A PRELIMINARY INVENTORY OF HUMAN DISTURBANCE OF WORLD ECOSYSTEMS

Human intervention in natural ecosystems was mapped using a three-cate gory system indicating different levels of anthropogenic disturbance: undisturbed, partially disturbed, and human dominated. Source data wer e transferred onto a set of 10 equal-area base maps covering the world . The maps were digitized and transferred into a geographic informatio n system for analysis. The surface area of each region and the proport ion in each of the three disturbance categories was determined, as wel l as a derived index of remaining natural habitat. A high habitat inde x value indicates that natural habitat dominates an area and that huma n disturbance is slight. A low habitat index value indicates that an a rea is largely disturbed, with little remaining natural habitat. Nearl y 90 million km2 of undisturbed land remains on the planet, roughly 52 % of earth's terrestrial area. However, the habitable portion of the p lanet, with areas of rock, ice, and barren land removed, is nearly thr ee-quarters disturbed in some way. The biological significance of the global pattern of disturbance was assessed by examining disturbance ca tegories for the eight biogeographic realms of Udvardy. Methodological advancements of this study over earlier efforts included an improved mapping resolution, an expanded categorization system, and employment of an ecologically-based definition of habitat.