USING MANGROVE TREES IN EUTROPHIC INLAND WATERS
KRISHNA MB, 2000.
[Presented at the Lake 2000 seminar organised by Centre for Ecological Sciences, Indian Institute of Science, Bangalore:
http://wgbis.ces.iisc.ernet.in/energy/water/proceed/section3/paper3/section3paper3.htm]
AN OVERVIEW
Removal of nutrients from waters entering lakes and tanks to prevent eutrophication is an important component of waste-water treatment. This can be achieved by a turnover of floating and emergent vegetation: with periodic removal or harvest of biomass from the lake, a continuous removal of nutrients from the water is possible. However, decomposing aquatic and semi-aquatic vegetation present in such lakes could itself return nutrients rapidly into the water. Therefore, there could be merit in substituting soft tissued plants with woody vegetation (trees). Trees from tropical intertidal and adjacent communities could be viable alternatives in afforesting inundated and foreshore areas of tanks and lakes. They could be much larger and capable of creating an aesthetically appealing microclimate of their own, and being woody, would be less likely to decompose and return nutrients to the water. These species could also grow better in such nutrient-rich and deoxygenated soils and sediments found in our tank and lake beds. Given that not less than twenty percent of the tanks in the larger Bangalore area could be eutrophic [1], there should be ample number of situations to try out these species. Moreover, a good tree growth in standing water could effectively ‘contribute’ to the ‘green space’ of urban Bangalore.
THE BACKGROUND
According to the Ramsar Convention, wetlands are defined as areas marginal between land and water, inundated or saturated frequently enough to support plant and animal communities adapted to a life dominated by water. It encompasses areas of marsh, swamp, standing or flowing water which is fresh, brackish or salty. This definition thus includes man made systems, and most wetlands in inland Peninsular India would fall into this category. In the Bangalore area, apart from the occasional seasonal stream, there are no natural wetlands. All the water bodies which occur in this area, are thus, man made [1]. A wetland of our parts basically consists of an impoundment across a stream to form a reservoir and irrigated fields down the embankment. As such these usually form a series, a number of them being found in a valley.
Remote sensing studies have revealed that wetlands account for just 4.8% of a sample area of 640 sq km covering both urban and rural zones of Bangalore [2]. The number of man made water bodies (or tanks as they are locally called), in the existing administrative area has fallen from 262 in 1960, to some 81 at present [3]. Obviously most of these were created to serve the needs of irrigated agriculture [4], but were destroyed once the pressure for land became high.
Thus, a vast majority of the wetlands in the Bangalore area occur on the outskirts, in the urban-rural fringe. The uneven distribution of Bangalore’s wetlands with reference to the city at present, is obviously the result of an explosive increase in the extent of the city from around 67 sq km in 1961 to over seven times that area today. The growth of the city has not only engulfed the tank beds but also disrupted the drainage pattern in these basins. In addition, the tanks which have survived in the city have sewage flowing into them.
From a local ecological point of view, these tanks form an unique and irreplaceable system. A tank can be visualised as a basin with several zones of water of varying depths, abutting a deeper zone that lies towards the embankment. This zonation is dynamic and fluctuates with the seasons, promoting the growth of a variety of emergent, floating, anchored floating and submerged vegetation, each of which shows a preference to a particular range of water depth. These fresh water plant communities in turn accommodate a large number of small organisms like periphyton, insects, molluscs, etc. which form the staple diet of many species of invertebrates and vertebrates in the tank’s food chain.
With sewage flowing into many of these urban tanks, the status of these waterbodies have changed. Many have become eutrophic and algal blooms are frequent and extensive [1]. They have lost their seasonally fluctuating water level and have attained a permanently flooded state. There could be much accumulation of sediments in the tank bed in which nutrients are trapped. These nutrients get released into the tank waters on disturbance (as when drag nets are used) and in turn lead to more algal blooms. In addition, many of these tanks (especially those within the city) have their sloping shoreline substituted with vertical stone walls. The eutrophic condition leads to extensive growth of Water Hyacinth (Eicchornia crassipes), with a loss of other structural plant forms. In a few cases, increasing growth of Ipomoea carnea is covering extensive stretches of tank beds. There could be thick impenetrable growth of tall emergent reeds, especially in tanks which are too silted up due to excavated soil and garbage dumping.
It is under these conditions that growing trees from the intertidal and adjacent communities could find merit. Being woody, they would decompose much more slowly, thus acting effectively a ‘nutrient sinks’ in these urban tanks. Being much larger, they could serve a greater aesthetic need of having larger green ‘lung’ spaces in the city. Given ground level disturbance by humans and their activity, trees might provide better substrates for urban wildlife to use these tank spaces. Since not all tanks are large, ‘elevating’ the substrates urban wildlife use might be a much better alternative than trying to spatially separate the habitat from areas of human use.
