Land use, fallow period and the recovery of a Caatinga forest

Caatinga vegetation continues to be converted into mosaics of secondary forest stands, but the affect of this process on biodiversity has not yet been examined. We used 35 regenerating and old-growth stands of Caatinga to examine the recovery of plant assemblages subsequent to slash-and-burn agriculture and cattle ranching/pasture in northeastern Brazil. Plant assemblages were contrasted in terms of community structure (stem density/basal area/species richness/diversity), functional (leaf habit/reproductive traits) and taxonomic composition. Soil attributes were also examined to infer potential drivers for cross-habitat differences. As expected, plant assemblages clearly differed across a large set of community-level attributes, including all trait categories relative to leaf habit and reproduction (pollination syndrome/floral color, size, type). Overall, old-growth forest stands supported distinct and more diverse assemblages at the plot and habitat level; e.g., long-lived tree species were almost exclusively found in old-growth forest stands. For most attributes, plant assemblages subsequent to pasture exhibited intermediate values between those exhibited by old-growth forest and those of agriculture-related stands. Surprisingly, soils exhibited similar fertility-related scores across habitats. Our results indicate that: (1) sprouting/resprouting represents an important mechanism of forest regeneration; (2) assemblage-level attributes suggest recovery at distinct rates; (3) forest regeneration implies community-level changes in both vegetative and reproductive functional attributes, including directional changes; (4) Caatinga is not able to completely recover in a period of 15-yr following land abandonment; and (5) historical land use affects recovery rates and successional pathways/taxonomic trajectories. Seasonally dry tropical forests may intrinsically cover a wide range of patterns relative to successional model, recovery rates and successional pathways.