Up in the sky

While walking on the canopy bridges in Meghalaya, I wondered how it feels to move in the higher strata being oblivion of what lies beneath. I heard about the artificial canopy bridges allowing animals to move from one section to another in fragmented forests where there is a dearth of neighboring canopies. Meghalaya has living root bridges and the state enjoys dense canopies in forests. Such is not the case elsewhere where there is less precipitation and no lower or middle forest strata and arboreal species have to get down on the ground for various reasons.

A study in 2017 confirmed the success of natural canopy bridges. The study in Peru by Dr. Tremaine, checked the usage of canopy bridges when in lower reaches gas pipeline was being expanded. It was observed that the animals were using the natural bridges in the canopy for movement at a higher rate than the ground. However, such studies are limited in India which establish the essential importance of canopy connectivity for arboreal species conservation.?However, in the event of fragmentation caused by roads and also road kill of primates and other small mammals, the artificial canopy bridge is promoted as a mitigation strategy in India. The functioning and usage of the canopy bridges are tested and modified for arboreal species by Hoolock Gibbon and Lion-tailed macaque. The different species of monkeys and their specific movement pattern requires specific engineering exploration for artificial bridges. The forest department is also promoting simpler canopy bridges with available materials for non-primate species.

The Red Squirrel reintroduction program observed that road traffic is a major threat to the squirrel; a solution for the same was the installment of canopy bridges for the safe passage of Reds.? India has a protected area named after the grizzled giant squirrel; Srivilliputtur Grizzled Squirrel Sanctuary. The squirrel habitat was threatened and a study indicated that the species population declined by more than 70 percent for the census duration of 1993 to 2007. The species' habitat is near the river having overlaps with human activities like picnics and vehicle movement, which has been concluded as a major threat. Also, arboreal species get lured by people feeding them on the roadside, which makes them vulnerable to roadkill. On the Coonoor to Mettupalayam Highway, roadkill of giant flying squirrels was reported. In Chinnar WLS, regular roadkill of squirrels was recorded. This led to the experimentation of the canopy bridge development in the WLS. In 2017, the brainchild of Chinnar’s eco-development committee (EDC), forest department officials, and local members of Chinnar’s and Alampetty’s tribal colonies; led to the creation of ‘canopy bridges’ for arboreal animals. The easily available material is bamboo which was used as the internal section using 1-1.5 m bamboo sticks tied with an iron twine and high-quality nylon ropes as the external lining. Such material was used to build canopy bridges at Thenmala Dam Junction and Pallamvetty and Shenduruny Wildlife Office?in?Shenduruny WLS,?as well as while developing in Annamalai Tiger Reserve.

For small mammals and reptiles, canopy bridge material can be easily figured out. However, technical expertise is needed when primates or any other large mammal are the species for whom the canopy bridges are developed.

In Hollongapar Gibbon Sanctuary, a railway line passes through the critical habitat of the Hoolock gibbon. The railway line was bringing forth challenges of maintaining canopy connectivity. Hoolock Gibbon's preferred mode of locomotion is brachiation and hence needs good material as a bridge while moving from one canopy to another. In 2015, an attempt was made to construct an artificial canopy bridge with an iron structure. However, it was considered not successful as Gibbon needed material to swing from one side to another (preferred) rather than walking across the structure. The Wildlife Institute of India in collaboration with Assam Forest Department, has developed new guidelines and reports for canopy bridge construction in the sanctuary and an attempt to monitor the new structure when functional would clarify the success of artificial bridges. However, a natural canopy bridge is always looked forward to. In the sanctuary, NGO Aaranyak along with local communities and the forest department planted saplings along the railway track, the fruit bore many years down the line when in 2019 Gibbon started using these natural canopies to cross.

We need more merging of ecological requirements with engineering solutions. Since species and their ecology vary, so does the availability of options for engineering marvels. Where natural connectivity is not available or availability is hampered for some time, the artificial canopy can help to connect the arboreal population without facing the challenges of crossing roads or railways.