Western Ghats Mountain Range Into a Single Biogeographic Unit

The South Western Ghats Moist Deciduous Forests [IM0150] lie adjacent to the montane rain forest ecoregion in the southern extent of the Western Ghats Mountain Range. This ecoregion creates a landscape that extends from the lowlands to the highest peaks of one of the bioregion's richest and most diverse ecosystems. The ecoregion is wider in the drier, leeward side of the mountain range, where it drops down to the dry Deccan Plateau to encompass some prime habitat where some of the most important populations of tiger (Panthera tigris), Asian elephant (Elephas maximus), and gaur (Bos gaurus) live. The ecoregion represents a transition area between the South Western Ghats Montane Rain Forests [IM0151] and the South Deccan Plateau Dry Deciduous Forests [IM0209], and includes species from both. Therefore, species richness is high. But more importantly, the ecoregion provides continuity of ecological processes between the lowland and montane ecosystems. The moister forests of this ecoregion support many of the larger vertebrates also found in the dry forest ecoregion but at higher densities.

SCIENTIFIC CODE

(IM0150)

ECOREGION CATEGORY

Indo-Malayan

SIZE

9,200 square miles

STATUS

Critical/Endangered

HABITATS

Description 

Location and General Description

The ecoregion represents the band of moist deciduous forests that surround the montane evergreen rain forests in the southern part of the Western Ghats Mountains. It extends across the southern Indian states of Kerala and Tamil Nadu. Being part of the Deccan Plateau, the ecoregion has Gondwanaland origins. But the moist deciduous nature of the vegetation is a manifestation of the geological uplift that occurred during the upper Tertiary period and created the Western Ghats Mountain Range, which then began to intercept the southwestern monsoon and create a complex rainshadow. The swath of moist deciduous forests is very narrow on the steeper, windward side of the mountain range, where the southwest monsoon rains promote a wet evergreen forest. But on the shallower leeward side, the drier conditions caused by the rainshadow result in a broader, uneven swath of moist deciduous forests that extends further, into the Deccan Plateau. Rainfall on the leeward side is influenced by the complex landform, with some areas receiving less than a fifth of the 3,000 mm or more of annual precipitation that is deposited higher in the mountains.

Champion and Seth (1968) classify these forests as a Southern Indian Moist Deciduous Forest. The vegetation is characterized by Adina cordifolia, Albizzia odoratissima, Albizzia procera, Alstonia scholaris, Bombax ceiba, Toona ciliata, Dalbergia latifolia, Grewia tiliaefolia, Holoptelea integrifolia, Hymenodictyon excelsum, Lagerstroemia lanceolata, Lagerstroemia speciosa, Lannea coromandelica, Miliusa velutina, Pterocarpus marsupium, Schleichera oleosa, Spondias pinnata, Radermachera xylocarpa, Tectona grandis, Terminalia bellerica, Terminalia paniculata, Terminalia tomentosa, Vitex altissima, Xylia xylocarpa, and Machilus macrantha (Champion and Seth 1968).

Biodiversity Features

Although it does not serve as home to as many endemic species as the montane rain forests, the moist deciduous forest ecoregion is actually richer in species, harboring more mammal and bird species. Among the eighty-nine mammal species known from here, six are near-endemic species (table 1). But none of the species are strict endemics, entirely limited to this ecoregion. Three mammal species, Nilgiri langur (Semnopithecus johnii), Malabar large-spotted civet (Viverra civettina), and Jerdon's civet (Paradoxurus jerdoni), also extend into the montane rain forests and the semi-deciduous coastal forests on either side, whereas the shrew Suncus dayi is also found in the coastal forests. Layard's striped squirrel (Funambulus layardi) is also found in the adjacent montane rain forest ecoregion.

Table 1 Endemic and Near-Endemic Mammal Species.

Family Species 

Soricidae Suncus dayi 

Pteropodidae Latidens salimalii 

Cercopithecidae Semnopithecus johnii 

Viverridae Viverra civettina 

Sciuridae Paradoxurus jerdoni 

Sciuridae Funambulus layardi

An asterisk signifies that the species' range is limited to this ecoregion.

Among the larger threatened mammal species in this ecoregion are the tiger, Asian elephant, gaur, Nilgiri langur, wild dog (Cuon alpinus), and sloth bear (IUCN 2000). Several of these large species need large spaces. Two of India's most important elephant populations-the Nilgiri-Eastern Ghats population, estimated at more than 6,300 animals, and the Anaimalais-Nelliampathis population, estimated at 1,200 to 2,000 animals (Sukumar 1989)-venture into this ecoregion. The ecoregion is also part of a high-priority (Level I) TCU (Wikramanayake et al. 1999) that also includes the montane rain forests. Some of the smaller threatened species include Jerdon's palm civet (Paradoxurus jerdoni), slender loris (Loris tardigradus), grizzled giant squirrel (Ratufa macroura), and Indian giant squirrel (Ratufa indica) (IUCN 2000).

