Dry forest in Brazil
Seasonally dry tropical forests (SDTF) in Brazil are highly threatened despite their wide distribution throughout the country. They are distributed across the large swath of land that extends from the North-eastern coastland to the Central and Western hinterlands beyond which they continue their distribution in Argentina, Paraguay and Bolivia. Because of its NE-SW distribution, this large area separating the Amazonian and Atlantic Rainforest Domains has been referred to as Diagonal of Open Formations. As we could expect, this vast Diagonal is highly heterogeneous in terms of both environment and vegetation and periods of water shortage is the only common feature all along. Rainfall regimes are themselves heterogeneous: annual precipitations range from 1500 to 500 mm and their yearly distribution vary from regularly seasonal and concentrated in the summer (monsoon pattern) to erratic both along the year and between years (semi-arid pattern).
The semi-arid pattern is found in North-eastern Brazil, which is home to the largest continuous area of SDTF in South America, the Caatinga Phytogeographic Domain (ca. 850,000 km²), which hosts a surprisingly high number of plant species, ca. 2500, one third of which is endemic. The families better represented in number of species and sometimes in number of individuals and habits are the Leguminosae (by far at the top), Cactaceae, Euphorbiaceae, Anacardiaceae, Bignoniaceae and Rhamnaceae. This vast Domain includes a heterogeneous mosaic of vegetation types chiefly related to both aridity levels and geomorphological features. Recent studies have demonstrated that this is also corresponded by a very heterogeneous plant species distribution pattern and, therefore, to smaller-scale patterns of endemism. In great contrast, the long history of human occupation resulted in a predominantly degraded landscape throughout the region and the number and extent of protected areas fall short of what is really necessary for long-term conservation.
All other Brazilian SDTF areas are found under the monsoon rainfall pattern. Some used to be continuous areas of deciduous forests, as those encircling the Caatinga Domain in its transition to the adjacent Atlantic Forest (East) and Cerrado Domains (South and West), known as Agreste and Caatinga Arbórea, respectively. There is little to nothing left of what used to be the Agreste because it has been replaced by croplands since the colonial times. The caatinga Arbórea is presently being devastated and very few and small conservation areas have been established, particularly in Minas Gerais and Piauí states. The families better represented are more or less the same of the Caatinga, though with a much smaller contribution of Cactaceae.
Another large continuous extent of seasonal forests in Brazil belongs to the Atlantic Forest Domain and lies between the coastal rain forests and the hinterland open formations, namely the Cerrado woody savannas, the Pampa prairies and the Chaco thorny woodlands. These hinterlands seasonal Atlantic forests extend between 14° and 35° S so that they include both tropical and subtropical forests. This also means a gradual switch in the leading environmental factor from rainfall seasonality, in the tropics, to temperature seasonality, in the subtropics, where frosts are regular and snowfall erratic. It is arguable whether Atlantic seasonal forests should be included in the SDTF concept. The fact is that they vary from semi-deciduous to evergreen (Araucaria forests) and there are very few true deciduous forests. In addition, most species are shared with rain forests and typical SDTF species blend into the flora as a small fraction.
The last but not least important Brazilian SDTFs are those found in a somewhat patchy distribution within the Cerrado Domain, where they usually replace the dominant cerrado vegetation (woody savannas) on soils derived from mafic bedrocks, particularly limestone and basalt, which are therefore richer in mineral nutrients. The families better represented in number of both species and individuals are Leguminosae, Anacardiaceae, Bignoniaceae, Apocynaceae and Malvaceae. Higher soil fertility explains why those forests are particularly threatened and have long been replaced by croplands (or limestone extraction). The largest patches, such as the Mato Grosso de Goiás and Vale do Paranã, have nearly vanished away and very few are sheltered within protected areas.
We believe that expanding the knowledge on the floristic composition patterns of Brazilian SDTFs will certainly encourage on-going conservation initiatives and help with the necessary guidance and support.
The semi-arid pattern is found in North-eastern Brazil, which is home to the largest continuous area of SDTF in South America, the Caatinga Phytogeographic Domain (ca. 850,000 km²), which hosts a surprisingly high number of plant species, ca. 2500, one third of which is endemic. The families better represented in number of species and sometimes in number of individuals and habits are the Leguminosae (by far at the top), Cactaceae, Euphorbiaceae, Anacardiaceae, Bignoniaceae and Rhamnaceae. This vast Domain includes a heterogeneous mosaic of vegetation types chiefly related to both aridity levels and geomorphological features. Recent studies have demonstrated that this is also corresponded by a very heterogeneous plant species distribution pattern and, therefore, to smaller-scale patterns of endemism. In great contrast, the long history of human occupation resulted in a predominantly degraded landscape throughout the region and the number and extent of protected areas fall short of what is really necessary for long-term conservation.
All other Brazilian SDTF areas are found under the monsoon rainfall pattern. Some used to be continuous areas of deciduous forests, as those encircling the Caatinga Domain in its transition to the adjacent Atlantic Forest (East) and Cerrado Domains (South and West), known as Agreste and Caatinga Arbórea, respectively. There is little to nothing left of what used to be the Agreste because it has been replaced by croplands since the colonial times. The caatinga Arbórea is presently being devastated and very few and small conservation areas have been established, particularly in Minas Gerais and Piauí states. The families better represented are more or less the same of the Caatinga, though with a much smaller contribution of Cactaceae.
Another large continuous extent of seasonal forests in Brazil belongs to the Atlantic Forest Domain and lies between the coastal rain forests and the hinterland open formations, namely the Cerrado woody savannas, the Pampa prairies and the Chaco thorny woodlands. These hinterlands seasonal Atlantic forests extend between 14° and 35° S so that they include both tropical and subtropical forests. This also means a gradual switch in the leading environmental factor from rainfall seasonality, in the tropics, to temperature seasonality, in the subtropics, where frosts are regular and snowfall erratic. It is arguable whether Atlantic seasonal forests should be included in the SDTF concept. The fact is that they vary from semi-deciduous to evergreen (Araucaria forests) and there are very few true deciduous forests. In addition, most species are shared with rain forests and typical SDTF species blend into the flora as a small fraction.
The last but not least important Brazilian SDTFs are those found in a somewhat patchy distribution within the Cerrado Domain, where they usually replace the dominant cerrado vegetation (woody savannas) on soils derived from mafic bedrocks, particularly limestone and basalt, which are therefore richer in mineral nutrients. The families better represented in number of both species and individuals are Leguminosae, Anacardiaceae, Bignoniaceae, Apocynaceae and Malvaceae. Higher soil fertility explains why those forests are particularly threatened and have long been replaced by croplands (or limestone extraction). The largest patches, such as the Mato Grosso de Goiás and Vale do Paranã, have nearly vanished away and very few are sheltered within protected areas.
We believe that expanding the knowledge on the floristic composition patterns of Brazilian SDTFs will certainly encourage on-going conservation initiatives and help with the necessary guidance and support.