Western Ghats, South Eastern Ghats & Central Indian Highlands among widely and densely invaded regions
More than half of India’s natural systems are threatened by invasive plant species, a new study highlighted.
About 66 per cent of the country’s natural systems are threatened with invasive species, according to the report published in the Journal of Applied Ecology.
The study offered the first account indicating distribution status of high-concern invasive plants spread across the country.
The findings are a result of a national-level survey conducted in India, which noted that 158,000 plots in 358,000 square kilometres of wild area are invaded by alien species. The 11 high-concern invasive plant species that showed presence in 20 states of the country included Lantana camara, Prosopis juliflora and Chromolaena odorata.
“The sampling effectively covered 31 per cent of savannas, 51 per cent of dry deciduous forests, 40 per cent of moist deciduous forests, 29 per cent of semi-evergreen forests, 44 per cent of evergreen forests and 33 per cent of moist grassland savannas,” the report said.
The findings from the core tiger populated regions become significant, Qamar Qureshi from the Wildlife Institute of India (WII) and co-author of the report, noted. This is because “the survival of apex predators like tigers depends on abundance of herbivores, which in turn depend on habitats free from the negative impacts of plant invasions. Proliferation of invasive plants jeopardises these delicate ecosystems, with far reaching impacts on species and people dependent on these ecosystems,” he added.
“Project Tiger was envisaged to serve as a flagship to monitor the changing status of carnivores, herbivores, and their habitat. Plant invasions alter habitats and reveal intricate ecological changes across biomes,” Qureshi said in a press statement issued by WII.
The study estimated that loss due to biological invasions would cost the Indian economy up to $182.6 billion.
According to the paper a total of 53 per cent of plots recorded at least one of the 11 high concern invasive plants that invaded 72 per cent that is 254,880 sq kilometres of land. Data also suggested that invasive cover increased with temperature to a certain threshold and dropped thereafter.
High concern invasive plants were recorded in 22 per cent natural areas and predicted to potentially threaten 66 per cent of natural areas, according to the report.
Analysis by researchers revealed the distinctive relationship between average invasion cover and independent variables. The data indicated that invasive cover increases with temperatures up to a threshold and declines with increasing rainfall, seasonal vegetation opening and human modification index. Human modification index is based on 13 anthropogenic sensors that provide a cumulative measure on impact of the human modification of terrestrial lands across the globe.
Savannas were reported to have the highest susceptibility (87 per cent) to invasions, followed by moist grasslands and dry deciduous forests each at 72 per cent. The evergreen forests were found to be least suitable for invasive species at 42 per cent susceptibility. However, the suitability of individual alien plants and its drivers varied for each species.
The study pointed out that Lantana camara had the largest expanse spread across 574,186 square kilometres, covering 50 per cent of natural areas occurring across all natural systems. Mikania micrantha had comparatively least expanse stretching over an area of 148,286 square km, covering 13 per cent of the natural area but mainly in moist grasslands and forests.
“Most species depicted the eco-climatic affinity of these plants. For example, 94 per cent invasion of Prosopis juliflora coincided with dry grassland savannas and dry deciduous forests. Species like Senna tora, Xanthium strumarium and Mesosphaerum suaveolens were predominant in dry savannas and deciduous forests, whereas Mikania micrantha and Ageratina adenophora were distributed in moist grasslands and evergreen forests,” the report said.
Nilgiri Biosphere Reserve in Western Ghats was one of the largest impacted hotspot areas due to invasion dominated by Lantana camara, Prosopis juliflora and Chromolaena odorata.
Besides, Southern Eastern Ghats were found to host the most densely invaded landscapes with maximum vegetation of Prosopis juliflora and Lantana camara.
“Fragmented forests of Central Indian Highlands were also largely and densely invaded forest systems, typically along the ecocline between dry and moist systems. Savannas were largely invaded by woody Prosopis juliflora, particularly surrounding semi-arid protected areas,” the researchers said.
The scientist said that human modifications, shifting soil moisture regime, historical propagation of invasive plants and altered cycles of natural disturbances are the main driving factors behind the invasions.
The increasing work population densities and proportional increase of demand for food, infrastructure, energy and socio-ecological drivers further threaten to intensify and possibly escalate the accelerating invasion, the authors of the report noted.
YV Jhala, a contributor to the study, told Down To Earth that “Increase in invasive species means loss in ecosystem services from forests and increased propagules that is a vegetative structure that if detached from a plant can give rise to a new plant into agricultural areas will result in economic losses.”
Speaking on the impact on carnivorous animals who depend on herbivores, he said that an increase in the invasive plants which are unpalatable will translate into lack of food and result in reduced carrying capacity for herbivores, eventually causing decline and shortage of food for the apex predators.
The scientists said that all hope is not lost and strategic high-priority restoration can help manage invasions.
“Managing invasive species demands more than mere removal — it necessitates context-sensitive restoration, stakeholder participation, and adaptive holistic policies that can enable positive changes,” Ninad Avinash Mungi from Aarhus University, Denmark, and co-author of the research said.
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