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Biodiversity in the urban environment

The perceived impoverished diversity of species and habitats in the urban environment has been sensitive both to invasive intrusion of species and to extravagant population fluctuations, as well as to functions seen principally in amenity and education. Biodiversity Plans can redress some of these imbalances and promote additional objectives.

In practice much has already been achieved particularly in identifying key areas of interest, significance and potential. However, I believe ecological experience may be more important in the practical imperatives of implementational programmes of action. Species and habitat action plans will need an understanding of the ecological processes in action and the benefit of the wide and specific knowledge that is rapidly developing across many locations with similar challenges. Liaison will be a key component, but is the constant need for SNH approval likely to prove a barrier rather than a benefit?

Objectives have been set for habitats and species, to encourage their consolidation, their expansion and their variety. Should the same rules hold true in the urban context, where the physical, chemical, geographic and biological criteria that shape the pattern and structure of wildlife communities often exhibit unique parameters.

It is comparatively easy to provide a characterisation of the key habitats and species that can be found within the geographic compass of any city, to identify location and species richness (or poverty). Even this activity in itself brings many benefits from the simple one of drawing the attention of biologists to the wildlife riches on their doorstep, to the more complex recognition of the environment as a component of social interaction and 'quality of life'.

The techniques of habitat recovery and species recolonisation, too, are now beginning to be well understood and spread, for example through the activities of the Society for Ecological Restoration. Indeed the whole concept of urban regeneration and renewal has a long history that includes the cosmetic educational approach to short term 'pocket habitats' in advance of development, and whose very success has led to a more strategic cost benefited process of restructuring the shape, and even purpose, of open space in cities.

As a result a philosophy of bringing the country into the town, based heavily on the biogeographic theories of islands and migration corridors, has developed rapidly. This philosophy, too, has been dependent on the dramatic physical and chemical change and improvements that have accompanied the industrial reformation of urban areas.

There is, of course, a paradox in this process of urban renewal and greening, or even perhaps a series of paradoxes. The laudable re-evaluation of urban land values in company portfolios incorporates a measure of reality in the estimation of restoration costs, a measure of stock market cooling of pressure, and a measure of objective and target re-evaluation. Included, too, in our paradox is the planning re-visualisation of city sizing and structure; the ability, opportunity and, in many cases, need to reinvent the image and design of the urban framework. The paradox, of course, is that as the country comes into the town, the town moves out into the country. The same fingers of ecological opportunity that point into the city are also corridors of development opportunity that stretch outwards along the communications network.

Two issues concern us here. Can the diversity of the 'truly rural' ever be replicated in the peri-urban or intra-urban environment? And what of the 'truly urban', are any of its ecological characteristics and inter-relationships worthy of consideration in their own right?

There is probably little benefit to be gained from exploring existing data on species richness in urban and rural areas, in that the entities selected are rarely comparable, survey histories are similarly unalike, and the impacts, both positive and negative, of human activity are not accounted for. Potential is likely to be assessed through an analysis of soil and climatic conditions. Rarely, if ever, will the neutral grasslands of urban backcourts have the same origins, soil structures, consolidation, permeability or micro-climate as those outwith the city.

Diversity, where it exists in the city, is more often a repository of the domestic garden and is characterised by the frequency of aliens, especially plant species from elsewhere. The aliens may be the chance occurrence of hemp on a rubbish tip or bush crickets in a greenhouse, the welcome splash of colourful monkey flower on a river bank or butterfly beloved buddleia on a railway siding, or the less than helpful dominance of grey squirrels in the park or Japanese (and Russian) knotweed crowding out its native competitors. Such characteristics are, of course, not unique to urban areas, but are usually more noticeable and more dramatic in their impact on an ecosystem. Monoculture, non-climactic ecosystems and rapid population fluctuations are typical of urban wildlife communities.

What are the specific challenges of urban biodiversity and how can they best be met? The edges of towns and cities will always be host to the occasional, usually fleeting though sometimes more permanent, visit or occupation by the unexpected species exploiting the habitat diversity that is there. The more that we can extend these fringe areas into the city environment and provide them with a degree of stability and permanance, the more these occassional occurances will become frequent.

But it is equally important to look more deeply at the populations at home within the city environment. Wild city dwellers have been divided into:

  • species that have established what might be described as a symbiotic relationship with man in the city, almost dependent on human artifacts and presence to survive
  • species that adapt well to the physical environment of the city but shun or tolerate direct contact with man.
  • species whose transitory appearance may exploit specific features of the urban environment as a temporary niche in their use of a wider environment.

There is surprisingly little scientific information on the relevant species characteristics and environmental constraints that define their occupation of the city. Anecdote and newspaper report substitute for ecological journals. Should any biodiversity plan go forward without the support of a local academic unit dedicated to the elucidation of its specific characteristics? What we do know of the wildlife inhabitants of the city affirms the significance of diversity but also emphasises the fragility of extreme habitats and their vunerability to change and invasion. What do we really know of the autecology of magpies in their dramatic spread from suburb to city, or the feeding preferences and techniques of urban foxes?

It is important to recognise the role that roofs, walls, gardens, alleys, backcourts, refuse, ledges etc as well as man himself play in the survival of wildlife within the city. Open water and the original terrain of the city, its hills and valleys, are also significant in the re-establishment of a vibrant and diverse urban environment. Biodiversity in urban areas is going to require not only corridors and good park management but a better understanding of roof gardens, pocket parks and storm drains in order to provide a permanent legacy of variety and stability.

The true challenges of urban biodiversity, perhaps, lie in continued progression towards the physical and chemical enhancement of soils, water and air in the city, on the accommodation of its foreign invaders and on the ecological support of native flora and fauna as it tries to return.

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