In theory, the grouping of plants which has developed in an area without human interference; since most landscapes have been changed by humans, it is argued that there are relatively few areas of truly natural vegetation left; many biogeographers use, instead, the concept of potential natural vegetation—the vegetation that would exist today if humans were removed from the scene and if the plant succession after their removal were telescoped into a single moment. The time compression eliminates the effects of future climatic fluctuations, while the effects of humans’ earlier activities are permitted to stand. The potential natural vegetation reveals the biological potential of all sites (US Env. Protect. Agency).