Rangelands: Where Anthromes Meet Their Limits

Silvopastoral management for lowering trade-offs between beef production and carbon storage in tropical dry woodlands

Tropical dry woodlands and savannas harbour high levels of biodiversity and carbon, but are also important regions for agricultural production. This generates trade-offs between agriculture and the environment, as agricultural expansion and intensification typically involve the removal of natural woody vegetation. Cattle ranching is an expanding land use in many of these regions, but how different forms of ranching mediate the production/environment trade-off remains weakly understood. Here, we focus on the Argentine Chaco, to evaluate trade-offs between beef production and carbon storage in grazing systems with different levels of woody cover (n = 27). We measured beef productivity and carbon storage during 2018/19 and used a regression framework to quantify the trade-off between both, and to analyze which agroclimatic and management variables explain the observed trade-off. Our main finding was that silvopastures had the lowest trade-off between beef production and carbon storage, as management in these systems seeks to increase herbaceous forage by removing shrubs, while maintaining most of the bigger trees that contain most above-ground carbon. The most important variable explaining the beef production/carbon storage trade-off was pasture management, specifically the number of shrub encroachment control interventions, with a lower trade-off for higher numbers of interventions. Unfortunately, more interventions can also result in woody cover degradation over time, and shrub encroachment management must therefore be improved to become sustainable. Overall, our study highlights the strong environmental trade-offs associated with beef production in dry woodlands and savanna, but also the key role of good management practices in lowering this trade-off. Specifically, silvopastoral systems can increase beef production as much as converting woodlands to tree-less pastures, but silvopastures retain much more carbon in aboveground vegetation. Silvopastoral systems thus represent a promising land-use option to lower production/environment trade-offs in the Dry Chaco and likely many other tropical dry woodlands and savannas.

Indigenous lands in protected areas have high forest integrity across the tropics

Intact tropical forests have a high conservation value.¹ Although perceived as wild,² they have been under long-term human influence.³ As global area-based conservation targets increase, the ecological contributions of Indigenous peoples through their governance institutions and practices⁴ are gaining mainstream interest. Indigenous lands-covering a quarter of Earth's surface⁵ and overlapping with a third of intact forests⁶-often have reduced deforestation, degradation, and carbon emissions, compared with non-protected areas and protected areas.^7,8 A key question with implications for the design of more equitable and effective conservation policies is to understand the impacts of Indigenous lands on forest integrity and long-term use, as critical measures of ecosystem health included within the post-2020 Global Biodiversity Framework.⁹ Using the forest landscape integrity index¹⁰ and Anthromes¹¹ datasets, we find that high-integrity forests tend to be located within the overlap of protected areas and Indigenous lands (protected-Indigenous areas). After accounting for location biases through statistical matching and regression, protected-Indigenous areas had the highest protective effect on forest integrity and the lowest land-use intensity relative to Indigenous lands, protected areas, and non-protected controls pan-tropically. The protective effect of Indigenous lands on forest integrity was lower in Indigenous lands than in protected areas and non-protected areas in the Americas and Asia. The combined positive effects of state legislation and Indigenous presence in protected-Indigenous areas may contribute to maintaining tropical forest integrity. Understanding management and governance in protected-Indigenous areas can help states to appropriately support community-governed lands.

Contingency and Agency in the Mountain Landscapes of the Western Pyrenees: A Place-Based Approach to the Long Anthropocene

Regional- and biome-scale paleoecological analyses and archaeological syntheses in the mountain landscapes of the western Pyrenees suggest that the Long Anthropocene began with agropastoral land use at the onset of the Neolithic. Historical and geographic analyses emphasize the marginality of the western Pyrenees and the role of enforced social norms exacted by intense solidarities of kin and neighbors in agropastoral production. Both are satisfying and simple narratives, yet neither offers a realistic framework for understanding complex processes or the contingency and behavioral variability of human agents in transforming a landscape. The Long Anthropocene in the western Pyrenees was a spatially and temporally heterogeneous and asynchronous process, and the evidence frequently departs from conventional narratives about human landscape degradation in this agropastoral situation. A complementary place-based strategy that draws on geoarchaeological, biophysical, and socio-ecological factors is used to examine human causality and environmental resilience and demonstrate their relationship with the sustainability of mountain landscapes of the western Pyrenees over medium to long time intervals.

Anthropogenic Biomes: 10,000 BCE to 2015 CE

Human populations and their use of land have reshaped landscapes for thousands of years, creating the anthropogenic biomes (anthromes) that now cover most of the terrestrial biosphere. Here we introduce the first global reconstruction and mapping of anthromes and their changes across the 12,000-year interval from 10,000 BCE to 2015 CE; the Anthromes 12K dataset. Anthromes were mapped using gridded global estimates of human population density and land use from the History of the Global Environment database (HYDE version 3.2) by a classification procedure similar to that used for prior anthrome maps. Anthromes 12K maps generally agreed with prior anthrome maps for the same time periods, though significant differences were observed, including a substantial reduction in Rangelands anthromes in 2000 CE but with increases before that time. Differences between maps resulted largely from improvements in HYDE’s representation of land use, including pastures and rangelands, compared with the HYDE 3.1 input data used in prior anthromes maps. The larger extent of early land use in Anthromes 12K also agrees more closely with empirical assessments than prior anthrome maps; the result of an evidence-based paradigm shift in characterizing the history of Earth’s transformation through land use, from a mostly recent large-scale conversion of uninhabited wildlands, to a long-term trend of increasingly intensive transformation and use of already inhabited and used landscapes. The spatial history of anthropogenic changes depicted in Anthromes 12K remain to be validated, especially for earlier time periods. Nevertheless, Anthromes 12K is a major advance over all prior anthrome datasets and provides a new platform for assessing the long-term environmental consequences of human transformation of the terrestrial biosphere.

