'Invasive alien species: Why are we concerned about them?' writes Jayshree Vencatesan

Most gardens, including those that have been in existence for decades now are comprised of a mixed bag of plant species including native and naturalised species as well. In fact, most of the ornamental plants that typified gardens in the past are those species that were brought into the country for gardening, which over the years became an inherent part of the landscape, thereby being considered naturalised. These were alien species that eventually turned ‘native’! The urge to create neo European landscapes in the subcontinent prompted the British to bring along a number of garden plants. Lantana camara is one such garden plant that was used for establishing hedges. 

Along with the garden plants, certain plant species that could grow rapidly and meet the timber demands of the British Empire for ship building, railway sleepers and war infrastructure were also brought in and planted extensively. The wattle is a good example of such species. 

In addition to the above, as India imported food grains to mitigate famine, some unwarranted weeds and pests made their way into the country. Likewise, to meet  the fuelwood and food demand of the poor and needy, the government imported certain fast growing, hardy plants into the country and embarked on missions to mass propagate the same. The thorny Prosopis julifora is one such case. 

What the world has since realised is that some of the alien species that were introduced into various countries have run wild creating amok and displacing native species. These species are designated as Invasive Alien Species. In fact the Invasive Alien Species have been designated as the second most serious threat to ecosystems and biodiversity after habitat loss. 

In economic terms, the example of Water Hyacinth (which is found in almost all the waterbodies of Chennai), a wetland Invasive Species is estimated to have caused USD 100 million per year in costs related to water use in developing countries. Likewise, the innocuous Lantana camara is estimated to have cost India a massive USD 300 million every year in terms of habitat loss. So profound is their impact  that the United Nations through the Convention on Biodiversity has stated that by 2020, the Invasive species and their pathways have to identified and prioritised for eradication and further introduction has to be curtailed. In India, Kerala is the only state which has drafted a blacklist of invasive alien species and has a plan of action in place for their removal.