The soil carbon erosion paradox reconciled

The acceleration of erosion, transport and burial of soil organic carbon (C) in response to agricultural expansion represents a significant perturbation of the terrestrial C cycle. Recent model advances now enable improved representation of the relationships between sedimentary processes and C cycling and this has led to substantially revised assessments of changes in land C as a result of land cover and climate change. However, surprisingly a consensus on both the direction and magnitude of the erosion-induced land-atmosphere C exchange is still lacking. Here, we show that the apparent soil C erosion paradox, i.e., whether agricultural erosion results in a C sink or source, can be reconciled when comprehensively considering the range of temporal (from seconds to millennia) and spatial scales (from soil microaggregates to the Land Ocean Aquatic Continuum (LOAC)) at which erosional effects on the C cycle operate. Based on the currently available data (74 studies), we developed a framework that describes erosion-induced C sink and source terms across scales. Based on this framework, we conclude that erosion is a source for atmospheric CO2 when considering only small temporal and spatial scales, while both sinks and sources appear when multi-scaled approaches are used. We emphasize the need for erosion control for the benefits it brings for the delivery of ecosystem services, particularly in low-input systems, but our analysis clearly demonstrates that cross-scale approaches are essential to accurately represent erosion effects on the global C cycle.

How Green Is Sugarcane Ethanol?

Biofuels offer one approach for reducing carbon emissions. However, the necessary agricultural expansion may endanger tropical forests. I use a dynamic model of land use to disentangle the roles of acreage and yields in the supply of sugarcane ethanol in Brazil. The model is estimated using remote sensing (satellite) information of sugarcane activities. Estimates imply that, at the margin, 92% of new ethanol comes from increases in area and only 8% from increases in yield. Direct deforestation accounts for 19% of area expansion at the margin in the long-run. I further assess carbon emissions and deforestation implications from ethanol policies.

Agricultural expansion and the ecological marginalization of forest-dependent people

Agricultural expansion into subtropical and tropical forests causes major environmental damage, but its wider social impacts often remain hidden. Forest-dependent smallholders are particularly strongly impacted, as they crucially rely on forest resources, are typically poor, and often lack institutional support. Our goal was to assess forest-smallholder dynamics in relation to expanding commodity agriculture. Using high-resolution satellite images across the entire South American Gran Chaco, a global deforestation hotspot, we digitize individual forest-smallholder homesteads (n = 23,954) and track their dynamics between 1985 and 2015. Using a Bayesian model, we estimate 28,125 homesteads in 1985 and show that forest smallholders occupy much larger forest areas (>45% of all Chaco forests) than commonly appreciated and increasingly come into conflict with expanding commodity agriculture (18% of homesteads disappeared; n = 5,053). Importantly, we demonstrate an increasing ecological marginalization of forest smallholders, including a substantial forest resource base loss in all Chaco countries and an increasing confinement to drier regions (Argentina and Bolivia) and less accessible regions (Bolivia). Our transferable and scalable methodology puts forest smallholders on the map and can help to uncover the land-use conflicts at play in many deforestation frontiers across the globe. Such knowledge is essential to inform policies aimed at sustainable land use and supply chains.

Drivers of Growth and Decline in Sahelian Livestock Sectors

Sahelian livestock systems, an indelible feature of its landscapes and significant contributor to its economies, are under significant pressures to change. Whereas high predicted demand increases for livestock products offer great prospects for income growth, expansion of croplands and settlements as well as climate change will likely negatively impact Sahelian producers. It is clear that for Sahel to respond to livestock market opportunities, changes in traditional trade and production practices are needed, in particular to improve reach of market signals to producers, reduce the high transaction costs, and improve productivity. The Sahelian markets have to date shown continued capacity to supply growing Sahelian and regional markets, and in fact the changes, are already evident. These include expansion and diversification of trader networks, changing procurement patterns, agricultural expansion, and increased use of supplemental feeds, among others. These changes are certain to further evolve.

Retrieving Intangibility to Avert Human-Driven Bio-Diversity Loss: The Case of Thathe Sacred Forest, Phiphidi Waterfalls and Lake Fundudzi, Northern South Africa

Human-driven biodiversity destruction are responsible for significant and sustained heritage losses in Africa. In Venda, northern South Africa, biodiversity losses are eroding the existence of sacred places. Such places define the essence of indigenous people’s identity and well-being. We highlight how developments in Venda such as mining and agricultural expansion since apartheid times have destroyed biodiversity in the broader landscape, undermining efforts to reduce hunger and poverty. Thathe forest, Lake Fundudzi and Phiphidi waterfalls are central to Venda mythology and legends, origins and identity and are key towards conserving current biodiversity and heritage losses.