their survivorship and relative growth rate (RGR) using the diameter, height, and canopy area of the surviving seedlings and the stem biomass for the cluster RGR estimation. Using linear mixed models, we analyzed how the planting designs and the functional traits affect species survival and their RGR. We underscored the significance of slow-growth traits (low SLA, and high SDM and WD) in enhancing species survival, whereas, maximizing species growth entails prioritizing seedlings with greater potential height. Cluster survival and growth improved with a greater abundance of species with low values of SDM (i.e., fast-growth species) and communities with low functional divergence (high similarity). Fertilized clusters improved the RGR of large-seeded species. Accounting for functional traits in restoration is advantageous for enhancing seedling performance at the species level, which is an important consideration for restoration practitioners. To optimize applied nucleation, clusters should target functional diversity at this community level and include competitive species to improve productivity.