Resilience and successional trends of woody vegetation in seasonally dry tropical forests

Abstract

Abstract Understanding the recovery time of vegetation structure and species composition to estimate the resilience of seasonally deciduous tropical forest (SDTF) is fundamental for conservation actions. Related information is still scarce for the semi-arid Brazilian SDTF (locally called Caatinga), which covers more than 800 000 km2 in the northeast of Brazil. We aimed to estimate how long it takes for 11 attributes of vegetation structure and species composition, separately and aggregated, to become similar to an old-growth forest (OGF). The attributes were floristic composition, species richness, Shannon diversity index, plant density, median and maximal diameters and height, basal area, volume and aboveground biomass. The attributes’ regeneration ratios were aggregated as an arithmetic average and a geometric average, based on a variance–covariance analysis. The ratios were determined in chronosequences (5, 15, 25 and 35 regeneration years and an OGF) of SDTF, in three different locations in Ceará state. Plant density, which had a unimodal tendency, reached a peak at 15 years and then decreased, although it was still greater than that of the OGF after 35 years. Richness and diversity, with monotonic trends, reached values similar to the OGF. All other attributes, especially floristic composition, volume and biomass, had lower values than the OGF. Based on the aggregate set of attributes, the SDTF was 79 per cent recovered after 35 years of regeneration. The variance–covariance analysis indicated that species richness and aboveground biomass contributed the most to the aggregate ratio of regeneration, while maximum diameter and basal area contributed the least. Recovery of this semi-arid forest takes longer than recovery of other SDTF and requires more than 35 years of regeneration to return to a composition and structure similar to the original one. Therefore, management plans should restrict destructive uses before at least 35 years of regeneration have been reached.