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close this bookBiodiversity in the Western Ghats: An Information Kit (IIRR, 1994, 224 p.)
close this folder5. Agriculture
View the document5.1 Rice diversity and conservation in the Konkan
View the document5.2 Conservation of traditional vegetables in the backyard
View the document5.3 Genetic diversity in mango and cashew
View the document5.4 Floriculture and arboriculture
View the document5.5 Enriched biodiversity by plant introductions
View the document5.6 Impact of introduced plants
View the document5.7 Effects of pesticides on biodiversity
View the document5.8 Khazan (saline) lands

5.6 Impact of introduced plants

Plants from all over the world have been brought to the Western Ghats and grown there. Some have vanished, while others have become naturalized and multiplied, either with or without active human intervention. Some have been beneficial, while others have become weeds or have had other serious consequences.


Chillies have substituted black pepper in trade, cultivation, research and culinary use. The colonial powers of the 16th century had sought exactly this when they discovered this easy-to-grow spice in South America.

Onions from Persia were used to keep slave labour healty while building the pyramids of Egypt. They have displaced vegetables during the winter cropping.


Coffee and tea are the products of plants introduced from Africa and China respectively. Large areas of virgin rainforests have been thinned down in Coorg and Wynad to grow these crops.

Revegetation programmes

Revegetation programmes have brought about the introduction of some many-seeded, quick-growing plant species suitable for adverse soil conditions and poor management practices. Two species of Acacia, many species and hybrids of eucalyptus and Casuarina equisitifolia have been brought from Australia for these projects. The high demand for wood pulp for the paper and rayon industries and for poles as construction props led to an exponential growth of areas under these species with little thought on their impact.

The Australian acacia's name has been indigenized within a decade of its introduction in social forestry programmes. It is called the "Bengal acacia" or "Bengali babool" so is confused with the native acacias called locally "babool" and "subabool".

Plants of the above three genera have been extensively grown along roadsides. They cause severe chest and bronchial sickness in many people, especially during pollen-shedding seasons.


Some introduced plants in the Western Ghats

- Spices
Chillies, onion, cloves, nutmeg, allspice, coriander

- Beverages
Tea, coffee, cocoa

- Fruits
Custard apple, pine apple, papaya, guava, chikoo, mango, iamun.

These three plant types shade the ground and their leaf-fall mats the ground below. Little or no undergrowth is present. In the high rainfall conditions of the Western Ghats, this results in soil erosion, poor rainwater percolation and low water table in the post-monsoon season. The high water-uptake efficiency of these xerophytic plants aggravates the water problem during summer.

The "leaf" of Australian acacia is a modified petiole (phyllode) while that of the casuarina is a modified branch (cladode). These and the true leaves of the eucalyptus do not decompose easily, suppressing insect and microbial activity and changing the soil characteristics. Casuarina has destroyed both the beauty and the sands of beaches which it was planted to protect against erosion.

Accidental introductions

Not all introductions are intentional. Eupatorium, Parthenium and Mexican Weed came along with American wheat. The blame for these weeds goes to PL480 aid and poor quarantine in the USA and India in the 1960s. These weeds first established near railway and shipyards handling the wheat and then spread to other areas. Eupatorium is a serious problem even in Goa's Cotigao Wildlife Sanctuary. It can cause immense damage to the plant, mushroom and animal diversity in this sanctuary. Lantana, Milkbush Euphorbias and some other plants have also become weeds in some areas.

Water Hyacinth

The Water Hyacinth has beautiful flowers. Fragments of the plant can regenerate and it sets many seeds. Once established in a lake, canal or marsh, it is almost impossible to eradicate. Salvinia is no different. These plants choke out all other life forms before drying up the lakes. They are a scourge to fisheries, agriculture and water transport.

Effects of - weeds

· Invade land and water area.
· Compete with native plants and crops for space, water, nutrients, light.
· Cause irritations and allergies.
· Poison animals and birds.
· Dry up water sources.
· Interfere with agriculture, aquaculture and waterborne transport.
· Require high expenditures for removal or eradication.
· Reduce native biodiversity of plants, fungi, insects.
· Suppress seedlings, causing poor regeneration of forests.


Any plant material must be certified by the exporting country as free of insect pests and diseases prior to export. Quarantine facilities must be established at the import points (airports and harbours) to monitor the performance of the plants. Genetic defects and effects are monitored in case of new plants species or varieties. The apex body in India for these services is the Central Plant Protection and Quarantine Centre in Faridabad, Haryana.

Suggested reference: George Usher, A dictionary of plants used by man. CBS Publishers and Distributors, Shahadara, Delhi.

Prepared by Miguel Braganza