Ecological succession

Source: Wikipedia, the free encyclopedia.
boreal forest one year (left) and two years (right) after a wildfire
.

Ecological succession is the process of change in the species that make up an ecological community over time.

The process of succession occurs either after the initial

lava flow or the emergence of a new island from the ocean. Surtsey, a volcanic island off the southern coast of Iceland, is an important example of a place where primary succession has been observed.[2][3] On the other hand, secondary succession happens after disturbance of a community, such as from a fire, severe windthrow, or logging
.

Succession was among the first theories advanced in

Indiana Dunes of Northwest Indiana and remains an important ecological topic of study.[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.[5]

History

Precursors of the idea of ecological succession go back to the beginning of the 19th century. As early as 1742 French naturalist Buffon noted that poplars precede oaks and beeches in the natural evolution of a forest. Buffon was later forced by the theological committee at the University of Paris to recant many of his ideas because they contradicted the biblical narrative of Creation.[6]

Swiss geologist

Danube river basin in 1863.[11]

sedges to moor vegetation followed by birch and finally spruce.[6]

H. C. Cowles

sere—a repeatable sequence of community changes specific to particular environmental circumstances.[4][13]

Gleason and Clements

From about 1900 to 1960, however, understanding of succession was dominated by the theories of

climax community regardless of starting conditions. Clements explicitly analogized the successional development of ecological communities with ontogenetic development
of individual organisms, and his model is often referred to as the pseudo-organismic theory of community ecology. Clements and his followers developed a complex taxonomy of communities and successional pathways.

Henry Gleason offered a contrasting framework as early as the 1920s. The Gleasonian model was more complex and much less deterministic than the Clementsian. 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. Gleason argued that species distributions responded individualistically to environmental factors, and communities were best regarded as artifacts of the juxtaposition of species distributions. Gleason's ideas, first published in 1926, were largely ignored until the late 1950s.

Two quotes illustrate the contrasting views of Clements and Gleason. Clements wrote in 1916:

The developmental study of vegetation necessarily rests upon the assumption that the unit or climax formation is an organic entity. As an organism the formation arises, grows, matures, and dies. 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.

— Henry Gleason[15]

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.

— Henry Cowles[16]

Eugene Odum

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."[17] Odum highlighted how succession was not merely a change in the species composition of an ecosystem, but also created change in more complex attributes of the ecosystem, such as structure and nutrient cycling.[18]

Modern era

A more rigorous, data-driven testing of successional models and community theory generally began with the work of

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. Debates continue as to the general predictability of successional dynamics and the relative importance of equilibrial vs. non-equilibrial processes. Former Harvard professor Fakhri A. Bazzaz introduced the notion of scale into the discussion, as he considered that at local or small area scale the processes are stochastic and patchy, but taking bigger regional areas into consideration, certain tendencies can not be denied.[19]

More recent definitions of succession highlight change as the central characteristic.[17] New research techniques are greatly enhancing contemporary scientists' ability to study succession, which is now seen as neither entirely random nor entirely predictable.[18]

Factors

Ecological succession was formerly seen as having a stable end-stage called the

Climate change often occurs at a rate and frequency sufficient to prevent arrival at a climax state. Additions to available species pools through range expansions and introductions can also continually reshape communities.[20]

The development of some ecosystem attributes, such as

nutrient cycles, are both influenced by community properties, and, in turn, influence further successional development. This feed-back process may occur only over centuries or millennia. 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.[21]

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

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.[23]

Communities in early succession will be dominated by fast-growing, well-

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.

Types

Primary succession

Successional dynamics beginning with colonization of an area that has not been previously occupied by an ecological community are referred to as primary succession.[1] This includes newly exposed rock or sand surfaces, lava flows, and newly exposed glacial tills.[1] The stages of primary succession include pioneer microorganisms,[24] plants (lichens and mosses), grassy stage, smaller shrubs, and trees. Animals begin to return when there is food there for them to eat. When it is a fully functioning ecosystem, it has reached the climax community stage.[25]

Secondary succession

An example of secondary succession by stages:
  1. A stable deciduous forest community
  2. A disturbance, such as a wild fire, destroys the forest
  3. The fire burns the forest to the ground
  4. The fire leaves behind empty, but not destroyed, soil
  5. Grasses and other herbaceous plants grow back first
  6. Small bushes and trees begin to colonize the area
  7. Fast-growing evergreen trees develop to their fullest, while shade-tolerant trees develop in the understory
  8. The short-lived and shade-intolerant evergreen trees die as the larger deciduous trees overtop them. The ecosystem is now back to a similar state to where it began.

