Human disturbances have probably had the most drastic effects on succession in both forested and non-forested lands. Activities ranging from over grazing, to land clearing and logging have dramatically changed the composition, structure and function of ecosystems around the world. In the western United States fire prevention is one of the most ecologically damaging practices humans have introduced. Other issues such as fragmentation may have greatly disturbed large scale ecosystem processes.

Other human caused disturbances include the introduction of non-native species, the elimination of species and climate change. The effects of these and other human caused disturbances has had dramatic effects on ecosystems on both local and landscape scales, and as with global warming the effects on vegetation and secession will be seen across the world.

Reto Stöckli, NASA Goddard Space Flight Center, www.nasa.gov

Dave Powell, USDA Forest Service, www.forestryimages.org