By Parag Ranjan Dutta

The story begins with some introduced species of terrestrial and aquatic organisms, which are otherwise known as ‘exotic’; the connotation here is purely from an environmental perspective, which means species introduced especially from a tropical country.

Following my relocation to Kolkata, Shillong continues to haunt me where I spent most of my life. The city witnessed unprecedented growth during the last few decades. All that was perhaps necessary, but at the cost of something greater… one that held the values of charm, silence and serenity.

In my younger days in Shillong, we would see a very common flowering hedge plant, Lantena Camara, growing in thickets. Interestingly, this plant formed the boundary line between properties. A native of South America, Lantenas were brought by the British, some 200 years ago.

Its history suggests a fascinating journey. In 1807, Lantena was introduced as an ornamental hedge at National Botanical Garden, Shibpur (Kolkata).

Because of the urban sprawl, Shillong has seen an unusual phenomenon… Lantenas began to disappear gradually. As a child, we hardly realised that it was a boon in disguise – to combat further spreading of this poisonous weed was of little help in other parts of the country – this plant is a very adaptable species.

The colonial rulers considered Lantenas to have aesthetic value and introduced it as a decorative plant. That said, it was invasive, with a reputation of taking over several ecosystems in no time. Not only could this shrub grow rapidly on ground, it could also climb as a creeper on trees to inhabit the environment, making it difficult for other native plants to survive and flourish.

For curious readers, observing this can go a long way in ensuring balance. Let’s have a look at some other species to get a better understanding.

Eucalyptus (or bluegum tree) was introduced from Australia… another environmental hazard. For economic value, eucalyptus forests have come up in different parts of the country, found especially along the national highways.

As a species, it demands water to an excessive degree, depleting the ground water level in an unprecedented manner. The introduction of eucalyptus on arid lands may cause adverse environmental impact in the form of competition for more water from other species.

It will help to remember that eucalyptus roots penetrate very deep inside the earth in search of water, hence, depriving the land of much needed moisture. These trees dominate the habitat and share nothing with other plants. With a capacity to quickly absorb moisture and nutrients from the earth, they leave other plants vulnerable, fighting for a single drop of water – in the process, they often meet their inevitable end.

In the long run, other smaller plants may disappear because of their inability to compete for available moisture.

Eucalyptus also produces some toxic chemicals in their leaves. When they fall to the ground, forming a carpet of their own, these chemicals leech and spread further. This inhibits the growth of other plants.

This phenomenon is known as “competition in ecosystem”.

Credit for introducing eucalyptus goes to Tipu Sultan, the ruler of Mysore. He planted it in 1790 in his summer palace at Nandi Hills near Bangalore. It is believed that he received the seeds from Australia.

Back in its native land, a strange little and docile animal, the Koala, thrive on its poisonous leaves. A recent study on the Koala population revealed a very gloomy picture. There is a decline in their population as eucalyptus forests (that they inhabit) have given way to other plant species. The infamous Australian bush fires, which are very common in El Nino years (2023 is El Nino year, for instance), spreads fast through the top branches of the eucalyptus.

Another species has, similarly, wreaked havoc.

Lake Victoria, named after the Queen Victoria, borders Tanzania, Uganda and Kenya. It is the second largest fresh water lake after Lake Superior of North America. Most locals living near the shores of this great lake earn their living from fish.

In order to boost the fishing industry, the British introduced Nile Perch, one of the largest fresh water fishes into Lake Victoria.

In tracing its origins, one gets to know that it is actually a native of one of the Great Rift Valley lakes of Africa, known as Lake Albert. British marine biologists had introduced the Nile Perch in Uganda before taking it to Lake Victoria in 1950, an experiment with disastrous consequences.

Never in their dreams had they thought that it would spell doomsday for hundreds of other fish species. The Nile Perch is a fierce predator that dominates its surroundings. The introduction of this species caused hundreds of native cichlids

(about 200 to be precise) to go extinct.

While the fry (in their juvenile form) consumes a lot of shrimps, snails and insects, adult Nile Perch prey on other fish and can turn into cannibals, consuming members of the same community. Introduced with a view to alleviate the economy of the fishermen, it did not serve the purpose for a long period.

Next comes another species, a native of South America – the water hyacinth – a free floating plant, with a large leafy area that was introduced by the British as an ornamental aquatic plant. Commonly found in innumerable ponds and water bodies of Bengal, they are a real menace.

Given their penchant to grow very fast, they may cover huge water bodies within a short time, where they help in dissolving oxygen, an act that can lead to loss of aquatic life, in particular, fish. In this context, it has been aptly referred to as the “Terror of Bengal”.

A large waterbody near Kolkata, Santragachi Jheel, attracts different flying visitors from Siberia every winter. In the recent past, however, a decline in the number of our special guests has been observed. Often, they fly nonstop to reach waterbodies like Santragachi Jheel for nesting and breeding. Unchecked, the growth of water hyacinth poses a serious problem for the winged travellers.

Thanks to the participation of the local NGOs and residents, aquatic environment has been made suitable for the visitors. They worked hand in hand to clear the thick mat of water hyacinth. Reports show an appreciable increase in the number of birds in the recent past, where they have visited the waterbody.

In many parts of the country, water hyacinth forms a very thick impenetrable mat that may clog the water body, making fishing, boating and other activities almost impossible. This, in turn, may lead to a tremendous loss of biodiversity as it outcompetes other aquatic species.

Though scores of such invasive species have been introduced in India, not all of them are healthy from the ecological perspective. It may very well be said that though introduced with good intentions, exotic species were not always favourable to a new environment.

(The author is former Head, Department of Geography, St.Edmund’s College)