Secondary succession follows severe disturbance or removal of a preexisting community that has remnants of the previous ecosystem.[1] Secondary succession is strongly influenced by pre-disturbance conditions such as soil development, seed banks, remaining organic matter, and residual living organisms.[1] Because of residual fertility and preexisting organisms, community change in early stages of secondary succession can be relatively rapid.[1]

Secondary succession is much more commonly observed and studied than primary succession. Particularly common types of secondary succession include responses to natural disturbances such as fire, flood, and severe winds, and to human-caused disturbances such as logging and agriculture. In secondary succession, the soils and organisms need to be left unharmed so there is a way for the new material to rebuild.[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".[26]

Secondary succession: trees are colonizing uncultivated fields and meadows.

Secondary succession can quickly change a landscape. In the 1900s, Acadia National Park had a wildfire that destroyed much of the landscape. Originally evergreen trees grew in the landscape. After the fire, the area took at least a year to grow shrubs. Eventually, deciduous trees started to grow instead of evergreens.[25]

Secondary succession has been occurring in

Moorman's and Rapidan rivers, which destroyed plant and animal life.[27]

Seasonal and cyclic dynamics

Unlike secondary succession, these types of vegetation change are not dependent on disturbance but are periodic changes arising from fluctuating species interactions or recurring events. These models modify the climax concept towards one of dynamic states.

Causes of plant succession

Autogenic succession can be brought by changes in the soil caused by the organisms there. These changes include accumulation of organic matter in litter or humic layer, alteration of soil nutrients, or change in the pH of soil due to the plants growing there. The structure of the plants themselves can also alter the community.[28] For example, when larger species like trees mature, they produce shade on to the developing forest floor that tends to exclude light-requiring species. Shade-tolerant species will invade the area.

Allogenic succession is caused by external environmental influences and not by the vegetation. 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. Animals also play an important role in allogenic changes as they are pollinators, seed dispersers and herbivores. They can also increase nutrient content of the soil in certain areas, or shift soil about (as termites, ants, and moles do) creating patches in the habitat. This may create regeneration sites that favor certain species.

Climatic factors may be very important, but on a much longer time-scale than any other. Changes in temperature and rainfall patterns will promote changes in communities. As the climate warmed at the end of each ice age, great successional changes took place. The tundra vegetation and bare glacial till deposits underwent succession to mixed deciduous forest. The greenhouse effect resulting in increase in temperature is likely to bring profound Allogenic changes in the next century. Geological and climatic catastrophes such as volcanic eruptions, earthquakes, avalanches, meteors, floods, fires, and high wind also bring allogenic changes.

Mechanisms

In 1916,

ecological theory.[citation needed
] According to Clements, succession is a process involving several phases:[14][page needed]

  1. Nudation: Succession begins with the development of a bare site, called Nudation (disturbance).[14]
  2. Migration: refers to arrival of propagules.[14]
  3. Ecesis: involves establishment and initial growth of vegetation.[14]
  4. Competition: as vegetation becomes well established, grows, and spreads, various species begin to compete for space, light and nutrients.[14]
  5. Reaction: during this phase autogenic changes such as the buildup of humus affect the habitat, and one plant community replaces another.[14]
  6. Stabilization: a supposedly stable climax community forms.[14]

Seral communities

Pond succession or sere A: emergent plant life B: sediment C: Emergent plants grow inwards, sediment accretes D: emergent and terrestrial plants E: sediment fills pond, terrestrial plants take over F: trees grow
A hydrosere community

A seral community is an intermediate stage found in an ecosystem advancing towards its

prisere
is a collection of seres making up the development of an area from non-vegetated surfaces to a climax community. Depending on the substratum and climate, different seres are found.

Changes in animal life

Succession theory was developed primarily by botanists. The study of succession applied to whole

ecosystems initiated in the writings of Ramon Margalef, while Eugene Odum's publication of The Strategy of Ecosystem Development is considered its formal starting point.[30]

Animal life also exhibits changes with changing communities. In the lichen stage, fauna is sparse. It comprises a few mites, ants, and spiders living in cracks and crevices. The fauna undergoes a qualitative increase during the herb grass stage. The animals found during this stage include nematodes, insect larvae, ants, spiders, mites, etc. The animal population increases and diversifies with the development of the forest climax community. 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.

