Thresholds in forest bird communities along woody vegetation gradients in the South American Dry Chaco

Ecological filtering shapes the impacts of agricultural deforestation on biodiversity

The biodiversity impacts of agricultural deforestation vary widely across regions. Previous efforts to explain this variation have focused exclusively on the landscape features and management regimes of agricultural systems, neglecting the potentially critical role of ecological filtering in shaping deforestation tolerance of extant species assemblages at large geographical scales via selection for functional traits. Here we provide a large-scale test of this role using a global database of species abundance ratios between matched agricultural and native forest sites that comprises 71 avian assemblages reported in 44 primary studies, and a companion database of 10 functional traits for all 2,647 species involved. Using meta-analytic, phylogenetic and multivariate methods, we show that beyond agricultural features, filtering by the extent of natural environmental variability and the severity of historical anthropogenic deforestation shapes the varying deforestation impacts across species assemblages. For assemblages under greater environmental variability-proxied by drier and more seasonal climates under a greater disturbance regime-and longer deforestation histories, filtering has attenuated the negative impacts of current deforestation by selecting for functional traits linked to stronger deforestation tolerance. Our study provides a previously largely missing piece of knowledge in understanding and managing the biodiversity consequences of deforestation by agricultural deforestation.

Livestock grazing impact differently on the functional diversity of dung beetles depending on the regional context in subtropical forests

The replacement of native forest by cattle pastures reduces functional diversity; however, little is known about whether the changes depend on regional variation. Dung beetles are one of the most diverse and functionally important taxa; through organic matter burial, dung beetles improve soil quality. We collected dung beetles in native forests and cattle ranching areas in subtropical forests with contrasting climatic conditions: the Atlantic Forest, the Humid Chaco, and the Dry Chaco. We measured 11 traits related to the ecology and the physiology of species. Irrespectively of the region, functional richness was higher in forests (native and with cattle) when compared to open pastures. Humid forests (Atlantic Forest and Humid Chaco) showed higher functional richness than Dry Chaco. Functional dispersion in humid forests was similar between native forest and livestock systems, however, functional dispersion in the Dry Chaco was higher in open pastures compared to native forest. According to our results, native forests and forests with cattle maintain functional diversity in all regions. However, in the case of open pastures, the response depends on the regional context; the replacement of native forest by open pastures strongly affected functional diversity in humid forests and showed less impact on dry forest.

Forest strips increase connectivity and modify forests' functioning in a deforestation hotspot

Land use changes are occurring with unprecedented magnitude and intensity, imposing global impacts on ecosystem services (ES) and biodiversity. While the impacts of land use changes are increasingly recognized, understanding how landscape connectivity is related to ecosystem functioning is lacking. In the Argentinian Dry Chaco, deforestation increased forest fragmentation but strips of native forest (linear remnants) were usually left after clearings. Although the number of ecological studies on forest strips has increased, their contribution to forest connectivity and functioning has not been assessed. We evaluated the contribution of forest strips to forest connectivity and estimated its effect on forests' functioning considering low, moderate, and high species' dispersal abilities in our estimation. The effects of forest strip connectivity contribution to the forests' Ecosystem Services Supply Index (Forests' ESSI) was also analyzed. Forest strips contributed on average 6% and up to 40% to forest connectivity for moderate dispersal abilities, while low and high dispersals presented low values in almost all cases. The connectivity contribution was highest (between 15 and 40%) and variable for moderate dispersal abilities in landscapes with between 25 and 35% of forest cover. High connectivity contribution was generally achieved for low and moderate dispersals when forest strips conformed a network among forest patches. Forest strip connectivity significantly increased the forests' ESSI (between 1.3 and 2.4% per unit of connectivity contribution) and its effect was higher in comparison to forest amount and fragmentation. This study provides insights for planning the location of forest strips and forest remnants in agricultural landscapes, thus increasing forest connectivity for enhancing ecosystem functioning.

Preserving 40% forest cover is a valuable and well-supported conservation guideline: reply to Banks-Leite et al

Banks-Leite et al. (2021) claim that our suggestion of preserving ≥ 40% forest cover lacks evidence and can be problematic. We find these claims unfounded, and discuss why conservation planning urgently requires valuable, well-supported and feasible general guidelines like the 40% criterion. Using region-specific thresholds worldwide is unfeasible and potentially harmful.

The suggestion that landscapes should contain 40% of forest cover lacks evidence and is problematic

A recent review suggests that forest cover needs to be restored or maintained on at least 40% of land area. In the absence of empirical evidence to support this threshold, we discuss how this suggestion is unhelpful and potentially dangerous. We advocate for regionally defined thresholds to inform conservation and restoration.

Multiple trade-offs regulate the effects of woody plant removal on biodiversity and ecosystem functions in global rangelands

Woody plant encroachment is a major land management issue. Woody removal often aims to restore the original grassy ecosystem, but few studies have assessed the role of woody removal on ecosystem functions and biodiversity at global scales. We collected data from 140 global studies and evaluated how different woody plant removal methods affected biodiversity (plant and animal diversity) and ecosystem functions (plant production, hydrological function, soil carbon) across global rangelands. Our results indicate that the impact of removal is strongly context dependent, varying with the specific response variable, removal method, and traits of the target species. Over all treatments, woody plant removal increased grass biomass and total groundstorey diversity. Physical and chemical removal methods increased grass biomass and total groundstorey biomass (i.e., non-woody plants, including grass biomass), but burning reduced animal diversity. The impact of different treatment methods declined with time since removal, particularly for total groundstorey biomass. Removing pyramid-shaped woody plants increased total groundstorey biomass and hydrological function but reduced total groundstorey diversity. Environmental context (e.g., aridity and soil texture) indirectly controlled the effect of removal on biomass and biodiversity by influencing plant traits such as plant shape, allelopathic, or roots types. Our study demonstrates that a one-size-fits-all approach to woody plant removal is not appropriate, and that consideration of woody plant identity, removal method, and environmental context is critical for optimizing removal outcomes. Applying this knowledge is fundamental for maintaining diverse and functional rangeland ecosystems as we move toward a drier and more variable climate.

Are Ecological Modernization Narratives Useful for Understanding and Steering Social-Ecological Change in the Argentine Chaco?

During the past decades, the Ecological Modernization Theory, and associated ideas such as the Forest Transition Theory and Land Sparing Hypothesis, have dominated the academic and policy arenas regarding the solutions to current environmental crises. However, critiques were raised as these theories, originally conceived for developed countries, started to be applied in developing countries for explaining and prescribing social-ecological transitions. Here, we assess the validity of five key assumptions of Ecological Modernization narratives as applied to the Argentine Chaco, a global deforestation hotspot. We reviewed existing literature and conducted straightforward analysis to disentangle relationships among key variables. Although agriculture intensified, there is no evidence that this intensification inhibited agricultural expansion. Rural depopulation took place between 2001 and 2010; however, deforestation rates did not decrease, and the quality of life of migrants did not increase compared to those that stayed in rural areas. Our review suggests that the consequences of agriculture intensification on biodiversity and the provision of multiple ecosystem services exceeds the area used. Therefore, available evidence does not support the assumed causal relationships of Ecological Modernization, and even contradicts most assumptions. We propose a series of analytical shifts to better capture the complexity of social-ecological transitions in modern commodity frontiers.