Colonies of snails on the march, giant trees smothered by creepers, rivers and lakes teeming with exotic fish, coral reefs colonised by new species -- Kerala is facing an alien invasion that threatens to dilute its rich native biodiversity and wreak havoc on the fragile ecosystem.
Hundreds of invasive species from trees, snails and waterweeds to fish, agricultural pests and seabed corals are posing a threat to native flora and fauna. In recent years, the State has emerged as a hotspot for invasive alien species, as the government struggles to come up with a management plan.
Many native species have suffered from predation and pressure on their natural habitat as the invasives continue their march.
Invasive species are considered the most serious threat to biodiversity after habitat destruction. It is estimated that three trillion dollars are spent every year across the world to manage the threat.
While most of the alien plant species found in Kerala were once imported for horticulture, forestry and agriculture, animals like snails and insects are believed to have reached the State as stowaways in timber consignments. Many of the invasive aquatic species were either imported for aquariums or introduced through the ballast water of ships entering ports.
In 2012, the Kerala State Biodiversity Board and the Kerala Forest Research Institute prepared a database of 89 alien invasive species of plants including trees, shrubs, herbs and climbers. The list classified invasive plants into three groups based on the risk factors.
As many as 21 species were classified as high risk, capable of edging out a large number of native plants. Many of the invasives like Nila grass ( Mimosa diplotricha ) and Bracken fern ( Pteridium aquilinum ) are tolerant to various environmental conditions, can cause heavy damage to crops and are even toxic to livestock.
Mucuna ( Mucuna bracteata ), known as Thottapayar in local parlance, and the Chinese creeper ( Mikania micrantha ) are aggressive climbing vines that can smother, choke and stunt the growth of native trees such as rubber, coconut and other plantation crops.
While Sleeper weed ( Lantana camara ), a fire-adapted species, grows in dense thickets, disrupting the growth of native species in forests, Black wattle is known to replace indigenous vegetation including grass, leading to heavy soil erosion and destabilization of riverbanks in the high ranges, posing a threat to shola forests.
“As a State bordering the Western Ghats biodiversity hotspot, Kerala cannot afford to ignore the threat. Over the years, many of the alien species have established themselves and spread to new areas, displacing natural vegetation,” says T.V. Sajeev, Scientist, KFRI.
Some species such as Manjakonna ( Senna spectabilis ) and Umbrella tree ( Maesopsis eminii ) that were earlier classified as medium risk have later emerged as major forest invasive species.
Climate change factor
Dr. Sajeev feels that globalisation and climate change are aggravating the vulnerability to biological invasion. “With better connectivity and more points of entry, Kerala has witnessed the introduction of more alien species than in the past. Many of the new species are capable of adapting to warmer temperatures triggered by climate change factors and go on to compete with less tolerant native species.”
The KSBB has also listed Nile Tilapia, Sucker catfish, cane toad, American bullfrog and Giant African snail as invasive animals posing a serious threat to biodiversity.
African snail has proved to be a tenacious invasive in Kerala, difficult to eradicate despite the best efforts of government agencies and local bodies. First reported from Palakkad in the 1970s, it is now present in all but four districts.
Experts recommend strict quarantine measures at seaports and airports in the State to control the import of alien species with the potential to become invasives.
Member Secretary, KSBB, Dinesan Cheruvat said efforts were on to formulate a participatory management plan for invasive species. “We are planning to use the panchayat-level Biodiversity Management Committees and Kudumbasree and MGNREGS workers for eradication of alien invasives,” he said.
Dr.Sajeev, who coordinates the Asia Pacific Forest Invasive Species Network (APFISN), said the Forest Department, in association with the KFRI, was working on the development of a protocol for management of invasives.
He advocates a single window approach to deal with the issue, with an institutional mechanism at the State level to coordinate control and management.
Experts also call for stepping up domestic quarantine measures in view of the increased interstate traffic of biological species.