Abstract
Both local- and landscape-scale processes drive succession of secondary forests in human-modified tropical landscapes. Nonetheless, until recently successional changes in composition and diversity have been predominantly studied at the patch level. Here, we used a unique dataset with 45 randomly selected sites across a mixed-use tropical landscape in central Panama to study forest succession simultaneously on local and landscape scales and across both life stages (seedling, sapling, juvenile and adult trees) and life forms (shrubs, trees, lianas, and palms). To understand the potential of these secondary forests to conserve tree species diversity, we also evaluated the diversity of species that can persist as viable metapopulations in a dynamic patchwork of short-lived successional forests, using different assumptions about the average relative size at reproductive maturity. We found a deterministic shift in the diversity and composition of the local plant communities as well as the metacommunity, driven by variation in the rate at which species recruited into and disappeared from the secondary forests across the landscape. Our results indicate that dispersal limitation and the successional niche operate simultaneously and shape successional dynamics of the metacommunity of these early secondary forests. A high diversity of plant species across the metacommunity of early secondary forests shows a potential for restoration of diverse forests through natural succession, when trees and fragments of older forests are maintained in the agricultural matrix and land is abandoned or set aside for a long period of time. On the other hand, during the first 32 years the number of species with mature-sized individuals was a relatively small and strongly biased sub-sample of the total species pool. This implies that ephemeral secondary forests have a limited role in the long-term conservation of tree species diversity in human-modified tropical landscapes.
Highlights
Today’s tropical landscapes are mostly dynamic mosaics of mature forest remnants, crop land, pastures, and regrowing secondary forests of different ages
We found that the use of site basal area consistently resulted in statistically stronger patterns and we focus on this explanatory variable in the main text
The first-axis site scores of non-metric multidimensional scaling (NMDS) based on species that occurred in at least 10%, 25%,or 50% of the sites were strongly correlated to the site scores calculated from the full data set (R2 .0.90)
Summary
Today’s tropical landscapes are mostly dynamic mosaics of mature forest remnants, crop land, pastures, and regrowing secondary forests of different ages. While changing socio-economic circumstances have led to longterm forest recovery over considerable areas in some regions [3,6,7,8], secondary forests more often are an integral component of agricultural land-use systems In these systems fallows form a dynamic patchwork of early successional plant communities across the landscape and rarely surpass a few years or decades in age [9,10,11,12,13]. This is relevant as increased demand for land and natural resources lead to increased pressure on mature forest, shorter fallow periods, and agricultural intensification To explore these questions, we evaluated the diversity of species that can persist as viable metapopulations in different successional age classes, using different assumptions about the average relative size at reproductive maturity
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