Ecosystem Profile: Western Ghats & Sri Lanka
The forests of the Western Ghats are some of the best representatives of non-equatorial tropical evergreen forests in the world. The Western Ghats have evolved into one of the richest centers of endemism owing to their isolation from other moist areas. The hills of the Western Ghats are embedded in a landscape that has much drier climatic conditions (Ramesh et al. 1997). South of Kodagu district in Karnataka, elevation increases. The topography creates several enclaves that have acted as refugia for species over the years as surrounding areas have steadily grown drier. Variation in the degree of endemism in the Western Ghats depends on both the latitudinal length-of–dry season gradient as well as the temperature-elevation gradient, with a greater number of endemics found in areas with a short dry season and higher altitudes (Ramesh et al. 1997).
Vegetation in the Western Ghats
According to a recent study conducted by the Indian Institute of Remote Sensing (IIRS), incorporating both field-based analysis of vegetation communities as well as satellite image interpretation, there are four major forest types in the Western Ghats: evergreen, semi-evergreen, moist deciduous, and dry deciduous. Together the forests cover approximately 20 percent of the total area of the Western Ghats. Among the four broad vegetation types, moist deciduous forests occupy the largest area followed by semi-evergreen, dry deciduous, and finally evergreen.
The majority of the area under moist forest types falls within the southern states of Kerala and Karnataka. Together they account for 80 percent of the evergreen forest and 66 percent of the moist deciduous forests in the Western Ghats (IIRS 2002).
The highest levels of endemism are found in the evergreen forests. These forests occur within a 200-1,500-meter elevational range and 2,500- to 5,000-millimeter rainfall range. They vary widely along the length and breadth of the Western Ghats. A broad distinction can be made between the northern evergreen forests and the southern evergreen forests. The Wayanad evergreen forests of Kerala represent a transition zone from the moist Cullenia-dominated forests in the south Western Ghats to the northern drier dipterocarp forests (Rodgers and Panwar 1988).
The habitat types of the southern Western Ghats tropical evergreen forests also include the wet montane evergreen forests and shola-grassland complexes in the higher elevations (1,900-2,200 meters). The montane evergreen forests are diverse, multistoried and rich in epiphytes, with a low canopy at 15 to 20 meters (Puri et al. 1989; Ganesh et al. 1996). More than half the tree species found in these forests are endemic, especially among the families Dipterocarpaceae and Ebenaceae. The majority of the fifty endemic plant genera are also monotypic. The distribution of richness and endemism is not uniform within this forest type, with some areas having higher concentrations of endemics than others.
Semi-evergreen forests occur primarily in the states of Maharashtra, Goa, and Karnataka in the Western Ghats, within an elevational range of about 300-900 meters (IIRS 2002). This forest type includes secondary evergreen dipterocarp forests, lateritic semi-evergreen forests, bamboo brakes, and riparian forests as described by Champion and Seth (1968). The structure and composition of these forests varies widely from north to south and especially from east to west. The dominant species include: Terminalia paniculata, Aporusa lindleyana, Olea dioica, Syzygium spp, Mesua ferrea, Vateria indica, Elaeocarpus tuberculatus, Celtis timorensis, Hopea parviflora, Lagerstroemia microcarpa, Holigarna arnottiana, Hydnocarpus laurina, Memcylon umbellatum, and Careya arborea. These forests also tend to have high levels of tree diversity and endemism (IIRS 2002).
Moist deciduous forests
The moist deciduous forest type occupies the largest area within the Western Ghats. It occurs within an elevational range of 500-900 meters in areas with mean annual rainfall of 2,500-3,500 millimeters. The swath of moist deciduous forests is very narrow on the steeper, windward side of the mountain range, where the southwest monsoon rains promote wet evergreen forests. On the less steep leeward side, the drier conditions caused by the rain shadow result in a broader, uneven swath of moist deciduous forests that extend further into the Deccan Plateau. Rainfall on the leeward side is influenced by complex landforms, with some areas receiving less than one-fifth of the 3,000 millimeters or more of annual precipitation that is deposited higher in the mountains.
