Individual-based trait analyses reveal assembly patterns in tree sapling communities

摘要

Question: Are trait-convergence assembly patterns (TCAP) and/ or traitdivergence assembly patterns (TDAP) of tree sapling communities related to microhabitat gradients in forest patches? If so, which traits are related to such patterns? What are the niche mechanisms potentially responsible for community assembly? Location: Grassland-forest mosaic in Serra do Sudeste region, southern Brazil (ca. 30.8 S, 53.1 W). Methods: We used individual-based trait information of 1132 tree saplings in 40 plots along gradients of canopy openness and grazing intensity in forest patches in southern Brazil. We used a trait-based approach, bypassing taxonomic identification, as a first assessment of sapling community assembly in forest patches. Results: Both TCAP and TDAP indicate nichemechanisms underlying assembly of tree sapling communities. Specific leaf area (SLA), mean leaf area (LA) and relative abundance of toothed leaf margin (TLM) maximized TCAP. SLA and TLMtended to increase undermore closed canopies, whereas LA had higher values at intermediate canopy openness. SLA and LA maximized TDAP and tended to vary more in more closed canopies, whereas SLA and presence of spines, which also maximized TDAP, showed higher variation under lower grazing intensity. Conclusion: The taxon-free approach was very useful to infer niche mechanisms of tree sapling assembly in forest patches. By adopting an individual-based trait approach, we assumed that both intra-specific and intra-population trait variability were relevant for revealing assembly patterns. We highlight that the use of individual-based trait data in ametacommunity framework is an excellent way to evaluate TCAP and TDAP at themetacommunity scale, since it takes into account the entire variation of traits throughout communities.