Microsuccession

Succession of

fungi and bacteria occurring within a microhabitat is known as microsuccession or serule. 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. To exploit locations or explore the landscape? Escherichia coli is a fugitive species, whereas Pseudomonas aeruginosa is a slower colonizer but superior competitor.[7] Like in plants, microbial succession can occur in newly available habitats (primary succession) such as surfaces of plant leaves, recently exposed rock surfaces (i.e., glacial till) or animal infant guts,[24] and also on disturbed communities (secondary succession) like those growing in recently dead trees, decaying fruits,[31] or animal droppings. Microbial communities may also change due to products secreted by the bacteria present. Changes of pH in a habitat could provide ideal conditions for a new species to inhabit the area. In some cases the new species may outcompete the present ones for nutrients leading to the primary species demise. Changes can also occur by microbial succession with variations in water availability and temperature. Theories of macroecology have only recently been applied to microbiology and so much remains to be understood about this growing field. A recent study of microbial succession evaluated the balances between stochastic and deterministic processes in the bacterial colonization of a salt marsh chronosequence. The results of this study show that, much like in macro succession, early colonization (primary succession) is mostly influenced by stochasticity while secondary succession of these bacterial communities was more strongly influenced by deterministic factors.[32]

Ecological micro-succession in a bacterial meta-community on-chip. (A) sketch of a micron-scale structured bacterial environment based on microfluidics technology; (B) Fluorescent microscopy image of Escherichia coli (magenta) and Pseudomonas aeruginosa (green) inhabiting a device of the type depicted in A and which has been wettened with growth media and inoculated with both species; (C) a sequence of five snapshots of the bacterial community distributed over five patches (of an array with 85) depicting the spatial dynamics of competition between E. coli (magenta) and P. aeruginosa (green); (D) Representation of the succession pattern exhibited by the two bacterial species when competing for space and resources in a patchy environment.[7]

Climax concept

According to classical

ecological theory, succession stops when the sere has arrived at an equilibrium or steady state with the physical and biotic environment. Barring major disturbances, it will persist indefinitely.[1]
This end point of succession is called climax.

Climax community

The final or stable community in a sere is the climax community or climatic vegetation. It is self-perpetuating and in equilibrium with the physical habitat.[1] There is no net annual accumulation of organic matter in a climax community. The annual production and use of energy is balanced in such a community.

Characteristics

  • The vegetation is tolerant of environmental conditions.
  • It has a wide diversity of species, a well-drained spatial structure, and complex food chains.
  • The climax ecosystem is balanced. There is equilibrium between
    gross primary production
    and total respiration, between energy used from sunlight and energy released by decomposition, between uptake of nutrients from the soil and the return of nutrient by litter fall to the soil.
  • Individuals in the climax stage are replaced by others of the same kind. Thus the
    species composition
    maintains equilibrium.
  • It is an index of the climate of the area. The life or growth forms indicate the climatic type.

Types of climax

Climatic Climax
If there is only a single climax and the development of climax community is controlled by the climate of the region, it is termed as climatic climax. For example, development of Maple-beech climax community over moist soil. Climatic climax is theoretical and develops where physical conditions of the substrate are not so extreme as to modify the effects of the prevailing regional climate.
Edaphic Climax
When there are more than one climax communities in the region, modified by local conditions of the substrate such as soil moisture, soil nutrients, topography, slope exposure, fire, and animal activity, it is called edaphic climax. Succession ends in an edaphic climax where topography, soil, water, fire, or other disturbances are such that a climatic climax cannot develop.
Catastrophic Climax
Climax vegetation vulnerable to a catastrophic event such as a wildfire. For example, in California, chaparral vegetation is the final vegetation. The wildfire removes the mature vegetation and decomposers. A rapid development of herbaceous vegetation follows until the shrub dominance is re-established. This is known as catastrophic climax.
Disclimax
When a stable community, which is not the climatic or edaphic climax for the given site, is maintained by man or his domestic animals, it is designated as Disclimax (disturbance climax) or anthropogenic subclimax (man-generated). For example, overgrazing by stock may produce a desert community of bushes and cacti where the local climate actually would allow grassland to maintain itself.
Subclimax
The prolonged stage in succession just preceding the climatic climax is subclimax.
Preclimax and Postclimax
In certain areas different climax communities develop under similar climatic conditions. If the community has life forms lower than those in the expected climatic climax, it is called preclimax; a community that has life forms higher than those in the expected climatic climax is postclimax. Preclimax strips develop in less moist and hotter areas, whereas Postclimax strands develop in more moist and cooler areas than that of surrounding climate.

Theories

There are three schools of interpretations explaining the climax concept:

  • 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.

Succession by habitat type

Forest succession

Forests, being an ecological system, are subject to the species succession process.

stand
has reached its climax. When a disturbance occurs, the opportunity for the pioneers opens up again, provided they are present or within a reasonable range.

An example of pioneer species, in forests of northeastern North America are Betula papyrifera (

shade-tolerant species in the absence of disturbances that create such gaps. In the tropics, well known pioneer forest species can be found among the genera Cecropia, Ochroma and Trema.[34]

Things in nature are not black and white, and there are intermediate stages. It is therefore normal that between the two extremes of light and shade there is a gradient, and there are species that may act as pioneer or tolerant, depending on the circumstances. It is of paramount importance to know the tolerance of species in order to practice an effective silviculture.