The 322 bird species known from this ecoregion include nine near-endemic species (table 2).

Table 2. Endemic and Near-Endemic Bird Species.

  Family Common Name Species 

Columbidae Nilgiri wood-pigeon Columba elphinstonii 

Bucconidae Malabar grey hornbill Ocyceros griseus 

Pycnonotidae Grey-headed bulbul Pycnonotus priocephalus 

Timaliidae Rufous babbler Turdoides subrufus 

Corvidae White-bellied treepie Dendrocitta leucogastra 

Muscicapidae Black-and-rufous flycatcher Ficedula nigrorufa 

Muscicapidae Nilgiri flycatcher Eumyias albicaudata 

Pycnonotidae Yellow-throated bulbul Pycnonotus xantholaemus 

Psittacidae Malabar parakeet Psittacula columboides

An asterisk signifies that the species' range is limited to this ecoregion.

These species are shared with the South Western Ghats Montane Rain Forests [IM0151], but five species that are endemic to the montane ecoregion are absent from this lower, moist deciduous forest ecoregion.

The globally threatened lesser florican (Eupodotis indica) can be found in patches of grassland habitats in this ecoregion. BirdLife International has included these moist deciduous forests within an EBA, Western Ghats (123) (Stattersfield et al. 1998).

Current Status

Nearly three-fourths of the natural vegetation in the ecoregion has been cleared or converted, and the remaining forests are severely fragmented. However, there are fourteen protected areas that cover almost 5,000 km2 (21 percent), of the ecoregion's intact habitat (table 3).

Protected Area Area (km2) IUCN Category 

Nagarahole 620 II 

Bandipur 1,110 II 

Wynad 430 IV 

Mudumalai 400 IV 

Bilgiri Ranga Swamy Temple [IM0209] 370 PRO 

Megamalai [IM0151] 310 PRO 

Periyar [IM0151] 470 IV 

Anamalai [IM0151] 620 IV 

Eravikulam [IM0151] 90 II 

Chinnar 50 IV 

Parambikulam (extension) 60 PRO 

Peppara [IM0151] 40 IV 

Neyyar 150 IV 

Kalakad 240 IV 

Total 4,960

Ecoregion numbers of protected areas that overlap with additional ecoregions are listed in brackets.

One protected area, Bandipur, exceeds 1,000 km2 and is contiguous with Nagarhole, Mudumalai, and Wyanad. Together this protected area complex includes the largest protected elephant population, estimated at more than 2,500 elephants in India. Two other protected areas that exceed 1,000 km2, Periyar and Anamalai, straddle this and the adjacent South Western Ghats Montane Rain Forests [IM0151]. But eleven of the other reserves are small, less than 500 km2, and four are less than 100 km2. Therefore, many of the protected areas cannot support viable populations of the focal large mammals in this ecoregion.

Types and Severity of Threats

The most significant threat to the remaining habitat and existing reserves is from livestock grazing and associated impacts such as trampling, excessive fodder collection, and burning to create grasslands for livestock (IUCN 1991). These threats are especially severe in Karnataka State. Dam construction for hydroelectricity and irrigation has also caused habitat fragmentation, concentrating elephant populations in forest fragments and exacerbating human-elephant conflicts. Habitat is also being fragmented by forest clearing for plantations. Rodgers and Panwar (1988) present a comprehensive review of the protected area gaps and conservation needs in this ecoregion.

Justification of Ecoregion Delineation

In earlier analyses, MacKinnon (1997), and Rodgers and Panwar (1988) placed the Western Ghats Mountain Range into a single biogeographic unit. But Rodgers and Panwar (1988) acknowledged that the Western Ghats Range is too large to represent a single unit for conservation planning and implicitly divided the mountain range into northern and southern areas. They used the Wyanad as a transition zone from the southern Cullenia-dominated forests and the northern drier dipterocarp forests in this division. We also used this transition to make a more explicit division of the northern and southern ecoregions in the Western Ghats. But in keeping with our definition of ecoregions, we also separated the distinct belt of moist deciduous forests that surround the montane rain forests and placed them in different ecoregions. Thus the moist deciduous forests to the south of the Wyanad area were placed in the South Western Ghats Moist Deciduous Forests [IM0150]. This ecoregion falls within Udvardy's Malabar rain forest biogeographic province.

We used the 1,000-m contour from a DEM and MacKinnon's (1997) map of original vegetation to define the boundary between the montane rain forests and moist deciduous forests. The outer boundaries, between the dry forests in the Deccan Plateau to the east and the distinctly different lowland moist deciduous forests along the Malabar coast to the west, were defined using MacKinnon's (1997) reconstruction of the distribution of the original vegetation types.