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Limited information on greenhouse gas emissions from tropical dry forest soils still hinders the assessment of the sources/sinks from this ecosystem and their contribution at global scales. Particularly, rewetting events after the dry season can have a significant effect on soil biogeochemical processes and associated exchange of greenhouse gases. This study evaluated the temporal variation and annual fluxes of CO₂, N₂O, and CH₄from soils in a tropical dry forest successional gradient. After a prolonged drought of 5 months, large emissions pulses of CO₂and N₂O were observed at all sites following first rain events, caused by the “Birch effect,” with a significant effect on the net ecosystem exchange and the annual emissions budget. Annual CO₂emissions were greatest for the young forest (8,556 kg C ha⁻¹yr⁻¹) followed by the older forest (7,420 kg C ha⁻¹yr⁻¹) and the abandoned pasture (7,224 kg C ha⁻¹yr⁻¹). Annual emissions of N₂O were greatest for the forest sites (0.39 and 0.43 kg N ha⁻¹yr⁻¹) and least in the abandoned pasture (0.09 kg N ha⁻¹yr⁻¹). CH₄uptake was greatest in the older forest (−2.61 kg C ha⁻¹yr⁻¹) followed by the abandoned pasture (−0.69 kg C ha⁻¹yr⁻¹) and the young forest (−0.58 kg C ha⁻¹yr⁻¹). Fluxes were mainly influenced by soil moisture, microbial biomass, and soil nitrate and ammonium concentrations. Annual CO₂and N₂O soil fluxes of tropical dry forests in this study and others from the literature were much lower than the annual fluxes in wetter tropical forests. Conversely, tropical dry forests and abandoned pastures are on average stronger sinks for CH₄than wetter tropical forests.

 

Old-growth tropical forests harbor an immense diversity of tree species but are rapidly being cleared, while secondary forests that regrow on abandoned agricultural lands increase in extent. We assess how tree species richness and composition recover during secondary succession across gradients in environmental conditions and anthropogenic disturbance in an unprecedented multisite analysis for the Neotropics. Secondary forests recover remarkably fast in species richness but slowly in species composition. Secondary forests take a median time of five decades to recover the species richness of old-growth forest (80% recovery after 20 years) based on rarefaction analysis. Full recovery of species composition takes centuries (only 34% recovery after 20 years). A dual strategy that maintains both old-growth forests and species-rich secondary forests is therefore crucial for biodiversity conservation in human-modified tropical landscapes.