Invasive plants, pests choke out native biodiversity

In 1997, when researchers from Ashoka Trust for Research in Ecology and the Environment (ATREE) began studying Lantana camara in the Biligiri Rangaswamy Temple (BRT) Tiger Reserve in Chamarajanagar, the invasive weed native to the American tropics was only beginning to spread. 

Today, the weed has become the most dominant species, in not only the BRT reserve, but across lakhs of acres of the deciduous forest and woodland savannah vegetation of Karnataka. 

Lantana is an invasive alien species (IAS), which is a class of animals, plants and other organisms introduced to new regions through human activities. They thrive at the cost of native and endemic species. Invasive species have been identified as the second biggest threat to biodiversity, after habitat destruction.

Shivanna Muttegowda (65) remembers the forests of the BRT reserve as lush green in monsoon and ashen in summer. Now, the landscape has changed. He lives in Kanneri colony, a tribal hamlet in K Gudi.

“The grass undergrowth would get dry and catch fire. But even in the middle of summer, we would see green shoots in a few days aided by nothing but dew. Over the last 20 years, Lantana has blanketed the B R Hills. A single spark can burn down the entire forest,” Muttegowda said.

"Surveys across the entire landscape of BRT in 1997, 2008 and again in 2018 showed that Lantana went from constituting 5% to 30% of all woody vegetation. Now, almost 50% of woody vegetation is constituted of Lantana weeds. This increase has been at the expense of native vegetation,” said Ankila Hiremath, a plant ecologist and senior adjunct fellow at ATREE.

Ankila said Lantana has changed the BRT reserve's vegetation as the dense understory of the weed has restructured the open savannah woodland. "This has altered habitat structure and quality — the forests are less navigable for large herbivores. Palatable forage has been replaced by unpalatable Lantana. Studies have shown that Lantana competes with native species like amla, an important non-timber forest product, thus affecting livelihoods of forest-dependent communities like the Soligas," she added.

Experts from the Wildlife Institute of India (WII) reported in 2020 that Lantana has taken over 44% of India's forests. The weed, however, is just one piece of the puzzle, as Euopatorium, Senna spectabilis, acacia and Ballari jali (Prosopis juliflora) have ravaged the biodiversity of deciduous forests and grasslands. The Environment Management and Policy Research Institute, which studied Jindal company’s 24-km long mining conveyor system in Ballari’s Toranagallu, found that Prosopis juliflora and parthenium had invaded 1.6 km of forest area along the conveyor. 

Economic impact

On September 5, the Intergovernmental Science Policy Platform on Biodiversity and Ecosystem Services (IPBES) warned that IAS were responsible for 60% of the species extinctions recorded in the world. The economic impact of this loss is also significant. About 37,000 IAS in the world were causing annual losses of Rs 42,300 crore as of 2019.

Ecologist and evolutionary biologist Alok Bang, who co-authored a study that estimated that damage due to IAS could have impacted the Indian economy to the tune of $127 billion in the last 60 years, said it was only a fraction of the real cost. The researchers used INVACOST, a database that involves systematically retrieving, collating and standardising the reported economic costs of IAS.

"We only calculated the cost of the documented claims that were peer-reviewed. In fact, we have only scratched the surface. This is clear when we consider that India has reported only about 300 IAS compared to the nearly 3,000 IAS reported by France. Indian ecologists and biologists have a long way to go in understanding and reporting," said Bang, a faculty at Azim Premji University. 

This ecological and economic impact will only grow if there is no intervention, said K V Sankaran, an expert on invasive species and coordinating lead author for the IPBES report. "Our estimations show that the costs due to IAS have increased four times every decade since 1970. It is also estimated that the number of alien species will increase 36% by 2050 (compared to the figures in 2005) if we do not adopt necessary control measures," he said. 

The accelerating global economy and intensive land and sea-use changes create a fertile ground for IAS. Climatic and demographic factors also help such species gain a foothold in these ecosystems. The costs would be much higher in 2023 compared to 2019. Invasive species and their negative impact will only increase if necessary measures are not adopted immediately.

Home to rich biodiversity, the country’s natural habitats have provided direct (forest produce) and indirect benefits (fodder and water) and services (climate regulation) to crores of people for generations. As the invasive species erode this diversity, the primary victims are vulnerable populations like forest dwellers, farmers and fisherfolk.

For instance, in the case of Soligas, researchers from ATREE noted that apart from tangible impacts on livelihoods, invasive species also significantly affected the well-being of the community. "Our work with Soligas tells us that the Lantana invasion has made the forests a more dangerous place for people by reducing visibility and increasing chance encounters with large wildlife,” said Ankila. 

As a result, over time, these invaded landscapes have reduced people’s access to places of cultural significance, and younger generations are growing up more distanced from the forests, their traditional knowledge and cultural practices, she added. 

