Investigating Successional Dynamics in Naturally-Regenerated Tropical Forests of Puerto Rico: Testing and Learning from a Chronosequence Approach

Abstract

Globally, naturally‐regenerated secondary forests account for 57% of total forest cover, with most regrowth occurring on former pasture and cropland. These anthropogenic forests may provide important ecosystem goods and services, but are often dominated by novel species assemblages, with unpredictable consequences for ecosystem processes and successional trajectories. Understanding how these forests change with age is a crucial part of efforts to conserve biodiversity, maintain ecosystem functioning, and manage them for services such as carbon sequestration. In 2012, I collected data from a chronosequence of naturally-regenerated tropical forests on abandoned pastureland in Puerto Rico in order to characterize changes in species composition, structure and aboveground biomass accumulation over 89 years of succession. Then, to test the ability of the chronosequence approach to predict changes through time, I compared my observations from 2012 with predicted changes based on patterns of changes seen across age classes at the same sites in 2003. Structural characteristics and aboveground biomass generally recovered rapidly to pre-disturbance levels, though changes in biomass with age varied by method of estimation. While species diversity also exhibited rapid recovery to pre-disturbance levels with age, assemblages remained distinct from reference forest communities after 89 years. Though patterns in 2003 data were indicative of some observed changes, they failed to correctly predict many changes in forest structure, biomass and species composition within age classes.