Invasive / Exotic Species

Forests play a vital role in nation’s economy. They provide tangible as well as intangible benefits. The tangible benefits include providing fuel wood, timber, non-timber forest products like bamboos, lac, gum, resin, katha, medicinal plants and raw materials for wood based industries like paper, pulp, plywood etc. They also provide materials for defence and communications as well as grazing for cattle. The intangible benefits include conservation of soil fertility and play an important role in the maintenance of the water regime of the land. The forests provide water, perhaps the most important forest product. The organic matter which they yield improves the fertility and increase the water holding capacity of the soil thereby reducing the run-off. The presence of vegetation acts as a physical check to the velocity of the run-off and reduces its soil carrying capacity. Thus forests protect the hilly areas against excessive soil erosion. Similarly, they protect flat lands against desiccation and erosion caused by winds. They exert a beneficial influence on the growth of agricultural crops and on the climate of the region in which they exist. The forests of India are endowed with rich flora and fauna. There are about 45,000 plant species in India which is 12% of the global plant wealth. The animal species are approximately 81,250. There are 92 National Parks and 500 Wildlife Sanctuaries in India. The total extent of protected areas include five designated World Heritage Sites, fourteen Biosphere Reserves, six Ramsar Sites, twenty eight (37761 square km) Project Tiger Reserves and nine Elephant Reserves.

The introduction of non-indigenous alien, invasive, or exotic species to an area has disrupted the ecosystem to such an extent that native species have become endangered. In some cases the invasive species compete with the native species for food or prey on the natives. In other cases a stable ecological balance has been upset by predation or other causes leading to unexpected species decline. New species also carries diseases to which the native species have no resistance.

Lantana camara is one of the most obnoxious weeds that has encroached most of the areas under community and reserve forestlands. This weed, not only ruins common agricultural and forestlands but also makes shade as well as allopathy impacts on the regeneration of important forestry species. Due to spread of Lantana, the yields of crops and pastures get reduced. The harvesting costs have increased manifolds. Heavy expenditure is incurred for afforestation of lands infested with this weed which requires frequent weedings so as to avoid suppression of young seedlings of planted species. Afforestation cost is also increased due to loss of stand and slower growth rate due to weed competition.

Parthenium weed is difficult to control as it seeds prolifically. Seed germinates readily and the plant tolerates a wide variety of conditions. The weed is a menace to agriculture because it has allopathic effect and competes with pastures and reduces their carrying capacity. The weed affects human and animal health by causing respiratory problems, severe dermatitis and tainted milk.

Eupatorium glandulosum is found in the temperate region of the south and the north; ecological disruptions have given way to this weed. This weed spreads fast and checks the regeneration of other species particularly in Western Ghats and has replaced the valued flora at places. It comes in disturbed soils. In most of the goat-travelled paths, it comes up well; that is why it is locally known as ‘goat weed’. Since the plant has no local or commercial use, it has widely spread in denuded and forestlands.

Ulex europaeus represents a fire hazard to private property in the Western Ghats. It invades watersheds, which supply a substantial amount of drinking water. It is threatening agricultural and grazing lands. Thickets of this weed are impenetrable to humans and have persistent spiny litter.

Acacia mearnsii was introduced in Western Ghats particularly in the Nilgiris to provide fuelwood to the rural people to save the shola forests, which were degraded in the past by human activities. It was also planted in the tea gardens to provide shade to the tea plants but now it has covered most of the shola forests and become menace in the Nilgiri Hills. Regeneration of shola forests is effected due to profuse regeneration and invasive nature of this species.

Mikania micrantha is a perennial fast growing weed of Neotropical origin and has become a major menace to the natural forests, plantations and agricultural systems in North-east and South-west India. This weed spreads very fast in areas where canopy is open.

Cytisus scoparius was introduced from European countries in the Western Ghats for ornamental purposes but now it has become menace in the Nilgiri Hills particularly in the shola forests and grazing lands. It reduces the regeneration of shola species and invades on the grasslands, thus decreases the production of grass for the cattle of Nilgiris. This species spreads fast in the areas distributed by forest fires or other biotic interferences. Euphorbia royleana in the Himalayan zones comes up profusely and has covered thousands of hectares of land. This plant represents a desert environment. Being cactus in habit, it has no use in conserving or making of soil.

Similarly, in this zone there are a few other plants viz. Artemisia vulgaris, Carrisa carander and Dodonea viscosa, which have spread like weeds and have large areas under their control.

Cannabis sativa weed has canvassed most of the deforested and community lands, complicating land management.