ADAPTATIONS OF MANGROVE AND ASSOCIATED TREES WHICH COULD MAKE THEM SUITABLE FOR URBAN USE
The word “mangrove” has generally been used to refer to either the constituent plants of tropical intertidal forest communities or to the community itself. In a more limited sense, it is used to refer to tropical trees restricted to intertidal and adjacent communities, while the term “mangal” is used to refer to the community itself. The term “mangrove” is therefore used in the restricted sense here. Even tidal influence can be interpreted narrowly, simply to mean the shoreline inundated by the extremes of tides, or it can more widely refer to river-bank communities where tides cause some fluctuation but no salinity. The term is therefore used in its wider sense here.
To quote Tomlinson [5]: ‘Most mangroves grow very well in fresh water and some penetrate considerable distances inland along river banks where water is permanently fresh and tidal fluctuations are small or absent… It is generally assumed that mangroves are excluded from terrestrial communities by competition with other kinds of plants that do not carry the burden of features that are adaptive only in stressed environments’.
There is evidence that the enzyme systems of these halophytes neither require salt or are particularly resistant to it. Tomlinson [5] gives a good review of salt balance as well as the biology of mangroves, and the readers are referred to it. Only some four genera of mangrove tree species like Avicennia are known to eliminate salt through salt glands. Others may have only epidermal structures that somewhat resemble these salt glands. The non-secreters are assumed to avoid salt at the water absorption stage itself.
Mangrove substrates are variable: from firm to soft mud, which can be rich in organic matter. In muddy substrates a disturbance produces a strong smell of hydrogen sulphide, indicating the completely anaerobic property of water-logged soil [5]. This tolerance would be of value in trying them out in inland urban eutrophic waters.
Thus, mangroves would be tree species which have the capability to grow under permanently inundated conditions, in soft mud and sediments which could be quite deoxygenated, and at high salt concentrations (when compared to that of fresh water). All these would not mean that they require these conditions to grow: literature suggests that it is only an adaptation for harsh conditions, which perhaps they could even do well without, when artificially planted.
USE OF WETLANDS BY BIRDS
Amongst the water bird species which occur in Bangalore and its environs [6], there can be some five broad groups which can be recognised based on wetland zones they frequent. Though most species have their preferences, there is some amount of overlap in the usages of these microhabitats. Some species also make use of more than one microhabitat. The five groups are as follows:
Open water birds
Waders and shoreline birds
Meadow and grassland birds
Birds of reed beds and other vegetation
Birds of open airspace above wetlands
The open water birds are those which keep to the unvegetated open water zone which is generally found in the middle of water bodies, away from the shoreline. Ducks, geese, grebes, cormorants, kingfishers, terns, gulls, and Pelican tend to keep to this zone. Except for the ducks and the geese, all the others are fish eating birds generally.
Stilt, Greenshank, sandpipers, storks, ibises, Spoonbill, herons, and egrets tend to make use of the shallow waters to wade in and feed. All are long legged, long necked birds which keep to the bare open shorelines, picking up animal matter by either a wait and strike strategy like the herons and egrets, or by actively probing and searching for animals. The larger birds like the herons, egrets, and storks take vertebrate food while the smaller forms feed on invertebrates. The taller birds wade into deeper waters while the short and the short legged birds keep to shallow waters or wet mud.
Rails, bitterns, Coot, jacanas, moorhens, snipe, Painted Snipe, etc make use of vegetated portions of a wetland. Birds like the jacanas keep to floating vegetation, their elongated toes enabling their weight to be distributed over floating leaves. Purple Moorhens are especially attracted to Water Hyacinth covered patches, which they feed on. Bitterns and snipe make use of reed covered areas with standing water beneath, while moorhens and Coot can be seen even swimming out onto the open water leaving the vegetation. Other rails usually keep to dense cover.
Swallows and pratincoles hawk flying insects over water, while wagtails, lapwings and plovers pick insects and other invertebrates off the ground in grasslands, meadows and fields bordering water bodies. Birds of prey too make use of the air space over the wetland, searching for suitable animals either perched on a vantage point or by flying over the wetland.
In addition to these birds, there are those like weaver-birds and munias which do make use of wetland and other marginal areas to feed and breed. The tend to make use of the bushy and tree vegetation along the waterline to build their nests, and even roost. Swallows which forage widely make use of reed beds to roost-in along with wagtails.
Invariably, there are both specialist and generalist users of the various habitats that birds make use of. Therefore, a variety of habitats and micro-habitats are required for the survival of a variety of species [7].
In Bangalore, there would be a gradient in the kind of microhabitats which would be provided by the sequence of tanks from within the city to the outskirts and the adjoining rural areas. The city tanks like Ulsoor and Yediur are walled, and others newly engulfed by the city would have lost the associated meadows and sloping shoreline. As one moves outwards, the sloping shorelines are seen but meadows are absent, until one reaches the rural areas where all zones could be present. This would have a major influence on the kind of birdlife that would be present in the urban tanks.
THE STATUS OF WATER BODIES AND WETLANDS IN BANGALORE
A survey of tanks within a forty kilometre radius of the GPO in 1995 [1] revealed that nearly a third of the tanks in the Bangalore area had lost their sloping margins and were either walled or had cut margins. Of the thirty tanks which had high water levels during the survey in the month of January, twenty five had sewage waters flowing into them [1].
