Print PageNatural regeneration restores biodiversity and ecosystem function to degraded tropical lands. Yet complex interactions between environmental factors, prior land use, and seed dispersal impact ecosystem processes and species composition during natural regeneration. Our study is among the first to unite patterns of community composition with functional traits during the first 10 years of succession in the premontane Neotropics to understand patterns of community assembly. Our study uses four naturally regenerating plots (0.3-0.6 ha) in the Coto Brus region of Costa Rica to address the following questions: 1) How does species composition vary within and across plots during the first 10 years of succession; 2) Does species composition influence functional trait composition; and 3) How do community level functional traits change over time? All plots were fenced off from cattle pasture in 1997, and species composition of woody stems >1m tall was monitored eight times between 1998 and 2007. In 2007, six leaf functional traits were measured for 3–5 individuals of species comprising the top ~80% abundance in each plot (N species total = 33). Similarity in species composition for each censused year was determined with the Morisita-Horn index. Community aggregate traits and functional diversity were compared over successional time.
Results/Conclusions
Initial species composition among the four plots was distinct, but became more similar over time (Morisita-Horn similarity index 0.37±0.12 in 1998, 0.58±0.07 in 2007). In general, community aggregate trait values did not show the expected changes over succession, although there was a slight increase in leaf thickness, toughness, and density with time. But the variance in community aggregate traits among plots decreased with plot age for all traits except leaf toughness (decreases in coefficients of variation from 1998 to 2007 were 35%, 15%, 56%, 10%, -27%, and 42% for leaf area, specific leaf area, leaf dry matter content, leaf thickness, leaf toughness, and leaf density, respectively). Likewise, functional diversity converged among plots through time, as shown by the increasing similarity in functional evenness and functional divergence with time. Our results suggest that these premontane communities are still in the stand initiation phase of succession, where dispersal limitation and heterogeneity of initial site conditions strongly influence community composition. The sites are becoming increasingly similar in both species and functional trait composition, suggesting that environmental filtering is beginning to impact community assembly, albeit more slowly than in less complex communities such as grasslands.
