DOI: 10.5061/dryad.8r8sj
title: Data from: Precipitation mediates the effect of human disturbance on the Brazilian Caatinga vegetation

description: Seasonally dry tropical forests (SDTFs) are one of the most threatened
 forests worldwide. These species-rich forests not only cope with several
 acute (e.g. forest loss) and chronic (e.g. overgrazing and firewood
 extraction) human disturbances, but also with climate change (e.g. longer
 and more severe droughts); yet, the isolated and combined effects of
 climate and acute and chronic human disturbances on SDTF vegetation are
 poorly known. Given the environmental filter imposed by drought in SDTFs,
 the composition and structure of vegetation is expected to be strongly
 associated with annual precipitation, and thus the effects of human
 disturbances on vegetation may also depend on precipitation (i.e.
 interacting effect). We tested these hypotheses in the Brazilian Caatinga
 – a SDTF threatened by climate change and human disturbances. We evaluated
 the isolated and combined (both additive and multiplicative) effect of
 precipitation, a chronic disturbance index and acute disturbance
 (landscape forest cover) on the diversity, stem density, evenness,
 taxonomic composition and aboveground biomass of adult trees and shrubs
 across 19 0.1-ha plots distributed along a disturbance and precipitation
 gradients. We recorded 5541 stems from 129 species. Precipitation showed a
 stronger (positive) effect on species diversity than acute and chronic
 disturbances and, as expected, the effect of disturbance depended on
 precipitation (interacting effect): i.e. species diversity (especially the
 number of rare species) was negatively related to forest loss but
 positively related to chronic disturbance in wetter sites, whereas in
 drier sites, species diversity was weakly related to forest cover, but
 strongly and negatively related to chronic disturbance. Contrary to
 species diversity, community evenness, stem density and biomass were
 weakly related to all predictors. Synthesis. Precipitation appears to be a
 strong environmental filter determining the distribution of
 water-demanding plant species. Chronic disturbance in wetter
 (high-productive) forests may favour species diversity by increasing
 ecosystem heterogeneity (intermediate disturbance hypothesis). Yet, the
 biodiversity costs of chronic disturbance are higher in drier
 (low-productive) forests; i.e. there is a co-limitation imposed by drought
 and disturbance in drier forests. Overall, our findings indicate that
 rapid climatic changes in the region will probably have strong negative
 effects on this SDTF.
description: Rito et al
 2016_JEcolData were collected in
 the Caatinga vegetation of the Catimbau National Park, Pernambuco state,
 Brazil (8º24'00'' and 8º36'35'' S;
 37º0'30'' and 37º1'40'' W). We sampled all
 shrubs and trees with diameter at soil height (DAS) ≥ 3 cm and total
 height ≥ 1 m. We measured the DAS and total height to calculate the stem
 density and total plant aboveground biomass per plot. Total aboveground
 biomass was calculated using an allometric equation for Caatinga
 vegetation (Biomass kg =0.173 DAS cm2.295) as proposed by Amorim, Sampaio
 & Araújo (2005), which is based on basal area and
 height.Rito
 et al_JEcol.xlsx