Ecological succession

[4] Over time, the understanding of succession has changed from a linear progression to a stable climax state, to a more complex, cyclical model that de-emphasizes the idea of organisms having fixed roles or relationships.

[6] Swiss geologist Jean-André Deluc and the later French naturalist Adolphe Dureau de la Malle were the first to make use of the word succession concerning the vegetation development after forest clear-cutting.

[12] In this classic publication and subsequent papers, he formulated the idea of primary succession and the notion of a sere—a repeatable sequence of community changes specific to particular environmental circumstances.

[4][13] From about 1900 to 1960, however, understanding of succession was dominated by the theories of Frederic Clements, a contemporary of Cowles, who held that seres were highly predictable and deterministic and converged on a climatically determined stable climax community regardless of starting conditions.

It differs most fundamentally from the Clementsian view in suggesting a much greater role of chance factors and in denying the existence of coherent, sharply bounded community types.

Clements wrote in 1916: The developmental study of vegetation necessarily rests upon the assumption that the unit or climax formation is an organic entity.

Furthermore, each climax formation is able to reproduce itself, repeating with essential fidelity the stages of its development.while Gleason, in his 1926 paper, said: An association is not an organism, scarcely even a vegetational unit, but merely a coincidence.Gleason's ideas were, in fact, more consistent with Cowles' original thinking about succession.

About Clements' distinction between primary succession and secondary succession, Cowles wrote (1911): This classification seems not to be of fundamental value, since it separates such closely related phenomena as those of erosion and deposition, and it places together such unlike things as human agencies and the subsidence of land.In 1969, Eugene Odum published The Strategy of Ecosystem Development, a paper that was highly influential to conservation and environmental restoration.

Odum argued that ecological succession was an orderly progression toward a climax state where “maximum biomass and symbiotic function between organisms are maintained per unit energy flow.

[18] A more rigorous, data-driven testing of successional models and community theory generally began with the work of Robert Whittaker and John Curtis in the 1950s and 1960s.

Among British and North American ecologists, the notion of a stable climax vegetation has been largely abandoned, and successional processes have come to be seen as much less deterministic, with important roles for historical contingency and for alternate pathways in the actual development of communities.

Coupled with the stochastic nature of disturbance events and other long-term (e.g., climatic) changes, such dynamics make it doubtful whether the 'climax' concept ever applies or is particularly useful in considering actual vegetation.

Net Primary Productivity, biomass, and trophic properties all show variable patterns over succession, depending on the particular system and site.

[9] As an example, in a fragmented old field habitat created in eastern Kansas, woody plants "colonized more rapidly (per unit area) on large and nearby patches".

[30] Secondary succession has been occurring in Shenandoah National Park following the 1995 flood of the Moorman's and Rapidan rivers, which destroyed plant and animal life.

For example, soil changes due to erosion, leaching or the deposition of silt and clays can alter the nutrient content and water relationships in the ecosystems.

Geological and climatic catastrophes such as volcanic eruptions, earthquakes, avalanches, meteors, floods, fires, and high wind also bring allogenic changes.

The fauna consists of invertebrates like slugs, snails, worms, millipedes, centipedes, ants, bugs; and vertebrates such as squirrels, foxes, mice, moles, snakes, various birds, salamanders and frogs.

Beagle: The often repeated description of the stately palm and other nobel plants, then birds, and lastly man, taking possession of the coral islets as soon as formed in the Pacific, is probably not quite correct; I fear it destroys the poetry of this story, that feather and dirt-feeding and parasitic insects and spiders should be the first inhabitants of newly-formed oceanic land.These naturalists note that prior to the establishment of autotrophs, there is a foodweb formed by heterotrophs built on allochthonous inputs of dead organic matter (necromass).

In artificial bacterial meta-communities of motile strains on-chip it has been shown that ecological succession is based on a trade-off between colonization and competition abilities.

A recent study of microbial succession evaluated the balances between stochastic and deterministic processes in the bacterial colonization of a salt marsh chronosequence.

[40] According to classical ecological theory, succession stops when the sere has arrived at an equilibrium or steady state with the physical and biotic environment.

There are three schools of interpretations explaining the climax concept: The theory of alternative stable states suggests there is not one end point but many which transition between each other over ecological time.

[41] There are "opportunistic" or "pioneer" species that produce great quantities of seed that are disseminated by the wind, and therefore can colonize big empty extensions.

An example of pioneer species, in forests of northeastern North America are Betula papyrifera (White birch) and Prunus serotina (Black cherry), that are particularly well-adapted to exploit large gaps in forest canopies, but are intolerant of shade and are eventually replaced by other shade-tolerant species in the absence of disturbances that create such gaps.

"[43] The idea that ponds and wetlands gradually fill in to become dry land has been criticized and called into question due to lack of evidence.

[46] Many grassland ecosystems are maintained by disturbance, such as fire and grazing by large animals, or else the process of succession will change them to forest or shrubland.

In fact, it is debated whether fire should be considered disturbance at all for the North American prairie ecosystems, since it maintains, rather than disrupts, an equilibrium state.

[47] Many late-successional grassland species have adaptations that allow them to store nutrients underground and re-sprout rapidly after "aboveground" disturbances like fire or grazing.

[48] In North American semi-arid grasslands, the introduction of livestock ranching and absence of fire was observed to cause a transition away from grasses to woody vegetation, particularly mesquite.