GUWAHATI: Guwahati’s rapid urban expansion is steadily eroding butterfly diversity, with forest-specialist species disappearing from many parts of the city and being replaced by a handful of hardy, disturbance-tolerant butterflies, according to a new study by researchers from Cotton University.
The study, authored by Nayanjyoti Moran, Renu Gogoi and Narayan Sharma, was recently published in the international journal Urban Ecosystems.
Based on surveys conducted across forest, semi-urban and urban landscapes in Guwahati, the researchers recorded 3,594 butterflies belonging to 174 species and six families, highlighting the city’s still-significant ecological richness despite mounting urban pressure.
However, the findings reveal a sharp decline in butterfly diversity as urbanisation intensifies. Species richness in urban areas was found to be nearly 50 per cent lower than in forest habitats.
Forest sites such as Garbhanga Reserved Forest and Amchang Wildlife Sanctuary supported the highest butterfly diversity, while densely urbanised locations such as Sarania Hills recorded the lowest numbers.
One of the study’s key findings is that Guwahati’s butterfly communities are not only shrinking but also undergoing a fundamental transformation. Researchers found that urbanisation is driving the replacement of forest-dependent butterflies with generalist species that are better adapted to heat, pollution and habitat disturbance.
The researchers described this process as “ecological homogenisation”, where cities gradually lose their unique native biodiversity and become dominated by a small number of widespread species.
“Urbanisation is increasingly reorganising biodiversity in Guwahati, favouring a handful of adaptable species at the expense of specialists. This growing functional homogenisation is a cause for concern, as ecosystems with fewer unique ecological roles are often less resilient and less capable of sustaining essential ecosystem services,” said researcher Narayan Sharma.
The most abundant butterfly recorded across all habitats was Catopsilia pyranthe, a highly adaptable species commonly found in disturbed landscapes. In contrast, several forest-associated species were found to be increasingly rare in urban environments.
The study notes that Guwahati’s hills — including Garbhanga, Amchang, Jalukbari, Sarania and Hengrabari — once formed interconnected forest ecosystems. Today, many of these habitats have become fragmented into isolated green patches surrounded by roads, buildings and expanding human settlements.
“It is important to understand how biodiversity responds to urbanisation, particularly in rapidly growing cities such as Guwahati, where natural habitats are becoming increasingly fragmented. Even small remnant forest patches can play a vital role in supporting native butterfly communities, and their conservation and connectivity should be important considerations in future urban planning,” said lead author Nayanjyoti Moran.
The researchers also highlighted the role of urban green spaces in supporting biodiversity. The Assam State Zoo-cum-Botanical Garden, for instance, maintained relatively high butterfly diversity compared with many other urban sites, largely because of its proximity to Hengrabari Reserved Forest.
According to the study, this demonstrates how partially connected green spaces can help sustain wildlife even within heavily urbanised landscapes.
Semi-urban forest patches such as Jalukbari Reserved Forest were also found to function as important transition habitats, supporting species found in both forest and urban environments.
Sharma noted that the findings mirror patterns observed in earlier studies on birds and spiders in Guwahati.
“Our studies on three taxa — birds, spiders and now butterflies — show similar patterns,” he said.
The researchers stressed that Guwahati lies within the globally significant Indo-Burma biodiversity hotspot, making the conservation of its remaining forest fragments critical not only for butterflies but also for broader ecological resilience.
The study recommends protecting remnant forests, restoring degraded hill ecosystems, creating ecological corridors between green spaces, and integrating biodiversity concerns into urban planning before the city loses more native species.
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