Deccan thorn scrub forests
Changeable hawk eagle (Spizaetus cirrhatus), India. Source: Rahula Perera
Contents
Introduction
The Deccan Thorn Scrub Forests ecoregion consists of approximately 131,400 square kilometers of relatively sparse vegetation; this ecoregion is classified as Critically Endangered habitat by the World Wildlife Fund. Notably, it harbors the last populations of the globally threatened Jerdon's courser (Rhinoptilus bitorquatus), rediscovered recently, eighty-six years since it was last recorded in 1900. Otherwise, this ecoregion is neither exceptionally species-rich nor high in endemism. Many ecologists believe that the southern tropical thorn scrub vegetation represents a degraded stage of the original tropical dry deciduous forests that covered this region, now modified by human and livestock use over millennia.
Location and General Description
World Wildlife Fund and Encyclopedia of Earth
The ecoregion represents the southern tropical thorn scrub vegetation in the arid parts of the Deccan Plateau. It sprawls across the Indian much of the states of Tamil Nadu, Andhra Pradesh, Karnataka, and Maharashtra and also includes part of northern Sri Lanka.
The Deccan Plateau itself was part of the ancient southern continent, Gondwanaland, that disintegrated during the Cretaceous to give rise to the Indian Subcontinent as well as Africa, Madagascar, Australia, South America, and New Guinea and some of the smaller islands such as New Caledonia and Tasmania. After the Deccan Plateau drifted northward to collide with the Eurasian continent approximately 50 million years ago, geological uplift gave rise to the Western Ghats Mountains along the western coast of the peninsula. This mountain range then intercepted the moisture-laden southwest monsoons and created a dry rain-shadow in the vast plateau, affecting its vegetation. But in the more recent past, human influences have altered the vegetation to create vast areas of thorn scrub from what was believed to have been tropical dry forests originally.
Annual rainfall in the ecoregion is less than 750 millimetres. All rain is chiefly received during the relatively brief wet season, and there is practically no rainfall from November to April. Ambient temperatures can exceed a sweltering 40o Celsius during the hottest months of the year.
The forest type in this ecoregion is primarily southern tropical thorn scrub, as defined by Champion and Seth (1968), but also includes patches of tropical dry deciduous forests, which are believed to be the original native vegetation. The former consists of open, low vegetation characterized by thorny trees with short trunks and low, branching crowns that rarely meet to form a closed canopy. The trees attain heights of six to nine metres. The second canopy story is poorly developed and consists of spiny and xerophytic species, mostly shrubs. During the brief wet season an ill-defined lower story can be discerned. The dominant vegetation is Acacia species, with Balanites roxburghii, Cordia myxa, Capparis spp., Prosopis spp., Azadirachta indica, Cassia fistula, Diospyros chloroxylon, Carrisa carandas and Phoenix sylvestris.
Champion and Seth (1968) have also identified several habitat types within this vast thorn scrub ecoregion. In areas of particularly sparse rainfall and rocky soils, the thorn scrub transitions into a Euphorbia-dominated scrub (i.e., the southern Euphorbia scrub). Here the soil surface typically is bare, although some grassy growth may appear during the brief monsoon season.
In parts of Tamil Nadu, where rainfall is even less than average for the ecoregion, the vegetation is chiefly comprised of open thorny forests with scattered Acacia planifrons, which are characterised by umbrella-shaped crowns. This vegetation has been described as Carnatic Umbrella Thorn Forests by Champion and Seth (1968).
Wildflowers found in the ecoregion include Tiger's paw glory (Ipomoea pes tigridis), Common psoralea (Psoralea corylifolia), Common tephrosia (Tephrosia purpurea), Senna sophera (Cassia sophera), Greater cat's ears (Cyanotis tuberosa). and Painted thornbush (Dicrostachys cinerea).
Scattlered amid the thorn scrub are patches of dry grasslands that provides habitat for the native fauna. For example, the grasslands of southern Andhra Pradesh support a good population of the Indian bustard (Ardeotis nigriceps) and Blackbuck (Antilope cervicapra). The typical grasses in this habitat include Chrysopogon fulvus, Heteropogon contortus, Eremopogon foveolatus, Aristida setacea, and Dactyloctenium spp.
