An invasive plant is threatening sloth bear habitats and could increase conflict

Previous research has examined the impact of invasive plant species on the diversity, population dynamics and richness of native woody species and its impact on wildlife and ecosystems. However, a recent study conducted within the Jessore Sloth Bear Sanctuary in Gujarat offers what probably is the first quantitative investigation into how Prosopis juliflora specifically affects sloth bear habitat utilisation in a semi-arid landscape.

According to the researchers, Gujarat was selected because of its significant sloth bear population and widespread presence of P. juliflora, especially in the northern regions connected with Rajasthan. “The study aimed to understand how this invasive plant affects sloth bear habitat use patterns. The state’s diverse ecology provided an ideal opportunity to investigate the interactions between invasive species and wildlife, offering insights for conservation planning,” says Ashish Jangid, one of the authors of the study.

Understanding Gujarat’s ecology

Gujarat has diverse agro-climatic zones based on rainfall patterns. The extreme north and northwest, including Kachchh and parts of Banaskantha, Patan and Jamnagar districts, are arid. In contrast, the extreme south, including Surat, Narmada, Navsari, Valsad and Dang districts, experiences a sub-humid climate with lush vegetation. The rest of the state falls under a semi-arid climate, characterised by sparse vegetation, frequent droughts and soil erosion vulnerability.

Naturally dry landscapes typically have less complex vegetation communities and pose less resistance to any newly introduced species, explains Chetan Misher, a researcher at the Ashoka Trust for Research in Ecology and the Environment (ATREE), who was not associated with the study.

Enter P. juliflora. Originally from Central and South America, it was introduced in India in 1877. Known for its resilience, it thrives in harsh environments and can withstand drought and disease. It can access groundwater with its robust root system, surviving even in peak summer. “This adaptability led to its deliberate planting across India’s dry landscapes, intending to transform deserts into green spaces while providing livelihoods and fuelwood to locals,” he says.

However, concerns arose over time. While research indicated that encroachment of this species had significant adverse effects on native vegetation, a comprehensive analysis, published in 2015, of 3,624 animal observations highlighted its detrimental impact on wildlife diversity, fitness and ecosystem functioning, with no documented benefits. Consequently, it was classified as an invasive alien plant species in India and is now ranked among the top invaders by the National Biodiversity Authority.

Among those affected by the rapid spread of P. juliflora is the sloth bear. Sloth bears are found widely across semi-arid regions of the Indian subcontinent and inhabit various ecosystems from grasslands to forests. However, they face population declines due to poaching and habitat degradation, leading to local extinctions and confinement to lowland areas in India, Nepal, Sri Lanka and Bhutan. Conflict with humans and retaliatory killings as a result of the sloth bear attacks have also hindered conservation efforts. So, understanding the factors influencing their habitat usage is essential for effective conservation and their long-term survival.

In Gujarat, sloth bears inhabit five wildlife sanctuaries: Shoolpaneshwar Wildlife Sanctuary, Jambughoda Wildlife Sanctuary, Ratanmahal Wildlife Sanctuary, Jessore Sloth Bear Sanctuary and Balaram-Ambaji Wildlife Sanctuary. They primarily feed on termites, ants and fruits and contribute significantly to forest regeneration and biodiversity maintenance here. “In many dry deciduous forests across India, sloth bears act as keystone and umbrella species, particularly in the absence of larger mammals such as tigers and elephants,” says Jangid.

Yet, despite their vital role, there is limited information available about their habitat use, dietary habits and movement patterns in semi-arid areas. To address this gap, the study focused on investigating seasonal changes in habitat usage within the Prosopis-infested habitat of the Jessore Sloth Bear Sanctuary.

Habitat alteration

The researchers conducted sign surveys along 1 km trails in the sanctuary during winter, summer and monsoon seasons. Analysing sloth bear signs in relation to factors like elevation, terrain ruggedness, forest density, open scrub areas, P. juliflora infestation and human encroachment revealed key findings.

Higher P. juliflora proportions negatively impacted sloth bear habitat use, while factors like elevation, terrain ruggedness, dense forest cover and open scrub areas positively influenced habitat suitability. “The most significant impact is habitat alteration, leading to a reduction in food resources by replacing native diet plants with P. juliflora and depleting shelter,” says Jangid. Surprisingly, the researchers found that sloth bears also occasionally used P. juliflora patches and consumed its pods, potentially aiding in seed dispersal.

The study also found that sloth bear habitat use varied seasonally. When forests and agricultural fields offered sufficient diversity and abundance of food plants, the bears tend to avoid Prosopis patches. However, in the absence of such food plants, they turned to Prosopis patches for resources.

Human encroachment varied across seasons, with higher bear occurrence near settlements during summer and winter, possibly due to food resource availability. “Our research also revealed sloth bears’ preference for specific farm products during these months, sourced from cropping areas, showcasing their adaptability in diet selection,” says Jangid.

Road ahead

These findings provide insights into sloth bear behaviour in semi-arid regions of India. However, the researchers feel further research is necessary to fully comprehend these interactions and devise effective strategies to manage the spread of P. juliflora.

At the same time, they recognise the roadblocks. For instance, raising awareness about the impact of invasive plants on sloth bears presents challenges due to competing priorities. Local communities often use these plants for timber and other purposes. Yet, the researchers feel that involving communities in eradication efforts and educating them about conservation can be impactful.

Another measure recommended to reduce sloth bear-human encounters is promoting agricultural practices that deter bear attraction. “We have been told to cultivate cash crops instead of bear-attracting plants and remove P. juliflora hedges near human settlements and fields,” says Madhav, a local farmer who attended a state government-funded session organised by the Gujarat Forest department last year to sensitise farmers in the area to sloth bears.

Controlling invasive species and supporting wildlife conservation efforts are essential to protect sloth bears and their habitats. “Without it, in the long term, P. juliflora invasion could exacerbate habitat loss and fragmentation, heightening human-bear conflicts. Addressing this threat is vital to safeguard sloth bears and prevent human-wildlife conflicts. Furthermore, P. juliflora’s invasion can negatively impact other wildlife by altering habitats and reducing biodiversity, disrupting the ecological balance. Preventing its spread is essential for preserving the entire ecosystem’s health,” says Jangid.

Read more: Life and struggles of the sloth bear in human-dominated areas

Banner image: Sloth bears are found widely across semi-arid regions of the Indian subcontinent and inhabit various ecosystems from grasslands to forests. Photo by N.A.Nazeer/Wikimedia Commons.