A survey of electrical conductivity (EC) of tank waters [1] indicated that twenty-one percent of the tanks had waters with the conductivity between one and two mmohs/cm, while 70% of the tanks showed lower EC. The urban tanks showed high EC, while three had abnormally high values with the maximum being 3.2 mmohs/cm. Since conductivity is an indicator of dissolved salts, the higher values recorded would be detrimental to the growth of sensitive plants. Chloride concentration was also more in tanks with sewage contamination.
By and large, the tanks in the Bangalore area are not deep; the embankments could be in the region of some two to five metres relative height as is indicated on the Survey of India topo sheets. During summer, many of the rain-fed tanks would tend to go dry from evoporation and water usage. The annual open-pan evoporation could itself amount to well over a metre to almost a metre and a half. However, the number of tanks still used for irrigation would just amount to a third of the total number surveyed [1].
THE FEATURES OF URBAN WETLANDS WHICH COULD BE OF USE FOR THE SILVICULTURE OF MANGROVE AND ASSOCIATED TREES
The features of urban tanks mentioned in the preceding parts make them ideal to try out mangrove species. Most have lost the sloping shoreline that is invariably found in the rural tanks used for irrigation. Instead they have steeply sloping margins. They are not used for irrigation purposes, and their waters could be eutrophic and even perhaps septic in some cases. Not all urban wetlands are large: the distance from the shoreline to the centre of the tank is generally quite small so that birds like ducks which are found day-roosting on the open waters would be disturbed by human activity and even presence on the shore. In those tanks where there is sewage inflow, the seasonal fluctuation in the level of water is lost and they tend to attain a permanently flooded state. The EC of these waters contaminated with sewage is higher, indicating a higher level of dissolved salts. Most of the tanks within the city which are in such a state have poor diversities, as is shown by the variety and numbers of birds [1,7], unless they are large or well protected and isolated from human activity on the shore.
THE ADVANTAGE OF SUCH TREES FOR BIRDS AND OTHER MACRO FAUNA IN URBAN SETTINGS
There are many advantages of having mangrove trees in urban tanks. First and foremost, they could grow in standing water forming living islands, which could be effectively used by birds and other urban wildlife. Birds could use these as substrates for roosting and breeding. Bats would find the blooms of many of these trees a source of food, as would the nectarivorous birds. They may be in a position to regenerate on their own, and spread, to there need not be a constant planting effort. Being woody, overgrowth would never be a problem, since even firewood has a good value today. Being able to withstand inundation, there is no need for periodic drying of the lake, which many other non-mangrove species might require. They are not thorny, hence unlike Acacia nilotica extensively used for foreshore plantations, they pose no threat to flying birds to get entangled in the thorns (there have been a few such reports). The knee and supporting roots could give additional perch sites for birds like herons and egrets while foraging. They could inhibit excessive growth of Water Hyacinth by a simple process of shading, as also algal blooms, while reeds could still perhaps grow in shallow water between trees where shading is not much. The green tree canopy could provide a continuum with the other tree cover of the city in spite of what substrate they themselves grow on.
THE POSSIBLE BENEFITS OF USING TREES FROM INTER-TIDAL AND ASSOCIATED COMMUNITIES FOR WASTE WATER TREATMENT
Growing beds of emergent plants or reeds, or cultivating Water Hyacinth and such fast growing floating plants in pre-treatment tanks have been suggested and tried to remove plant nutrients from wastewater. These processes require a lot of maintenance action if plants are not to die and decompose in situ. The shortest time soft tissued plants could take to decompose, as for example during composting, would be around three weeks. Woody tissue, on the other hand, would never decompose so fast. Hence substituting soft tissued plants with woody vegetation could be a better alternative to remove nutrients from waste water.
THE ADVANTAGES OF SUCH TREES FOR AESTHETICS, LANDSCAPING, FORESTRY AND LAW ENFORCEMENT IN URBAN SETTINGS
Bangalore is on a plateau, and all the water which flows, flows out. Tanks are thought to be good sources of groundwater recharge. Hence, it makes sense to retain these tanks in good condition with adequate levels of fairly good water. Again, given that land value is high in urban areas, there is a lot of pressure on tank beds from encroachments [8]. The most easily maintained deterrent to encroachments therefore, is standing water itself. Thus, trees in tanks could provide an aesthetic screen and pleasant greenery, especially in sites which are too small to have a scenic value.
TREES OF INTER-TIDAL AND ASSOCIATED COMMUNITIES WHICH ARE ALREADY IN CULTIVATION IN INLAND AREAS
There are lot of woody plants and trees which withstand inundation and salinity, found planted and growing well in inland areas. Many of these are from the intertidal and associated plant communities. A classic example would be the extensively grown Coconut, and Pongamia pinnata (Derris indica) both of which do well even with the roots dipping in sea water. There are others like Barringtonia and Pandanus growing well even in fresh water where there is no salinity. The botanical gardens would have littoral species like Heritiera littoralis (commonly referred to as the ‘Looking Glass Tree’ because of the shiny undersurface of the leaves) growing well on dry ground without salinity and salt [eg. 9]. All this would indicate that salt and salinity are not a prerequisite for these species to be cultivated. Some of the other species from the intertidal and associated communities doing well inland are: Cerbera manghas, Terminalia catappa, Calophyllum inophylum, Hibiscus tiliaceus, Thespesia populnea, to name a few.
