Caatinga Dry Woodland
The Caatinga Dry Woodland is a unique seasonal dry tropical forest biome located in northeastern Brazil, covering approximately 328,187 square miles (850,000 square kilometers), which constitutes about ten percent of the country's territory. The name "Caatinga" derives from the Tupi language, meaning "white forest," and refers to its open, deciduous vegetation. This biome is characterized by a semiarid climate, with annual rainfall averaging less than 30 inches (75 centimeters) and marked by long periods of drought. The flora includes various plant types, such as cacti and deciduous trees like the Ipê, which have adapted to conserve water during dry spells.
Biodiversity in the Caatinga is notable, with over 900 species of plants and animals, including many endemic species. However, the biome faces significant threats from human activities, such as deforestation for agriculture and cattle ranching, which have led to habitat degradation and increased vulnerability to desertification. Conservation efforts are challenged by local poverty and the pressing need for sustainable land use practices. Interestingly, climate change may alter the dynamics of the Caatinga, potentially leading to its expansion, albeit at the expense of surrounding rainforests. Overall, the Caatinga Dry Woodland's ecological significance and the socio-economic challenges it faces make it an important subject for further exploration and conservation efforts.
Caatinga Dry Woodland
- Category: Forest Ecosystems.
- Geographic Location: South America.
- Summary: The Caatinga dry woodland consists of dry forests and xerophytic woodlands in northeastern Brazil. The biome is fragile and under threat from human development, but is likely to expand due to global warming.
The term Caatinga comes from Tupi, the language of the indigenous people who originally lived in the region, and means white forest, denoting a rather open, deciduous vegetation formation. Today, Caatinga refers to the seasonal dry tropical forest biome in northeastern Brazil, covering an area of approximately 328,187 square miles (850,000 square kilometers), which corresponds to ten percent of the Brazilian territory and spans eight Brazilian states.
After European colonization, forest cover was reduced by timber harvest and by deforestation to open areas for cattle ranching. In consequence, today, the biome consists mainly of dry shrub vegetation, mostly deciduous species in both the woody and herbaceous layers, and fragments of tall forests. Altogether, the biome includes a broad range of vegetation types, from cactus shrubland to tall forest. Some similarities exist to the Cerrado biome (central Brazilian savannas) and the Chaco in northern Argentina, western Paraguay, and southeastern Bolivia, both of which are likewise seasonal dry tropical forest biomes.
The climate in the Caatinga region is semiarid, with total annual rainfall of less than 30 inches (75 centimeters) in the larger part, and most precipitation is concentrated in the Southern Hemisphere summer months. Erratic rainfall and long drought periods, sometimes lasting several years, are common. The mean annual temperature lies around 73 to 81 degrees F (23 to 27 degrees C), with little variation around the year. Evapotranspiration is high, at 59 to 79 inches (150 to 200 centimeters) per year.
In terms of geomorphology, the Caatinga region is contained in a depression at an altitude of around 984 to 1,640 feet (300 to 500 meters), characterized by sandstone from the Cretaceous Period on Precambrian crystalline rock. Soils are heterogeneous, however—in general fertile, but with high rock and low organic-matter content. Altogether, it is clearly a lack of rainfall, not soil fertility, that limits vegetation growth.
Today, we know that in the past 220,000 years, there have been several phases of rainforest expansion and retraction in what today is the Caatinga biome as a consequence of shifting climate conditions. The biome has not been stable over the past millennia. Relicts of rainforests are the so-called brejos de altitude (highland swamps), which can be found at elevations above 1,640 feet (500 meters) and which, due to their geographic situation, receive orographic, or mountain-driven, rainfall of more than 47 inches (120 centimeters).
Vegetation and Fauna
The biome exhibits a wide range of vegetation physiognomies, which vary according to topography, type of soil, and rainfall. Biodiversity in the Caatinga biome is high for some species and groups. The area is home to more than 900 animal and plant species.
The woody (tree and shrub) species of the Caatinga are characterized, in general terms, by the high importance of flowering species from the bean family (Fabaceae), the spurge family (Euphorbiaceae), and the cactus family (Cactaceae). Example of trees in the remnants of the original white forests are different Ipê or trumpet tree species (genus Tabebuia, family Bignoniaceae), with their beautiful flowers. Many of the woody plants are of short stature, with small leaves that they throw off during the dry season to minimize water loss, a strongly branched structure, and spines as a defense against herbivory.
During the dry season, much of the vegetation seems to be dry and dead, conferring a somewhat hostile expression to the environment. As soon as there is some precipitation, however, plants rapidly develop leaves and flowers. Grasses and forbs produce their biomass only in the short rainy season. The herb layer is characterized by a high proportion of annual species that complete their entire life cycle in the short season with better moisture availability and survive dry periods in the form of seeds.
Among its animals, the Caatinga has high endemism (species found exclusively in this biome) in insects and fishes but less in birds, mammals, and terrestrial invertebrates. In 2006, the Caatinga woodpecker (Celeus obrieni) was rediscovered; the species had been considered to be extinct for more than eighty years. The parrot Spix's macaw (Cyaopsitta spixii) is thought to be extinct in the wild as a consequence of habitat loss and illegal capture. An example of an endemic mammal is the Brazilian three-banded armadillo (Tolypeutes tricinctus), which had been considered extinct as well before being rediscovered in 1988.
Amphibians here include the vulnerable frog species Scinax fuscomarginatus,Adelophyrne baturitensis, and Odontophyrnus carvalhoi. There are dozens of reptile species considered vulnerable or rare, such as the lizard Leposoma baturitensis, the snake Atractus ronnie, and the turtle Mesoclemmys perplexa.
Conservation and Human Land Use
The Caatinga is a fragile biome with respect to biodiversity and its conservation, but also with respect to land use and the situation of the human population. Large parts of the Caatinga biome are characterized by scarcity of water and are vulnerable to desertification, with very low aptitude for agricultural use. Due to the environmental conditions, the people of the Caatinga are among the poorest in Brazil. Large infrastructure projects—specifically, irrigation—are planned to improve conditions for planting fruits and crops, but the intensification of land use may lead to further degradation of the biome; thus, big irrigation projects are subject to controversy and debate.
Human use of the land has threatened the habitat and its species. Slash and burn agricultural practices are still used in the region, threatening plant biodiversity and conservation efforts in the region. Further, overgrazing caused by livestock reduces biodiversity in the region and accelerates desertification by reducing soil fertility.
Currently, despite some considerable advances in conservation in the past few years, coverage of conservation units is still low, and not all major ecosystem types are included in protected areas. Ways need to be found to reconcile biodiversity conservation and reduction of rural poverty in the Caatinga biome.
Global warming has begun to create conditions that will lead to the expansion of the Caatinga, westward and southward, but also eastward, over the next 80 to 100 years—at the expense of rainforests there. In 2021, the area had an extreme drought. In the future, central parts of today's Caatinga likely may turn to desert. The fact that the Caatinga has historically been very poorly considered in biodiversity-related research can be considered a severe obstacle to addressing environmental problems.
Bibliography
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