To set the Scene

Ana Maria Giulietti, Raymond Mervin Harley,
Luciano Paganucci de Queiroz &
Alessandro Rapini

The Brazilian semi-arid zone is located almost exclusively in the Northeast of the country. This is one of the five geopolitical regions into which the country is divided, and which includes nine States. Only eight of these, at least in part, fall within the semi-arid zone, together with the northern sector of Minas Gerais State (Southeast Region) which borders its southern boundary. These eight States are Piauí, Ceará, Rio Grande do Norte, Paraíba, Pernambuco, Alagoas, Sergipe e Bahia. Only Maranhão State, bordering the Northern Region, which includes the Amazon basin, falls outside the Semi-arid zone. This large expanse of drylands, which stretches between 3–17° S and 35–45° W and covers almost 8% of the territory of Brazil, occupies an area of about 900.000 km²: that is larger than Texas or the entire Iberian Peninsula , including Spain and Portugal.

The climate of Northeast Brazil is one of the most complex systems in the world. This is due not only to the size of the huge land mass involved, and its diverse physiography, but also to the conjunction of two major weather systems, provided by the NE and SE trade winds, which create an enormous diversity and instability in rainfall patterns.

The precipitation within the region varies from being extremely wet, with an annual rainfall of up to around 2,000 mm along the coast, to only 300–500 mm in the semi-arid zone, where the rainfall is usually restricted to a few months during the year. It is indeed this factor of water availability, which is the controlling influence over the vegetation and fauna, as well as, to a great extent, human exploitation of natural resources, throughout the region.

Although the region is dissected by many rivers, both large and small, distributed through the river basins of the Rio São Francisco, the Rio Parnaíba, and the smaller systems which feed the NE and E Atlantic coasts, only the larger of these normally remain flowing throughout the year. In the major part of the semi-arid zone, as soon as the drought months get under way, the smaller rivers become ever more sluggish, eventually drying up completely. The Rio São Francisco, the largest in the region and one of the great rivers of Brazil, has its source in the Serra da Canastra, in Minas Gerais, flowing north and then east for about 2,700 km (almost 1,700 miles). It crosses a large part of Minas Gerais before entering Bahia, which contains 48.2% of its river basin, bordering Pernambuco to its north (10% of its basin) then finally flowing into the Atlantic Ocean further north between the States of Sergipe (1.1%) and Alagoas (2.3%). The second largest river in NE Brazil, the Rio Parnaíba, with an extent of 1,400 km (870 miles) has its basin almost entirely within the State of Piauí (90%), with 10% in the neighbouring State of Ceará. The hydrography of this region is of special interest, owing to the aquiferous rocks, which store large underground reserves of water, of the utmost economic potential for the area. Further east, the hydrographic region ‘Nordeste Oriental’ includes much of the northern part of the region with five of the State Capitals ranged along the eastern seaboard, and a great part of the semi-arid interior. Here, a number of smaller rivers shed their waters into the Atlantic . The principal States which are included in this region are: Ceará (46%) mainly with the Rio Jaguaribe, Paraíba (20%) and Pernambuco (10%). In the hydrographic region ‘Atlântico Leste’, further south, the rivers which flow eastwards into the Atlantic , mostly rise in the mountain ranges of the interior of Bahia and Minas Gerais: the Espinhaço Range . The Rio Jequitinhonha, flows mainly through Minas Gerais and is more or less at the southern limit of the semi-arid zone, its water-catchment area occupying 26.2 % of the region. Another 66.8%, however, is occupied by the rivers that have their source in or near the Chapada Diamantina of Bahia: rivers such as the Jacuípe, Paraguassu, Contas e Pardo.

This set of contrasting physical and climatic factors have combined to provide the astonishing diversity of vegetation types that characterize the semi-arid region and appear as a mosaic, reflecting the local conditions which are encountered. If we make a journey from the Atlantic coast westwards towards the Rio São Francisco; a transect through the interior, we can readily observe the changes that take place. We can note a gradual increase in altitude, which stabilizes at around 500 m, and this is paralleled by a reduction in rainfall, dropping from 2000–1000 mm per annum and leveling out at between 500–700 mm, associated with a very irregular distribution during the course of the year, with several (seven to nine ) months of drought.

This gradual change of rainfall and altitude, as one moves inland, can be modified, however, by local orographic changes, such as those caused by the presence of hills or mountains, providing a range of local conditions such as cooler temperatures with altitude, increased rainfall on slopes with an easterly aspect and dryer conditions in the rain-shadow of the hills. Such situations can be observed on the Borborema Plateau and in other mountain areas in the Semi-arid, especially in the Chapada Diamantina, where striking changes occur, as the altitude rises from 1000–2000 m, and annual rainfall can reach up to 1,500 mm.

