Canopy science – emerging new area

The diversity in forest canopy can be attributed to its complex three-dimensional structure which affords opportunities for niche diversification and vertical stratification (August 1983, Ozanne et al 2003). With such high biodiversity one could easily expect that tropical forest canopies are also an arena for a multitude of interactions; many of which still need to be understood (Ozanne et al 2003). The function of forest canopies and the ecosystem services that they provide remain unknown.

Canopy programme in India

Canopy research in India is still in its infancy. Despite encompassing four of the 25 biodiversity hotspots of the world, the canopies of our forests remain relatively unexplored. They may not only harbour new species, their value in providing ecosystem services and influencing climate at a regional scale also needs to be addressed. A study on the social bee pollination of canopy trees in Kalakad Mundanthurai Tiger Reserve (Devy 1999) was a pioneering canopy study in India. The same site has many studies underway on keystone species, epiphytes, birds and small mammals and new results are emerging.

Goods from the canopy
In India, a staggering estimate of one million kg of epiphytic lichens is harvested annually from the wild, providing an important source of income for tribal peoples in rural areas. However, the absence of management plans raises doubts about its sustainability in terms of abundance and species composition. We used Paliyan tribals in the Western Ghats to estimate the time since harvesting, with one year accuracy (up to 8 years), on the basis of changes in the colour and structure of the tree bark. This capability was tested by comparing estimates of professional lichen harvesters. Lichens in the Western Ghats are traded by weight, independent of the species in the sample. Interestingly, we found that Paliyan tribals apply two different harvesting methods: shallow and deep harvesting. In the latter they remove a deep section of bark, and attached lichens, in order to increase sample bulk weight. We also found that shallowly harvested patches showed good regeneration in terms of species richness and abundance after 8 years. Deep harvesting, however, had a profound negative impact on regeneration capacity.

Soubadra Devy, R.Ganesan, Jan Wolf
We acknowledge the support of Act India Foundation and the Paliyan assistants for this work.

Cameras in the Canopy

Many of the creatures inhabiting forest canopies are uniquely adapted to live in the tree tops. While some can be easily seen, such as the monkeys; some others are more elusive, for example civets and martens. Documenting animals, whether insects or mammals, in the canopy has therefore always been a challenge. However with advances in commercially available still and video camera traps, it has become easier to capture some of these elusive animals on film. Camera traps allow the observation of shy, elusive animals without disturbing them. The biggest advantage is continuous observation across day and night on the presence and movement of animals in any location.

Our purpose in using camera traps in the canopy was not just to document mammals but also investiagte the frequency of use of a particular patch of resource, such as flowers, fruits and to study exclusion of species over time at these resources. We used passive infrared camera traps developed by Trail Master USA and CEDT, Bangalore. These traps were mounted in wooden boxes with a frame mesh to protect it from macaques, which showed a strong preference for such new gadgets in their domain. We tested these traps to document frequency of visits of animals to flowers by carrying out parallel observations from hides. Both these observations could be matched only after several rounds of testing.

All in all, such initial efforts helped us document the resource use by arboreal animals over a prolonged period.

Camera trap recording of diurnal and nocturnal visitation by non-flying mammals to the flowers of Cullenia exarilliata a canopy tree in wet evergreen forests of Kalakad–Mundanthurai Tiger Reserve (mean ‚SD, n = 1680 h).

The graph here shows how visits to a patch of flowers in the canopy varied across the day and night. Camera traps might be excellent for such purposes where long term monitoring at one point in the canopy is required but we would suggest use of digital camera traps and video monitoring for faster and more useful data.