ABSTRACT
Mosaics are evident at all scales from the submicroscopic to the planet and universe. All mosaics are composed of spatial elements (Forman 1995). Cities develop mosaics of land use and land cover types, vegetation types, social conditions, surface conditions, heat absorption and emission as a function of human activities, particularly the subdivision of properties into smaller lots and then changes in the use of those lots. The simple paving of the yard in front of a house represents a change in the mosaic from vegetation to a hard surface. Essentially urban areas are fine-scale mosaic areas where jobs, homes, shops and recreation are close together with efficient transportation connecting built areas (Forman 1995). In the suburban mosaic, vegetation has a major role. In the densely built-up central areas of big cities, vegetation is less prominent, save in formal squares and parks. The basic elements of the suburban mosaic are vegetation, buildings and hard, usually impermeable, surfaces, such as roads and car parks. Plants contribute to the spatial structure of urban systems both through their presence in parks, gardens and reserves, and through street trees and shade trees throughout the entire urban mosaic. In urban areas, the amounts, structure and condition of these three components (vegetation, buildings and surfaces) (Table 21.1) reflect human agency (Pickett and Cadenasso 2008). Suburbia comprises a mosaic of contrived plant diversity, blatantly people-made, to which nature had added a variety of species of animals and plants that have adapted to urban life. These gardens respond rapidly to inputs of nutrients and usually tend to receive supplementary fertilizers and applications of water. Insects exploit the full variety of the gardens but may be the target of chemical sprays, though probably less intensively in gardens than areas of intense horticulture and arboriculture. Such gardens are important bird habitats and support a variety of animals, such as the squirrels and foxes now common in British suburbs. Within this category there are contrasts due to the age of the suburb. The new suburbs of cities, often built on former farmland, usually differ from older suburbs by having a smaller number and lower height of trees, and a greater proportion of lawn and mown grass than of shrubs and cultivated flower and vegetable gardens. The total plant biomass of such suburbs is much less than that of older inner suburban areas with consequently a less varied suburban fauna. Comparisons of urban bird populations in newly developed suburbs and in older well-established suburbs show a richer avifauna, in both diversity and population, in the older suburbs.
