Changes in vegetation structure and composition along a tropical forest chronosequence: implications for wildlife

Changes in tropical forest structure and species composition that occur during regeneration following land abandonment may have important consequences for wildlife populations. Many animals rely on forest resources as sites for foraging, nesting, and protection that may vary in abundance in forests of different ages. In this study, we examined aspects of forest composition and structure thought to be important to wildlife along a tropical moist forest chronosequence in the Barro Colorado Nature Monument (BCNM) of central Panama. Secondary forests of approximately 20, 40, 70, and 100 years in fallow as well as two stands of old-growth forest (>500 years) were intensively studied. All stands were located on relatively fertile soils and were in close proximity to old-growth forest. Within 70 years following cessation of active management, many structural aspects of secondary forests resembled those of old-growth stands. Large living tree (≥65 cm diameter) density and coarse-woody debris volume increased with secondary forest age and were equivalent to old-growth levels by 70 years. Snag density and basal area did not differ with stand age. Species composition and availability of food resources in secondary forests did not converge on old-growth characteristics as quickly as most structural aspects, but many resources available to generalist frugivores were common across the chronosequence. Tree, but not liana, species composition of secondary stands became more similar to old growth with increasing forest age. Understory fleshy fruit availability was highest in young secondary stands, while importance values of trees and lianas with animal-dispersed fruits remained unchanged across the chronosequence. The importance of species particularly important to some frugivores, such as Ficus and Virola, had unpredictable distributions, but palm importance value increased with stand age. We suggest that young secondary forests may provide adequate nesting, foraging, and roosting resources for many animal taxa, but some populations of animals specializing on coarse-woody debris, large trees, or particular species of trees may be limited in secondary forest less than 70 years old.