M. Kumaravelu

Unobtrusive invasion by alien species of plants is being considered as a major issue, which if curtailed and controlled, could save the Nilgiri Biosphere Reserve.

In India, serious conservation efforts began after independence. The enactment of the Wildlife (Protection) Act, 1972, could be cited as one of the major efforts in this direction. The Central Board of Wildlife (established in 1952), which was later known as Indian Board for Wildlife, mooted the conservation effort, wherein both the biological diversity and the genetic diversity were emphasized equally. The declaration of 53 National Parks and 247 Wildlife Sanctuaries, covering an area of about 1,00,000 square kilometers, has ensured their protection further. UNESCO, under the Man and Biosphere Reserve (MAB) programme, evolved the concept of Biosphere Reserve. It is desired that Biosphere Reserves give equal importance to the protection of both the biological and genetic diversity.

The floristic diversity of the Nilgiri Biosphere Reserve is the most exploited in India. Due to encroachment by exotic species, extinction of many indigenous species has occurred.

 The Nilgiri Biosphere Reserve encompasses six National Parks and Sanctuaries (refer Table). It encompasses a wide floristic diversity that includes  a series of ecosystems ranging from thorn forests    in the North to the deciduous forests of Nagarhole, savanna-woodlands of Mudumalai and Bandipur, evergreen forests like those of Silent Valley, montane forests (sholas) and grasslands of the hill tops. The faunal diversity is equally distributed in respect to the floristic diversity.

State Name of the Sanctuary / National Park Extent
Karnataka Bandipur National Park 880 sq. km.
Karnataka Nagharhole National Park 572 sq. km.
Kerala Wyanad Wildlife Sanctuary 344 sq. km.
Kerala Silent Valley National Park 78 sq. km.
Tamilnadu Mudumalai Wildlife Sanctuary & National Park 321  sq. km
Tamilnadu Mukkurthi National Park

80 sq. km

The floristic diversity of Nilgiri Biosphere Reserve is the most exploited in India. Forest fires, overgrazing and encroachments have become a common threat to the native species of flora. The entire Western Ghats continues to face a wide array of threats. Exotic plants have a tendency to multiply rapidly, whereby leading to the disappearance of indigenous insects, birds and mammals and creating a situation for local plants to vanish simultaneously.

In the upper reaches of the Western Ghats, particularly in the Nilgiris, Scotch broom (Cytisus scoparius) spreads as a silent killer through the grasslands. This could lead to the loss of grassland dwelling species, including the pride of our state, the Nilgiri Tahr, and numerous ground orchids. Eucalyptus and acacia species have already caused enough damage to the native forest types.

In the lower elevations, particularly on the western slopes, exotic species such as lantana and eupatorium have taken a stronghold. Presently, parthenium has also joined forces in this destructive march. Species like sambar and spotted deer are entirely dependent on the native shrubs and grass. A visible change in their habitats due to anthropogenic problems could affect them badly and their predators as well, and could become a threat to their survival.

Due to encroachment by exotic species, extinction of many indigenous species has occurred. It has also been observed that arable weeds reduce the forage and degrade the soil quality as well. When Scotch broom invaded the grasslands of the upper reaches, the water catchment area and swamps started to disappear gradually. In this context, it may be worth mentioning that the change in climatic conditions and factors of pollution are referred to as other causes for the overwhelming growth of exotic plants. Destruction of the native grasslands by forest fire, encroachment and grazing has assisted the spread   of exotic plant species.


Fig 1

To curb the spread of exotic species of plants the following are recommended:

  • Control forest fires, encroachments and grazing that remove native species of plants
  • Stop major developmental projects that threaten the native ecosystem
  • Periodically monitor the private forestlands adjoining the Biosphere Reserves or near the ecologically fragile zones to check invasion by exotic species of plants
  • Physical remove of exotic species of plants for effective clearing of the areas of invasion
  • Increase local knowledge and community awareness to check the entry of such alien plant species to keep them under control.


  • http:/ “Guidelines for the preservation of Biodiversity”
  • Proceedings of the First National Symposium, Udhagamandalam, 1986


Eco News, Vol 9, No 4, January to March, 2004

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