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Fragile land

Analyses of satellite images indicates a loss of 266,000 km2 of vegetation in the Cerrado and 90,000 km2 in the Caatinga, increasing the risk of water shortages and desertification

Burnoff in the Cerrado in 2006, in Emas National Park, Goiás State

FÁBIO COLOMBINIBurnoff in the Cerrado in 2006, in Emas National Park, Goiás StateFÁBIO COLOMBINI

Catolé do Rocha, a town of some 30,000 inhabitants located in the sertão scrublands of Brazil’s Paraíba State, is becoming increasingly hot and dry, and the area’s natural vegetation is disappearing. According to a study conducted by researchers from universities in the states of Paraíba and Rio Grande do Norte, in an eight-year period from 2005 to 2013, the land area covered by sparse Caatinga scrub vegetation shrank by 48%, and dense Caatinga shrank by 13.5%, while the land area devoted to agriculture increased sharply by 823%, from 2,450 to 22,640 hectares. The authors of the survey concluded that “the local vegetation has been indiscriminately eliminated,” and there has been “exorbitant growth” of areas occupied mainly by extensive cattle-raising.

Through the cumulative effect of many such situations, between 1990 and 2010 the Caatinga lost 9 million hectares—or 90,000 square kilometers (km2), nearly the size of Portugal—of native vegetation, as a result of deforestation, expanded farming and cattle-raising, and the use of wood from native tree species as an energy source (firewood) in homes and small-scale industry, according to a more comprehensive survey published in March 2015 in the journal Applied Geography. The study shows that the rate at which natural vegetation in the Caatinga was cleared over the 20-year period increased from 0.19% per year in 1990 to 0.44% a decade later, while surveys conducted by the Ministry of the Environment indicate a decline in the deforestation rate in that ecosystem. According to the authors of the paper, the discrepancy arises from the definition of “natural landscape”—they chose not to include the areas covered exclusively by grasses, which the federal government did include—and from a difference in temporal scale, which was two decades in one case and almost a decade in the other.

The elimination of native vegetation—which is even more harmful when fire is used, as this destroys the organic matter in the soil—leaves the earth bare and more vulnerable to absorption of solar radiation. The lack of cover raises the local temperature, accelerates water evaporation and lowers resistance to wind- and rain-driven erosion, which in turn carries away organic matter and reduces the fertility of already-poor soils as well as their water retention capacity. In addition, the experts caution, erosion caused by rain—which is rare but usually torrential—promotes silting of rivers, increases the risk of flooding, and exposes rocks previously covered by earth, thus impeding revegetation and rendering it difficult to use the land for agriculture. In Catolé do Rocha, the exposed land area with rocky outcrops has increased by 27%, from 578 to 734 hectares, over a span of eight years.

Burnoff of Cerrado vegetation and buriti palms in Boa Vista, Roraima State, in 2014

FÁBIO COLOMBINIBurnoff of Cerrado vegetation and buriti palms in Boa Vista, Roraima State, in 2014FÁBIO COLOMBINI

In the Caatinga scrubland, desertification poses another escalating threat. “The factor that is most instrumental in triggering the process of desertification is misuse of land, along with deforestation and often the use of fire, aggravated by climate conditions,” says Iêdo Bezerra Sá, a researcher with Embrapa Semi-Arid. Sá and his team examined the area around Cabrobó, in the scrubland of Pernambuco State, a desertification hotspot in the Brazilian Northeast that lies 400 km southwest of Catolé do Rocha. The soils there are sandy, permeable and unable to retain rainwater. The surveys conducted by Sá’s team indicated that the size of the area of severe desertification, associated with farming and cattle-raising, was 100,000 hectares (1,000 km2); and the area with pronounced desertification, on land occupied by arboreal Caatinga, came to 519,000 hectares (5,000 km2).

Sá is currently completing a survey which indicates that 9 of the 12 regions in Pernambuco—or 122 of the state’s 185 municipalities—mainly in the sertão scrublands, are at high risk of desertification. One of his recent studies indicated that nearly the entire São Francisco scrublands development area, known for irrigated fruit production, is at risk of becoming a barren, sandy plain (75% of the area is at moderate risk and 23% is at severe risk). There, he explained, water consumption for crop irrigation exceeds the capacity of the rivers, which are discharging less and less water, thereby endangering the entire area they serve. “The Caatinga is very fragile,” he says. “Sometimes, it’s best not to meddle.”

