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
- 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