Cerrado grasslands

• Category: Grassland, Tundra, and Human Biomes.
• Geographic Location: South America.
• Summary: The Cerrado grasslands, a large neotropical biome with tropical and subtropical grassland, savanna, and shrubland, is threatened by agricultural expansion, water projects, and other development.

The Cerrado biome is a diagonal strip in the center of South America that is roughly oriented from northeast to southwest, occupying large areas in central Brazil (nearly 25 percent of the country), eastern Bolivia, and northeastern Paraguay. The biome is mostly coincident with the Brazilian Precambrian shield, one of South America's largest and oldest geological areas. These rocks of this area, mainly granite and gneiss, have been affected by several erosion cycles since Paleozoic times, and now form a landscape of plateaus and undulating peneplains. Some have low hills, composed of less ancient geological materials such as sandstone, limestone, and shale.

Because the region has been mostly unaffected by subsequent marine transgressions, the soils have developed over long periods under warm, semi-humid, tropical-climate conditions, with strongly seasonal rainfall. There is a general predominance of old, weathered, and impoverished red and yellowish soils. The Cerrado biome is highly adapted to soils that are poor in nutrients, and to the strong seasonal rainfall, which can reach 31 to 67 inches (800 to 1,700 millimeters) annually. The rain occurs primarily in the warmer months, November to April, with an opposing significant water deficit that extends over four to five months. This prolonged dry season favors the high incidence of fires, both naturally caused and human-induced. Consequently, many researchers consider the Cerrado to be a pyrophytic or pyrogenic ecosystem that has at least partially evolved by adapting to periodic fire disturbance.

Biota

The vegetation of the Cerrado is comprised of several dynamic savanna physiognomies and structures, varying in their respective extension and landscape importance on the basis of the incidence and intensity of fires, as well as human management modalities. This physiognomies include almost pure grassland savanna (campo limpo); open scrub and shrubby savanna (campo sujo); arboreal savanna (campo cerrado); and patches of low, partly open woodland (cerradão). Both the herbaceous and woody Cerrado floristic components show a set of morphological and anatomical specializations that various scientists have interpreted as being adaptations to fire, the poverty and toxicity of soils, and seasonal drought. Among these adaptations, the most significant is the low-lying, contorted trees with thick, corky, fire-resistant barks; the frequent sclerophyllous leaves with thick cuticles and or silicified tissues; and the presence of several swollen woody underground vegetal structures called xylopodia.

Animals of the biome include the maned wolf (Chrysocyon brachyurus), giant anteater (Myrmecophaga tridactyla), jaguar (Panthera onca), marsh deer (Blastocerus dichotomus), and the pampas cat (Oncefelis colocolo). Among the bird species are the rhea (Rhea americana); red-legged seriema (Cariama cristata); and the Spix's macaw (Cyanopsitta spixii), which is critically endangered due to habitat loss and capture for the pet trade. Additionally, over 10,000 plant species are found in the region.

Environmental Threats

Fire and livestock pressure on vegetation are very important factors determining the density and frequency of the Cerrado woody component. Overgrazing and excessive frequency or intensity of the fire regime both favor the progressive reduction or disappearance of woody plants and, conversely, grass predominance, in transforming the savanna woodlands and arboreal savanna (cerradão, campo cerrado) to savanna grasslands and thickets (campo limpo, camposujo).

According to several researchers, the natural potential vegetation of the Cerrado is the woodland and arboreal savanna physiognomies. The grasslands and thicket–grasslands are successional degraded phases; they can evolve through ecological succession to woody savanna if the excessive fire or livestock pressure ceases or diminishes. These ideas are consistent with field observations that show a recovery of woodland and arboreal savanna in the interior of existing Cerrado protected areas in Brazil, as well as the general dominance of woody savanna aspects in the better-preserved Cerrado areas of Bolivia and Paraguay.

Effects of Human Activity

Most of the Cerrado biome is not suitable for agriculture because of strong soil and climatic constraints. Therefore, the main natural land potential use is cattle ranching on natural pastures and browsing in the woodland savanna, where fire is used annually to encourage the growth of tender grass after burning. Extensive range management has been the dominant economic activity since the 17th century when cattle were introduced by Portuguese and Spanish settlers. In Bolivia and Paraguay, the traditional use of the Cerrado has continued, leading to a predominance of semi-natural landscapes with still-remarkable levels of ecosystem conservation. Today, both countries have the best naturally preserved areas of the Cerrado biome.

In Brazil, by contrast, different social characteristics and greater economic capacity to transform the environment have resulted in a dramatic conversion of much of the Cerrado to large areas of mechanized agriculture. With the extensive addition of lime and fertilizer after deforestation, the Brazilian Cerrado has largely been replaced by cultivated soybeans, cotton, rice, and oil palms, among other crops. Experts note that mechanized agricultural expansion has put the area under immediate threat, with up to 2.5 million acres (1 million hectares) cleared each year.

Climate change has also contributed to the degradation of the region. Changes in ground temperature and rainfall have affected its biodiversity. Extreme weather is also a threat. However, experts contend that despite the damage, it is possible to save the Cerrado. Enough cleared land exists to meet the expected global food demands without clearing another acre. Sustainable agriculture is key to the region's rehabilitation.

Bibliography

De Siqueira, Martinez Ferreira and Andrew Townsend Peterson. “Consequences of Global Climate Change for Geographic Distributions of Cerrado Tree Species.” Biota Neotropica 3, no. 2 (2003).

Killeen, T. J. A. and T. S. Schulenberg, eds. A Biological Assessment of the Parque Nacional Noel Kempff Mercado, Santa Cruz, Bolivia. Washington, DC: Conservation International, 1998.

Navarro, Gonzalo. Clasificación de la Vegetación de Bolivia. Santa Cruz de la Sierra, Bolivia: Editorial Centro de Ecología Simón I. Patiño, 2011.

Oliveira-Filho, Ary T. and James A. Ratter. The Cerrados of Brazil: Ecology and Natural History of a Neotropical Savanna. New York: Columbia University Press, 2002.

Wenzel, Fernanda. "Cerrado Desertification: Savanna Could Collapse within 30 Years, Says Study." Mongabay, 28 Jul. 2021, news.mongabay.com/2021/07/cerrado-desertification-savanna-could-collapse-within-30-years-says-study/#:~:text=Cerrado%20desertification%3A%20Savanna%20could%20collapse%20within%2030%20years%2C%20says%20study,-by%20Fernanda%20Wenzel&text=Deforestation%20is%20amplifying%20climate%20change,temperatures%20between%201961%20and%202019. Accessed 7 Nov. 2024.