What we need to be trying out is the core mangrove species (as some would consider) like Avicennia, Bruguiera, Ceriops, Heritiera, Nypa, Rhizophora, Sonneratia, and Xylocarpus in sewage contaminated, even possibly septic, highly eutrophic urban tanks with heavy deposits of sediments which would have accumulated over many decades.
REFERENCES
[1] Krishna, MB; Chakrapani, BK; Srinivasa, TS; (1996). Waterbirds and wetlands of Bangalore: a report on the status, water quality, plankton, and bird populations of the lakes in and around Bangalore and Maddur, Karnataka, India. Birdwatchers’ Field Club of Bangalore and Bangalore Urban Division, Karnataka State Forest Department. Bangalore.
[2] Behera, G; Nageswara Rao, PP; Dutt, CBS; Manikiam, B; Balakrishnan, P; Krishnamurthy, J; Jagadeesh, KM; Ganesha Raj, K; Diwakar, PG; Padmavathy, AS; Parvathy, R. 1985. Growth of Bangalore City since 1900 based on maps and satellite imagery. ISRO technical report number isro-eos-tr-55-85.
[3] Lakshman Rau, N; Issar, TP; Parthasarathy, MA; Patil, SM; Vijaya Devi; Giri Gowda, P; Shenoy, PD. 1986, 1993. Report of the High Power Committee set up by the Government of Karnataka on ‘Beautification of Bangalore’. Published by Shivashankar Engineering Co. Pvt. Ltd, Bangalore for the Government of Karnataka.
[4] Hasan, MF. 1970. Bangalore through the Centuries. Today and Tomorrow Publishers, Bangalore.
[5] Tomlinson, PB; (1986). The Botany of Mangroves. Cambridge University Press, Cambridge.
[6] Krishna, MB. 1996. The Birds of Bangalore’s Wetlands. Proceedings of the Seminar on Environment related Issues of Bangalore, pp.106-114. Environment Association of Bangalore & Civil Engineering Division, Department of Space, Bangalore.
[7] Chakrapani, BK; Desai, M; George, Joseph; Karthikeyan, S; Krishna, MB; Harish Kumar, U; Naveein, OC; Sridhar, S; Srinivasa, TS; Srinivasan, N; Subramanya, S. 1990. Survey of Irrigation Tanks as Wetland Bird Habitats in the Bangalore Area, India, January 1989. Birdwatchers’ Field Club of Bangalore. Sponsored by the Karnataka State Forest Department.
[8] Jayaram, C. 1996. Management of lake systems and surface water bodies in Bangalore. Proceedings of the Seminar on Environment related Issues of Bangalore, pp.94-104. Environment Association of Bangalore & Civil Engineering Division, Department of Space, Bangalore.
[9] MariGowda, MH; Krishnaswamy, M; 1968. Plant Wealth of Lalbagh. Department of Horticulture, Government of Mysore.
[10] Krishna, MB; Chakrapani, BK; Jayaram, C. 1995. National Lakes Conservation Plan, a proposal for Bangalore. Department of Ecology, Environment and Forests, Government of Karnataka.
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E&OE,
KRISHNA MB.
making free time is culture!
Wednesday, 28 September 2016
Using Mangroves Inland
Wetlands for Wildlife and Education in the Bangalore Area [*]
[*] Presented at the Public Affairs Centre and the Max Mueller Bhavan collaborative workshop on “Water”, October 2002.
M. B. Krishna.
The Background
“Water is essential to the survival of any plant or animal and natural wetlands are vital cogs in the ecological machine. Linking one habitat to another like a silver thread, the waterways and wetlands of the world are like the bloodstream of the body, vital and highly efficient distribution and cleansing systems.” [1]
Wetlands are defined as areas marginal between land and water, inundated or saturated frequently enough to support plant and animal communities adapted to a life dominated by water. It encompasses areas of marsh, swamp, standing or flowing water, which is fresh, brackish or salty. This definition thus includes man made systems, and the lakes in and around Bangalore fall into this category. Apart from the occasional seasonal stream, the Bangalore area has no natural wetlands. All the lakes (technically ‘tanks’, used interchangeably here), which occur in the area, are thus, man made. A wetland of our parts basically consists of an impoundment across a stream to form a lake, and irrigated fields down the embankment. As such these usually form a series, a number of them being found in a valley.
A vast majority of our wetland areas occur in the outskirts, on the urban-rural fringe. The uneven survival of Bangalore’s lakes with reference to the city at present is obviously the result of the explosive increase in the extent of the city from around 67 km2 in 1961 to presumably over nine times that area today. The growth of the city has not only engulfed the lakebeds but also disrupted the drainage pattern in these basins. In addition, the lakes which have survived in the City area have sewage flowing into them. A survey of tanks within a forty-kilometre radius of the GPO in 1995 revealed that, of the thirty tanks which had high water levels during the survey in the month of January, twenty-five had sewage waters flowing into them [4]. Today we treat wetlands as wastelands, dumping our refuse in them or filling them in order to provide farmland or building land [1].