Data from the Forest Department shows that the total number of human-animal conflict cases — from crop and cattle loss to casualties on both sides — has doubled in 10 years from 20,244 in 2013-14 to 40,258 in 2022-23 in the country. As the IAS renders even protected areas uninhabitable for wildlife, the cases are likely to climb further.

Means for prevention

Bang said identifying and classifying IAS is possible only when subject experts start looking into a problem. "For instance, a pest in an agricultural crop may be identified, but to classify it as IAS, a domain expert with knowledge of invasive species needs to get involved,” he said.

The researcher added that it is safe to assume that numerous IAS have not been identified. “This is worrying because delay in action will only lead to multiplication of costs," he said.

Sankaran noted the root of the problem was in the lack of a policy to check IAS. "Only 17% of countries across the globe have national laws or regulations to address invasive alien species issues. And 45% of all countries do not invest in the management of invasive alien species," he said.

Officials agreed that prevention is better than management in the case of invasive species. “We need close to Rs 30,000 per acre to remove Lantana, plant native species of grass and manage it for the next two years. The whole process is very slow compared to the speed of the invasive weed which spreads like wildfire,” said Subhash Malkhede, Principal Chief Conservator of Forests (PCCF), Wildlife.

Former PCCF B K Singh noted that human activity inside natural forests was the first driver of IAS. “The natural ecosystem is disturbed by fragmentation and fire, paving the way for IAS. Some of the Lantana-infested areas in Bandipur, BRT reserve and Nagarahole are so dense that even elephants cannot navigate through them. We have to prevent forest diversion and fragmentation for better protection of habitats,” he said.

Widespread issue

The problem is not limited to forests — agriculture, horticulture, animal husbandry and fisheries are already in the middle of an emerging crisis. A case in point is the fall armyworm, a pest native to the Americas, that has proved deadly for maize and other crops. In India, it was first reported in Karnataka in May 2018. By August 2019, researchers saw its presence in the entire country, except Jammu and Kashmir.

During the course of their research, S S Deshmukh and others from the University of Agricultural and Horticultural Sciences, Shivamogga, and the International Maize and Wheat Improvement Centre in Nairobi, Kenya, studied 150 small farmers and found that the cost of cultivation had gone up by Rs 3,600 per hectare as they invested in more pesticide. “These additional costs are considerable for resource-constrained small landholders. The maize yields during 2020 were largely at par with those in 2017, but the cost of plant protection per hectare per season increased 10 times in 2020,” they concluded.

Notably, they observed that pesticide application frequency increased significantly from “0.10 pesticide sprays per season in 2017 to 2.10 applications”, an increase of 2000%.

In yet another case, the Centre told the Rajya Sabha last year that 40% to 80% of the chilli crop in Telangana and Andhra Pradesh was destroyed by an invasive pest called Thrips parvispinus, also known as the South East Asian thrip. “Excessive use of chemical pesticides and staggered plantings also might be the reasons for their outbreak,” the government said, citing a report by experts.

Out of the 300+ species classified as IAS in India, about 99 marine and 19 freshwater invasives have been identified by the Zoological Survey of India. The ramifications of their impact are visible. The IPBES report cited the displacement of native clams and oysters caused by Caribbean false mussel, a development that directly affects the fisherfolk.  

Climate change

Complicating the situation further is climate change, which makes ecosystems more vulnerable to invasive alien plants by reducing the resistance of native species to invasion. “There are many complexities that make it hard to predict the full impact. Climate change can interact with invasive alien plants and can result in intensive fires. The movement of certain IAS plants from low altitude areas to high altitude areas, which we have evidence of in India, is proof of the impact of IAS,” Sankaran said.

In its commitment to fight climate change, India announced in the Paris Summit (COP 21) its target to create carbon sinks of 2.5 to 3 billion tonnes of CO2. This essentially meant promising to increase the forest cover to 33% of the total land cover, from the current 21%.

In July, over 400 ecologists who opposed the Amendment to the Forest Conservation Act wrote in a letter to the Centre that commercial plantations, forest fragments and urban parks “in no way, can replace the ecological functions performed by intact natural forests”. Domain experts have warned that dilution of the strictures will lead to further deforestation, diversion of forests and disturbance to natural areas.

As governments reinforce the utilitarian model of conservation, where value is ascribed to an ecosystem only if it benefits people, the significance of biodiversity has taken a backseat. Bang noted that recognising the importance of biodiversity, regardless of its immediate social benefits, was a key step forward in conservation and protection against IAS. “Protecting the natural ecosystem should be a proactive measure to avoid loss and extinction of native and endemic species. It has to be seen outside the framework of a utilitarian perspective,” he said.