Thiruvananthapuram: Invasive species, especially senna, are being eradicated from forests and their fringes but flourish as avenue trees in the city. Senna trees planted along Kowdiar-Pattom road have flowered, though no agency has studied invasive trees in public spaces or planned replacements, and neither state govt nor the corporation has formulated a policy.An earlier study on the health of avenue trees by the city corporation identified three invasive species: Senna spectabilis, Senna siamea and Leucaena leucocephala (lead tree), native to tropical America and Southeast Asia.Tree lovers say many flowering trees on the city’s main roads, including gulmohar, are exotic but not invasive, unlike species that spread fast and harm local flora. Trees on Kowdiar-Vellayambalam, Vellayambalam-Vazhuthacaud, Vellayambalam-Palayam and Edapazhinji-Pangode stretches, including acacias, are also exotic but considered harmless.Anita Sharma of Tree Walk, an NGO, said, “We have to be alert about planting exotic species. There is no alarming situation in the city like it is the case of forest and forest fringe areas. But have to encourage local species.” Tree Walk has not surveyed the city but has noticed senna trees on Kowdiar-Pattom road.“Years ago, urban bodies preferred ornamental trees that looked attractive and provided shade for planting along major roads. The forest department’s social forestry wing also raised saplings of such species, including senna. However, the mistake was recognised over time, and the department now raises and distributes only native species,” said a former forest department official. Senna spectabilis is considered the most dangerous, choking out local plants.Though the department no longer distributes such saplings and corporation guidelines favour local species, there is no control over planting by people or institutions.“There is a need for a well-thought-out policy to remove these trees only after native species have been planted and grown, as many shelter birds at a time when private owners are cutting down trees,” said an official of state biodiversity board.The board has submitted an invasive and alien species policy to state govt, circulated to the agriculture, animal husbandry and local self-govt departments. It is also indexing the city’s biodiversity with the corporation, begun recently, to count such species and suggest protective steps, the official said, adding that removing all the trees at once is not feasible since many shelter birds. “It is also important to note that all exotic trees cannot be called invasive.”