Dry deciduous forests
The dry deciduous forests occur on the leeward side of the Western Ghats Mountain Range within an elevational range of 300-900 meters in areas of 900-2,000 millimeters mean annual rainfall. They extend across the southern Indian states of Karnataka and Tamil Nadu. The tall Western Ghats mountain range intercepts the moisture from the southwest monsoon, so that the eastern slopes and the Deccan Plateau receive relatively little rainfall, from 900 to 1,500 millimeters. The undulating hillsides have very shallow soils. Thorny plants become more common in areas where grazing pressure is high.
Although not exceptionally outstanding for biological richness or endemism by itself, the dry deciduous forests are contiguous with the moist deciduous forests that lie along the foothills of the southern extent of the Western Ghats mountains and provide valuable wildlife habitat. Two of India's most important elephant conservation areas, the Nilgiris-Eastern Ghats and the Anamalais-Nelliampathis (Sukumar 1989) and one of the most essential landscapes for global tiger conservation (Wikramanayake et al. 1999) extend across this region. Hence, these forests together with the moist deciduous forests and montane evergreen forests provide important, contiguous habitat landscape for conservation of Asia's largest terrestrial herbivore and predator.
Other vegetation types
Other vegetation types that occur in the Western Ghats include:
- Scrub jungles located in areas 200-500 meters in elevation with 300-600 millimeters of annual rainfall. This vegetation type is dominated by short trees (15-20 meters high). The dominant genera are Actinodaphne, Elaeocarpus, Eunymus, Michelia, Rhodomyrtus, Schefflera and Symplocos, among others (Nair and Daniel 1986).
- Savannas located in areas 1,700-1,900 meters in elevation with medium to high rainfall. The dominant genera are-Chrysopogon, Arundinella, Eulalia, and Heteropogon, among others (Nair and Daniels 1986).
- High rainfall savannas located in montane areas. The vegetation consists of herbaceous to shrubby cover: Ligustrum, Rhododendron, Anaphalis, and Phlebophyllum, among others (Nair and Daniel 1986).
- Peat bogs located above 2,000 meters in high rainfall areas. Vegetation consists of grasses, sedges and mosses: Carex, Cyanotis, Cyperus, and Eriocaulon, among others (Nair and Daniel 1986).
- Myristica swamps, which are a unique vegetation type in the Western Ghats occurring from sea level to around 600 meters in elevation in areas with medium to high rainfall. The dominant genera are Myristica, Knema, Hydnocarpus, and Lophopetalum (Nair and Daniel 1986).
The ecoregions of the Western Ghats broadly correspond to the distribution of the major vegetation types. According to World Wide Fund for Nature (WWF 2001), there are five major ecoregions in the Western Ghats: the North Western Ghats Montane Rain Forests, the Southern Western Ghats Montane Rain Forests, the Northern Western Ghats Moist Deciduous forests, the Southern Western Ghats Moist Deciduous Forests, and the South Deccan Plateau Dry Deciduous Forests.
The remarkable biological richness and endemism of the Western Ghats region is inherent in its inclusion among the 34 global hotspots. The recent discovery of a new family of frogs, the first in the last 77 years, bears testimony to the uniqueness of the region, where many species of higher plants and vertebrates are still being discovered. Furthermore, the region is the center of diversity for some of the world's most economically significant plants such as mango, banana, black pepper, and nutmeg. Superimposed on this biological diversity is the human diversity in the form of richness of cultures, ethnicity, and traditional knowledge systems.
It is estimated that there are four thousand species of flowering plants known from the Western Ghats and 1,500 (nearly 38 percent) of these are endemic (Nair and Daniel 1986). Approximately 63 percent of India’s woody evergreen taxa are endemic to the Western Ghats (Johnsingh 2001). Of the nearly 650 tree species found in the Western Ghats, 352 (54 percent) are endemic (Daniels, 2001). The tree genera endemic to the Western Ghats include Blepharistemma, Erinocarpus, Meteromyrtus, Otenophelium, Poeciloneuron, and Pseudoglochidion. Other plant genera endemic to the Western Ghats include Adenoon, Griffithella, Willisia, Meineckia, Baeolepis, Nanothamnus, Wagatea, Campbellia, and Calacanthus (Nair 1991). The grass family Gramineae (Poaceae) has the highest number of endemic genera and the genus Nilgirianthus has the maximum number of endemic species (20) across all genera in this family (Nair 1991).
