Browsing by Author "Jha, R.R.S"

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    Implementing artificial canopy bridges to connect fragmented population of Hoolock gibbon in Hollongapar Gibbon Sanctuary, Assam
    (Wildlife Institute of India, Dehradun, 2023) Jha, R.R.S; Zangmo, S.; Gopi, G.V.
    Habitat loss and habitat fragmentation are two principal threats to most terrestrial biodiversity across ecosystems and geographies. Gibbons are a particularly vulnerable group of primates inhabiting the forests of South and Southeast Asia. Of the 20 gibbon species – all threatened, according to the International Union for Conservation of Nature or IUCN – the endangered Western Hoolock gibbon Hoolock hoolock is the only one found in India inhabiting the forests in the southern bank of the Brahmaputra-Dibang river system. The Hollongapar Gibbon Sanctuary (HGS) is a small ~21 sq.km Protected Area (PA) in Jorhat, Assam and is one of the species’ stronghold supporting around 125 individuals living in more than two dozen family groups. It is also the only PA in India named after a primate species. Apart from the W. Hoolock gibbon, the Sanctuary also harbours six other primate species – capped langur Trachypithecus pileatus, stump-tailed macaque Macaca arctoides, northern pig-tailed macaque M. leonina, Assamese macaque M. assamensis, rhesus macaque M. mulatta, and Bengal slow loris Nycticebus bengalensis, thereby having the distinction of harbouring the highest primate species diversity for any Indian PA. However, a single track ~1.65 route-km long railway line (currently broad-gauge, but un-electrified as yet) has fragmented the Sanctuary since 1887 into two unequal parts. Over time, the Sanctuary has become a ‘forest island’ having lost connectivity with surrounding forest patches. Since gibbons are exclusively arboreal animals inhabiting the forest upper canopy, they are particularly sensitive to canopy gaps. Gibbon families on both sides of the railway track have, thus, been effectively isolated from each other, thereby compromising their population genetic variability and further endangering their already threatened survival in the HGS. Worldwide, and even in India, several conservation initiatives have attempted bridging such canopy gaps in forests through artificial canopy bridge (ACB) structures to facilitate arboreal species’ movements. The Wildlife Institute of India, Dehradun was approached by the Divisional Forest Officer, Jorhat (Territorial) Division of the Assam State Forest Department (ASFD) to provide specific design inputs towards the installation of such canopy bridges at the HGS. In this context, this report provides design guidelines and considerations as well as specific location-wise details of seven (07) potential sites within HGS for such canopy bridges installation, following thorough literature survey, field data collection and interaction with stakeholders such as ASFD officials and field staff, railway officials and consultants, and local conservationists. We recognise and emphasise that the design, successful installation and post-installation monitoring of canopy bridges require the involvement of several individuals with professional expertise in fields such as forestry, ecology/primatology, engineering and mountaineering/climbing. Post-installation monitoring of the canopy bridge structures – both behavioural observations of animals around canopy gaps and installed structures as well as through arboreal camera traps to assess bridges’ use – is one of the most important aspect of this project. As is clear, the present un-electrified single-track ~1.65 route-km railway line passing through the HGS has caused distress and posed significant conservation issues to arboreal animals. Hence, a future doubling of the line (if planned) will increase the canopy gap to a large extent and render any conservation interventions (such as ACB installations) futile. Over the longer period of time, it will be best if the status quo is maintained, although electrification of the existing single track may be permitted subject to necessary statutory approvals with appropriate mitigation and compensation measures implemented after detailed investigation of its ecological impacts. Forest regeneration on both sides of the existing track through afforestation activities to gradually enable natural canopy connectivity, adherence of trains to speed limits when passing through HGS and its Eco-Sensitive Zone/wildlife corridors, ensuring landscape connectivity of the isolated ‘forest island’ HGS with neighbouring patches of forests, and rerouting of the existing railway line outside Sanctuary limits, and establishing and supporting low-impact home-stay based ecotourism facilities are some of the longer-term interventions necessary to ensure that W. Hoolock gibbons and other canopy-dwelling species persist and thrive within HGS and in the immediate larger landscape.