Vegetation composition and structure of forest patches along urban - rural gradients

The urban landscape is highly altered by human activities and is a mosaic of different land covers and land uses. Imbedded in this are forest patches of different origins (Zipperer et al .• 1997). How these patches influence and are influenced by the urban landscape is of ecological importance when managing the urban forest for ecosystem goods and services. To evaluate how forests respond to altered environmental conditions of urban landscapes. McDonnell and Pickett (1990) proposed an urban-ta-rural gradient approach. The approach builds on an established ecological methodology. gradient analysis. to evaluate species response to changes in environmental conditions (Whittaker. 1967; Pickett et al .• Chapter 3). 1Wo basic categories of gradient analyses exist direct and indirect. Simplistically. direct gradient analysis is typically employed when a single factor is used or the underlying environmental factors are organised linearly. whereas indirect gradient analysis is used when the multiple interacting factors and the environmental factors are not organised linearly across a landscape or in a regular pattern (Ter Braak and Prentice. 1988). Other approaches exist for studying the response of ecosYstems to altered environmental conditions in urban environments. such as biotope mapping (Breuste. Chapter 21) and patch dynamic approaches (Nilon. Chapter 10).