Aims
Wetlands are key ecosystems due to their economic, social and environmental contributions. Because of their highly productive habitats and their dependence on hydro‐meteorologic regimes, they ...are threatened worldwide by land use and climate change. In most wetlands, intensification of productive activities has been mostly accompanied by the implementation of a water management infrastructure, disrupting water and nutrient dynamics. Our aim was to analyze whether intensification of livestock raising erodes the structure and function of plant communities, as well as the quality and fertility of soils in wetlands.
Location
Non‐insular portion of the Lower Delta of the Paraná River, Argentina.
Methods
Plant communities were characterized on the basis of their floristic composition, structural and functional diversity. Soil samples were also collected to assess soil fertility, texture and quality. Generalized mixed linear models were used to contrast these attributes across livestock management practices characterized by differing water management infrastructure (polders and channelizations) and livestock type (bovine, bubaline).
Results
Remarkably fertile hydromorphic soils supported a structurally rich and functionally diverse species composition. Nevertheless, most dominant populations were terrestrial, perennial, invasive species, partially adapted to conditions of temporary flooding. Polderized livestock fields exhibited not only the lowest quality, least fertile, most compacted soils, but also lower species richness and diversity, as well as the lowest values in all non‐redundant components of functional diversity. Channelized livestock fields exhibited lower species richness and taxonomic diversity as well as reduced soil quality and fertility, yet an overall increase in most non‐redundant components of functional diversity.
Conclusions
Promoting the loss of native flora, water management infrastructure impairs the sustainability of anthropic activities and thwarts biodiversity conservation efforts. Traditional and sustainable practices that embrace the periodicity of the flood pulse are required to preserve the taxonomic and functional diversity of plant communities, as well as the quality and fertility of soils.
In the context of livestock raising intensification, fertile hydromorphic soils support structurally rich and functionally diverse plant communities. Water management infrastructures promote the disappearance and intensification of the flood pulse, disrupting plant species composition, as well as the quality and fertility of soils. A remarkable capacity of plant communities to preserve their structural and functional parameters was observed nonetheless.
Commodity agriculture continues to spread into tropical dry forests globally, eroding their social-ecological integrity. Understanding where deforestation frontiers expand, and which impacts this ...process triggers, is thus important for sustainability planning. We reconstructed past land-system change (1985–2015) and simulated alternative land-system futures (2015–2045) for the Gran Chaco, a 1.1 million km² global deforestation hotspot with high biological and cultural diversity. We co-developed nine plausible future land-system scenarios, consisting of three contrasting policy narratives (Agribusiness, Ecomodernism, and Integration) and three agricultural expansion rates (high, medium, and low). We assessed the social-ecological impacts of our scenarios by comparing them with current biodiversity, carbon density, and areas used by forest-dependent people. Our analyses revealed four major insights. First, intensified agriculture and mosaics of agriculture and remaining natural vegetation have replaced large swaths of woodland since 1985. Second, simulated land-system futures until 2045 revealed potential hotspots of natural vegetation loss (e.g. western and southern Argentinian Chaco, western Paraguayan Chaco), both due to the continued expansion of existing agricultural frontiers and the emergence of new ones. Third, the strongest social-ecological impacts were consistently connected to the Agribusiness scenarios, while impacts were lower for the Ecomodernism and Integration scenarios. Scenarios based on our Integration narrative led to lower social impacts, while Ecomodernism had lower ecological impacts. Fourth, comparing recent land change with our simulations showed that 10% of the Chaco is on a pathway consistent with our Agribusiness narrative, associated with adverse social-ecological impacts. Our results highlight that much is still at stake in the Chaco. Stricter land-use and conservation planning are urgently needed to avoid adverse social-ecological outcomes, and our results charting the option space of plausible land-system futures can support such planning.
Moisture content of live fuels (LFMC) is one of the main factors determining fuel flammability and, therefore, a key indicator of fire danger. In this study, we modeled the relationship between ...spectral indices derived from satellite imagery and field estimations of LFMC in the Chaco Serrano subregion; then, we analyzed the relationship between fire danger estimations based on LFMC calculations and fire activity. Empirical LFMC models fitted for grasslands, Chaco Serrano forests, and glossy privet forests may be considered very accurate R 2 > 0.80, whereas the model corresponding to shrublands still needs to be improved (R 2 = 0.57). Monthly maps of fire danger reflected the occurrence of fires consistently during years of both high and low fire activity. Most fires occurred mainly in areas with high or extreme fire danger, demonstrating a clear relationship between LFMC and fire activity in the Chaco Serrano subregion. Our LFMC models may be useful to assess the spatiotemporal distribution of fire danger in the Chaco Serrano subregion using remote sensing data. The associated fire danger maps represent a valuable tool for improving decision making processes to organize early warning and fire suppression activities.
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 (
= 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;
= 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.
