Post-agricultural tropical forest succession: Patterns, processes and implications for conservation and restoration

Depending on scale, intensity and duration, effects of agriculture on tropical forestland range from enhancement of species diversity to creation of wastelands. Understanding effects of varied agricultural strategies on ecological succession is crucial for effective land management, yet few comparative studies exist. To help fill this gap, I described post-agricultural succession in Guatemala's northern lowlands and explored some of the interspecific interactions that determine successional patterns.; Facilitation among plants promotes succession in the face of the formidable array of barriers to regeneration on degraded sites. I review mechanisms of positive interaction among plants and identify circumstances under which such mechanisms are most likely to contribute to succession and to ecological restoration.; In the field, I quantified post-agricultural succession across the range of farming activities practiced in El Petén, Guatemala: agroforestry, swidden, cattle ranching and input-intensive monocultures. Succession was dramatically faster on agroforestry and swidden sites than following pastures or monocultures. Animal-dispersed colonists were particularly favored beneath the structurally-diverse agroforestry canopies. Competition from weedy vegetation and lack of seed-disperser activity appeared to be major barriers to succession on low-structural-diversity sites.; Two mechanisms of indirect facilitation help surmount these barriers on some sites. I produced experimental evidence that indirect interactions between pairs of growth forms contribute to tropical forest succession: vines suppress herbs to the benefit of pioneering woody seedlings and later in succession, pioneer shrubs and trees lift vine growth, allowing later-successional trees to establish. I also demonstrated that moderate densities of Attalea cohune palms in combination with small forest reserves are sufficient to maintain seed dispersal and colonization processes on heavily used sites. However populations of A. cohune and other remnant trees are threatened by burning, grazing and tilling on many sites.; Conservationists seek to alleviate pressure on El Petén's forests by promoting techniques that eliminate fallowing and allow farmers to produce more income from a smaller area. Such techniques include low-diversity field cropping. My findings suggest that intensifying production in this way causes enduring damage to the regenerative capacity of forests. Instead, improved swiddens and agroforestry should be promoted as ecologically appropriate ways to maximize returns to land.