Urban Natural Areas #1 – Disturbance II
To determine the scale at which this non-equilibrium disturbance pattern is appropriate, Pickett and Thompson (1978) investigated what they termed the “minimum dynamic area” that could sustain the occurrence of natural disturbance regimes. These minimum dynamic areas were defined as “the smallest areas with a natural disturbance regime, which maintain an internal recolonization source.” The minimum dynamic area should be able to sustain itself without human intervention. Given the size, shape and present biological condition of the reservoir forests and the matrix of natural, cultivated and human infrastructure features in the landscape, this does not appear feasible.
Disturbance is a natural occurrence within forest landscapes of North America. Disturbance can be localized, widespread, acute or chronic in its influence on the forest community and its physical structure. Insect infestation, disease, ice and windstorms and hurricanes are examples of the types of disturbance that have influenced the forests within metropolitan regions.
Isolated forest patches such as urban forest natural areas are vulnerable to intense stochastic disturbances. One hurricane or ice storm can result in the destruction of an important plant community or a portion of the old regrowth forest, or topple a stand of trees, setting off a series of events that leads to both short and long-term losses of important water quality and biological values. Thus small conservation tracts require more intensive management to maintain them in the condition that allows a higher degree of certainty in reaching the goals of conserving regional biological diversity. (White and Bratton 1980).
Urban conservation practices should attempt to mitigate the effects of both small and large scale disturbance within geographically imbedded natural areas, and large scale disturbance within the urbanizing forest lands of the broader metropolitan region.
S.T.A. Pickett and Thompson J.N. 1978. Patch dynamics and the design of nature reserves. Biological Conservation 13 (1) pp. 27 – 37.
White, P.S., and S.P. Bratton. 1980. After preservation: Philosophical and practical problems of change. Biological Conservation 18 pp. 241–255.