Pervasive impacts of climate change on the woodiness and ecological generalism of dry forest plant assemblages

Abstract

1. Climate emergency is a significant threat to biodiversity in the 21st century, but species will not be equally affected. In summing up the responses of different species at the local scale, we can assess changes in the species quantity and composition of biotic assemblages. 2. We used more than 420K curated occurrence records of 3060 plant species to model current and future patterns of plant species distribution in one of the world's largest tropical dry forests-the Caatinga. While allowing different model extrapolation scenarios, we estimated potential changes in the species richness and composition of dryland plant assemblages in response to projected climate change, and assessed how the ecological generalism and woodiness of plant assemblages can be impacted by the climate crisis. 3. More than 99% of plant assemblages were projected to lose species by 2060, with biotic homogenisation-the decrease in spatial beta diversity-forecasted in 40% of the Caatinga. The replacement of narrow-range woody species by wide-range non-woody ones should impact at least 90% of Caatinga plant assemblages. The exacerbated species loss in the dryland plant assemblages was connected to the heterogenisation and homogenisation of biotic assemblages. Still, the magnitude of climate change impacts on ecological generalism and woodiness patterns of dryland plant assemblages differ according to the direction of the biotic change process. 4. Synthesis. The future increase in aridity will change the patterns of woodiness and ecological generalism of tropical dry forest plant assemblages by decreasing vegetation diversity and complexity. The projected biotic changes in dryland plant assemblages indicate the erosion of ecosystem services linked to biomass productivity and carbon storage. We highlight the importance of long-term conservation planning for maintaining tropical dry forests.

Climate change should drive mammal defaunation in tropical dry forests

“…The highly fragmented and diminished vegetation cover of eastern Caatinga (Castanho et al, 2020) impose additional challenges for non-volant mammals to track suitable habitats (Alves et al, 2020), further contributing to depauperate the trophic structure of species assemblages (Mendoza & Araújo, 2019). Although mammal assemblages subject to high species loss exhibit more future uncertainty, a more optimistic outlook is unlikely as these regions also overlap with heavily settled human-modified landscapes in the Caatinga (Antongiovanni et al, 2018(Antongiovanni et al, , 2020 and regions projected to lose vegetation complexity and diversity (Moura et al, 2023). Therefore, the severe defaunation of Caatinga mammal assemblages is a probable outcome, with small-sized species loss driven by climate change-at least partially-and the depauperating of large-sized mammals further exacerbated by overexploitation and habitat destruction (Alves et al, 2023;Bogoni et al, 2020).…”

“…However, species redistribution can increase the spatial heterogeneity in assemblage composition, either due to the gain of disturbance‐adapted species or to the loss of widespread species (Socolar et al, 2016). Although studies on the effects of climate change over biodiversity patterns often emphasize the biotic homogenization due to species loss (Clavel et al, 2011; Hidasi‐Neto et al, 2019; Moura et al, 2023), the prevalence each of those process is likely context dependent, and spatial patterns will vary according to species composition, the level of spatial heterogeneity in environmental conditions and the severity of climate changes.…”

“…For instance, drylands are expected to become hotter, drier, and less suitable for a significant portion of their species (Aguirre‐Gutiérrez et al, 2020). If these projections are confirmed, it is likely that drylands will gradually become impoverished, homogenized, and driven towards desertification (Moura et al, 2023; Torres et al, 2017). One of Earth's most vulnerable drylands, the Caatinga, is also the largest tropical dry forest in South America (Banda‐R et al, 2016; Hoekstra et al, 2004; Silva, Barbosa, et al, 2017).…”

“…For instance, drylands are expected to become hotter, drier, and less suitable for a significant portion of their species (Aguirre-Gutiérrez et al, 2020). If these projections are confirmed, it is likely that drylands will gradually become impoverished, homogenized, and driven towards desertification (Moura et al, 2023;Torres et al, 2017).…”

Changes in quantity and timing of foliar and reproductive phenology of tropical dry-forest trees under a warming and drying climate

“…Climate change, such as increasing drought and aridity, is expected to severely weaken the role of tropical forests as carbon sinks (Corlett, 2016). Tropical dry-forest assemblages, despite their long evolutionary history under water deficit, are also not exempt from diversity loss (Siyum, 2020;Moura et al, 2023). These seasonally dry forests, characterised by alternating wet and dry seasons that last between four to seven months (Allen et al, 2017), are widespread across sub-Saharan Africa where they are central to biodiversity conservation and people's livelihoods (Siyum, 2020).…”