The process of natural succession in urban areas
Succession has been a fundamental concept in ecology. Its classical definition is the orderly change in vegetation at a site that is predictable and directional towards a climax state or end point (Clements 1916). A general assumption of succession is that early seres are governed by allogenic processes, environmental processes external to the site, and early seres facilitate later successional stages. As the community matures, autogenic processes, biotic interactions, become important in facilitating later-successional assemblages and the movement of the community towards an end point (Connell and Slatyer 1977). Field studies often showed trajectories were not always predictable, end points were not always achieved, and allogenic processes played an important role in community dynamics throughout successional development.To shift the focus of successional studies away from descriptive to mechanisms or interactions that contribute to successional change, Connell and Slatyer (1977) proposed three distinct mechanisms-facilitation, tolerance, and inhibition-at the community level. This shift enabled experimental approaches to studying succession, but it failed to capture the complexity of vegetation dynamics (pickett et al. 1987 a).