ABSTRACT
A fundamental and universal feature of the global biomass is its susceptibility to change in amount and composition through time. Fluctuational change in vegetation can be a consequence either of seasonal phenological changes in the component species or of short-term environmental variation. Secondary successions differ from primary ones in that they occur on sites which have been biologically modified and which may retain some of the previously formed soil organic matter and or vegetation. Concepts of succession were originally concerned only with plant or vegetation changes. Few areas of uncultivated vegetation have escaped the direct or indirect impact of human activities and those where unmodified primary vegetation persists are dwindling rapidly. As in vegetation succession, a distinction has been made by some soil scientists between primary and secondary soil evolution. The concepts of soil development and of soil maturity are, it must be stressed, difficult to substantiate in reality.
