Biodiversity in patches

Biodiversity in patches

URBAN ECOLOGY There is insufficient recognition of the significant role that home gardens play in supporting urban ecology. City planners, horticultural societies, green groups and resident associations should actively encourage greening, and provide information on species and organic planting practices that support biodiversity, observes Harini Nagendra

For those of us who live in cities – an increasing proportion of India’s population these days – urban green spaces provide one of the few remaining avenues for us to observe and interact with nature. There is now an increasing body of research that finds that vegetation in cities has a critical role to play in reducing stress and maintaining a psychological feeling of well being, in addition to the obvious list of health services that urban greenery provides.

What comes to your mind, though, when you think of green spaces in Bangalore? Chances are that most of you would respond with ‘Lal Bagh’, or ‘Cubbon Park’, perhaps widening your scope to include a few lakes. Yet, how many of you would think of the humble domestic garden? Bangalore’s bungalows, so characteristic of the City in previous decades, are giving way to apartments across the City.

Yet a large part of Bangalore’s residential areas continue to be dominated by individual homes, and even the smallest of these often manage to make some place for a tiny patch of greenery. The total impact of such small scale efforts can be quite substantial. Although we do not have the numbers for cities in India, domestic gardens occupy as much as one-fourth of urban land cover in many cities in the UK, and over one-third of the total area in a city in New Zealand.

Although home gardens can be quite small in extent, in total, the plants and trees in these residential yards provide important habitats for urban birds, insects and other species. Yet these private gardens tend to be ignored by city planners, in part because there is such little information available on these aspects.

Our research group was interested in examining the diversity, composition and distribution of plant species in Bangalore’s home gardens and apartments. This  forms part of a longer programme wherein we have been documenting plant diversity in Bangalore’s streets, parks, lakes, slums, and other types of land use.

Stress on rarity

Across Bangalore, we sampled a total of 328 locations between 2008-2010, documenting plants in 18 large apartment complexes (over 50 residential units), 63 small apartment complexes (less than 50 residential units), 75 large home gardens (plot area greater than 2400 square feet), 85 moderate sized home gardens (1200 - 2400 sq ft), and 87 small gardens (less than 1200 sq ft). We documented over 1,668 trees belonging to 91 species, as well as 192 species of shrubs and herbs.

Given that the number of apartment and home gardens in Bangalore is much greater than we can hope to sample, the number of tree and plant species that these everyday locations harbour is likely to be much larger! As much as 90% of the tree species and 80% of the plant species are uncommon, found in less than 5% of the gardens. Thus, it seems that Bangalore’s garden enthusiasts are an informed and idiosyncratic lot, prizing rarity and disdaining most common species – as I am sure any of you who have a garden, or have a relative or friend who is an avid gardener, will agree!

Only one tree species – the ubiquitous Bangalore coconut – could be considered widespread, and is found in more than 30% of the gardens. Five species of plants – rose, anthurium, areca palm, hibiscus and the indispensable tulasi – were found in more than 20% of the gardens studied, with tulasi being the most common plant.

Many garden species were purely ornamental, but about one in three tree species and one in four plant species had some utilitarian value, being used either for food, medicine, or worship. 28 tree species (such as jackfruit, mango and drumstick) and 36 plant species (including papaya, banana, coriander and avarekaalu) provided fruits, vegetables or spices used for cooking. This is in contrast to studies of urban domestic gardens in western countries, which have found an almost exclusive focus on ornamental plants.

Large apartments and home gardens had more trees of larger sizes and more species of herbs and shrubs compared to small gardens, quite naturally, because of space limitations. Also, most small and moderate-sized homes were less than 20 years old, while large homes were usually older. Again, this seems quite consistent with what we know of escalating land prices in Bangalore – it is very difficult to purchase even a small sized plot in the city these days, and the days of large Bangalore bungalows seem numbered.

We found different types of species planted in homes and apartments. Many traditionally planted species such as rose, hibiscus, jasmine, tulasi and curry leaves are found in older, large and moderate sized gardens, and rarely encountered in apartments.

In contrast, some plants such as aloe vera, lilies and cannas tend to be mostly found in apartments. Some species such as anthurium, bougainvillea, ixora and the ever-present coconut tree, appear equally popular with apartments and home owners. Finally, some species like the Christmas tree, guava, mango and sampige are popular with large home owners and also found in some large apartments – but the large size of many of these trees makes them sadly unsuitable for planting in most small to moderate gardens.

Visitors from the wild

People have observed a variety of urban wildlife visiting their gardens, mentioning butterflies, squirrels, birds, bats, earthworms, frogs, insects, monkeys, snails and snakes – as well as bandicoots and rats! Sadly, however, most residents pointed to a decline in biodiversity over time.

Supporting the popular perception of Bangalore as a nature-friendly city, a majority of home owners said they made special efforts to support biodiversity, by placing rice out to feed birds, providing water baths, and leaving sugar out for ants.

Unfortunately, many residents had already decreased their existing garden area or intended to do so, because of an intention to construct on existing garden space, water scarcity, and/or difficulty in hiring gardeners. When we revisited many of these sites after a few months to collect data, we also found sadly that several houses had built over some part or all of their garden area.

Interestingly, we find that many large apartment complexes have set aside areas for planting, with a significant proportion of large sized trees, and high species diversity.

Yet, it must be pointed out that many large apartments in Bangalore are constructed in locations that were once agriculture, plantations, or wetlands, thus leading to an overall decrease in green space.

In another disturbing trend, many homes are being converted to small-sized apartments with reduced garden area, or beginning to reduce garden space due to further construction, and challenges of garden maintenance. This trend can be expected to accelerate in future years. Domestic gardens thus appear endangered, while there is insufficient recognition of their significant role in supporting the City’s ecology. City planners, horticultural societies, green groups and resident associations can take a major step in this direction by actively encouraging greening, and providing information on species and organic planting practices that support biodiversity.

(Harini Nagendra, Madhumitha Jaganmohan, Lionel Sujay Vailshery & Divya Gopal conducted this research at the Ashoka Trust for Research in Ecology and the Environment (ATREE),  Bangalore.)

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