Biological invasions are one of the most detrimental aspects of global change, and a main factor of ecosystem degradation and biodiversity loss. Housing growth can foster biological invasions, but ...the relationship of housing growth and invasions is not well understood. The objective of my dissertation was to analyze the relationship between housing and the distribution of exotic invasive plants in forested areas to inform management and to understand the ecological consequences of future housing growth. My results showed first, that in New England's counties, housing was equally or more strongly related to richness of invasive exotic plants than other human and environmental factors. Suburban areas in contact with areas dominated by native vegetation were particularly important. Second, In the Baraboo Hills, Wisconsin, richness of invasive exotic plants was higher closer to houses and in area surrounded by more houses, as was invasive plant species cover. At the landscape scale, the distribution of invasive exotic plants was as strongly related to rural housing as to forest fragmentation (distance to roads and distance to forest edges). Invasive plant species with a history of ornamental use were most strongly related to housing. Third, ecological legacies of past housing patterns affect present distributions of invasive exotic plants. In the Baraboo Hills, invasive exotic plants were more strongly associated with housing in 1938 (particularly plant species with the longest use as landscaping plants), than with housing in 2001. Finally, I examined the spread of the invasive tree glossy privet ( Ligustrum lucidum) in Argentina using Landsat satellite imagery. Glossy privet has expanded greatly between 1983 and 2001. The proportion of glossy privet decreased with distance from the urban area. In summary, my results show that housing should be considered as a primary factor when managing for invasive exotic plants and as a main focus of research to clarify the role of humans in fostering exotic plant invasions. Expected urban growth could result in more invasions of exotic plants, and present housing patterns will determine exotic plant invasions for decades.
•We assessed the role of soybean as underlying driver in the Chaco using panel regression.•Soybean expansion a proximate cause of deforestation in the Argentinian Chaco only.•Substantial time-delayed ...effects of soybean expansion in Argentina and Paraguay and deforestation in the Chaco.•Deforestation in the Chaco mainly driven by global soybean demand, but locally other proximate causes are important.
South America’s tropical dry forests and savannas are under increasing pressure from agricultural expansion. Cattle ranching and soybean production both drive these forest losses, but their relative importance remains unclear. Also unclear is how soybean expansion elsewhere affects deforestation via pushing cattle ranching to deforestation frontiers. To assess these questions, we focused on the Chaco, a 110 million ha ecoregion extending into Argentina, Bolivia, and Paraguay, with about 8 million ha of deforestation in 2000–2012. We used panel regressions at the district level to quantify the role of soybean expansion in driving these forest losses using a wide range of environmental and socio-economic control variables. Our models suggest that soybean production was a direct driver of deforestation in the Argentine Chaco only (0.08ha new soybean area per ha forest lost), whereas cattle ranching was significantly associated with deforestation in all three countries (0.02 additional cattle per hectare forest loss). However, our models also suggested Argentine soybean cultivation may indirectly be linked to deforestation in the Bolivian and Paraguayan Chaco. We furthermore found substantial time-delayed effects in the relationship of soybean expansion in Argentina and Paraguay (i.e., soybean expansion in one year resulted in deforestation several years later) and deforestation in the Chaco, further suggesting that possible displacement effects within and between Chaco countries may at least partly drive forest loss. Altogether, our study showed that deforestation in the Chaco appears to be mainly driven by the globally surging demand for soybean, although regionally other proximate drivers are sometimes important. Steering agricultural production in the Chaco and other tropical dry forests onto sustainable pathways will thus require policies that consider these scale effects and that account for the regional variation in deforestation drivers within and across countries.
Carbon emissions from land‐use changes in tropical dry forest systems are poorly understood, although they are likely globally significant. The South American Chaco has recently emerged as a hot spot ...of agricultural expansion and intensification, as cattle ranching and soybean cultivation expand into forests, and as soybean cultivation replaces grazing lands. Still, our knowledge of the rates and spatial patterns of these land‐use changes and how they affected carbon emissions remains partial. We used the Landsat satellite image archive to reconstruct land‐use change over the past 30 years and applied a carbon bookkeeping model to quantify how these changes affected carbon budgets. Between 1985 and 2013, more than 142 000 km2 of the Chaco's forests, equaling 20% of all forest, was replaced by croplands (38.9%) or grazing lands (61.1%). Of those grazing lands that existed in 1985, about 40% were subsequently converted to cropland. These land‐use changes resulted in substantial carbon emissions, totaling 824 Tg C between 1985 and 2013, and 46.2 Tg C for 2013 alone. The majority of these emissions came from forest‐to‐grazing‐land conversions (68%), but post‐deforestation land‐use change triggered an additional 52.6 Tg C. Although tropical dry forests are less carbon‐dense than moist tropical forests, carbon emissions from land‐use change in the Chaco were similar in magnitude to those from other major tropical deforestation frontiers. Our study thus highlights the urgent need for an improved monitoring of the often overlooked tropical dry forests and savannas, and more broadly speaking the value of the Landsat image archive for quantifying carbon fluxes from land change.
Theories of frontier expansion in the last four decades have been mostly shaped by studies of state-driven smallholder colonization. Modern-day agricultural frontiers, however, are increasingly ...driven by capitalized corporate agriculture operating with little direct government intervention. The expansion of contemporary frontiers has been explained by the existence of spatially heterogeneous "abnormal" rents, which can be caused by cheap land and labor, technological innovation, lack of regulations, and a variety of other incentives. Here, we argue that understanding the dynamics of these frontiers requires considering the differential ability of actors to capture such rents, which depends on their access to production factors and their information, preferences, and agency. We propose a new conceptual framework drawing on neoclassical economics and political economy, which we apply to the South American Gran Chaco, a hot spot of deforestation for soy and cattle production. We divide the region into a set of distinct frontiers based on satellite data, field interviews, and expert knowledge, to review the drivers and actors of agricultural expansion in these frontiers. We show that frontier expansion in the Chaco responded to the rents created by new agricultural technologies, infrastructure, and rising producer prices but that the frontier dynamics were strongly influenced by actors' abilities to capture or influence these rents. Our findings thus highlight that understanding contemporary commodity frontiers requires analyzing the novel ways by which the agency of particular groups of actors shapes land-use outcomes.
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