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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Ecological succession | 2/6 | https://en.wikipedia.org/wiki/Ecological_succession | reference | science, encyclopedia | 2026-05-05T07:17:58.613092+00:00 | kb-cron |
Monoclimax or Climatic Climax Theory was advanced by Clements (1916) and recognizes only one climax whose characteristics are determined solely by climate (climatic climax). The processes of succession and modification of environment overcome the effects of differences in topography, parent material of the soil, and other factors. The whole area would be covered with uniform plant community. Communities other than the climax are related to it, and are recognized as subclimax, postclimax and disclimax. Polyclimax Theory was advanced by Tansley (1935). It proposes that the climax vegetation of a region consists of more than one vegetation climaxes controlled by soil moisture, soil nutrients, topography, slope exposure, fire, and animal activity. Climax Pattern Theory was proposed by Whittaker (1953). The climax pattern theory recognizes a variety of climaxes governed by responses of species populations to biotic and abiotic conditions. According to this theory the total environment of the ecosystem determines the composition, species structure, and balance of a climax community. The environment includes the species' responses to moisture, temperature, and nutrients, their biotic relationships, availability of flora and fauna to colonize the area, chance dispersal of seeds and animals, soils, climate, and disturbance such as fire and wind. The nature of climax vegetation will change as the environment changes. The climax community represents a pattern of populations that corresponds to and changes with the pattern of environment. The central and most widespread community is the climatic climax. The theory of alternative stable states suggests there is not one end point but many which transition between each other over ecological time.
== Factors ==
=== Diversity of possible trajectories === Ecological succession was formerly seen as an orderly progression through distinct stages, where several plant communities would replace each other in a fixed order and eventually reach a stable end point known as the climax. The climax community was sometimes referred to as the 'potential vegetation' of a site, and thought to be primarily determined by the local climate. This idea has been largely abandoned by modern ecologists in favor of nonequilibrium ideas of ecosystems dynamics. Most natural ecosystems experience disturbance at a rate that makes a "climax" community unattainable. Climate change often occurs at a rate and frequency sufficient to prevent arrival at a climax state. The trajectory of successional change can be influenced by initial site conditions, by the type of disturbance that triggers succession, by the interactions of the species present, and by more random factors such as availability of colonists or seeds or weather conditions at the time of disturbance. Some aspects of succession are broadly predictable; others may proceed more unpredictably than in the classical view of ecological succession. 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.
=== Stochastic events === Succession is influenced partially by random chance, but it is debated how much random chance directs the trajectory of succession, as opposed to more deterministic factors. The timing of a disturbance such as a weather event may be random and unpredictable. Dispersal of propagules to a new site may also be random. However, community assembly is also determined by processes that select species non-randomly from the local species pool.
=== Dispersal limitation vs. environmental filtering === Succession is impacted both by the ability of seeds to disperse to new sites, and the suitability of site conditions for those seeds to grow and survive. Dispersal limitation means that even though favorable sites for a plant to live might exist, the plant's seeds may be unable to reach those sites. Environmental filtering, also called establishment limitation, implies that although seeds may be distributed to a site, those seeds may be unable to survive due to various characteristics of the site. The predicted impact of these two factors varies under different models of ecological succession.
=== Feedback loops === Ecological succession is driven by feedbacks between plants and their environment. As plants grow following a disturbance, they change their environment, for example by creating shade, attracting seed dispersers, contributing organic matter to the soil, changing the availability of soil nutrients, creating microhabitats, and buffering temperature and moisture fluctuations. This creates opportunities for different plants to grow, which causes directional change in the ecosystem. The development of some ecosystem attributes, such as soil properties and nutrient cycles, are both influenced by community properties, and, in turn, influence further successional development. This feed-back process may occur over centuries or millennia. Plants may facilitate the establishment of other plants by creating suitable conditions for them to grow, for example by providing shade or allowing for soil formation. Plants may also competitively exclude or otherwise prevent the growth of other plants.
=== Patterns === Though the idea of a fixed, predictable process of succession with a single well-defined climax is an overly simplified model, several predictions made by the classical model are accurate. Species diversity, overall plant biomass, plant lifespans, the importance of decomposer organisms, and overall stability all increase as a community approaches a climax state, while the rate at which soil nutrients are consumed, rate of biogeochemical cycling, and rate of net primary productivity all decrease as a community approaches a climax state. Communities in early succession will be dominated by fast-growing, well-dispersed species (opportunist, fugitive, or r-selected life-histories). These are also called pioneer species. As succession proceeds, these species will tend to be replaced by more competitive (k-selected) species. Some of these trends do not apply in all cases. For example, species diversity almost necessarily increases during early succession as new species arrive, but may decline in later succession as competition eliminates opportunistic species and leads to dominance by locally superior competitors. Net Primary Productivity, biomass, and trophic properties all show variable patterns over succession, depending on the particular system and site.