- Riparian buffers are lands adjacent to streams where vegetation is influenced by presence of water. They follow the course of the stream or river and may range from thirty to a hundred feet wide on either side of the stream.
- Among their several services these diverse and unique forest ecosystems nurture and moderate the flow of the stream, regulate water quality in agrosystems and act as corridors for animals like elephants, thus mitigating conflict with humans.
- In his commentary, Gopakumar Marayil calls for a specific legislation to protect riparian forests, perhaps even reverting to their historic status as sacred forests.
It was around noon when I crossed the mud path and entered the little strip of forest that led to the stream, gingerly picking my way down through the vegetation. A moment later, I was under a dense canopy with sunlight just about filtering through, amidst a stillness and the sound of water. Cormorants flew by and I heard a grey hornbill’s call in the distance, a cackling ruckus from the canopy, but there was an overwhelming mood of sombre, drowsy silence all around. And, all of a sudden, as I took a wrong step and slid down the slippery bank, two brown fish owls – large, brooding figures that had been watching my every step – took off from their perch a few feet away, giving me quite a start. I sat there for a moment, watching them fly to a branch a short distance away, with awe. Further down at the edge – where river sand meets the forest in this dry season – there was elephant dung in plenty. I expected to see this, for the herd had made its noisy way along the river last night.
This forest that I was in – on either side of a stream that is a headwaters tributary of the Cauvery River in Kodagu (Coorg) district of Karnataka – is a rich strip of riparian buffer, a unique forest that is among the most precious in the Western Ghats; indeed, everywhere in the world where they exist, riparian forests are special.
The term “riparian buffer” is used to describe lands adjacent to streams where vegetation is strongly influenced by the presence of water. When seen from the air, they are often thin lines-of-green that follow the sinuous course of the stream or river and may range from just about thirty feet to a hundred feet wide on either side of the stream. These forests merge with the forested landscape in protected areas, with a noticeable change in the forest composition.
Riparian buffers are ecosystems unto themselves, with grasses, flowers, shrubs and trees that have adapted, over their evolution, to withstand seasonal flooding and strong currents. In an interesting study done along the Cauvery, eighty sampling plots riparian forest over 318 kilometres were studied for tree diversity. A total of 177 tree species, belonging to 52 families, were recorded, with differences in diversity between forest and agro ecosystem landscapes. Along the Cauvery’s middle course, beautiful stands of tall Terminalia arjuna trees line the banks – giving it a sort of flagship status – while peepal, banyan and pongamia are abundant.
Yet, beyond the sheer diversity, riparian forests are special. In addition to the ecosystem services that forests provide, these buffer-patches have evolved to nurture and moderate the flow of the stream. The intact buffers in the headwater streams of the Western Ghats, such as the one I was strolling through, have a dense canopy on either side and, on occasion, the branches of trees intertwine to create a bridge across the stream for langurs and macaques. These trees are a major source of energy and nutrients, with woody debris and leaf litter contributing much of the enrichment.
The shade keeps the stream cool and fish thrive as a result; Densin Rons, a fish-researcher at the veterinary college in Wayanad, documented 94 species in the headwater streams of the Kabini and only a fraction of that number lower down, an important cause for such diversity depletion being the damage to the buffers. This habitat’s suitability for fish and for spawning has brought in specialised predators as well, the two iconic ones along the Cauvery being the brown fish owl and the lesser fishing eagle, while smooth-coated and small-clawed otters thrive in these stretches.
The usage of these buffers by elephants, as was in evidence that afternoon, isn’t unusual and has been documented by the Nature Conservation Foundation at Valparai in Tamil Nadu. Indeed, there is considerable anecdotal evidence in Kodagu (and elsewhere) that intact riparian buffers – by allowing the elephants to pass through them at night – actually mitigate human-elephant conflict. Where these buffers have been damaged, elephants enter coffee plantations and encounter hostility: conflict is inevitable.
The role of riparian forests in regulating water quality in agroecosystems is now acknowledged: by preventing sediment, nitrogen, phosphorus and pesticides from reaching the stream, singularly because of their rich root network, they reduce leaching into streams by as much as 80 percent, an incalculable ecosystem service.
And if all of this wasn’t enough, riparian buffers stabilise the flow of the stream, particularly in the higher regions where the gradient can be steep. Rich buffers slow down floodwaters and rainwater runoff and thereby reduce erosion, helping in the process to maintain stable streambanks. This, in turn, allows groundwater recharge. This property of buffers – the ability to apply brakes, so to speak – allows the riparian zone to function as a site of sediment deposition, trapping sediments that build stream banks in a breathtaking natural cycle of runoff and renewal.
The destruction of these forest strips is therefore worrisome. As agriculture and settlements have taken over riparian stretches along the Cauvery and other rivers in India, there has been a decline in important tree species such as Hydnocarpus pentandra, Elaeocarpus tuberculatus, Madhuca neriifolia and Palaquium ellipticum. Even though such destruction, along with sand mining, is disquieting, greater will be the impact of the proposed river-linking projects; as these buffers are destroyed to link rivers across India, floods will have a far greater impact, defeating the original objective of the linking itself.
The odd part is that there is no law – either at the national or state level – to protect these buffers. Rivers were, until recently, a state subject, so each state has its own policy (or none at all) on just how much of land on either side of a river belongs to it, engendering a free-for-all approach, and assured destruction, along human-dominated river stretches. A specific legislation to protect riparian forests is urgently needed. Riparian buffers were historically treated as sacred forests. They need that status once again, for the ecosystem services they offer, for our water security and for their ineffable beauty and diversity.
The author is a keen wildlifer and a trustee of The Nityata Foundation, which works on conservation issues along riverine ecosystems.
CITATION:
Sunil, C., Somashekar, R. K., & Nagaraja, B. C. (2016). Diversity and composition of riparian vegetation across forest and agroecosystem landscapes of river Cauvery, southern India. Tropical Ecology, 57(2), 343-354.
Banner image: Forests along the bank of Bhavani River in Tamil Nadu. Photo by A. J. T. Johnsingh, WWF-India and NCF.
Credits
