It has not proved possible to assess the extent of London’s urban wasteland resource. Urban wastelands were severely under-sampled in the London Wildlife Habitat Survey 1984/85 and more recent assessments of urban wasteland, derelict land and brownfield land, undertaken by other agencies, have used various incompatible definitions.

Whatever the true extent of London’s urban wasteland resource in the mid-1980s, there is no doubt that there has been a substantial reduction in its extent within the last decade. London’s former docklands contained a significant proportion of the capital’s urban wastelands, but most of this area has been redeveloped to accommodate London’s burgeoning service sector industries. Other large areas have been lost in more recent years to provide land for new housing. Despite the losses to some of the most extensive areas of urban wasteland in London, new sites, albeit smaller and more widely dispersed, are constantly being created as a result of abandonment · a feature of the development cycle in a major conurbation.

As a whole, urban wastelands may be one of the most diverse of London’s habitats. They encompass a wide range of sites with varying substrates, topographies and other factors that determine the distribution of plant and animal species. The variation in other habitat types such as grassland and heathland may be rather subtle, as a result of minor changes in soil chemistry and hydrology, for example. However, the variation amongst urban wasteland communities can be quite striking, because of the different substrates and the source of primary colonisation. Some of the most important attributes of urban wasteland habitats are essentially ephemeral. Micro-topographical features and microclimatic effects are rapidly created as land is disturbed or surrenders to natural processes after abandonment. However, they are rapidly destroyed when land is recycled for new development or natural succession leads to eventual dominance by secondary woodland or Buddleia ‘scrub’.

A common feature of many urban wastelands is the dominance of species that are considered to be ‘weedy’, ruderal or pioneer species. These species are best able to colonise disturbed or hostile environments, but often succumb to competition once conditions ameliorate or stabilise. For this reason many of the species that flourish in urban wastelands are exotics which would normally be out-competed by native species, or are species which have exacting climatic or biological requirements that are rarely available except in the unusual conditions which arise on urban wastelands. The importance of urban wastelands for invertebrates is becoming increasingly apparent. The bird most often cited as a wasteland species - the black redstart · does indeed occur on urban wasteland sites, but can be found in less derelict areas where the characteristics of the habitat are very diffuse.

The single most prominent threat to urban wastelands is redevelopment. All urban wastelands are previously developed land, or land which has had an industrial use (usually the disposal of waste material). As such, urban wastelands are usually subject to redevelopment or decontamination proposals. Redevelopment of land or the restoration of contaminated land frequently results in the almost total loss of species present on the site, as there is often a requirement for the complete removal or capping of the existing surface material and vegetation. Although this will result in local extinctions of some species, many other species will maintain local populations if there are adjacent wasteland habitats or incipient wasteland habitats (newly cleared or abandoned sites) nearby. However, in modern day London the loss of urban wastelands far outstrips the creation of new ones. The debate concerning the environmental benefits and losses attributable to redevelopment or restoration of urban wastelands cuts to the quick of the sustainability debate in London.