Agricultural wetlands, big and small
Waterbirds use them all
Wetlands in India's agricultural landscape are maintained for use by people. Are such wetlands also useful for bird conservation? Are big wetlands better than small ones? We explore wetlands across western Uttar Pradesh to answer these questions, and find that assumptions driving wetland conservation are erroneous.
Habitats ignored; assumptions galore
Most freshwater inland wetlands in India are ignored as subjects worthy of exploration and study. A very large proportion of these occur amid cropfields. In semi-arid areas, agriculture is the reason for the creation of these wetlands - they hold water to irrigate crops outside the brief rainfall season. In the well-watered northern Indian floodplains, however, most are natural. Wherever they occur, these wetlands invite enormous human use. The variety of uses includes pumping the water, collection of vegetation such as lotus and reeds, grazing livestock, cultivating water chestnut, collection of clay, fishing, as also dumping of waste from rural and urban towns. Given this enormous and continuous "human disturbance", it is no surprise that such unprotected wetlands are assumed not to be useful as wildlife habitat, and largely ignored by wildlife ecologists and conservationists.
The focus of efforts to conserve wetlands in India is biased towards very large wetlands. It is implicitly and explicitly assumed that (1) wetland size is overwhelmingly important, (2) conserving few large-sized wetlands is adequate to preserve wetland-dependent biodiversity, and (3) human use of wetlands renders these areas unfit as wildlife habitat, and therefore requires to be reduced, or altogether removed. Consequently, the primary management focus is keeping human use minimal, and it is not known if assumptions driving conservation efforts and policy are valid.
Assessing assumptions: setting up a field test
In this project, we set out to address the two major assumptions driving wetland conservation: (1) wetlands with very high human use are not suitable as wildlife habitat, and (2) large wetlands hold the majority of wetland biodiversity. Additionally, we were interested to understand landscape-scale patterns of wetland use by waterbirds. Specifically, we set out to understand if waterbirds used areas with more and larger wetlands differently compared to areas with smaller and fewer wetlands. If waterbirds used areas having wetlands of varied numbers and sizes differently, this would indicate "scale-dependent" wetland use: an aspect that is ignored despite its implications for conservation planning.
We used LISS-III satellite imageries (for the winter of 2009-10) to identify and map all wetlands in 7 districts of south-western Uttar Pradesh where rice is the primary monsoonal crop and wheat is the primary winter crop (see (a) and (b) below). To ensure landscape-scale sampling, we overlaid the imageries with a grid of 5' x 5' that approximated 10x10 km (see (c) and (d) below). For each grid, we extracted (i) the number of wetlands, and (ii) the area (in ha) of wetlands. Four strata differing in the numbers and sizes of wetlands in each were recognized; one grid of each strata in each district was chosen randomly (see (e) in map below), and also one wetland in each chosen grid to survey. We then visited these wetlands during the winter of 2013 to count the birds in them.
Human use does not deter waterbird use of wetlands
Our mapping exercise revealed 10,991 wetlands spread over 14,745 ha. This, however, covered <1% of the total land area of the 7 districts. The mapping (see (c) and (d) maps above) also showed that wetlands were not distributed uniformly across the landscape. Areas with large numbers of wetlands (e.g. Aligarh district) were not necessarily areas with the biggest wetlands (e.g. southern Mainpuri and Kannauj districts). Since information from the past is absent, it is not clear if and where wetland numbers and sizes have changed.
We identified 99 species during the systematic bird counts in the 28 focal wetlands. This number is not the total bird diversity using wetlands, but a subset of what exists in them since we used a one-time count to address ecological questions. This number, however, is the highest known for waterbird counts using agricultural wetlands anywhere. Clearly, human use does not deter birds from using these wetlands!
Analyses showed that bird communities using areas with varying wetland numbers and densities were very different. This is clear evidence for "scale-dependent" wetland use - previously unknown from the tropical and sub-tropical world. Several species used multiple strata as expected. Among those, a few like the Sarus Crane, Woolly-necked Stork, Black-headed Ibis and Grey Herons were far more numerous in the larger wetlands. Others like the Red-wattled Lapwing, Black-winged Stilt and Common Moorhen were found everywhere equally.
Sparse, numerous, big & small: birds need them all
That wetlands constitute <1% of the landscape is a serious finding. There is a real need to conserve every wetland of all sizes that currently survives, and initiate long-term efforts to restore illegally converted wetland.
Clearly, the dominating assumptions regarding biodiversity conservation in wetlands are erroneous. At least in south-western Uttar Pradesh, waterbirds use all existing wetlands, not withstanding their use by humans, and even show strong landscape-scale patterns of usage. It may well be that differential human use in wetlands is driving scale-dependent wetland use by waterbirds here. Understanding the levels of wetland use by humans, and how different uses affects bird use of wetlands is necessary.
Conservation efforts here cannot take the short cut of focusing on large wetlands, but need to ensure that wetlands of all sizes, and areas with differing densities of wetlands are preserved. Ensuring that large wetlands will remain on the landscape is of importance for some species: beginning conservation work with large wetlands is certainly a great way to start, but should not stop here. It is of high conservation value perhaps to realize that conserving/ restoring even small wetlands will have real benefits to biodiversity here.
A caveat of our work is that we did not compare protected large wetlands with unprotected wetlands of similar sizes used by humans. There are yet many additional applied studies to undertake; we will be taking on some of those!
- Journal Article2013Can wetlands maintained for human use also help conserve biodiversity? Landscape–scale patterns of bird use of wetlands in an agricultural landscape in north IndiaBiological Conservation 168: 49-56. http://dx.doi.org/10.1016/j.biocon.2013.09.016
Wetlands in tropical agricultural landscapes are maintained largely by local institutions explicitly for human use, which is assumed to deter biodiversity. Conservation efforts have been biased towards protecting large wetlands that are assumed to be adequate to conserve the majority of species of focal taxa, usually birds. These assumptions remain untested, and landscape-scale conservation planning for wetlands is largely absent, as is a generalised understanding of wetland use by focal taxa. We designed a landscape-scale survey to understand patterns and processes determining beta diversity of birds using agricultural wetlands in south-western Uttar Pradesh, India where wetlands have experienced prolonged and intensive human use for several centuries. Observed bird species richness (99 species in 28 wetlands) is the highest known for any agricultural landscape in south Asia signifying that even intensive human use of wetlands does not necessarily deter their ability to retain biodiversity. Birds exhibited strong scale
dependent wetland use underscoring the need to conserve wetlands of varying sizes and at varying densities on the landscape. Beta diversity was due largely to species turnover (0.877) with minimal effect due to nestedness (0.055) suggesting that conserving a few large wetlands will not adequately meet goals of conserving the majority of wetland bird species. Prevailing assumptions regarding biodiversity conservation in tropical agricultural wetlands require being revised, and a landscape-scale approach that incorporates ecological realities is needed. Incorporating local institutions alongside formal protectionist methods offer a potential win–win situation to maximise conservation of biodiversity in tropical agricultural wetlands.