Remote sensing studies have revealed that water bodies and wetlands account for just 4.8% of a sample area of 640 km2 covering both urban and rural zones of Bangalore [2]. The number of man made lakes, in the existing BCC and BDA area, has fallen from 262 in 1960, to some 81 lakes at present [5]. Obviously most of these lakes were created to serve the needs of irrigated agriculture, but were destroyed once the pressure for land became high.
Wetland Birds and other Wildlife
“Freshwater habitats can be as productive as any on earth, and support natural communities of great beauty and diversity. Many wetland birds are large and spectacular creatures, nesting in huge colonies. Many are also long distance migrants, with long established flyways linking one wetland habitat to another.” [1]
From an ecological point of view, the lakes in the Bangalore area form a unique and irreplaceable local system. A man-made lake of our parts can be viewed as a basin with several zones of water of varying depths, abutting a deeper zone that lies towards the embankment. This zonation is dynamic and promotes the growth of a variety of emergent, floating, anchored floating and submerged vegetation, each of which shows a preference to a particular range of water depth. These fresh water plant communities accommodate a large number of small organisms like periphyton, insects, molluscs, etc. which form the staple diet of many species of invertebrates and vertebrates in the lakes’ food chain [3].
Light, temperature and the availability of oxygen and nutrients govern the growth of plants, of which the smallest and simplest are phyto-plankton, which in turn are devoured by zooplankton, insect larvae and fish fry. There are even some adult plankton feeding fish and birds [3].
Even the lake sediments support a large variety of soil invertebrates, which thrive on organic matter from decaying plants and animals. These invertebrates are in turn eaten by a variety of other predatory animals such as fish and birds, sometimes along with the sediment itself. Food chains in these lakes can often be complex, lengthening and branching, and forming a food web. Often, at the end of this food web is man himself.
Wetlands account for a disproportionately large number of bird species compared to the physical extent of the habitat. Over three hundred and thirty species of birds have been recorded in Bangalore and its environs so far. Of these, around a hundred and forty bird species are found in or near lakes and wetlands [6], spread over some nineteen different bird families. Though the area accounted for by wetlands in the Bangalore area is just around five percent, the bird species accounted for is around forty percent of Bangalore’s total.
These birds make use of a variety of conditions from dry ground and meadows bordering lakes to the open water zone. There are also birds which just make use of the open air space above these wetlands. Depending upon their size, the availability of food and suitable conditions for foraging, different bird groups can be seen occupying different regions of the lake. A large number of species can be found in regions with shallow water. Often large congregations of migratory ducks can be found massed on the open waters of large lakes. Sheer distance from the shoreline affords protection to these birds, and they can even be seen sleeping over the water with their beaks tucked-in on their back!
Counts of birds taken in the wetlands and water bodies in and around Bangalore in winter indicate that as high as eighty percent of the individuals that we see, could be migratory. We get many species which only breed around the Arctic Circle, and almost all migratory wetland birds that come to our tanks and man made lakes breed beyond the Himalayas. Unlike popular impression, many of these birds are small, and fly fast, enabling them to cover large distances in reasonable time.
Not all these birds are common, nor are they found in every wetland right through the year: for example, a large number of trans-continental migrants are present only between September and April. The occurrence and numbers of birds is a complex interplay of food and resource availability, population movements, seasonal fluctuation, water levels and wetland structure, compounded by disturbance and other factors introduced by man.
Therefore, a variety of habitats and microhabitats are required for the survival of a variety of species. In Bangalore, there would be a gradient in the kind of microhabitats which would be provided by the sequence of tanks from within the city to the outskirts and the adjoining rural areas. The city tanks like Ulsoor and Yediur are walled, and others newly engulfed by the city would have lost the associated meadows and sloping shoreline. The 1995 survey revealed that nearly a third of the tanks in the Bangalore area (within a 40 km radius from the GPO) had lost their sloping margins and were either walled or had an abruptly sloping margin [4]. As one moves outwards, the sloping shorelines are seen but meadows are absent, until one reaches the relatively remote rural areas where all zones could be present. The shoreline and the water spread would have a major influence on the kind of birdlife that would be present in urban tanks. Preliminary investigations in the Karnataka region reveal that the extent of the water body would have a bearing on the bird populations but not diversity, which would be determined by the quality of the wetland and the shoreline [7].
Life began in water, and even the larger forms of life like amphibians and fish, depend on it for survival. More than fifteen forms of amphibians and over twice that number of fish have been recorded in the Bangalore area so far [8], and one even new to science!