Satellite view of southern India and northern Sri Lanka. Source: National Geographic Society Patches of dry deciduous forests, especially along the Tirupathi Hill Ranges, are known for a large number of medicinal plants and various other species of botanical interest, among which are the rare endemic cycad (Cycas beddomei) and Psilotum nudum). The latter usually is found along steep escarpments. A small patch of the dipterocarp Shorea talura exists within the Chittoor forest division, part of which is being maintained as a preservation plot by the Forest Department of Andhra Pradesh.
The Srilankamalleswara Sanctuary between the Nallamalais and Sechachalam hill ranges is known for a rare, endemic tree species, Red sanders (Pterocarpus santalinus). This area is also the southern distributional limit of the Nilgai (Boselaphus tragocamelus) in the Indian Peninsula.
Biodiversity Features
Until the recent past, this ecoregion provided important habitat for the Bengal tiger (Panthera tigris tigris) (in the Indian sector) and Asian elephant (Elephas maximus). But over the years, their populations have dwindled and even become locally extirpated because of the adverse influences from the dense human population.
The mammal fauna in the ecoregion includes two endemic rodents and an endemic bat (Table 1). An asterisk signifies that the species' range is limited to this ecoregion. The endemic rodents are threatened. Other threatened species in the ecoregion (Deccan thorn scrub forests) include tiger, Gaur (Bos gaurus), Wild dog (Cuon alpinus), Sloth bear (Melursus ursinus), Chousingha (Tetracerus quadricornis), and Blackbuck (Antilope cervicapra). The important elephant populations are now only marginally included within this ecoregion. Small wolf populations may still be remnant, although most have been eliminated by a combination of loss of prey and poisoning by native people as retribution for livestock predation.
| Family | Species |
|---|---|
| Rhinolophidae | Hipposideros schistaceus* |
| Muridae | Millardia kondana* |
| Muridae | Cremnomys elvira* |
The ecoregion's bird fauna amounts to almost 350 species, of which three are near-endemics (Table 2). The Jerdon's courser (Rhinoptilus bitorquatus) is a globally threatened species that was rediscovered in this ecoregion in 1986, after the last record in 1900 (Grimmet et al. 1998). The known population of this species is limited to a small area in this and the neighbouring Central Deccan Plateau Dry Deciduous Forests. The Ceylon junglefowl (Gallus lafayetii) is limited to the northern Sri Lankan portion of ecoregion. The globally threatened Lesser florican (Eupodotis indica) and Indian bustard are other birds of conservation importance in this ecoregion (Deccan thorn scrub forests).
| Family | Common Name | Species |
|---|---|---|
| Glareolidae | Jerdon's courser | Rhinoptilus bitorquatus |
| Phasianidae | Ceylon junglefowl | Gallus lafayetii |
| Capitonidae | Yellow-fronted barbet | Megalaima flavifrons |
Representative sauria species found in the ecoregion include the Indian golden gecko (Calodactylodes aureus); Beddome's Mabuya (Eutropis beddomei); the Barred tree skink (Dasia johnsinghi), found only in the southern India portion of this ecoregion; Aaron Bauer's house gecko (Hemidactylus aaronbaueri); the Seashore skink (Eutropis bibronii), which, despite its common name is found well inland within both the India and Sri Lankan part of the ecoregion.
Example snakes in the ecoregion are the Buff striped keelback (Amphiesma stolatum); Indian bronzeback (Ahaetulla dispar).
Early Recorded History of the Region
The Satavahana family produced the first recorded historical dynasty in this region, with earliest recorded writings of their prominence dating to the latter first century BC, with some evidence of that dynasty appearing as early as mid third century BC. At first, the Satavahana kingdom emerged in the west of the Deccan, with cave drawings remnant at Karli, Nanaghat, Nashik, Karli and Kanheri, marking such early rulers as Krishna and Simuka. Notable trade with the Roman Empire was recorded around the first century AD.
Earliest recorded warfare of the region began in the second century AD, with invasion of the Satavahana empire by the Western Satraps. Coinage of the Western Satraps and Satavahana commemorates the first two centuries AD. Satavahana dominance was resurgent via the most successful warrior leader Gautamiputra Shatakarni (reigned c. 106–130 AD). His conquests covered a sizeable territory from Rajasthan at the northwest to Andhra at the southeast, and from Gujarat to Kalinga in the east.
