Flora and fauna

The variety and extent of green spaces in urban areas results in some urban areas having a far greater proportion of semi- natural habitat than equivalent-size areas of countryside, especially those which are intensively farmed. The range of flora and fauna contained in this green space is varied and rich, with characteristics which differentiate it from the flora and fauna of rural areas.

Flora

Many of the plant species to be found growing naturally in disturbed ground or on ‘wasteland’ in urban areas are ruderal or pioneer species, which are the first plants to colonise disturbed ground. Many of these species used to thrive on arable land, but some have become uncommon in the countryside due to herbicides and modern cultivation methods. On newly disturbed ground in urban areas they find a refuge, but unless the site is disturbed annually, they are suppressed as the opportunity to seed onto bare ground diminishes, and perennial and woody species take over.

Also found on urban ‘wasteland’ are the common perennials such as nettle and couch, which have roots that can survive frequent disturbance, but can also persist in grassland and other undisturbed ground.

'Wasteland' annuals/biennials

‘Wasteland’ perennials

In urban areas, many ruderal species may be naturalised species. Some of these are garden escapes, that have been deliberately introduced into Britain to grow in gardens, and then become naturalised on waste ground, spread by wind-borne seeds or birds, or by being dumped as garden refuse. In places these species can become abundant, and waste ground of particular towns become dominated by the locally dominant species, such as buddleia, Michaelmas daisies or evening primrose. Some naturalised species are cultivated hybrid crop plants such as strains of clover. Other naturalised plants become established from seed brought into the country in imported goods, with docks and other handling areas being the focus for these plants to establish.

Naturalised species

As described above, urban areas have a significantly warmer climate than surrounding rural areas, allowing southern species to thrive further north than in the countryside. These include both native species, and naturalised aliens.

Urban areas thus have the bare land for plants to establish, the seed source from gardens and imported goods, and the climate for exotics to survive. As described previously, some industrial sites also have unusual substrates which support plants typical of salt marsh, sand dune or other habitats, thus increasing the range of the urban flora. For a full discussion of this subject see The flowering of the cities: the natural flora of urban commons, English nature (1992).

In contrast to these recent arrivals are the relict areas of woodland, meadow, wetland and other ancient semi- natural habitat encapsulated in the urban areas, and which contain assemblages of mainly native plants.

Fauna

The ancient relict areas of semi-natural habitat are especially important for invertebrates, many of which are immobile and require continuity of habitat. These include invertebrates dependent on trees and other plants, dead wood, and those living in the soil. Provided there is continuity of habitat, urban areas can be rich in invertebrates, and even small areas can support significant populations. Warmer temperatures in towns, and the presence of nectar bearing plants over a long season  can  favour  invertebrates.  Urban  beekeepers are able to produce high volumes of honey because of the good quality, abundant food supply from garden plants.

Recently disturbed sites with areas of bare ground may be good for early stage colonisers such as carabid beetles, and also for solitary ground-nesting bees and wasps. Buddleia and other shrubs may attract stem-nesting bees and wasps. Trampling and grass-mowing are detrimental to the development of the invertebrate community.

Non-native invertebrates possibly comprise 15% of the urban soil invertebrate species, a higher proportion than in rural areas. Most species have little or no effect on the local ecosystem, and have integrated well. The factors in urban areas which encourage the ingress of plant species, also favour invertebrates. These include the importing of goods or plants, the presence of disturbed ground and vacant niches to be exploited, and the means for dispersal along transport corridors. Importing of plants is controlled by plant health regulations, with the aim of preventing the import and spread of pests and diseases. Invertebrate pests are mostly specific to particular ornamental plants and greenhouse crops, and do not cause a problem in the wider environment. However, one particular invertebrate, the New Zealand flatworm, is threatening native earthworm populations in the areas where it has become established. The flatworm is thought to have arrived in this country and spread via the soil in container-grown plants.

Many birds have adapted well to the abundant woodland glade habitat provided by surburban gardens and parks, and ‘garden birds’ form a major category in a description of the birds of Britain. Garden bird populations increase with suitable nesting cover in overgrown gardens and wilder patches of green space, and with abundant food supplies. These include the insects, berries and fruit of gardens and green spaces, plus additional food put out in bird feeders during the winter. Other birds, particularly those that naturally nest and roost on cliffs, have adapted to city centre living. These include pigeons,herring gulls, swifts, house martins, black redstarts and kestrels. Scavenging species such as the black-headed gull thrive on the food from refuse tips, and starlings have become prolific winter visitors, roosting at night on urban rooftops and feeding by day in parks and fields. Birds of prey, particularly kestrels, are now quite numerous in urban areas, partly due to the abundant food source on motorway and other road embankments. Reservoirs, restored gravel workings, sewage works and other waterways and wetlands within urban areas support abundant populations of resident birds, as well as winter visitors.

Amphibians are able to survive in the wilder green spaces in towns and suburban gardens, provided their habitat is not fragmented and there is safe access to a pond or wetland. Amphibians need fish-free ponds with gently sloping banks, and plenty of cover and foraging habitat nearby. However, populations can be severely reduced by thoughtless actions, such as the cutting of long grass around ponds at the time froglets are emerging. Some drains and other man-made structures can be lethal traps for amphibians, as well as for other animals such as hedgehogs and grass snakes.

Many small mammals are locally abundant in urban areas, and thrive wherever there is suitable cover of long grass, shrubs and other undisturbed vegetation. Several species  are  good  colonisers,  able  to  take  advantage of new habitats. Hedgehogs, bats, grey squirrels and weasels are found in many urban areas. Of the larger mammals, foxes have become adept at exploiting the abundant food source in towns, making their earths in railway embankments and waste land. A night-time drive around a town will often include the sighting of a confident-looking fox, quite at home and unworried by car headlights or traffic noise. Rural foxes are much more elusive. In recent years, muntjac deer have spread into suburban habitats, especially in the southern and central Midlands, where they graze on the ground flora in woods and large gardens.