Featured image: Lantana camara. Photo: Mauricio Mercadante/Flickr, CC BY 2.0
While India talks about the impacts of developmental projects on biodiversity, an exotic plant with pretty flowers has diligently carved its way to degrade its forests. This plant, Lantana camara, is a thicket forming shrub native to tropical America.
Arriving in India as an ornamental plant in the early 1800s, lantana has escaped from gardens and taken over entire ecosystems, now occupying 40 percent of India’s tiger range alone.
Multiple hybrid varieties of lantana were brought to India and over the 200 years of its introduction, the varieties have hybridized and formed a complex. The species is now able to climb up the canopy as a woody vine, entangle other plants by forming a dense thicket, and spread on the forest floor as a scrambling shrub.
Lantana is one of the world’s ten worst invasive species and a species of high concern for India. It competes with native plants for space and resources, and also alters the nutrient cycle in the soil. This invasion has resulted in the scarcity of native forage plants for wild herbivores. If eaten, the leaves can induce allergies on the muzzles of animals. In some cases, extensive feeding on lantana has led to diarrhoea, liver failure, and even the animal’s death.
Indian forests: green cover is not always forest cover
Lantana has long escaped India’s manicured gardens and has spread across the length and breadth of the country, invading roadsides, fallow plots, agricultural fields, and forests.
A recent study published in Global Ecology and Conservation reports that lantana occupies 154,000 sq.km forests (more than 40% by area) in India’s tiger range. Among forests, Shivalik Hills in the North, fragmented deciduous forests of Central India, and Southern western Ghats are worst hit by its invasion.
The study has analyzed data from one of the most extensive known systematic surveys done for evaluating the status of invasive plants at multi-landscape scale. These surveys were part of the National Tiger Estimation Project. They were conducted both inside and outside of protected areas in India by the forest guards of respective State Forest Departments and a team of wildlife biologists.
During the survey, the forests in 18 tiger states of India were divided into units of 25 sq.km. Each unit was sampled to record native and invasive plants and human disturbance. In this way, 117,104 plots were sampled across 200,000 sq.km of forest area. Along with this information, data on factors known to facilitate the spread of invasive plants (like soil fertility, water availability, climate, fire, roads, and other human modifications) was used in a model, which was used to predict the spread of lantana in these forests.
This research shows that forests degraded due to human influence and those occurring in warm and humid regions are most affected. Madhya Pradesh, which has the highest reported forest cover in India, was found to have a substantial part of its forests invaded. Likewise, Bandipur Tiger Reserve, which was shown to be ‘greening’ by another study, was found to be substantially invaded by lantana.
The study also points out, lantana in India is growing in climatic conditions quite different from its native climate in Central America. “Nearly 60% of lantana occurred outside its native climatic niche”, mentioned Ninad Mungi, a researcher at the Wildlife Institute of India and the lead author of this study. “Lantana can tolerate warmer temperature and more moisture [in India], as compared to its native region. This can help it utilize the changing climate, where most of the native plants are failing,” he added.
The models estimate that 300,000 sq.km forest area (an extra 44% of forest area) across India is threatened with lantana invasion – which means there is a high risk of biodiversity loss due to lantana invasions in these areas.
Invasion scenario with development, fragmentation, and EIAs
While more than 40% of Indian forests are invaded, the rest 50% holds the potential to conserve the native forms of our forest ecosystems. The study identified such uninvaded forests to be present in northeastern India, and in parts of Odisha (Simlipal and Satkosia), Chhattisgarh (Hasdeo Arand forests), Jharkhand (Palamau) and Maharashtra (Bander – Tadoba Andhari Tiger Reserve). However, most of these forests have been earmarked for developmental projects (like dams, coal mining, etc.).
When human influences are overlaid on forests along with the effects of invasion, the situation becomes grim. Widening of roads, mining, and submergence due to dams lead to forest fragmentation, increased invasion, and ultimately loss of biodiversity. The study reports forest degradation to be one major driver of lantana spread. Unsustainable human modifications of the uninvaded forests can degrade them, which can, in turn, help lantana invade these forests.
