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Legacy invasive plants like lantana cannot be allowed to run wild

Invasives outcompete, outperform and outmanoeuvre native species, leading to huge economic, ecosystem service and carbon sequestration losses

The lantana is invasive in India.
The lantana is invasive in India. (iStockphoto)

The flowerhead gleamed softly, a wonder to behold. It looked like a tiny flower in a flower, or perhaps a bunch of flower-dots making up a bigger one. The leaves and blooms, when fondled, smelt of mint, and walking through a jumble of lantana bushes made you smell like a blossom: heady and lingering.

You could pick lantana colours in the way you pick “gems” candies—yellow and pink flowers, red, purple, golden yellow, marigold rust, and just pink. Initially, Lantana camara dotted hedges, snaked through abandoned lots, and grew upright in genteel, decorous rows. With the passing of time though, lantana bushes were no longer polite borders waiting on thresholds—they were the entire garden. In tiger reserves I visited later, lantana was the towering tree, the crouching bush, the foreground and the bokeh—it had essentially taken over entire swathes of land. A recent study (Mungi et al, 2020) estimates that 40% of Indian forest has been taken over by Lantana camara. Other observations note the takeover of invasive species leads to human-wildlife conflict, as animals like elephants venture out to fulfil nutritional needs.

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Fortune favours the brave, they say, but in ecology there is something suspect about things that conquer an entire place. A single kind of bright flower dominating an understorey or a single kind of tree taking over the horizon does not signify survival of the fittest (or bravest). It usually denotes an invasive species—a foreigner that outcompetes, outperforms and outmanoeuvres native species. Invasives lead to huge economic, ecosystem service and carbon sequestration losses.

This month, the lantana of childhood came to mind as I visited the Mudumalai tiger reserve in the Western Ghats. All around me stood trees with branches that speared out, like a crown of thorns. The crown was tipped with eye-meltingly yellow flowers. Like the lantana, these were ornamental and pleasing. But also like the lantana, the Senna spectabilis is invasive in India. Invasives present a kind of easy beauty that is beguiling, but this is also beauty with teeth and venom.

For the first time, though, we have a law to change how things stand. An amendment to the Wild Life (Protection) Act (also called the WLPA), brought in last year, has directions for the tackling of invasive species. If you have visited island nations like the UK and Australia, you already know you are not allowed to carry foreign fruit or seeds into these countries, because they are either unknown exotics or invasives. India has islands too, which are hyper-sensitive to invasive species; so is the mainland. Yet, despite major economic and ecological threats, we still lack a national action plan to identify, eliminate and monitor invasive species. Shockingly, despite the changes to the law, invasive species of fish and plant are easily available for sale. Nurseries sell Lantana camara in as many colours as you would like—all the gems in candy colours. You can sow a field of golden lantana, fringed by pink and yellow ones, and not feel the guilt of, say, owning an anachronism like a piece of ivory.

Water hyacinth coats a wetland in Haryana.
Water hyacinth coats a wetland in Haryana. (Neha Sinha)

The WLPA is a start but the urgent need now is to hit the ground running. Firstly, we must draw up a complete list of invasive species in land and water. Invasives are an equal opportunity offender that strike waters too. The water hyacinth, another striking, easy to grow invasive, covers wetlands with its emerald green mat and purple blossoms; choking the wetland and causing hypoxia, or the reduction of oxygen.

Secondly, we must identify strategies to destroy invasives. Some stubborn invasives need burning, complete uprooting and further monitoring. Thirdly, we must not act at cross-purposes—all stakeholders must be made aware of the dangers of invasive species.

Next, innovative livelihood practices must be incentivised to manage invasives—such as cane-like furniture made from water hyacinth or lantana. And finally, we have a huge communications and outreach challenge in front of us—we must start from the very beginning in educating resident welfare associations, farmers, gardeners, governments and more.

“We have taken an important first step in recognising the problem of invasive species,” says Abi Vanak, senior fellow at the Ashoka Trust for Research in Ecology and the Environment. He adds: “From a policy perspective, this needs to be incorporated across the board with all ministries and departments that handle biological material of any sort. This requires multi-sectoral coordination between all the relevant ministries so that minimum standards for inspection and quarantine are set in place, with the National Biodiversity Authority (NBA) being a coordinating agency, as is mandated under the Biological Diversity Act. Furthermore, we need to ensure that ministries are not acting at cross-purposes with each other. For example, the Indian Council of Medical Research has issued guidelines for introducing the highly invasive Gambusia fish to control mosquitoes, without taking into consideration that the NBA has listed them as an invasive species.”

Another complication is that invasive species may perversely become integrated in ways of living, even if they harm the overall ecosystem. In the famed Delhi Ridge forest, you can easily spot a thorny, feathery leafed tree with a twisted trunk—this is more a snarl than a tree, and this snarl covers kilometres of forest. This is the Vilayati kikar or Prosopis juliflora, the chief enemy to ecosystems. This South American tree renders the land under it virtually incapable of supporting other trees, in classic invasive fashion. Yet, pastoralists use the tree in some landscapes. This means that there could be social barriers to clearing an invasive, which implies they have to be destroyed before they can establish themselves.

I have seen birds and animals sitting on Vilayati kikar, but very few feed on its thorny branches. In the Delhi Ridge, I watched a male Grey hornbill delicately feed a female, while sitting on the Vilayati kikar. The birds were framed with a luminous, uniform green hue from other foreign kikars. It was a perfect, good-looking scene. But optics isn’t everything. If the Prosopis was actually a Goolar fig tree (which grows clusters of figs), a sprawling Banyan, or even a hardy Peepal, the birds would be feeding each other figs from the same tree. They would be joined by monkeys, barbets and bats, and likely squabble with a few. They would, in fact, be at the centre of a thriving, native ecosystem. This is what reclaiming hundreds of kilometres covered by invasive lantana, juliflora or senna will mean—native forests actually behaving like forests.

Yesterday, state governments were wilfully (and cheerfully) planting Prosopis julifora, looking for a quick green fix. Today, a huge, invasive top predator from the Amazon—the Arapaima fish—swims in Kerala’s waters. And tomorrow will be a green desert if we don’t take care of our legacy invasives.

Neha Sinha is a conservation biologist and author of Wild And Wilful: Tales Of 15 Iconic Indian Species. Views expressed are personal.

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