Experts have ascertained that 94% of the Brazilian Northeast, as well as northern Minas Gerais State and Espírito Santo State, display a moderate to high susceptibility to desertification, and they have identified the areas with the greatest potential for becoming barren, sandy plains by the year 2040. In that survey, the most susceptible areas expanded by nearly 5%–equivalent to 83 km2—from 2000 to 2010. “That was the first study in Brazil to produce an assessment based on an integrated analysis of the principal indicators of degradation and desertification,” says Rita Vieira, a researcher at the National Institute for Space Research (INPE) and principal author of the paper, published in the journal Solid Earth. Vieira says that the findings have been presented to the National Commission to Combat Desertification, which guides the implementation of international commitments undertaken by Brazil.

“Reducing the risk of desertification is a slow process. The first step is to change how the land is used and stop clearing timber,” says Carlos Magno, one of the coordinators of Centro Sabiá, a non-governmental organization based in Recife, in the state of Pernambuco. The center is using funding from the federal government to work with 200 families of small rural landowners in the agreste (sub-humid) and sertão (dry) scrublands of Pernambuco to recover 100 hectares of area susceptible to desertification. To do so, they are using agroforestry systems, in which a variety of plants are grown amidst Caatinga vegetation. These plants include corn, beans, squash, potatoes, forage plants, and fruits such as Brazil plum and hog-plum.

“We are rebuilding the idea that the Caatinga is a forest and needs to be preserved,” Magno says.

Xique-xique cactus in rocky soil of the Caatinga, in Caicó, Rio Grande do Norte State: fragile environment

FÁBIO COLOMBINIXique-xique cactus in rocky soil of the Caatinga, in Caicó, Rio Grande do Norte State: fragile environment FÁBIO COLOMBINI

On April 16, 2015, he left his office in the city of Caruaru and traveled 30 km to the town of Bezerros to visit Maria Idalvonete Julião da Silva, who owns three hectares of land and is taking part in the project. Motivated by the prospect of increasing her food production even in the driest of times, da Silva divided off one hectare and planted forage palms and lead trees for cattle fodder, as well as pigeon peas, papayas and pineapples. “In addition to their usefulness for animals and people,” Magno reasons, “crops promote soil conservation. When we get rain, it stays in the root-filled soil instead of washing away.” In a survey of 15 families who adopted this strategy more than 10 years ago, he found that “after major droughts and rains, agroforestry systems return to food production more quickly than do conventional agricultural systems, which implies that there is overexploitation of the soil in the Caatinga.”

In the paper published in Applied Geography, the team coordinated by René Beuchle of the Joint Research Centre of the European Commission in Italy also examined another extensive Brazilian ecosystem, the Cerrado savannah, which has lost even more vegetation than the Caatinga. In a span of 20 years, the Cerrado has lost 26 million hectares, or 260,000 km2, equal to twice the land area of England. There too, the loss was caused by an expansion of farming and cattle raising. Another finding indicated a decrease in the rate of clearing of natural vegetation in the Cerrado (from 0.79% per year between 1990 and 2000 to 0.44% per year in the following decade), this time agreeing with the government’s findings on the reversal of deforestation.

To see what was happening in the Caatinga and the Cerrado, the team led by Beuchle analyzed 974 Landsat satellite images with a resolution of 30 meters. The images recorded the changes in plant cover of the soil in 1990, 2000, 2005 and 2010 in 243 sample areas, each measuring 10 x 10 km. The two ecosystems encompass 35% of the Brazilian territory and are among the Earth’s most threatened natural environments owing to the conversion of native forest areas to agricultural use. Today the native vegetation of the Caatinga occupies 63% of its original area, and the present-day Cerrado occupies 47%, according to the study. Surveys conducted by the federal government judge the remaining area of plant cover to be slightly smaller in both cases. There is consensus, however, that the area of native vegetation preserved in conservation units is very small, occupying 7.5% of the Caatinga and 8% of the Cerrado.

