Scientists have mapped how infrastructure projects in India, particularly linear infrastructures such as roads, railway lines, power transmission lines, canals and pipelines, affect forest fragmentation. Such infrastructure has led to a 6% rise in the number of small forest patches and a 71.5% fall in the number of large forest patches – greater than 10,000 square km – found the researchers.

One of the most diverse ecosystems, tropical forests cover only 6% of the Earth’s surface, yet they support 80% of the world’s species. However, these biodiversity hotspots are threatened by human activities that split large forested areas into multiple small patches, resulting in a loss of connectivity for wildlife and a host of other problems. One activity that causes increasing fragmentation, is infrastructure development.

When forests become fragmented into smaller patches due to linear infrastructure, which acts as a barrier, habitat areas for wildlife become smaller and more isolated, hindering the movement of species such as big cats, and elevating the risk of extinction in some cases. The impacts adversely affect the entire ecosystem, which could ultimately harm humans.

“These fragmented and isolated patches can serve as outbreak hotspots from which diseases such as Covid-19 can emerge, and enhance transmission between people and wildlife,” warned Krithi Karanth, chief conservation scientist at the Centre of Wildlife Studies. Past studies have shown that forest fragmentation and human encroachment are linked to a rise in diseases.

The study enables policymakers to decide “where” and “how” future infrastructure development activities should be implemented in a way that smartly aligns with biodiversity conservation objectives – potentially resulting in a win-win scenario.

Connectivity between forest patches is important to maintain gene flow for populations of big cats such as tigers and leopards. Credit: Santosh Saligram via Mongabay

The study is a comprehensive and “excellent background to the current state of forest fragmentation in India,” said Miriam Goosen, Principal Research Fellow at James Cook University, who was not involved in the study.

“A startling result is that the density of major roads through Indian forested areas is similar to that in the USA and greater than in New Zealand, China and Brazil,” observed Goosen. “The analysis could only consider major roads, so the actual fragmentation by linear infrastructure would be much higher if smaller rural roads were able to be included,” she noted.

As one of the fastest-growing economies in the world, India is rapidly upgrading and expanding its infrastructure. To understand the impact of linear infrastructure developments on the distribution, size and connectivity of forest patches, the team developed a forest layer by using land-use land-cover map by the National Remote Sensing Agency and on this, they overlaid infrastructure layers – roads, railway lines, power lines, canals, mines and reservoirs. They studied the sizes of the forest patches, the amount of perforation in the patches and distance between two adjacent patches.

They compared the existing forest patch characteristics to a scenario that excluded all linear infrastructures. Using this information, they classified patches into three different fragmentation categories: large and less isolated, intermediate and less isolated; and small and isolated.

Central India vs Western Ghats

Among the protected forested areas they studied, 70% had some linear form of linear infrastructure passing through them, mainly high-tension power transmission lines and major roads. And the density of the infrastructure in protected areas was similar to that in non-protected forested areas.

Several differences emerged in the size and connectivity of forest patches in Central India compared with the Western Ghats – both regions are undergoing rapid infrastructure development. Central India has a larger proportion of large forest patches, comprising 42% of the forest area, than the Western Ghats, which has only 29%.

“Linear Infrastructure density is greater in the Western Ghats, and that’s a possible reason for less number of large patches,” explained Rajat Nayak, lead author of the study from the Foundation for Ecological Research based in Tamil Nadu. “However, other land-use types such as large scale agriculture, settlements and urban areas are less prevalent in the Western Ghats, resulting in more forest cover,” he added.

Forests in Central India were more isolated – greater inter-patch distance and perforation – than those in the Western Ghats. “Less isolation in the Western Ghats implies that connectivity between patches could be established with little effort through structures such as underpasses and canopy bridges across linear structures,” said Nayak.

Re-routing infrastructure

Overall, India still has several large-intact patches, which could sustain a high species richness and genetic diversity, Nayak said. To minimise forest fragmentation, future infrastructure projects should consider avoiding large forest patches or build effective mitigation measures.

Currently, the road or highway development policy is to establish the shortest route, explained Nayak. Consequently, many national highways such as NH766 cut through prime forested habitats in Nagarhole and Wayanad. But according to Nayak, re-routing the same highway through villages surrounding the Protected Area will not only conserve forests but also provide connectivity to villagers.

The presence of roads and other linear infrastructure hinders the movement of wildlife. Credit: Arvind Ramamurthy via Mongabay

In the Western Ghats, several East-West infrastructure projects could be bundled together, the team suggested. And for projects connecting the North to South in this landscape, they recommended aligning them along the coast or on the leeward side of the hill range.

Invasive species can sometimes flourish along the edges of tropical forest clearings where the habitat “is completely different from the microclimate and vegetation structure of the forest understorey,” explained Goosen.

“Maintenance by reducing weeds and reduction in width of clearings is important,” she points out. “For example, if the road verge is narrow and has forest canopy overhead, microclimate changes and thus weed and non-native fauna invasions, edge and barrier effects are minimised.”

Goosen said that the findings regarding fragmentation are similar to studies conducted in Australian tropical forests. She notes that the wet tropics of the Queensland World Heritage Area in Australia, “has similarities with the Western Ghats in terms of being a long relatively linear forested area, much of the escarpment of low mountains.”

Due to the difficulty of finding routes through the terrain, major roads are avoided, Goosen explained. “In this case, one wide power line was removed and the clearing is currently restoring both via anthropogenic [human-assisted] and natural regeneration. Another power line clearing was strung above the canopy and is maintained via helicopter, thus removing the linear clearing intrusion.”

This article first appeared on Mongabay.