Questions: Premontane tropical forests harbour exceptionally high plant species diversity; understanding which factors influence their species composition is critical to conserving them, and to predicting how global environmental change will affect them. We asked: (1) how do aand b-diversity vary at the landscape scale; (2) how important is environmental filtering in structuring these communities; and (3) which soil and climate variables account for the most compositional variation?Location: Old-growth premontane forest, Fortuna Forest Reserve, western Panama.Methods: All trees ≥5-cm DBH were censused in 12 1-ha plots up to 13 km apart. For each plot, we measured soil properties (0-10 cm depth) at 13 locations, and estimated or measured monthly rainfall. To evaluate how the environmental and spatial variables are associated with community composition, we used ordination and Mantel tests.Results: Diversity varied nearly three-fold among plots (68-184 speciesÁha À1 ).b-Diversity was also high, with only one of 364 species present in all plots. Turnover reflected distinct forest community types that have developed on different parent materials: forests on rhyolite had an abundance of either ectomycorrhizal-associated trees or canopy palms, while forests on the other rock types (andesite, dacite and basalt) were dominated by trees that form arbuscular mycorrhizal associations. While NMDS ordination showed that species turnover was significantly correlated with rainfall seasonality, and also co-varied with geographic distance. Nonetheless, large compositional differences were apparent among sites <2 km apart with similar rainfall but differing soils. Partial Mantel tests controlling for geographic distance highlighted the relationship between total phosphorus and species composition.Conclusions: Soil nutrient availability and rainfall seasonality in premontane forests at Fortuna are associated with striking variation in the taxonomic and functional composition of nearby tree communities, and with plot differences in species richness comparable in magnitude to those reported over >1000 m a.s.l. in previous studies. Accounting for how local edaphic conditions structure premontane and montane tropical forests will be critical to predicting how tree communities will respond to climate change.
Deadwood is a large global carbon store with its store size partially determined by biotic decay. Microbial wood decay rates are known to respond to changing temperature and precipitation. Termites are also important decomposers in the tropics but are less well studied. An understanding of their climate sensitivities is needed to estimate climate change effects on wood carbon pools. Using data from 133 sites spanning six continents, we found that termite wood discovery and consumption were highly sensitive to temperature (with decay increasing >6.8 times per 10°C increase in temperature)—even more so than microbes. Termite decay effects were greatest in tropical seasonal forests, tropical savannas, and subtropical deserts. With tropicalization (i.e., warming shifts to tropical climates), termite wood decay will likely increase as termites access more of Earth’s surface.
Niche differentiation among tropical forest plants can generate species turnover along gradients of soil, topography, climate, and land use history. In this study we explore the relative importance of these variables as drivers of floristic composition in Cueva de Los Guacharos National Park. We established twenty 0.1-ha plots, within which trees, lianas, and shrubs (diameter ≥ 2.5 cm) were censused. We selected plot locations in primary and disturbed forests, and we measured topography and soil variables. Despite their structural similarity, primary and disturbed forests differed floristically, and also differed in environmental variables measured. A NMDS ordination showed that variation in the floristic composition across plots is highly correlated to the exchangeable acidity, elevation, temperature, and magnesium availability. Variance partitioning analysis shows that together spatial and environmental variables explain 24.2 percent of the variation in species composition. 'Pure environmental' variables were more important in explaining compositional variability than 'pure spatial' processes (9.8% and 1.4%, respectively). Residual variance may be attributed to stochastic process or non-measured biotic effects.Abstract in Spanish is available with online material.
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