Current Status
More than 90 percent of the ecoregion's natural habitat has been degraded or cleared, but one large block of habitat remains in southern Andhra Pradesh. The eleven protected areas cover more than 4000 kilometres 2, but this represents just about one percent of the ecoregion area (Table 3). The Great Indian Bustard reserve accounts for most of the protected areas system.
| Protected Area | Area (km2) | IUCN Category |
|---|---|---|
| Chandikulam | 120 | IV |
| Vettangudi | 20 | IV |
| Srivenkateswara | 500 | IV |
| Nandur Madmesh War | 80 | IV |
| Jaikwadi | 230 | IV |
| Great Indian Bustard | 2600 | IV |
| Great Indian Bustard (extension) | 250 | PRO |
| Sagareshwar | 50 | IV |
| Ghataprapha | 110 | IV |
| Tungabadra | 90 | DE |
| Ranebennur | 60 | IV |
| TOTAL | 4110 |
Some ecoregion area numbers of protected areas overlap with certain other ecoregions, beyond the Deccan thorn scrub forests.
Types and Severity of Threats
The forests in this ecoregion have been degraded to thorn scrub solely as a result of numerous human activities. Among the more serious sources of degradation is pastoralism, both from cattle overgrazing and from forest produce extracted by the pastoralists. Several village pastures have been taken over by an exotic (Exotic species) thorny shrub, Prosopis juliflora, resulting in the loss of grazing areas for cattle and encroachment into the reserved forests or protected areas for grazing. The conservation status of the ecoregion has been changed from Endangered to Critically Endangered after the analysis of ongoing and projected threats from the human population. There is a perception by some that these dry forests are not important for conservation. Consequently, livestock overgrazing and forest clearing, especially for fuelwood, are rampant.
Justification of Ecoregion Delineation
In a previous analysis of conservation units, Rodgers and Panwar (1988), and subsequently MacKinnon (1997), divided the Deccan Peninsula into five biotic provinces.
This ecoregion includes Rodgers and Panwar's Central Plateau North (6B) biotic province and partially includes the Deccan Plateau South (6A) biotic province.
In keeping with the Encyclopedia of Earth definition of an ecoregion (i.e., an ecosystem of regional extent), and following the encyclopedia rules for ecoregion delineation (represent distinct vegetation types of regional extent in separate ecoregions), the thorn scrub is placed as mapped by MacKinnon (1997), extending across these two biotic provinces within the Deccan Thorn Scrub Forests.
Additional Information on this Ecoregion
- For a shorter summary of this entry, see the WWF WildWorld profile of this ecoregion.
- To see the species that live in this ecoregion, including images and threat levels, see the WWF Wildfinder description of this ecoregion.
- World Wildlife Fund Homepage
Further Reading
- Puri, G.S., Gupta, R.K., and Meher-Homji, V.M.P.S. 1989. Forest Ecology Volume 2. New Delhi, India: Oxford & IBH Publishing Company.
- Champion, H. G., and S. K. Seth. 1968. A revised survey of the forest types of India. Government of India Press.
- Rawat, G.S. and Babu, M.M. 1995. Ecological Status of Forests in and around protected areas of Andhra Pradesh. A Report on Andhra Pradesh Forestry Project, WII, Dehra Dun.
- IUCN. 2000. 2000 IUCN Red list of threatened species. Viewed November 2000. The IUCN Species Survival Commission and the International Union for Conservation of Nature and Natural Resources (IUCN – The World Conservation Union).
- Jha, A. and D. Rajgor. 1992. Studies in the Coinage of the Western Ksatraps, Nashik: Indian Institute of Research in Numismatic Studies.
- Kehimkar, Isaac. 2000. Common Indian Wildflowers. Oxford University Press
- Grimmett, R., C. Inskipp, and T. Inskipp. 1998. Birds of the Indian Subcontinent. Christopher Helm, London. ISBN: 9628711075
- Rodgers, W. A. and H. S..Panwar. 1988. Planning a wildlife protected areas network in India. Vol 1 and 2. Dept of Environment, Forests, and Wildlife/Wildlife Institute of India report. Wildlife Institute of India.
- MacKinnon, J. 1997. Protected areas systems review of the Indo-Malayan realm. Canterbury, UK: The Asian Bureau for Conservation (ABC) and The World Conservation Monitoring Center (WCMC)/ World Bank Publication. ISBN: 2880326095
- Strabo. Geographica. Chapter Seven. circa 7 BC
- Wikramanayake, Eric; Eric Dinerstein; Colby J. Loucks; et al. (2002). Terrestrial Ecoregions of the Indo-Pacific: a Conservation Assessment. Island Press; Washington, DC.
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