Brazil contains semiarid and dry sub-humid areas, according to the UNCCD classification, both of which are considered Areas Susceptible to Desertification (ASD). As defined in Brazil, these ASD, which correspond closely to the Caatinga biome, occupy an area of 1.34 million km² and are home to 17% of Brazil’s population over 11 states, nine of which are in the Northeast (Maranhão, Piauí, Ceará, Rio Grande do Norte, Paraíba, Pernambuco, Alagoas, Sergipe and Bahia, from north to south) and two in the Southeast (Minas Gerais and Espírito Santo). The region has the world's greatest concentration of population in semiarid areas and is home to 85% of the country's poor. ASD are defined based on three criteria: annual precipitation under 800mm; an aridity index of 0.5 or lower (based on the balance between rainfall and evapotranspiration) and a drought risk index higher than 60%. The ASDs can be subdivided into the semiarid area (63% of their land area with 64% of their population) and the dry sub-humid area (37% of their land with 36% of their population). As a result of LD, ASDs had lost 41% of their natural vegetation by 2002 and an estimated additional 3% between 2002 and 2008. In many ASDs, soil losses are estimated at between 11 and 15 t/ha/year on degraded land without vegetation cover. This is leading to increasing nutrient and water losses over large land extensions. In spite of such natural and anthropogenic stress, Caatinga vegetation is remarkably resilient when water is available and it can sustain frequent harvests when properly managed.
This project is focused on the state of Sergipe, which represents on a workable scale the issues facing Brazil’s other ASDs. With an area of 21,918 km², Sergipe is Brazil's smallest state, although it is comparable in size to Israel and larger than El Salvador and 74 other countries of the world. The neighboring states, which share similar ecological and socioeconomic characteristics, are Alagoas to the north, Pernambuco to the west and Bahia to the west and south. The state is composed of three strips: 1) a semiarid northwestern strip, known locally as Alto Sertão Sergipano(herein abbreviated SAS), a region with high risk of desertification and acute land degradation problems; 2) a central strip (Agreste) running along the north to south axis of the State that contains sub-humid dry areas at risk of desertification processes and has moderate levels of land degradation and 3) a narrow coastal strip (zona da mata or Atlantic Forest) with no desertification risk. A total of 74.2% of Sergipe's land area, covering 16,269 km2 in 49 of the 75 state municipalities, is classified as being areas susceptible to desertification (ASD). This is in part due to climatic and edaphic conditions. Average temperatures in Sergipe, which is located along 10o and 11o South Latitude, range from 26o to 32º Celsius. Sergipe has erratic precipitation levels, as in much of the NE, typically below 700 mm per year and a dry season lasting seven to eight months, although there is considerable variation among years. The state has high and increasingly frequent drought incidence. Water deficits are significant and inland river courses are irregular and intermittent, with the exception of the São Francisco River, which extends for 2,814 km. between its source in Minas Gerais and its mouth between Sergipe and Alagoas. Sergipe is part of the lower Sao Francisco river basin. The entire basin is considered International Waters (IW). This major river provides water for energy generation and irrigation. In Sergipe, it supplies 70% of the water for the state capital, Aracaju. Of the six river basins present within the state, only the Sergipe river, which originates in the SAS area and flows east to the state capital, Aracaju, is entirely within the state boundaries. The soils in the SAS are litholic and regolithic neosoils, planosoils, luvisoils, red and yellow argisoils, which are suited for pasture and some agriculture with potential for irrigation.
Inland and in all of the ASD, the dominant vegetation type is the xerophytic Caatinga (meaning “white woods” in Tupi-Guarani), found only in Brazil, interspersed with isolated small patches of Cerrado (savanna woodland). There are three types of Caatinga: i) Shrub Caatinga, also known as steppe savanna, dominated by shrubs and a herbaceous strata of grasses with only a few individual trees under 4 m, being the most common Caatinga in Sergipe and in SAS; ii) Shrub-Arboreal Caatinga, with shrubs and trees not exceeding 6 m and tree crowns touching in most areas, allowing for full soil cover; and iii) Arboreal Caatinga comprised primarily of individual trees with an average height of 8 m forming a closed canopy, allowing complete soil cover, with few individual shrubs. The Cerrado in Sergipe is characterized by the relatively open savanna categories of campo limpo (natural grassland without scrub) and campo sujo (natural grassland with low scrub). As recently as 2003, 17% of the original vegetation remained, but a 2010 forest diagnosis indicates that this level had dropped to 13%. Large forest blocks are rare. The largest blocks are the Grota do Angico Natural Monument (MONA), a state protected area of 2,183 ha. created in 2007 along the São Francisco River in the municipalities of Canindé do São Francisco and Poço Redondo, and the Rio São Francisco Natural Monument, a federal protected area of 26,736 ha. created in 2009 farther north in Pernambuco, Alagoas and Sergipe, with about one third of its area in Canindé de São Francisco. A total of 90% of Sergipe’s forest land is concentrated in forest patches of sizes greater than 500 ha. Many of these are located in the southern part of the ASD and along the São Francisco River in the northwest part of the state, where new land reform settlements are being established on land that belonged to large estates considered idle or unproductive before being expropriated for official reasons of "social interest". The remaining 10% of Sergipe's forest land is made up of small patches that are predominantly smaller than 50 ha. Over the whole state, there are also countless small fragments, windbreaks, alleys, green fences, rows, thickets, coppices and isolated trees that, while not constituting forests, perform important environmental and socioeconomic functions.
Despite the broad classification of LD established in the National Action Plan (PAN), more detailed data on land degradation in the entire state is patchy. However, vegetation cover is a clear indicator, as its loss is one of the major anthropogenic drivers of land degradation. The above figures indicate the gravity of vegetation loss and it is not surprising that land degradation levels are also high. The highest levels of LD are found in the northwestern part of the state called Alto Sertão Sergipano (herein abbreviated SAS), a territory which covers 4,908 km² over seven municipalities, almost all of which is classified as semiarid. Table 2 summarizes the existing and potential land degradation levels for the six largest municipalities of the SAS, although there is considerable local variation within the largest municipalities (Canindé do São Francisco, Poço Redondo and Monte Alegre).
