Restoration of soil processes in Mexican dry forests

The tropical dry region along the Pacific Coast of Mexico is a dynamic mosaic of land-use types in diverse stages along a degradation-rehabilitation continuum. In contrast with the tropical humid region, water availability strongly limits the natural or induced recovery of plant cover and soil biogeochemical processes after disturbance. Studies in primary forest have shown a wide range of water and fertility conservation mechanisms and their vulnerability to drastic or persistent disturbance. Our ongoing research in the Chamela region of Mexico has aimed at understanding the controls and constraints for the recovery of vegetation and soil biogeochemical processes after disturbance of primary forest. Total and available nutrients, water content, pH, enzyme activity, and microbial communities in soil, plus mycorrhizal associations, vegetation, and microclimate were examined in 25-year old pastures, 25-year old secondary forests and primary forests.  Results suggest that secondary forests show some patterns in plant richness, microbial diversity, and soil biogeochemical processes approaching conditions similar to primary forest. However, other processes show that 25 years of natural regeneration are not enough to re-establish long-term water and nutrient conservation mechanisms. Soil structure, for example, was still similar in pastures and secondary forests and had important consequences in fertility and microbial activity. Results are consistent with other case studies in dry secondary forests of Mexico, where soil nutrient processes have been assessed. Specifically, our results show that phosphorus seems to be a key element and may serve as a good diagnostic tool to approach restoration of biogeochemical processes in this ecosystem.