The Issues
“Nature conservationists are recognising that battles to save biodiversity can not be won if they are only fought in habitats such as rain forest. The urban population are the key group to be motivated. Attitude change has to come in the areas of greatest political importance and highest resource consumption, and it is well recognised that such changes need to begin close to hand.” [9]
It is always good to remind ourselves that the largest body of tomorrow’s technical manpower comes from today’s cities. Nowhere else would ecological education and awareness be more relevant than in the urban context. There is a great opportunity in making the most of what is available locally, and to get an idea and feel of the processes which go on in nature, in our own environs and habitations. If used well, it would be but a stepping stone for further understanding of the processes in wilderness areas and a strong foundation to manage our own urban system. However, the ability to appreciate the plants and animals around us, and the ability to comprehend their value to us, is of paramount importance. The necessity to educate the citizens of today, as well as the necessity to sustain this teaching process for the citizens of tomorrow, is an aspect which can hardly be over-emphasized. It is in this context that maintaining urban wildlife habitats and green spaces takes a very special meaning.
If one takes even a cursory look at the amount of research work that has gone on in our universities on lake and wetland ecology related issues, one would see a distinct bias towards local sites being used for study. This is hardly surprising given that logistics and accessibility to analytical resources often determines the choice. But if one looks at awareness and education at a lower level, there is a fair amount of ignorance about what local habitats have to offer. This is notwithstanding the richness and accessibility of local habitats for informal and extramural education and learning.
Much of the general biology portions in the school and college syllabi review organisms which are essentially aquatic, from algae and other aquatic plants, to fish and amphibians. Traditional syllabi have perhaps not given enough importance to field biology to the extent non-destructive studies could have given an opportunity for. In a changing world where technology is shrinking barriers, non-destructive observational learning and studies could very effectively find a place. This is where natural urban habitats could play a key role. And urban lakes and wetlands would be very accessible habitats which could be used to even illustrate ecological processes.
There has been a tendency to view and use every urban lake for recreation purposes. Most urban lakes are eutrophic, and letting people come into contact with contaminated water may not be a wise thing to do. This also includes proposals for aquatic sports, where people in their prime are involved. Again, boating dives birds away [e.g. 10] and could have serious consequences for other wetland wildlife too. Even rescue, under our local conditions, in the case of a mishap would become difficult in large lakes. It could perhaps be said that any medium or lager sized lake, say larger than say 7 hectares, would be problematic for rescue efforts in time, without some danger to the individuals involved.
Many of the eutrophic urban lakes are seeded with fish and the harvests sold subsequently. It is well known in biology that contaminants could get concentrated in successive stages of a food chain and reach damaging levels, by a process which is referred to as ‘biological amplification’. In spite of this, consumption of fish from such sites continues. The global experience as in the case of DDT and mercury contamination should serve to warn people.
Land value in many urban areas is high, and there is a lot of pressure on tank bed land from encroachers [11]. The most easily maintained deterrent to encroachments therefore, is standing water itself.
The past attitude of viewing lakes and wetlands as wastewater lagoons should change. Lakes and wetlands could effectively be very useful in an urban setting, in more ways than one. Lakes and wetlands could effectively double up with urban green spaces and also be used for increasing urban tree cover. Trees in lakes and tanks could provide an aesthetic screen and pleasant greenery, especially in sites which are too small to have a scenic value, and also be useful for treating the water [12].
Bangalore is on a plateau, and all the water which flows, flows out. Tanks are thought to be good sources of groundwater recharge, though how some five percent of the surface area could effectively recharge the rest of the ninety-five percent is to be elucidated. Whatever the reason, it makes sense to retain these tanks in good condition with fairly good water, and wildlife!
References
01. Diamond, AW; Schreiber, RL; Attenborough, D; Prestt, I; 1987. Save the Birds. Pro Natur GmbH & Cambridge University Press.
02. Behera, G; Nageswara Rao, PP; Dutt, CBS; Manikiam, B; Balakrishnan, P; Krishnamurthy, J; Jagadeesh, KM; Ganesha Raj, K; Diwakar, PG; Padmavathy, AS; Parvathy, R; 1985. Growth of Bangalore City since 1900 based on maps and Satellite imagery. ISRO technical report number: isro-eos-tr-55-85.
03. Chakrapani, BK; Desai, M; George, Joseph; Karthikeyan, S; Krishna, MB; HarishKumar, U; Naveein, OC; Sridhar, S; Srinivasa, TS; Srinivasan, N; Subramanya, S; 1990. Survey of Irrigation Tanks as Wetland Bird Habitats in the Bangalore Area, India, January 1989. Birdwatchers’ Field Club of Bangalore. Sponsored by the Karnataka State Forest Department.
04. Krishna MB; Chakrapani BK; Srinivasa TS; 1996. Waterbirds and Wetlands of Bangalore: a report on the status, water quality, plankton and bird populations of the lakes in and around Bangalore and Maddur, Karnataka, India. Birdwatchers’ Field Club of Bangalore and Bangalore Urban Division, Karnataka State Forest Department.
05. Lakshman Rau, N; Issar, TP; Parthasarathy, MA; Patil, SM; Vijaya Devi; Giri Gowda, P; Shenoy, PD; 1986, 1993. Report of the High Power Committee set up by the Government of Karnataka on ‘Beautification of Bangalore’. Published by Shivashankar Engineering Co. Pvt. Ltd, Bangalore for the Government of Karnataka.
