Grazing reduces plant species diversity of Caatinga dry forests in northeastern Brazil

Abstract

QUESTIONS: In many arid and semi‐arid regions of the world, livestock husbandry is the main land use and grazing is one of the main challenges for biodiversity conservation. This also applies to the Caatinga, a unique seasonally dry tropical forest in northeastern Brazil. It is considered one of the most threatened ecosystems of Brazil. To protect semi‐arid regions from biodiversity loss, degradation, and desertification, sustainable management practices are urgently needed. However, the effect of different grazing intensities on plant diversity is not yet fully understood. In this study, we examined the effect of different grazing intensities on plant species composition, alpha and beta diversity. LOCATION: Vicinity of the Itaparica Reservoir, northeastern Brazil. METHODS: We assessed the effects of different grazing intensities (high, intermediate, no/low) on species composition, alpha and beta diversity of the tree and shrub, and the herb layer in a Caatinga area. Plant diversity of the tree and shrub layer was assessed on 45 study plots (each 20\xa0m\xa0×\xa020\xa0m), while the diversity of herbs was studied on a subset of 36 plots (four subplots, each 2\xa0m\xa0×\xa02\xa0m). RESULTS: In total, we recorded 140 plant taxa including morphospecies. Grazing at high intensities significantly reduced almost all measures of alpha and beta diversity (tree and shrub layer) compared to areas with no or low grazing. In contrast, species composition was not significantly related to grazing but instead to altitude, which serves as an indicator of reduced anthropogenic impact such as slash‐and‐burn agriculture or tree harvesting. CONCLUSION: Overall, the study results show that the current livestock management has negative effects on plant diversity in Caatinga ecosystems. These results have been incorporated into guidelines provided to regional stakeholders including recommendations for adapted land‐management practices that protect and foster the biodiversity of dry forests while sustaining local livelihoods.