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
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
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 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
Chillies, onion, cloves, nutmeg, allspice, coriander
Tea, coffee, cocoa
Custard apple, pine apple, papaya, guava, chikoo,
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
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.
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.
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
· Compete with native plants and crops
for space, water, nutrients, light.
irritations and allergies.
· Poison animals
· Dry up water sources.
· Interfere with agriculture, aquaculture and
· Require high
expenditures for removal or eradication.
Reduce native biodiversity of plants, fungi, insects.
· Suppress seedlings, causing poor regeneration of
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