06. Krishna, MB; 1996. The Birds of Bangalore’s Wetlands. Proceedings of the Seminar on Environment related Issues of Bangalore, pp.106-114. Environment Association of Bangalore & Civil Engineering Division, Department of Space, Bangalore.
07. Hussain, SA; Subramanya, S; Naveein, OC; Krishna, MB; 2002. Inland Wetlands of India Project: Preliminary Field Report for Karnataka Wetlands. Unpublished.
08. Karthikeyan, S; 1999. The Vertebrates and Butterflies of Bangalore: A Checklist. WWF-India, Karnataka State Office, Bangalore.
09. Rhode, CLE; Kendle, AD; 1997. Nature for People. In Kendle, T; Forbes, S; Urban Nature Conservation. E & FN Spon. London.
10. Krishna, MB; Gadgil, M; 1993. The Impact of Boating on the Birds of Lalbagh tank. Enquiry report submitted to the Department of Ecology and Environment, Government of Karnataka, Bangalore. CES, IISc, Bangalore. Unpublished.
11. Jayaram, C; 1996. Management of lake systems and surface water bodies in Bangalore. Proceedings of the Seminar on Environment related Issues of Bangalore, pp.94-104. Environment Association of Bangalore & Civil Engineering Division, Department of Space, Bangalore.
12. Krishna, MB; 2000. Using Mangrove Trees in Eutrophic Inland Waters. Proceedings of the Lake 2000 Seminar, CES, IISc, Bangalore. http://ces.iisc.ernet.in/…;
WETLANDS FOR WILDLIFE AND EDUCATION
KRISHNA MB, OCTOBER 2002.
//Online from June 22nd, 2012//
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E&OE,
KRISHNA MB.
making free time is culture!
Shorebirds and lake shores in Bangalore
Changes over the past two decades.
An important thing we have learnt in many of the bird migration studies is that birds require areas called ‘staging grounds’ where they rest and put on weight before migration. This in a way ties them down to the land. They are thus ruled by the state of the habitat they are part of and become vulnerable to human activities which destroy their habitat. Sadly, two-thirds of the endangered bird species globally are threatened because of habitat loss, and not all of them are migratory.
The local scenario for example, too has been the same story. Birdwatchers in Bangalore used to count the number of water birds found in our lakes every January for a decade ending 1996. Nearly a lakh birds would be counted in about eighty to a hundred sites. Sadly much of these sites are gone and just about a third are perhaps remaining. The birds which wade into the shoreline, the shore-birds, are vastly reduced and hardly a couple of individuals figuratively, are to be seen in those sites today, while they used to occur in the hundreds and thousands earlier. The singular loss of a sloping shoreline in our lake-tanks would have mainly led to this decline locally.
The magnitude of decline is shown in the graph with the magnitude of change in the lakes themselves. And it is not a happy story.
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E&OE,
KRISHNA MB.
making free time is culture!
Tuesday, 27 September 2016
Use of Roadside Trees by the Birds of Bangalore
There are many birds and animals which live on and make use of roadside trees. They may be using the trees for shelter, for getting their food or, even using it as a travel corridor to move from place to place. If one considers birds of Bangalore for example, there might be birds of quite different lifestyles living in or using these trees. They might come to these trees just for roosting, or come to these trees to catch insects or eat fruit, or do both. They could even build their nests on roadside trees and feed their young there. There are even water birds like Night Herons which build their nests and raise their young on large trees in Bangalore.
Roadside avenues play a very important role in connecting the various green spaces still surviving in the city. The green spaces could not only be the parks and public gardens that we have, but could also be the various other gardens distributed in other private areas. The following lists the lifestyles of birds that could be using roadside trees (both large and small) in our city. It should be noted that in many cases, though certainly not all, roadside trees take more importance in conjunction with appropriate other greenery, including gardens.
Fruit eating birds
Nectar feeding birds
Sallying insectivores
Foliage gleaning insectivores
Bark gleaning insectivores
Far ranging roosting birds
Birds of prey
Scavenging birds
Singing birds
Birds using it as a corridor for movement and dispersal
Birds which use buildings
Water birds nesting or roosting in roadside trees
Even though birds can fly, they very often keep close to shelter and are loath to cross large open spaces away from cover. Quiet residential areas with closed canopies could even have the spill over from neighbouring gardens and harbour the more woodland kind of birds. There is a common misconception that roadside trees serve no use for wildlife in urban areas. Nothing could be farther than the truth. All the examples considered herein could come under the preview of the Wildlife Protection Act and revisions and perhaps under the treaties for the conservation of migratory birds. These are some of the birds found in each category mentioned above:
Fruit eating birds
There are many fruit eating birds which come to take fruit from roadside trees. Many of these are even part of our folklore and culture like the Koel. Small Green Barbet and the Coppersmith Barbet are two of the more prominent species. In addition, both Redwhiskered and Redvented Bulbuls can come to roadside trees in appropriate habitats. Roseringed Parakeets and the colourful Blossomheaded Parakeets come to roadside trees. The two myna species and the starlings, namely Jungle and Common Mynas; the Grey-headed, Black-headed and Rose-coloured Starlings come to roadside trees to take fruit. At the other end of the size spectrum, we have the almost thumb sized Tickell’s Flowerpecker visiting the mistletoe on roadside trees.