Economics of managing lantana
Eradicating lantana has been practised religiously in several protected areas in tropical India, where on an annual basis, hectares of lantana invaded patches are either burnt, or are uprooted. Most of the time, the frontline forest staff works across the summer months in these forests manually uprooting this thorny plant one after the other. But, the impact of dealing with this plant on human health is little known, nor are the wages for these labours promising.
The study also mentions that controlling lantana in one sq.km costs 14 lakh rupees and with the current expanse it would need 10 billion dollars more than the total funds allocated to the Ministry of Environment, Forest and Climate Change (MoEFCC), in the year 2019!
Tackling invasion: A challenge for ecologists and managers
Protecting biodiversity and patrolling the forests against illegal activities becomes difficult with the presence of these invasive plants. Today, some forests (like Bandipur Tiger Reserve) are completely covered with lantana bushes, raising concern for both scientists and managers.
But what leads to such a monstrous spread of this invasive plant? Well! The answer lies in the numerous ways it is propagated. Lantana is mainly dispersed by fruit-eating birds, monkeys, bears, etc., but it also has a capability to grow from its root-stock, and nodes (via vegetative propagation). When Geetha Ramaswami and her colleagues studied the dispersal of lantana in Rajaji National Park, they observed that a lot of fruit-eating birds are attracted to lantana. Bulbuls in particular. “They rapidly disperse lantana seeds from source plants to managed areas. These areas are often not very far from fruiting source plants [of lantana] and they fall well within the median dispersal range of bulbuls!,” said Ramaswami, who is currently with the Nature Conservation Foundation.
In every Tiger Reserve, a few hectares of land is cleared of lantana each year, but the area requires intensive surveillance. Since lantana seeds are already present in soil and they are also dispersed by many birds from surrounding areas, lantana regrows rapidly. To tackle this, a follow-up removal of lantana seedlings is necessary for a minimum of two years. It is a mammoth task and results have not yielded much.
“It is already known that lantana needs to be uprooted, rather than merely cut above-ground, to prevent aggressive regrowth from the root-stocks. Our work has confirmed this,” said Jayashree Ratnam, Associate Director of Wildlife Biology and Conservation programme at NCBS, Bengaluru.
Ratnam’s work on lantana highlighted that even with weeding, the recovery of native grasses is limited. “We, therefore, recommend uprooting, followed by weeding and some seeding of native grasses, for the most effective return to native understories in deciduous forests, which are amongst the most commonly invaded forest types in India”, she added.
Rajesh Gopal, Secretary General of the Global Tiger Forum mentioned that “lantana has naturalized itself since long in our forests, and its spread is considerable in several tiger reserves, warranting recurring actions for phased eradication as a strategy under the Tiger Conservation Plan. However, this needs to be done with due consideration to the prevailing carrying capacity of the habitat for tigers.”
Mungi and his colleagues strongly emphasize on habitat-oriented management. Whereas, Ramaswami’s research shows that increasing distance from source plants along with long term removal may be a way to prevent regeneration from seeds in managed areas. On the other hand, Ratnam highlights the importance of fire-based management in these grassland-woodland systems, commonly called savannahs.
Lantana has replaced grasses (primary fuel for forest fires) from the understory, changing the intensity and spread of fire when it occurs. “We suspect that controlled fires to destroy seeds in the seed-bank may be an important management tool in controlling rates of lantana re-invasion, but this idea remains to be tested. In my view, using fire to control lantana has to be carefully orchestrated and managed”, Ratnam said.
These forests are rich in native biodiversity and provide ecosystem services worth millions of dollars. Unless prioritized, biodiversity loss due to the presence of invasives and fragmentation can lead to unhealthy ecosystems and may result in ecosystem disservices. Hence, along with early detection and monitoring, there is a need for management-oriented research.
On a priority basis, we need to study how native vegetation responds to various lantana removal practices like uprooting, weeding, fire, etc. Many countries have informed policy through similar exclusion experiments (e.g., United States, Australia, Hawaii) but evidence from India is rare.