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AimThe intensification of livestock systems generates structural and functional changes in native grassland, which alter their capacity to respond to disturbances. Our objective was to evaluate the resilience to an extraordinary consecutive droughts event, across an intensification gradient of pastoral systems. Our prediction is that sites with more intensive management (less diverse) will have lower resilience (as resistance and/or recovery) to drought.Location: South-central region of Uruguay. MethodsWe evaluated the resilience (as resistance and recovery) to consecutive droughts, across an intensification gradient of pastoral systems. We analyzed the effect of diversity on resilience at two scales: 1. regional, where we compared the resilience of three systems with an increasing level of intensification that determine changes in diversity, 2. patch, we carried out a manipulative experiment with different grazing management systems (different level of defoliation, and fertilization). In both experiments the response variables, resistance and recovery, were calculated from the Normalized Difference Vegetation Index, a remotely sensed proxy of aerial net primary productivity. ResultsOur results showed that sown pastures (the less diverse) had significantly lower resistance, than native grassland and overseed grassland. Also, sown pastures showed the lowest recovery rate, although differences were only significant with overseed grassland. Grazing treatments at the plot level (manipulative experiment) did not show clear differences among treatments neither for resistance nor recovery. However, resistance of the individual plots showed a positive significant association with evenness and diversity of functional groups. ConclusionThis study showed that the different grazing managements studied were resilient, in terms of their ANPP, to a major drought disturbance event. Differences in resilience was expressed in resistance rather than recovery. These results support our prediction, both at the regional and plot scales, that the least rich and diverse situations showed the lowest resilience, at least in terms of resistance.

The Patagonian steppes and the Río de la Plata grasslands occupy a vast proportion of the plains, plateaus, and hills of southern South America, and are characterized by the almost absolute absence of trees. Prairies and steppes (grass and low shrubs) are the dominant physiognomic types, and forests are restricted to some riparian corridors. Savannas become important only in the ecotones of these regions, whereas meadows may be locally important under particular topographic or edaphic conditions. The Río de la Plata grasslands (RPG), one of the most important grassland regions in the world, extend between 28°S and 38°S latitude, covering about 700,000 km2 of eastern Argentina, Uruguay, and southern Brazil. The boundaries of these grasslands include the Atlantic coastline to the east, dry temperate forests to the south and west, and subtropical humid forests to the north. Woody vegetation within the region is restricted to small areas near water bodies, such as the gallery forests along the large Paraná and Uruguay rivers and their tributary streams. The Patagonian steppes occupy the southern tip of the continent from approximately 40°S, and are framed by the Andes to the west and the Atlantic coast to the east and south and cover more than 800,000 km2 of Chile and Argentina. Toward the west, the region displays a sharp ecotone with the subantarctic forests, whereas to the north it grades into a broad zone of Monte scrublands in central Argentina. The RPG and the Patagonian steppes are separated by a wide strip of woody vegetation, the Monte and Espinal phytogeographic units (see chapter 10; Cabrera and Willkins, 1973). In this chapter, we describe the heterogeneity and main characteristics of the dominant ecosystems of the Patagonian steppes and the RPG, focusing on environmental controls and human-induced changes. Although numerous criteria have been applied to describe the internal heterogeneity of both regions, we emphasize here the structural and functional attributes of vegetation as integrators of climate, physiography, and land use.

In this article we review the main characteristics of the Patagonian climate, the spatial and temporal patterns of the most important climatic variables, and the influence of climate on ecosystem processes. The winter distribution of precipitation determines an asynchrony between the wet and the growing season in Patagonia. The amount of water that can be transferred from the wet season to the growing season depends mainly on the physical characteristics of the soil. In the semiarid steppe of Chubut, drainage accounted for 10% of annual precipitation. Winter distribution of precipitation determines also an asynchronic dynamics of evaporation and transpiration fluxes. The ENSO phenomenon have a significant impact on regional precipitation. In central-west Patagonia, spring precipitation (September to November) was lower than normal during La Niña events and greater than normal during El Niño events. From December to February the opposite pattern can be observed: higher than normal precipitation during La Niña events and lower than normal precipitation during El Niño events. The impact of this phenomenon on the seasonal temperature was not as clear as for precipitation. We did not detect any temporal trends in annual precipitation for the period 1961-1996. The phenology of carbon gains is quite homogeneous in Patagonia. Most of the region showed a peak of production in November, when, simultaneously, water availability and temperature are high. Toward the west, production peaked later (December). Deciduous forests showed the peak in January and February.

One hundred years of grazing by domestic herbivores hampered the ecological sustainability of the Patagonian steppes. We propose three management-related factors of such ecosystem degradation: (1) overestimation of carrying capacity of the rangelands, (2) inadequate distribution of animals in very large, heterogeneous paddocks, and (3) year-long continuous grazing. We suggest that these three management factors interact with the highly selective grazing habit of sheep generating a pattern of grazing heterogeneity at three scales: landscape, community, and population. Grazing differs in intensity among areas of the same paddock, among plant species, and even among individuals of the same species. As a consequence, the most palatable species within a patch are almost continuously subjected to a very high frequency of defoliation in the most preferred areas, which increases the mortality of the most preferred individuals of these forage species. We review the available ecological knowledge and range management technologies that may contribute to revert degradation. A quick assessment of both the availability and spatial heterogeneity of forage resources is now possible with the aid of remote sensing. Range assessment will allow to estimate the carrying capacity of each paddock, and separate different vegetation units. From information on the phenology of the different vegetation units it is possible to decide the timing of grazing and/or resting periods of single paddocks. Rotational grazing methods allow for a recovery of the most preferred species and for a reduction of the heterogeneity of defoliation at the three mentioned levels. Research efforts are needed to develop warning systems, improve the productivity and use efficiency of meadows, and design and evaluate grazing methods for the most arid areas of the region.

Deforestation control is one of the major challenges worldwide. The aim of this study was to analyse deforestation under the Forest Law in the Argentine Dry Chaco ecoregion a decade after its enactment and to assess compliance with forest protection standards in this region. For this purpose, we overlapped the provincial land zoning maps with an annual plot level deforestation database and, for some provinces, with the rural cadastral cartography. Deforestation exceeding the values allowed by the Forest Law and the provincial zonings during this period totalized 722,782 ha (28% of the total deforested area in this period), of which 59,732 ha were deforested in high conservation value areas, 644,396 ha in medium conservation value areas and 18,654 ha in low conservation value areas. While Santiago del Estero was the province with the highest deforested area in medium conservation value areas, Córdoba was the province with the highest deforested area in high conservation value areas. Our results are an important step towards identifying discrepancies between the legal objectives and the observed results and represent an input to think about solutions to improve the environmental governance of the region. © 2021 Elsevier B.V.