Forest Regeneration in a Chronosequence of Tropical Abandoned Pastures: Implications for Restoration Ecology

TLDR

During the mid‑1900s Puerto Rico was largely deforested, but economic shifts in the 1950s led to agricultural abandonment and secondary forest recovery. This history offers a chance to study secondary forest succession and propose tropical restoration strategies. The authors surveyed woody vegetation in 71 abandoned pastures and forest sites across four Puerto Rico regions to describe succession patterns. After roughly 40 years, secondary forests achieved densities, basal areas, biomass, and species richness comparable to >80‑yr old growth, yet species composition differed, with exotic species abundant but variable in impact, indicating that protecting areas from fire and planting generalist species can accelerate recovery when seed sources remain and soils are intact.

Abstract

Abstract During the mid‐1900s, most of the island of Puerto Rico was deforested, but a shift in the economy from agriculture to small industry beginning in the 1950s resulted in the abandonment of agricultural lands and recovery of secondary forest. This unique history provides an excellent opportunity to study secondary forest succession and suggest strategies for tropical forest restoration. To determine the pattern of secondary succession, we describe the woody vegetation in 71 abandoned pastures and forest sites in four regions of Puerto Rico. The density, basal area, aboveground biomass, and species richness of the secondary forest sites were similar to those of the old growth forest sites (>80 yr) after approximately 40 years. The dominant species that colonized recently abandoned pastures occurred over a broad elevational range and are widespread in the neotropics. The species richness of Puerto Rican secondary forests recovered rapidly, but the species composition was quite different in comparison with old growth forest sites, suggesting that enrichment planting will be necessary to restore the original composition. Exotic species were some of the most abundant species in the secondary forest, but their long‐term impact depended on life history characteristics of each species. These data demonstrate that one restoration strategy for tropical forest in abandoned pastures is simply to protect the areas from fire, and allow natural regeneration to produce secondary forest. This strategy will be most effective if remnant forest (i.e., seed sources) still exist in the landscape and soils have not been highly degraded. Patterns of forest recovery also suggest strategies for accelerating natural recovery by planting a suite of generalist species that are common in recently abandoned pastures in Puerto Rico and throughout much of the neotropics.