Nectar feeding birds
Many nectar feeding birds like the Purplerumped Sunbird and the Purple Sunbird come to roadside trees. The much rarer Maroon-breasted Sunbird also comes to roadside trees.
Sallying insectivores
A large number of sallying insectivorous birds also use roadside trees. Various flycatchers could make use of the under-canopy space to carry on their food gathering activities. Many of these are migratory. The Grey Drongo which is again a migratory species, makes use of the air space over the canopy using the upper branches as perching sites.
Foliage gleaning insectivores
There are quite a number of birds in this category. There are warblers which are abundantly found here. They search leaves at different levels depending on the species. The migratory Greenish Leaf Warblers are quite prominent. Tailor-birds, and occasionally Ashy Long-tailed Warblers make use of the lower branches, and in the wooded outskirts, the Franklin’s Long-tailed Warbler.
Bark gleaning insectivores
Grey Tit is a prominent member of this guild. On the outskirts, woodpeckers are found too.
Ground feeding birds
Many birds which feed on the ground or near to the ground fly up into trees on disturbance, and roost there. They could be both insect eating birds like the various species of babblers or seed eating birds like the Spotted Dove. The many babblers include, depending on the part of the city and time, the most common of them all, the White-headed Babbler. In addition we have a class of birds which perch on low trees but swoop on insects on the ground like the Roller, though this is essentially on the outskirts. The Roller is known to breed on roadside trees.
Far ranging roosting birds
There are long flying birds like the crows and mynas which commute long distances from their feeding to roosting places. Depending on the season, even Roseringed Parakeets are found abundantly on Roadside trees.
Birds of prey
Most birds of prey make use of the large roadside trees for roosting, feeding and nesting. Shikra, Brahminy and Common Kites are all found on roadside trees. In addition many species of owls like the Spotted Owl, the Collared Scops Owl, the Barn Owl and the Mottled Wood Owl could come to or roost in roadside trees.
Scavenging birds
Crows are one of the main users of roadside trees. Common Kites are another species found abundantly on this substrate.
Singing birds
Quiet roadside trees are places where our proverbial cuckoos, the Koels roost and sing from. Many warblers and flycatchers, thrushes and the Magpie-Robin sing from the shelter of roadside trees.
Birds using it as a corridor for movement and dispersal
The critical function of the roadside avenue to provide a corridor for movement of our avifauna cannot be underestimated. Many species are loath to leave their sheltered places and fly across open ground. For all such species and others in general, avenues provide the corridor.
Birds which use buildings
Birds which sit on building like Blue Rock Pigeons also perch on trees. Often they land on to trees before settling down on the ledges of buildings. Another bird which shows a similar behaviour is the Barn Owl.
Water birds nesting or roosting in roadside trees
This is a classic example of the unexpected happening. Many species of shoreline water birds like Night Herons, Egrets and other herons roost and breed on roadside trees, often within Bangalore.
And then, there are Endemic birds
Many of the species which occur on these roadside trees are endemic to this part of the world, and found nowhere else. They include the Small Green Barbet, the Purple-rumped Sunbird and the Mottled Wood Owl.
[09 July 2011. Not formally edited]
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E&OE,
KRISHNA MB.
making free time is culture!
Are 'invasive plants' really so?
To call every plant invasive is silly. A species becomes colonising only if it is able to integrate into existing conditions and often provides resources to pollinating and dispersal agents which help it adapt better and spread. And it is able to do that because there are vacant niches to be filled, ecologically speaking. Which also means that they are not facing competition form other species. It is is often the non colonising 'equilibrium' species that are more competitive, since they are the ones which survive in species rich seral stages and late communities during succession.
Plants were introduced for very specific reasons, and lower 'pest' attacks mean lesser pesticides need to be used. So is it with fungal and other infection and its cure.
There is nothing wrong promoting native species, but not with the arguments used. To say that only native plants and trees are good and every introduced plant is bad is being shortsighted.
A coconut tree palm is an exotic in the inland areas it is planted. It is a littoral species which grows in areas with abundant water and very high humidity. A coconut tree consumes as much water as an elephant does every day, and mass planted, can desertify areas much more effectively than any other introduced species in our conditions. Just look at the Arsikere area for example.
Still, the coconut is not exotic for all the biased campaigners out there. But for much of the inland habitats, it is alien. It may be from the same political construct, but certainly a species adapted to a totally different habitat. But it does not become an exotic for people. The coconut actually spreads much more since humans as dispersal agents are more effective than a myna dispersing the seeds of say a fig. So why is it acceptable? Just because of usefulness, in this age of transporting resources?
It is therefore necessary to get the right ideas in, and not get carried away by misinformation.
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June 13, 2016 at 1:47pm
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E&OE,
KRISHNA MB.
making free time is culture!