LONG-TERM RESPONSE OF DISTURBANCE LANDSCAPES TO HUMAN INTERVENTION AND GLOBAL CHANGE

The structure of landscapes subject to patch-forming catastrophic dist urbances, or ''disturbance landscapes'', is controlled by the characte ristics of the disturbance regime, including the distribution of distu rbance sizes and intervals, and the rotation time. The primary landsca pe structure in disturbance landscapes is the structure of the mosaic of disturbance patches, which can be described by indices such as patc h size and shape. The purpose of this research was to use a geographic al information system-based spatial model (DISPATCH) to simulate the e ffects of the initial density of patches on the rate of response to al teration of a disturbance regime, the effects of global warming and co oling, and the effects of fragmentation and restoration, on the struct ure of a generalized temperate-zone forested disturbance landscape ove r a period of 400 yr. The simulations suggest that landscapes require 1/2 to 2 rotations of a new disturbance regime to adjust to that regim e regardless of the size and interval distributions. Thus alterations that shorten rotations, as would be the case if global warming increas es fire sizes and decreases fire intervals, produce a more rapid respo nse than do alterations that lengthen rotations, such as cooling and f ire suppression. Landscape with long rotations may be in perpetual dis equilibrium with their disturbance regimes due to a mismatch between t heir adjustment rate and the rate of climatic change. Landscapes with similar rotation times may have different structures, because size and interval distributions independently affect landscape structure. The response of disturbance landscapes to changing disturbance regimes is governed by both the number and size of patch births.