There are several centers of plant endemism and species richness within the Western Ghats. For instance, of the 280 woody endemic species found south of Karnataka, 70 species are endemic to the southernmost Travancore region (Nair 1991). Herbaceous species richness is the highest in the stretch of hills to the south of Kodagu district in Karnataka (Nair 1991). The Nilgiri Mountains are one of the most important centers of speciation for flowering plants in the Western Ghats, with 82 species restricted to this area alone (Daniels 2001).
Several species are endemic to the Agastyamalai-Nilgiri Hills and the Sri Lankan highlands, including Abarema subcoriacea, Biophytum nudum, Chrysoglossum maculatum, Eugenia rotundata, Fahrenheitia zeylanica, Filicium decipens or fern tree, Pavetta zeylanica, and Rubus micropetalus or wild aspberry. The flora of the Agastyamalai Hills bears a remarkable similarity to that of Sri Lanka’s southwestern wet zone not just in terms of shared taxa, but also with respect to the remarkably high incidence of highly localized “point” endemics (Nayar, 1996; Ramesh & Pascal, 1997). Tree species endemism is the highest in the southern Western Ghats (Figure 2), while herb species endemism appears to be highest in the north (Daniels 2001).
Figure 2. Subregional Distribution of Tree Species Endemic to the Semi-Evergreen and Evergreen Forests of the Western Ghats
The Western Ghats supports a diverse fauna. Among the vertebrates, birds represent the largest number of known species (508 species), followed by fishes (218), reptiles (157), mammals (137), and amphibians (126). Many of these species are endemic to the Western Ghats region. The greatest number of endemics is found among the amphibians (78 percent) followed by reptiles (62 percent), fish (53 percent), mammals (12 percent), and birds (4 percent).
Daniels (2001) reports around 218 species of fish from primary and secondary freshwaters in the Western Ghats, of which 116 (53 percent, representing 51 genera) are endemic to the region. Streams and rivers in the southern parts of the Western Ghats tend to support greater diversity than those in the north and east-flowing streams and rivers have richer fish faunas than west-flowing ones. High levels of endemism are also associated with the ichthyofauna of the southern Western Ghats, which includes several endemic genera (Brachydanio, Lepidopygopsis, Bhavania, Travancoria, Horabagrus, Horaglanis, Horaichthys). Several other freshwater-fish genera occurring in the southern Western Ghats are not recorded from Sri Lanka, including Gonoproktopterus, Neolissochilus, Salmostoma, Barilius, Balitora, Batasio, Silurus, Glyptothorax, Pristolepis, and Osteochilichthys. The highest diversity of freshwater fishes is in deep, slow-moving waters. The species composition of many freshwater fish assemblages has been extensively modified by the introduction of invasive alien species, which are now naturalized. The distribution of many species is also adversely affected by the construction of dams to create artificial lakes and reservoirs (Daniels, 2001).
Approximately 126 species of amphibians from 24 genera are known from the region, with new species being frequently added to the list (Daniels 2001). The Western Ghats has the highest levels of amphibian endemicity in India. The largest family is Ranidae (49 species) followed by Rhacophoridae (30 species). The Western Ghats also harbor a remarkable number of caecilians (Families Ichthyophidae and Caeciliidae)—16 species, all of them endemic to the region. Distribution within the region varies from extremely widespread e.g. black-spined toad (Bufo melanostictus), skittering frog (Euphlyctis cyanophlyctis), Indian bullfrog (Hoplobatrachus tigerinus, to highly restricted (e.g., Malabar torrent toad (Ansonia ornata), Indirana gundia and Micrixalus kottigeharensis), with species occurring south of ca. 13°N latitude tending to have patchy distributions (Nair 1991, Daniels 1992).
Approximately 157 species of reptiles are reported from the Western Ghats, representing 36 genera: 2 genera of turtles/tortoises, 14 genera of lizards, and 20 genera of snakes (Ishwar, unpublished information). Of these, nearly 50 percent are endemic. Among the different habitats of the Western Ghats, the evergreen forests alone are known to support approximately 130 species of reptiles. Certain groups of reptiles have a very high proportion of endemic species; for example, about 70 percent of the Uropeltid snakes are endemic to the Western Ghats. Endemism is also high among lizards (65 percent). Many of the rare and endemic reptiles are known only from single locality records. A major challenge to conservation efforts in this region is the lack of a complete understanding of the distributional patterns, habitat requirements, and conservation status of reptiles in the Western Ghats.
