Nearly half of India prone to invasive alien plants

Nearly half of India’s geographical landmass is prone to invasion by alien plant species, a new study has found¹. The study suggests that ‘invasion hotspots’ that fall within croplands, rangelands and village biomes must be given immediate attention to control and eradicate such species.

Invasive species — which colonise, spread and invade new territories — are considered a threat to local biodiversity and are estimated to trigger annual economic losses amounting to US$ 314 billion² in the agriculture and forestry sectors, of which India’s share is around US$ 116 billion.

The study has created the first nation-wide catalogue of regions most susceptible to invasion and identified ‘hotspots’ — regions that are climatically and geographically most suited for alien species — using ecological niche modelling (ENM) and geographical information system (GIS) data. “Delineating invasion hotspots would facilitate formulation of appropriate policy for their control and management,” says co-author of the study Saroj K Barik, a professor at the Centre for advanced studies in Botany, NEHU, Shillong.

ENM is a well-tested suite of environmental conditions in which a species persists and produces offspring. ENM analyses the natural habitat of a species to understand the characteristics of its niche and uses this information to identify areas having similar ecological conditions. The researchers generated ecological niche models for 155 alien species invasive to India and overlaid them with data from GIS to generate maps. The maps show the various species that a particular geographical region could sustain. Subsequently, they identified invasion hotspots by intersecting this map with anthropogenic biomes and overlaying on the ecoregions of India.

“Most ecologically sensitive regions of India, including the biodiversity hotspots, islands, coastal forests, freshwater swamp forests, mangroves and forest reserves, coincide with the identified 'invasion hotspots', indicating their vulnerability to alien plant invasion,” Barik says. Also, Andaman and Nicobar Islands, Andhra Pradesh, Assam, Dadra and Nagar Haveli, Daman and Diu, Goa, Kerala, Manipur, Meghalaya Mizoram, Nagaland, Odisha, Pondicherry, Tamil Nadu, Tripura and West Bengal were labelled with a ‘high risk’ of invasion.

Some regions, such as the Andaman rainforests, Godavari-Krishna mangroves, Odisha semi evergreen forests and Sundarbans swamps, were found to have more than 90% area climatically suitable for diverse invasive alien plants. Major port towns such as Mumbai, Ratnagiri, Panaji, Nagapattnam, Chennai, Kakinada, Paradip, and Haldia, fell within the identified invasion hotspots, offering avenues for introduction of invasive plants via shipping routes.

The coinciding of invasion hotspots with biodiversity hotspots in some places endangers many resident and endemic species. The authors recommend enumeration of invasive species and analysis of their impact on natives in these regions.

The study contributes to the small but growing invasion ecology literature in India, says Ankila Hiremath, a fellow at the Ashoka Trust for Research in Ecology and Environment (ATREE). However she says changing the methodology to recognise disproportionate contributions of different source regions of invasive plants might result in a different map of hotspots.

The best strategy, says Sohail Madan, Centre Manger at Bombay Natural History Society, Conservation Education Centre, is to work to protect forests to stop the spread of invasive species. “Once invasives get established, it is both time and labour intensive to eradicate them and reclaim that land,” Madan, who works at the Asola Bhatti wildlife sanctuary and is running a programme called Delhi Seed Bank Project to reclaim land from invaders in Delhi region, says.