Deccan thorn scrub forests
The Deccan thorn scrub forests are a xeric shrubland ecoregion of south India and northern Sri Lanka. Historically this area was covered by tropical dry deciduous forest, but this only remains in isolated fragments. The vegetation now consists of mainly of southern tropical thorn scrub type forests. These consist of open woodland with thorny trees with short trunks and low, branching crowns; spiny and xerophytic shrubs; and dry grassland. This is the habitat of the great Indian bustard and blackbuck, though these and other animals are declining in numbers; this area was at one time home to large numbers of elephants and tigers. Almost 350 species of bird have been recorded here. The remaining natural habitat is threatened by overgrazing and invasive weeds, but there are a number of small protected areas which provide a haven for the wildlife.
Location and description
This ecoregion covers the arid portions of the Deccan Plateau, extending across the Indian states of Maharashtra, Telangana, Karnataka, Andhra Pradesh, and Tamil Nadu to the Northern Province of Sri Lanka. Only small patches of natural habitat remain, as most of the region has been cleared for grazing.
The annual rainfall is less than 750 mm (30 in), all falling during the short rainy season, and the area receives no rainfall during the months of November to April. Temperatures can exceed 40 °C (104 °F) during the hotter months.
Today the remaining forest is mostly southern tropical thorn scrub, and also includes patches of the original vegetation, tropical dry deciduous forests. The southern tropical thorn scrub forests consist of open, low vegetation with thorny trees with short trunks and low, branching crowns that rarely meet to form a closed canopy. The trees grow up to 6–9 m (20–30 ft). Typical grasses of the ecoregion include Chrysopogon fulvus, Heteropogon contortus, Eremopogon foveolatus, Aristida setacea, and Dactyloctenium species.
The second storey of the thorn scrub forests in Maharashtra is poorly developed and mainly consists spiny and xerophytic species, mostly shrubs. An ill-defined lower storey can also be seen during the brief wet season. The plant species that dominate the vegetation in these forests are Acacia species, Balanites roxburghii, Cordia myxa, Capparis spp., Prosopis spp., Azadirachta indica, Cassia fistula, Diospyros chloroxylon, Carissa carandas, and Phoenix sylvestris. There are also several other habitat types found in these forests.
The driest, rockiest areas of the ecoregion are covered with a scrub dominated by species of Euphorbia. The soil is usually bare in these areas; however, some grassy growth may also appear during the short monsoon season.
The parts of the ecoregion found in Tamil Nadu receive even less rainfall than most, and the vegetation in these parts is mainly made up of thinly spread thorny forests of Acacia planifrons, with umbrella-shaped crowns.
The remaining patches of forest are also home to a large number of plants, some of medicinal and botanical interest, including an endemic cycad (Cycas beddomei) and Psilotum nudum. A small patch of the tree Shorea talura also exists within the Chittoor forest division, part of which is being maintained as a preservation plot by the Forest Department of Andhra Pradesh.
Finally, the area between the Nallamala and Seshachalam Hills is well known for the red sanders (Pterocarpus santalinus), a rare, endemic tree species that is harvested for the medicinal value of its wood.
The dry grasslands that predominate do provide habitat for the native fauna remaining scattered amid the thorn scrub. The grasslands of southern Andhra Pradesh support a good population of the great Indian bustard (Ardeotis nigriceps) and blackbuck (Antilope cervicapra), although these and other species are declining in number.
The forests used to provide habitat for three prominent mammal species, the Bengal tiger (Panthera tigris tigris), the Indian elephant (Elephas maximus indicus), whose populations have recently dwindled and may have even become locally extinct, and the nilgai antelope (Boselaphus tragocamelus).
The ecoregion is home to 96 mammal species, out of which three are considered endemic: split roundleaf bat (Hipposideros schistaceus), Kondana soft-furred rat (Millardia kondana), and Elvira rat (Cremnomys elvira). Other threatened mammal species found in these forests include the tiger, gaur (Bos gaurus), dhole (Cuon alpinus), sloth bear (Melursus ursinus), chousingha (Tetracerus quadricornis), and blackbuck (Antilope cervicapra). Little-known ones like the Slender loris also occur here.
The Deccan thorn scrub forests are home to a richer variety of birds: almost 350 species, of which three are considered near-endemic: Jerdon's courser (Rhinoptilus bitorquatus), Sri Lanka junglefowl (Gallus lafayetii), and yellow-fronted barbet (Megalaima flavifrons). Among these, the Jerdon's courser is also considered a globally threatened species, and was rediscovered in this ecoregion in 1986 after being recorded for the last time in 1900. Other globally threatened bird species such as the lesser florican (Sypheotides indicus) and Indian bustard can also be found in the ecoregion.
Over 60 species of herpetofauna are known to occur in such forest types. Unique species of amphibians and reptiles do occur here. Such species include the Duttaphrynus hololius, lizards viz. Hemidactylus scabriceps, Hemidactylus reticulatus, Ophisops leschenaultii, Eutropis beddomii and snakes viz. Coluber bholanathi, Chrysopelea taprobanica. Apart from such forms, most of the widespread species of herpetofauna, occurring on a pan-Indian scale, including the endangered Indian star tortoise, Indian chameleon, and Bengal monitor also occur here.
Threats and conservation
The remaining deciduous woodland continues to be cleared for grazing land, while the pasture that has been created is itself threatened by overgrazing and invasive weeds. One large area of natural forest remains in southern Andhra Pradesh and there are eleven protected areas, but all of these are small: the largest is the Rollapadu Bird Sanctuary for the great Indian bustard near Nandikotkur in Kurnool, Andhra Pradesh.
- Champion, H. G., and S. K. Seth. 1968. A revised survey of the forest types of India. Government of India Press
- Wikramanayake, Eric; Eric Dinerstein; Colby J. Loucks; et al. (2002). Terrestrial Ecoregions of the Indo-Pacific: a Conservation Assessment. Island Press; Washington, DC.
- "Deccan thorn scrub forests". Terrestrial Ecoregions. World Wildlife Fund.