The status and distributions of bird species in the Western Ghats are relatively well known. A total of 508 species have been recorded in the region, including 324 resident species (64 percent). This figure also includes 144 (28 percent) species of aquatic birds, many of them from the western coastline. The central parts of the region (especially Uttara Kannada district) harbor the highest diversity of bird species. Due to the interspersion and juxtaposition of different habitat types in secondary and disturbed evergreen and moist deciduous forests, these forests have the highest number of bird species occurring in them (including many habitat generalists and migrants in addition to resident and endemic species). Sixteen species are endemic to the Western Ghats region (Daniels, 2001), most of them occurring in the areas southwards of Goa. Many of the endemics are obligates of evergreen forests and shola-grassland systems.
Of the 137 species of mammals recorded in the Western Ghats, the largest representation is from the orders Chiroptera (41 species), Rodentia (27 species) and Insectivora (11 species). Of the 127 species, 14 are endemic (Daniels, 2001) and three are listed as Critically Endangered. One of the Critically Endangered species, Wroughton’s free-tailed bat (Otomops wroughtonii), is restricted to a single cave within the Western Ghats and has been recently discovered in Cambodia and Northeastern India (Walston & Bates 2001; Thabah & Bates 2002). Wide-ranging and flagship mammal species such as the tiger and elephant have attracted significant conservation efforts, both by the Indian government as well as by several conservation NGOs, but relatively little is known about the distribution and conservation status of the smaller mammals, particularly small carnivores and rodents.
A total of six species of mammals are endemic to the southern Western Ghats and Sri Lanka as a unit: the mountain shrew (Suncus montanus), slender loris (Loris tardigradus), stripe-necked mongoose (Herpestes vitticollis), Sri Lankan giant squirrel or grizzled giant squirrel (Ratufa macroura), Layard’s striped squirrel (Funambulus layardi), dusky striped squirrel (Funambulus sublineatus), and the Travancore flying squirrel (Petinomys fuscocapillus).
Much of the research on invertebrates in the Western Ghats has focused on butterflies and ants. Very little is known about other groups of insects. In addition much of the research is of a taxonomic nature; very few studies address questions of ecology and biodiversity (Daniels 2001).
Butterflies in the Western Ghats belong to five families, 166 genera, and 330 species, of which 37 species are endemic (Gaonkar 1996). The southern Western Ghats extending from Agasthyamalai to the Palghat Gap holds the highest diversity of butterfly species with the most number of endemics (Gaonkar 1996). Goa and Uttara Kannada are other regions within the Western Ghats with high levels of butterfly diversity. According to a recent study, there are at least 200 species of spiders in the Western Ghats. The dominant families are Argyopidae, Salticidae, Thomisidae, Oxyopidae, Lyniphidae, and Hersilidae (Rajashekhar and Raghavendra 2001, cited in Daniels 2001).
Studies have indicated that there have been declines in the diversity of aquatic insects in some areas of the Western Ghats due to anthropogenic interference leading to habitat loss and pollution (Daniels 2001).
A total of 58 protected areas consisting of 14 National Parks (NP) and 44 Wildlife Sanctuaries (WLS) fall within the boundaries of the Western Ghats. The total area covered by these protected areas is 13,595 square kilometers representing 9.06 percent of the Western Ghats. Although protected area planning and design have not been based on biogeographic principles, the Western Ghats is one of two biogeographic zones (the other being the Andaman and Nicobar Islands) with the highest level of coverage by protected areas (Rodgers & Panwar 1988).
Analysis done for this profile indicates that of the major vegetation types in the Western Ghats, high altitude grasslands are the best represented, with 61 percent of their area falling within the protected area network. Twenty-nine percent of the area of evergreen forests in the Western Ghats and 25 percent of the area covered by moist deciduous forests are represented within the protected area network. Dry deciduous and scrub forests are represented by 14 percent and 26 percent respectively. Areas above 2,500 meters elevation are the best represented (27 percent) by the distribution of the current protected area network, followed by areas between 1,000-1,500 meters. Areas at or below 500 meters are the least represented (12 percent) within the current protected area network in the Western Ghats.