A sign of the expansion of cattle-raising in Currais Novos, Rio Grande do Norte State

Fábio ColombiniA sign of the expansion of cattle-raising in Currais Novos, Rio Grande do Norte StateFábio Colombini

The transformations in these ecosystems have not been chronicled as extensively as those in other Brazilian biomes, such as the Atlantic Forest and Amazonia, in part because they are not as easy to detect. In the satellite images taken during the dry season—and most of the images used are from this period because of the absence of rain clouds—“it is hard to separate the leafless trees of the Cerrado and the Caatinga from other land covers, including agricultural areas,” Beuchle says. Conversely, the images of the Atlantic Forest and Amazonia display a clear-cut contrast between the tall, dense forest and the lower, deforested areas.

Moreover, unlike the Atlantic Forest and Amazonia, the Caatinga and the Cerrado have not been recognized as natural heritage areas. The Ministry of the Environment offers this comment on its website: “We must recognize that the Caatinga still lacks regulatory frameworks, actions and investment in its conservation and sustainable use.” According to the Ministry, one essential step in that direction would be approval of the proposed constitutional amendment to turn the Caatinga and the Cerrado into national heritage areas, which could make it easier to implement measures aimed at preserving these environments.

Edson Sano, a researcher at Embrapa Cerrados who worked with Beuchle on the analysis, found that the reduction in native plant areas, mainly in the Cerrado, coincides with the agricultural expansion of the late 1990s, “when land in the Central-West region was still cheap and production in the South and Southeast was already saturated.” Sano says that, beginning in the year 2000, however, the expansion slowed due to the higher cost of land, greater oversight (ranchers must now obtain a permit from federal or state agencies to cut down native vegetation, under penalty of losing the right to use the area) and productivity gains afforded by new cultivation technologies. “The trend now is towards reduction,” he says.

In the state of São Paulo, according to the most recent mapping survey in 2010, the Cerrado occupies 847,400 hectares—the equivalent of 8.5% of the original area of 9.9 million hectares, and only 25,900 hectares are protected by some kind of conservation unit. Forests of this type of vegetation can still be seen in Ribeirão Preto, Franca, São José do Rio Preto, Bauru, Sorocaba, Campinas and other regions, surrounded by sugarcane plantations (see Pesquisa FAPESP Issue No. 170). “In order to reach the recovery targets stated in international agreements, which propose the recovery of 17% of the original land area of each biome, we would have to plant nearly 800,000 hectares of Cerrado vegetation in São Paulo,” notes Marco Aurélio Nalon, a researcher at the Forestry Institute and one of the coordinators of the São Paulo State Forest Inventory of Native Vegetation.

With numbers and maps at hand, Nalon met with other experts from state environmental bodies for the purpose of restoring the lost forests to the greatest extent possible. It is not just São Paulo that is mobilizing. In January 2015, the Ministry of the Environment presented for public debate the preliminary version of the National Plan for Recovery of Native Vegetation, based on the Native Vegetation Protection Act of 2012. The Plan is designed to encourage the planting of native species, restoration of degraded areas, and agricultural practices that promote recovery of at least 12.5 million hectares of native vegetation over the next 20 years by planting or restoring degraded areas.

There are existing agricultural techniques that prevent soil depletion and reduce the need for other land for planting or pastures. Sano highlights two of them. The first is crop rotation, in which part of the grazing area is occupied by an agricultural crop that in the following years will occupy other parts of the property, in an alternating pattern. The second technique is the planting of commercial trees in pastures, which offer shade for the cattle and can later be sold. “Nothing prevents a farm from having an integrated mix of crops, livestock raising and forest cover,” he says.

In accordance with the goal stated in the federal government’s plan, the native vegetation area to be recovered comes to more than half of the 21 million hectares that represent Brazil’s national deficit of native vegetation, measured by the sum of the native forest areas that rural landowners must maintain by law on their land or near rivers and streams. “The recovery of native vegetation is very important, particularly in areas around headwaters,” Sano points out. “If we don’t preserve the headwaters, in a few years we won’t have any more water, even for drinking.”

Scientific articles
OLIVEIRA, R. A. N. de et al. Dinâmica do processo de desmatamento de caatinga no município de Catolé do Rocha-PB. Agropecuária Científica no Semiárido. V. 10, No. 4, p. 1-4. 2014.
BEUCHLE, R. et al. Land cover changes in the Brazilian Cerrado and Caatinga biomes from 1990 to 2010 based on a systematic remote sensing sampling approach. Applied Geography. V. 58, p.116-27. 2015.
VIEIRA, R. M. S. P. et al. Identifying areas susceptible to desertification in the Brazilian Northeast. Solid Earth. V. 6, p. 347-60. 2015.