Succession in Wetlands
Succession refers to the change in vegetation over time driven by disturbances and the maturation of plant species. In wetlands, these disturbances include water and salinity level changes along other factors that can alter vegetation. The historical view of succession (Clementsian) was that vegetation change represented the linear progression of through stages of vegetation toward a climax state. These stages were thought to be comprised of species that were interlocked with each other. These days the idea that succession is represented by the successive replacement of highly related sets of communities over time has been deemphasized, in favor of the idea that species in the community act more independently of one another (Gleasonian). An important example of this Gleasonian perspective model has been developed for prairie wetlands of North America by van der Valk. In this view, succession proceeds in a cyclic fashion, with flooding and drought driving changes in specific species, so that the individualistic species responses to water regime and other disturbances drive changes in the system (Environmental Sieve Model). The succession of many other world wetlands types is thought to occur in a similar way. These recent ideas of succession emphasize that species that are able to regenerate after disturbance via seed banks and propagules, and that the nature of post-disturbance regeneration is the most important determinant of later succession (initial floristics). Notably, the idea that lakes and bogs represent an early state of succession, and that depressions fill in to become dry land (terrestrialization) has little evidence. With climate change, wetlands are likely to have altered successional trajectories, particularly as these ecosystems become exposed to different climatic temperatures, flooding/drought cycles, salinity intrusion and increased CO2.
KeywordsClementsian succession Gleasonian succession primary succession secondary succession relay floristics
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