Developing restoration strategies that accelerate successional processes and are resource-efficient is critical to facilitating tropical forest recovery across millions of hectares of deforested lands in the tropics. Studies are needed that evaluate the effect of these strategies on both ecosystem structure and function beyond the first few years, given that successional trajectories change quickly. We assessed the effect of applied nucleation (i.e. planting patches of trees), as compared to both natural regeneration and a plantation-style tree planting approach, on forest recovery in a well-replicated experiment in the premontane wet forest zone of southern Costa Rica. Specifically, we measured tree seedling recruitment and litterfall biomass and nutrients at multiple sites within four 50 × 50 m treatment plots: natural regeneration (no planting), applied nucleation (planting trees in six patches of three sizes), plantation (entire area planted), and reference forest. We present data collected a decade after restoration plot establishment and compare them to earlier patterns and reference forest targets.
Density of small-seeded (<5 mm), animal-dispersed recruits was lower in natural regeneration than in applied nucleation, plantation, or reference forest plots. Species richness, species density, and density of medium- (5–10 mm) and large- (>10 mm) seeded, animal-dispersed recruits were greatest in reference forest, intermediate in applied nucleation and plantation, and lowest in natural regeneration plots. Recruit composition differed substantially between reference forest and all restoration treatments with the strongest difference between natural regeneration and reference forests. Litter production and inputs of Ca, Mg, P, N, C, Cu, Mn and Fe into the soil did not differ between applied nucleation, plantation, or reference forest after a decade, but all were greater than in natural regeneration. We conclude that applied nucleation is as effective a strategy as plantation-style planting in accelerating forest succession; the approach has the added benefit of being less costly and better simulating the natural recovery process. Results also suggest that nutrient cycling functions are recovering more quickly than plant species composition. Even with active restoration interventions, recovery of forest vegetation is a multi-decade process that proceeds at highly variable rates.