Urban Environmental History: the importance of relict communities in urban biodiversity conservation

摘要

With increasing urbanisation world-wide (The World Commission on Environment and Development, 1987), the possible importance of urban areas to biodiversity conservation, is of particular interest (Adams and Dove, 1989; Sukopp and Hejny, 1990; Sukopp, Numata and Huber, 1995). Many urban areas consist of patchworks of often fragmented, isolated environments offering habitats for a varied range of plant and animal species (Gilbert, 1989). Many of the typical species of so-called 'urban commons' faunas and floras, are highly adaptive, native ruderals of catholic habitat requirements and cosmopolitan occurrence (Hodgson, 1989). These are found along with aliens, again either broadly adapted to a range of disturbed and often productive sites, and more specialised plants able to exploit more extreme environmental conditions (Gilbert, 1992a and b) The diversity and ecological interest of these communities is often inherently ephemeral. However, where relict landscapes occur within urban areas, they may hold remnant populations of animal and plant species which are relatively stable, and are increasingly rare in the wider environment. Furthermore, the loss of relict or remnant species is often linked to the history of settlement and of urbanisation. So-called 'habitat patches' such as woods or grasslands may hold relict species, but this ability varies considerably between different ecosystems. Where pockets of rich, native biodiversity remain, it is often along steep stream valleys such as Rock Creek Park in Washington D. C. (Murphy, 1988), or the Rivers Don, Porter, Sheaf and Rivelin in Sheffield (Bownes et al., 1991). These relict species are typical constituents of communities of seminatural, unimproved environments. In urban-fringe zones around towns and cities in the UK, they have often avoided the consequences of habitat degradation and destruction, which characterise much of the wider countryside. These relict areas may therefore offer long-term, sustainable environments of regional significance in terms of biodiversity conservation. The habitattypes and their associated communities are often relatively stable and robust, especially if appropriate site management can be achieved. These areas may therefore help achieve the twin goals noted by Tylka et al. (1987), for wildlife management and conservation in urban areas. These are the maintenance of regional species composition and abundance (regional biodiversity), and provision of opportunities for contact with nature. The implications of broad ecological studies (such as Hodgson, 1986) and of specifically urban ecological research (such as Gilbert, 1989; and for example, Nilon and Pais, 1997), demonstrate the importance of more fully understanding ecological processes in urban areas if strategic planning for urban biodiversity, particularly in countries such as the UK, is to be successful. These arguments are highlighted by appropriate case-studies and examples, to place relict, urban communities in a strategic context.