<P> Climatic factors may be very important, but on a much longer time - scale than any other . Changes in temperature and rainfall patterns will promote changes in communities . As the climate warmed at the end of each ice age, great successional changes took place . The tundra vegetation and bare glacial till deposits underwent succession to mixed deciduous forest . The greenhouse effect resulting in increase in temperature is likely to bring profound Allogenic changes in the next century . Geological and climatic catastrophes such as volcanic eruptions, earthquakes, avalanches, meteors, floods, fires, and high wind also bring allogenic changes . </P> <P> In 1916, Frederic Clements published a descriptive theory of succession and advanced it as a general ecological concept . His theory of succession had a powerful influence on ecological thought . Clements' concept is usually termed classical ecological theory . According to Clements, succession is a process involving several phases: </P> <Ol> <Li> Nudation: Succession begins with the development of a bare site, called Nudation (disturbance). </Li> <Li> Migration: It refers to arrival of propagules . </Li> <Li> Ecesis: It involves establishment and initial growth of vegetation . </Li> <Li> Competition: As vegetation becomes well established, grow, and spread, various species begin to compete for space, light and nutrients . </Li> <Li> Reaction: During this phase autogenic changes such as the buildup of humus affect the habitat, and one plant community replaces another . </Li> <Li> Stabilization: A supposedly stable climax community forms . </Li> </Ol> <Li> Nudation: Succession begins with the development of a bare site, called Nudation (disturbance). </Li>

Signs of ecological succession in a local ecosystem