These changes, as one moves westwards are also associated with changes in the landscape. From the coast to about 100 to 200 km inland, the vegetation is (or in many areas was, until recently) dominated by Atlantic Forest, with its lush, evergreen canopy of leaves. Further inland, as rainfall decreases, the rain forest gives way to a forest in which the canopy is semideciduous, with some species losing their leaves during the dry season. Then, with increasingly dry conditions, this in turn is replaced by a deciduous forest, in which, during the dry season the bare branches, devoid of leaves, are bleached by the full intensity of the sun. These last two forest types can be used to delimit the semi-arid region and together, constitute the Caatinga Biome. The predominant vegetation type in this region is composed of several forms of caatinga, from which the biome gets its name. The word is derived from the Tupi dialect: “caa” meaning forest and “tinga” meaning white. The structure of these forests can vary considerably from forests composed of often spiny trees, 6 to 10 m tall, deciduous to semideciduous, and often with a ground-layer of small deciduous shrubs and annual herbs, with a predominance of Leguminosae, to deciduous woodland of lower stature, with a high proportion of shrubs and subshrubs and characterized by the presence of many cacti, bromeliads and Euphorbiaceae. With the coming of the first rains, there is a miraculous transformation from bare, bleached branches and the dusty, brown, scorched and lifeless earth, which characterizes the dry season. Almost suddenly, there is an exuberance of green foliage clothing the trees, the ground is moist and hazy green with annual herbs, or with small pools of water filled with myriad life-forms, and the sounds of insects fill the air. Soon, the green is accompanied by a tapestry of colours as the caatinga trees and shrubs burst into flower. If we consider only the flowering plants of the caatingas of the Semi-arid, we now know that there are more than 5,000 species present, of which over 300 species and 23 genera are found to be uniquely growing there . However, as we ascend into the mountain zone, we begin to notice a gradual change in humidity which, associated with changes in the type of soils, produces enclaves of a very different type of vegetation. At altitudes between 800 and 1,000 m, especially in the northern part of the Semi-arid, Altitudinal Evergreen Forest, locally known as Brejo forest and which can provide protection for the springs of water, from which some of the important caatinga rivers have their source. Many of these brejos gave rise to human settlements, some of which are now large towns, such as Juazeiro do Norte and Crato in Ceará, Campina Grande in Paraíba and Garanhuns and Pesqueira in Pernambuco. In the southern part of the Semi-arid, this gradient can be observed principally in areas dominated by the Chapada Diamantina massif. Here the Caatinga can be seen gradually giving way to other plant formations, such as Cerrado, Evergreen Altitudinal, or Montane, Forests, Cloud Forests and Campos Rupestres, these last two being restricted to altitudes in excess of 1000 m and extending upwards to 2000 m. The Cerrados of the region, in spite of generally being less vigorous than those of Central Brazil and of western Bahia, display a range of species exclusive to the region, as well as others which are typical of the cerrados throughout Brazil. The Montane forests are usually composed of trees between 10 and 15 m high, often evergreen, with an species-rich understorey and, especially at higher altitudes a very diverse epiphytic flora which includes a large number of orchids. In general, the northern montane forests display greater floristic affinities with the Atlantic Forests of similar latitudes, along the coast of NE Brazil, while the southern montane forests, as might be expected, considering their occurrence at generally higher altitudes, show most floristic affinity with the Atlantic Forests of SE Brazil, where the climate is somewhat more temperate. Such genera as Drimys (Winteraceae), Weimannia (Cunoniaceae) and Podocarpus (Podocarpaceae) are common to these regions. The Campos Rupestres represent a specialized form of savannah vegetation whose physiognomy has been likened to that of the Fynbos of the Cape Region of South Africa. Its various components include herbs, evergreen shrubs and subshrubs, characterized by families such as Velloziaceae (canela-de-ema) and Eriocaulaceae (sempre-viva) and numerous epilithic species of Orchidaceae and Bromeliaceae. The formation is mainly restricted to the Espinhaço Range , which extends from Minas Gerais State to Bahia (Chapada Diamantina) and is renowned for its rich biodiversity associated with a very high degree of endemism. As mentioned above, the Espinhaço Range, where many rivers have their source, plays a vital role in furnishing water to the semi-arid zone.

Caatinga covers about 735,000 km². It is the most degraded vegetation type in the Semi-arid, and has less than 1% of it protected in permanent reserves. More recently, Brazilian government put forward some initiatives in order to better preserve its biodiversity. Areas of extreme biological interest were selected overlapping information of different groups of organisms and ecoregions were proposed for the biome combining biotic and abiotic information . The Caatinga Biome was divided in eight proposed Natural Ecoregions: Campo Maior Complex (Piauí and Maranhão), Ibiapaba Complex (basically comprising Piauí and Ceará); Northern Sertaneja Depression (basically comprising Rio Grande do Norte, Paraíba and Pernambuco); Borborema Plateau (basically comprising Paraíba and Pernambuco); Raso da Catarina, Southern Sertaneja Depression, Chapada Diamantina Complex and Dunes of the Rio São Francisco, particularly in Bahia. Associated with these ecoregions, 57 areas were delimited within the Caatinga Biome, which considered to be of Exceptional Importance for conservation, 27 of which were designated as of Extreme Importance (see map, Chapter 2).

Unlike many other Semi-arid of the world, that in Brazil is densely populated, with over 20 million inhabitants, representing more than 10% of the total population of the country. Life expectancy and per capita income in this region are the lowest in Brazil, while the illiteracy rate is the highest. Because of these low levels of human development, the traditional ‘Sertanejo’ ― or inhabitant of the Semi-arid ― is considered an ‘iron man’. In order to survive such hard conditions, he has developed a peculiar socio-cultural structure and has a close relation with his environment, and a good knowledge of the uses of natural resources available in the region. Characteristic features of the Sertanejo include the robust leather riding outfit which protects him and his horse from the spiny vegetation and from the heat and the burning rays of the sun; the ‘forró’, their typical dance, always played with the accordion, the triangle and the ‘zabumba’; the ‘pau-de-arara’, a truck adapted for carrying many people, which has been the main means of transportation in the region.

Giulietti, A.M. et al. 2002. Espécies endêmicas da caatinga. In E.V.C.B. Sampaio et al. (eds.) Vegetação & Flora da Caatinga. Associação Plantas do Nordeste, CNIP, Recife, pp. 103-108.

da Silva, J.M.C. et al. (orgs.) 2004. Biodiversidade da Caatinga: Áreas e Ações Prioritárias para Conservação. Ministério do Meio Ambiente, Brasília-DF.

Velloso, A.L. et al. 2002. Ecorregiões Propostas para o Bioma Caatinga. TNC-Brasil, Associção Plantas do Nordeste, Recife.