Multiple alien species affected soil nutrients in Kanha Tiger Reserve, put pressure on native forage plants and drove away herbivores
A forest in Kanha Tiger Reserve with a dense growth of invasive Lantana camara. These areas were restored timely following the study by the forest department. Photo: Rajat Rastogi Several alien invasive plants growing together can have a detrimental effect to the biodiversities in tiger habitats, a new study has found. The plants can put pressure on native forage plants and drive away wild herbivores — the food source for the big cats.
The research paper has deciphered many negative impacts of multiple co-occurring alien plants on biodiversity and what it means for conservation in the era of global changes. The study is the first of its kind in India and was published in journal Forest Ecology and Management by the Wildlife Institute of India (WII).
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India’s biodiverse ecosystems are threatened by a variety of alien plants like Lantana camara, Parthenium hysterophorous, Prosopis juliflora, etc, introduced during British colonisation. Lantana alone has pervasively invaded 44 per cent of India’s forests.
Apart from its spread in different ecosystems and occasional reports on its association with birds, little is known about how invasive plants affect an ecosystem in the long term. There is even greater confusion when one asks about how alien plants impact native ecosystems.
Many naturalist observations would rightly suggest that alien plants like Lantana camara are associated with rich sightings of birds and butterflies and provide ‘green cover’ for many other wildlife. At the same time, many others would count its harmful impacts on native plants and other ecosystem components.
Due to the absence of reliable scientific data and mixed opinions on the impact of alien species, there exists a dilemma regarding the need to manage them. In the face of rapid, pervasive invasions, this inaction could threaten ecosystems’ sustenance.
The study was conducted in Kanha Tiger Reserve, comparing uninvaded native forests with old-growth invasions of single and multiple alien plants. The researchers evaluated the differences in soil parameters, native grasses, herbs, shrubs, tree regeneration, habitat use by mammals, herbivory, bird occurrence, etc.
“Native forests are packed with biodiversity, particularly with rare species and interactions. Contrastingly, invaded areas only sustain a few commonly found species,” said Rajat Rastogi, the lead author of the study.
Co-occurring invasive plants like Lantana, Ageratum conyzoides, Pogostemon benghalensis, etc, have a magnified cumulative impact than their individual impacts, causing ecological homogenisation in invaded regions, the paper found.
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Multiple alien species together affected soil nutrients, which may have depleted the richness of diverse plants. “The abundance of rich grasses and herbs, the signature component of these ecosystems, was the most affected. There was hardly any regeneration of important plants like amla or even the most common tree — the sal,” reported Rastogi.
Native wild herbivores like chital and sambhar did not prefer the commonly found plants in invaded areas. They preferred rare forage plants, which were already depleted in infested areas.
“Although wild herbivores consumed a limited portion of alien plants. With monotonous invasion stands, their dependence on native forage increases”, the lead author said.
An elevated herbivory pressure on native plants and reduced habitat use in areas with a pervasive long-term invasion of multiple alien plants was noted by the research. “Invasions might slowly deplete the native plant populations and might lead to diseases in the herbivores,” it said.
Reduced forage availability for herbivores like sambar and chital, which are major prey for tiger, leopard, and dhole in this landscape, threaten the sustenance of these carnivores in invaded regions.
“The future of these tiger ecosystems can thus be grim. It is indicative of an ‘invasion-centric forest ecosystem’ historically unmatched, defaunated and functionally downgraded with homogenised biodiversity,” said Rastogi.
Alien plants have invaded majority of natural areas, while invasion management still operates at a truncated scale, said Y V Jhala, supervisor of this study.
“It is necessary to prioritise restoration investments in the least invaded regions to retain native biodiversity and slowly upscale such restored habitats,” Jhala said.
Read more: How alien invasive plant species threaten Western Ghats
The study highlighted the importance of investments in scientific restoration in India to mitigate the impacts of biological invasions.
“Many forest systems in India are restored by removing human impacts and maintaining rigorous protection. However, we see that these steps are important but not enough to sustain our ecosystems in our rapidly changing and increasingly invaded world,” it said.
The study was funded by WII Grant-in-aid and Banjaar Tola, Taj Safari. It was conducted in collaboration with Madhya Pradesh Forest Department.
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