Uruguayan Savannas Pampa grasslands

Category: Grassland, Tundra, and Human Biomes.

• Geographic Location: South America.

Summary: One of the most diverse grassland ecosystems in the world, the Uruguayan Savannas Pampa Grasslands biome harbors a unique mix of native winter and summer plant species.

The landscape of the Uruguayan Savannas Pampa Grasslands biome is shaped by large areas of natural grasslands, mostly under grazing by cattle, interspersed with gallery forests and shrublands. The 135,136-square-mile (350,000-square-kilometer) biome encompasses parts of three countries: southern Brazil, a section of Argentina, and the whole of Uruguay. The climate is temperate within most of the biome and subtropical in the northern reaches, with less extreme conditions in comparison with areas of similar latitude because of the influence of the Atlantic Ocean.

Annual precipitation in Uruguay is roughly 40 inches (1000 millimeters) in the south but is heavier in the north. Temperature is greatly variable across the region, with means of 50–77 degrees F (10–25 degrees C) and occasional frosts. Summer temperatures are more uniform than winter ones, generally 68–90 degrees F (20–32 degrees C) in the north, 63–86 degrees F (17–30 degrees C) in most of the areas, and 59–81 degrees F (15–27 degrees C) along the moderating Atlantic coast.

The Uruguayan Savannas Pampa Grasslands biome cradles a rich biodiversity of plants and animals; it is among the most extensive grasslands on Earth. Grasslands serve as a backbone to food production and environmental stability wherever they exist worldwide, providing for meat, milk, wool, and leather production by range lands. They also contribute to soil formation and global temperature regulation through the sequestration of carbon dioxide, with their plant roots helping to control soil erosion, and their biomass providing vital genetic material for the species that consume them.

Flora and Fauna

The fertile plains here include a variety of grasses such as those in the Poaceae family, which dominate and determine most of the landscape. Other flora includes legumes (Fabaceae), sunflowers (Asteraceae), and sedges (Cyperaceae). Pampas grass (Cortaderia selloana) is an iconic component of this ecoregion, which includes some 25 species, large perennial grasses known variously as feather grass, needle grass, and spear grass; they are widespread. There is no complete account of grassland plant species for the entire biome, but up to 380 species of grass have been recorded in the whole region.

Although apparently uniform at a first glance, the Uruguayan Savannas Pampa Grasslands are extremely rich and diverse, with 30 or more herbaceous plant species often occurring in a single 11-square-foot (1-square-meter) plot. In addition to their overall variety, grassland ecosystems vary widely in space and time. In particular, species composition and abundance vary in space according to differences in soil, latitude, climate, and human land use.

These grasslands present a unique mix of winter and summer native species. The winter types apply the C₃ photosynthetic cycle, a productive and energy-efficient option to use in moderate-light and moist conditions . The summer types use the C₄ cycle. The C₃-C₄ ratio varies along a latitudinal gradient within the biome: C₄ species predominate in the northern areas, under subtropical climate, and become less abundant toward the south, whereas C₃ species follow an inverse pattern. The distinct phenological rhythm of C₃ and C₄ species adds to the variation of grassland vegetation over time.

Although forests in this ecoregion are mostly restricted to strips along watercourses, larger forest patches can be found in the southern Brazilian and Uruguayan highlands. Forests within the biome are comprised of Araucaria, a genus of evergreen coniferous tree; forests in the northern parts are seasonal deciduous; and parkland vegetation is restricted to the western boundaries of the grasslands.

The biome has about eighty bird species, many of which are endemic, or found only here. These include the cinereous harrier (Circus cinereus), buff-breasted sandpiper (Calidris subruficollis), yellow cardinal (Gubernatrix cristata), and saffron-cowled blackbird (Xanthopsar flavus). One species, the blue-gray glaucous macaw, was believed to have a 2018 population of under fifty and are categorized as critically endangered (or may be possibly extinct) in 2020s. There are more than seventy species of mammals, many of which are threatened with extinction as climate change, human-driven land-use changes, and invasive species encroachment accelerate. Among the flagship mammals are Pampas deer (Ozotoceros bezoarticus), puma (Puma concolor), maned wolf (Chrysocyon brachyurus), and giant anteater (Myrmecophaga tridactyla).

History and the Environment

Fossil records indicate that the Uruguayan Savannas Pampa Grasslands biome was populated by large grazing herbivores in the geological past, although the extent to which these animals influenced the modern ecosystem is under debate. The extinction of these herbivores coincided with an increase in the rate of fire disturbances in grasslands, which may have been related to hunting and land-management practices carried out by Indigenous people in past millennia. Widespread plant adaptations, such as underground storage organs and high resprouting ability after disturbance, indicate that the grasslands have a long history of co-evolution with dry climatic conditions, herbivory, and/or fire.

In the seventeenth century, European settlers introduced cattle to the region, and this influence on local economies continues in the 2020s. The most expressive and traditional economic activity in the biome is beef-cattle livestock farming, fostered by the natural fit of the ecosystem with this activity. Productivity in such systems is often low but may be increased threefold when simple management practices such as controlling stocking rates and forage offer are followed.

Natural pasture is the main livestock feed in this system, which is important for the conservation of the ecosystem. A 2020 study reported that in 2015 about 36 percent of the natural vegetation (mainly grasslands) was converted to croplands and exotic forest plantations, and by extrapolating the rate of conversion, by 2030, the value would be at 48 percent of overall loss of the original habitat, most of which would include grasslands. Also, livestock farming is culturally important because of its relationship with the gaucho, the typical South American cattle herder—part of a rich folklore and cultural legacy.

Scientific evidence supports the hypothesis that the grasslands here are natural, ancient ecosystems that once dominated even greater expanses of southern South America. However, there also is evidence that forests have been expanding over these grassland-dominated landscapes for roughly 5,000 years, as the climate has turned increasingly favorable to forest establishment. Grazing and fire seem to be disturbances that keep this process at bay, especially at the northern limits of the biome.

Large areas of these savannas are being transformed into plantations of introduced tree species such as pine, eucalyptus, or acacia, threatening the ecology of the region. The introduction of nonnative plants potentially threatens the grasslands by reducing acreage for grazing. Other threats include farmland encroachment, animal poaching, and illegal development.

Climate change poses additional challenges. Increased rainfall in the region has led to increases in pasture productivity by 5 to 10 percent in Argentina and Uruguay in the first decades of the twenty-first century, as well as higher yields of soybean, corn, wheat, and sunflowers. More lush pastures could have positive effects on livestock production. Although they may seem positive, these changes could push humans to clear more of the grasslands for conversion to cropland or tip the grazing use into overgrazing. In the mid-2020s, about 80 percent of Uruguay’s land was used for cattle ranching purposes, with Brazil’s land area being the least protected.

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