Exploring the economic, social and environmental prospects for commercial natural annual grasslands by performing a sensitivity analysis on a multidisciplinary integrated model

This paper presents an integrated modelling study aimed at exploring the possible effects of drivers of change in commercial natural annual grasslands. We consider drivers as factors that affect the rangeland but are not affected by it. Thus, the stocking rate is not treated as a driver, but as an endogenous factor ultimately determined by drivers. This approach, which call for integrated multidisciplinary studies, is rare in the rangeland literature. We try to alleviate this lack by presenting and utilizing a novel multidisciplinary integrated system-dynamics model (108 equations) which represents an area of privately owned extensive farms, its farmers (their numbers and decisions), herds or flocks, herbage production, soil erosion and the linked local markets. By means of a global sensitivity analysis of this model we evaluated the sensitivities of key endogenous factors to the same percentage variation in 70 factors, including economic and climate drivers. The analysis considered the behaviours of 288,000 variants of the modelled system, each under a different 300-year driver scenario. We found that the environmental component of the model was almost exclusively sensitive to biophysical factors, whereas the socio-economic component was almost exclusively sensitive to socio-economic factors, despite the model takes account of key feedbacks connecting both components. Our results suggest that cautiously-managed commercial natural grasslands could socially and economically cope with climate change, especially in a scenario of rising prices of animal products, and also that, even though stocking rates would increase due to an increase in the demand for livestock products, the main threat to the provision of ecosystem services in the studied system would be climate change.

Traversing the Wasteland: A Framework for Assessing Ecological Threats to Drylands

Drylands cover 41% of the Earth's terrestrial surface, play a critical role in global ecosystem function, and are home to over two billion people. Like other biomes, drylands face increasing pressure from global change, but many of these ecosystems are close to tipping points, which, if crossed, can lead to abrupt transitions and persistent degraded states. Their limited but variable precipitation, low soil fertility, and low productivity have given rise to a perception that drylands are wastelands, needing societal intervention to bring value to them. Negative perceptions of drylands synergistically combine with conflicting sociocultural values regarding what constitutes a threat to these ecosystems. In the present article, we propose a framework for assessing threats to dryland ecosystems and suggest we must also combat the negative perceptions of drylands in order to preserve the ecosystem services that they offer.

Spatial variation of human influences on grassland biomass on the Qinghai-Tibetan plateau

An improved understanding of increased human influence on ecosystems is needed for predicting ecosystem processes and sustainable ecosystem management. We studied spatial variation of human influence on grassland ecosystems at two scales across the Qinghai-Tibetan Plateau (QTP), where increased human activities may have led to ecosystem degradation. At the 10 km scale, we mapped human-influenced spatial patterns based on a hypothesis that spatial patterns of biomass that could not be attributed to environmental variables were likely correlated to human activities. In part this hypothesis could be supported via a positive correlation between biomass unexplained by environmental variables and livestock density. At the 500 m scale, using distance to settlements within a radius of 8 km as a proxy of human-influence intensity, we found both negatively human-influenced areas where biomass decreased closer to settlements (regions with higher livestock density) and positively human-influenced areas where biomass increased closer to settlements (regions with lower livestock density). These results suggest complex relationships between livestock grazing and biomass, varying between spatial scales and regions. Grazing may boost biomass production across the whole QTP at the 10 km scale. However, overgrazing may reduce it near settlements at the 500 m scale. Our approach of mapping and understanding human influence on ecosystems at different scales could guide pasture management to protect grassland in vulnerable regions on the QTP and beyond.

EcoAnthromes of Alberta: An example of disturbance-informed ecological regionalization using remote sensing

Humans influence ecosystems on magnitudes that often exceed that of natural forces such as climate and geology; however, frameworks rarely include anthropogenic disturbance when delineating unique ecological regions. A critical step toward understanding, managing and monitoring human-altered ecosystems is to incorporate disturbance into ecological regionalizations. Furthermore, quantitative regionalization approaches are desirable to provide cost-effective, repeatable and statistically sound stratification for environmental monitoring. We applied a two-stage multivariate clustering technique to identify 'EcoAnthromes' across a large area - the province of Alberta, Canada - at 30 m spatial resolution, and using primarily remotely sensed inputs. The EcoAnthrome clusters represent regions with unique ecological characteristics based on a combination of natural ecological potential (e.g., climatic and edaphic factors) and disturbance, both natural and anthropogenic. Compared to existing expert-derived Natural Subregions in Alberta, the model-based EcoAnthromes showed greater class separation and explained more variance for an assortment of variables related to land cover, disturbance and species intactness. The EcoAnthromes successfully separated important ecological regions that are defined by complex assemblages of topography, climate and disturbance, such as gravel-bed river valleys, boreal forests, grasslands, post-fire recovery areas and highly disturbed agricultural, industrial and urban landscapes. In addition to presenting a flexible method for EcoAnthrome regionalization, we group and describe the EcoAnthromes created for Alberta and discuss how they can complement expert-derived regionalizations to aid in environmental management efforts, such as species recovery planning and monitoring for threatened species.