Secondary forest dynamics in abandoned fields in tropical wet and dry agricultural landscapes

World-wide, deforestation and land use change cause the rapid loss of tropical forests with negative consequences for biodiversity and ecosystem function and services. One of the most urgent challenges in forest ecology research is to understand the processes and mechanisms that limit or facilitate the forest regeneration after different agricultural land uses. Here, we compare rates of change in community structure (abundance, species richness, and diversity) and species composition attributes of secondary vegetation developing in abandoned pasture and milpa fields in two climatically contrasting tropical areas of Mexico. Both in the humid region of La Selva Lacandona (Chiapas) and in the seasonally dry area of Chamela (Jalisco), we obtained dynamic data on seedling, sapling, and tree recruitment, survival, and growth from permanent plots established across chronsequences (encompassing fields with time since abandonment from one up to 12-17 years and old-growth forest sites). Additionally, we explored the influence of vertebrate herbivorous on successional regeneration dynamics using exclosure experiments. Within the humid area, rate of change was faster in milpas than in pastures; secondary vegetation in milpas attained higher biomass and lower species richness in same time unit. Additionally, milpas and pastures strongly differ in species composition and different pioneer species dominate succession in each agricultural type. Successional rates of change were faster in abandoned pastures in the humid than in the dry area. Overall, successional trends predicted by chronosequence analysis strongly departed from that indicated by the dynamic data. In both areas, vertebrates limit species richness in early successional stages and played an important community organizing role in the old-growth forest. Based on these results, we offer some guidelines for forest recovery in tropical abandoned agricultural lands.