The legal notification status is preliminary and final for 19 and 29 protected areas, respectively. [The preliminary notification is a notification of intent to constitute a protected area; the final notification is issued following the completion of the rights settlement process]. Although protected area establishment dates back to 1942, most of the protected areas in the Western Ghats were notified in the 1980s.
The Western Ghats ranges north to south across the states of Goa, Maharashtra, Karnataka, Tamil Nadu and Kerala. The largest proportion (45 percent) of the area protected in the Western Ghats (13,465 square kilometers) lies within 19 protected areas in the state of Karnataka (Figure 3).
Figure 3. Area Distribution of the Protected Areas of the Western Ghats by State
Protected areas span a wide range of sizes with the largest protected area being Indira Gandhi Wildlife Sanctuary and National Park at 850 square kilometers in Tamil Nadu and the smallest being Gudavi Bird sanctuary at 0.74 square kilometers in Karnataka. Fifty-nine percent of the protected area network is represented in 31 protected areas ranging from 100 to 500 square kilometers in area. The remaining area includes seven protected areas of greater than 500 square kilometers each (34 percent) and 20 protected areas less than 100 square kilometers (7 percent) (Figure 4). Bird sanctuaries are relatively smaller in size; Thattekad Bird Sanctuary in Kerala, with an area of 25 square kilometers, is the largest of four bird sanctuaries with the remaining three sanctuaries each less than 5 square kilometers in area. In certain cases several of these smaller individual protected areas lie adjacent to one another, in neighboring states, thereby effectively increasing the contiguous area under protection.
Figure 4. Size Distribution of Protected Areas in the Western Ghats
Protected areas in the Western Ghats are embedded in a human-dominated landscape and hence are subject to intense land-use conflicts. Although the region has had human influence for several millennia, the most significant ecological changes occurred from the early 19th century onwards, following British colonization and the ensuing exploitation of forests with increasing populations and changing technologies playing a significant role in intensifying human impacts (Chandran 1997; Gadgil and Guha 1992; Raman, 2001).
The 58 protected areas (national parks and sanctuaries) contained within the boundaries of the Western Ghats were analyzed for local-level threats such as extraction of minor forest produce (MFP) and nontimber forest products (NTFPs), livestock grazing, and hunting, and landscape-level threats such as mining and development projects.
Ninety percent of all protected areas surveyed (n = 58) were recorded with more than 12 types of threats, with four protected areas recording 20 out of the 23 types of threats. Bird sanctuaries appear to have relatively fewer types of threats compared to other wildlife sanctuaries and national parks. Local hunting emerged as the most common type of threat occurring in 57 out of the 58 protected areas. Illegal timber felling, presence of exotic and invasive species, fuelwood and fodder removal and human-wildlife conflicts were found to occur in 97 percent of the protected areas surveyed. In general, local level threats such as hunting, fuelwood and fodder collection and livestock grazing appear to be more common than landscape level threats such as mining, railways and pipelines. Livestock grazing, MFP/NTFP collection, tourism, fire, and illegal encroachments occur in more than 90 percent of protected areas and are indicative of the impacts of growing human populations both within and outside protected areas. Threat occurrence is independent of age and size of protected areas.
There are large gaps in information on biological richness of protected areas in the Western Ghats. Consistent presence/absence data on endemic mammals and birds is lacking for most protected areas independent of their size. Complete species lists are not available for most protected areas including those less than 10 square kilometers in area. However, 41 out of the 58 protected areas were recorded as having 6-8 widely known and easily identified species such as tigers (Panthera tigris), leopards (Panthera pardus), elephants (Elephas maximus), gaur (Bos gaurus), hornbills (Buceros bicornis), wild dogs (Cuon alpinus), sambhar (Cervus unicolor), and king cobra (Ophiophagus hannah). Information on species richness of protected areas among other taxa such as vascular plants, trees, shrubs, grasses, butterflies, fishes, reptiles, amphibians, and birds is sparce.
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