Wetland succession

Since many types of wetland environments exist, succession may follow a wide array of trajectories and patterns in wetlands. Under the classical model, the process of secondary succession holds that a wetland progresses over time from an initial state of open water with few plants, to a forested climax state where decayed organic matter has built up over time, forming peat. However, many wetlands are maintained by regular disturbance or natural processes at an equilibrium state that does not resemble the predicted forested "climax."[35] 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.[5]

Wetland succession is a uniquely complex, non-linear process shaped by

tides moving in and out continuously acts upon the ecological community. Fire may also maintain an equilibrium state in a wetland by burning off vegetation, thus interrupting the accumulation of peat.[35]
Water entering and leaving the wetland follows patterns that are broadly cyclical but erratic. For example, seasonal flooding and drying may occur with yearly changes in precipitation, causing seasonal changes in the wetland community that maintain it at a stable state.[5] However, unusually heavy rain or unusually severe drought may cause the wetland to enter a positive feedback loop where it begins to change in a linear direction.[36] Since wetlands are sensitive to changes in the natural processes that maintain them, human activities, invasive species, and climate change could initiate long-term changes in wetland ecosystems.[35]

Grassland succession

For a long time, grasslands were thought to be early stages of succession, dominated by weedy species and with little conservation value. However, comparing grasslands that form after recovery from long-term disruptions like agricultural tillage with ancient or "old-growth" grasslands has shown that grasslands are not inherently early-successional communities. Rather, grasslands undergo a centuries-long process of succession, and a grassland that is tilled up for agriculture or otherwise destroyed is estimated to take a minimum of 100 years, and potentially on average 1,400 years, to recover to its previous level of biodiversity.[37] However, planting a high diversity of late-successional grassland species in a disturbed environment can accelerate the recovery of the soil's ability to sequester carbon, resulting in twice as much carbon storage as a naturally recovering grassland over the same period of time.[38]

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.[39] 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. Disturbance events that severely disrupt or destroy the soil, such as tilling, eliminate these late-successional species, reverting the grassland to an early successional stage dominated by pioneers, whereas fire and grazing benefit late-successional species.[37] Both too much and too little disturbance can damage the biodiversity of disturbance-dependent ecosystems like grasslands.[40]

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.[41] However, the means by which ecological succession under frequent disturbance results in ecosystems of the sort seen in remnant prairies is poorly understood.[42][40]

See also

References

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  2. ^ "Surtsey". UNESCO World Heritage Centre.
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  4. ^ a b Smith S, Mark S (January 2009). "The historical roots of The Nature Conservancy in the Northwest Indiana/Chicagoland region: from science to preservation". South Shore Journal. 3: 1–10.
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  9. ^ a b Thoreau HD, Emerson RW (1887). The succession of forest trees: and wild Apples. Houghton, Mifflin. Retrieved 2014-04-12 – via Archive.org.
  10. ^ Thoreau HD (2013). Cramer JS (ed.). Essays: A Fully Annotated Edition. New Haven, Connecticut: Yale University Press.
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  25. ^ a b Biology Dictionary Editors (2017-01-31). "Ecological Succession - Definition, Types and Examples". Biology Dictionary. Retrieved 2019-05-08.
  26. ^ Cook WM, Yao J, Foster BL, Holt RD, Patrick LB. "Secondary succession in an experimentally fragmented landscape: Community patterns across space and time". The U.S. Department of Agriculture. Retrieved 2013-09-30.
  27. ^ Banisky S (July 3, 1995). "Floods change face of Shenandoah Park". The Baltimore Sun. Retrieved 2019-07-05.
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  32. ^ McEvoy T (2004). "Positive Impact Forestry". Species Succession and Tolerance. Island Press. p. 32.
  33. ^ a b Budowski G (1965). "Distribution of tropical American rain-forest species in the light of successional processes". Turrialba. 15 (1): 40–42.
  34. ^ a b c Moseley, Kendra. "Wetland Ecology- Basic Principles" (PDF). United States Department of Agriculture.
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  38. ^ Evans, E.W.; Briggs, J.M.; Finck, E.J.; Gibson, D.J.; James, S.W.; Kaufman, D.W.; Seastedt, T.R. "Is Fire a Disturbance in Grasslands?" (PDF).
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  41. ^ Bomberger, Mary L.; Shields, Shelly; Harrison, L. Tyrone; Keeler, Kathleen. "Comparison of Old Field Succession on a Tallgrass Prairie and a Nebraska Sandhills Prairie". {{cite journal}}: Cite journal requires |journal= (help)

Further reading

External links