Ecological succession, a fundamental concept in
ecologyEcology is the interdisciplinary scientific study of the interactions between organisms and the interactions of these organisms with their environment....
, refers to the predictable and orderly changes in the composition or structure of an ecological
communityIn ecology, a community is an assemblage of two or more populations of different species occupying the same geographical area. This term is used only to describe biotic factors....
. Succession may be initiated either by formation of new, unoccupied habitat (
e.g., a lava flow or a severe
landslideA landslide is a geological phenomenon which includes a wide range of ground movement, such as rock falls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments...
) or by some form of
disturbanceIn ecology, a disturbance is a temporary change in average environmental conditions that causes a pronounced change in an ecosystem. Outside disturbance forces often act quickly and with great effect, sometimes resulting in the removal of large amounts of biomass...
(
e.g. fireFire is the rapid oxidation of a combustible material releasing heat, light, and various reaction products such as carbon dioxide and water. If hot enough, the gases may become ionized to produce plasma. Depending on the substances alight, and any impurities outside, the color of the flame and the...
, severe
windthrowIn forestry, windthrow refers to trees uprooted or broken by wind. Breakage of the tree bole instead of uprooting is sometimes called windsnap.- Causes :Windthrow is common in all forested parts of the world that experience storms or high wind speeds...
,
loggingLogging is the process in which certain trees are cut down for forest management and timber.In forestry the term logging is sometimes used in a narrow sense concerning the logistics of moving wood from the stump to somewhere outside the forest, usually a sawmill or a lumber yard. In common usage...
) of an existing community. Succession that begins in areas where no
soilSoil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics. It is composed of particles of broken rock that have been altered by chemical and...
is initially present is called
primary successionPrimary succession is one of two types of biological succession and ecological succession of plant life, and occurs in an environment in which new substrate, devoid of vegetation and usually lacking soil, is deposited...
, whereas succession that begins in areas where soil is already present is called
secondary successionSecondary succession is one of the two types of ecological succession of plant life. As opposed to primary succession, secondary succession is a process started by an event that reduces an already established ecosystem Secondary succession is one of the two types of ecological succession of plant...
.
The trajectory of ecological change can be influenced by site conditions, by the interactions of the species present, and by more
stochasticStochastic means random.A stochastic process is one whose behavior is non-deterministic in that a system's subsequent state is determined both by the process's predictable actions and by a random element....
factors such as availability of colonists or seeds, or
weatherWeather is a set of all the phenomena occurring in a given atmosphere at a given time. Weather phenomena lie in the troposphere. Weather refers, generally, to day-to-day temperature and precipitation activity, whereas climate is the term for the average atmospheric conditions over longer periods...
conditions at the time of disturbance. Some of these factors contribute to predictability of successional dynamics; others add more
probabilisticProbability is a way of expressing knowledge or belief that an event will occur or has occurred. In mathematics the concept has been given an exact meaning in probability theory, that is used extensively in such areas of study as mathematics, statistics, finance, gambling, science, and philosophy...
elements. In general, communities in early succession will be dominated by fast-growing, well-
dispersedBiological dispersal refers to a species movement away from an existing population or away from the parent organism. Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population...
species (opportunist,
fugitiveA fugitive is a person who is fleeing from custody, whether it be from private slavery, a government arrest, government or non-government questioning, vigilante violence, or outraged private individuals. As a verbal metaphor and psychological concept, one might also be described as a "fugitive...
, or r-selected life-histories). As succession proceeds, these species will tend to be replaced by more competitive (k-selected) species.
Trends in
ecosystemAn ecosystem is a system of interdependent organisms which share the same habitat, in an area functioning together with all of the physical factors of the environment. Ecosystems can be permanent or temporary. Ecosystems usually form a number of food webs...
and community properties in succession have been suggested, but few appear to be general. For example,
species diversitySpecies diversity is an index that incorporates the number of species in an area and also their relative abundance. It is generally a much more useful value than species richness....
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 competitorsIn community ecology, the competitive exclusion principle, sometimes referred to as Gause's Law of competitive exclusion or just Gause's Law, is a proposition which states that two species competing for the same resources cannot stably coexist if other ecological factors are constant...
.
Net Primary Productivity400px|thumb|Global oceanic and terrestrial photoautotroph abundance, from September [[1997]] to August 2000. As an estimate of autotroph biomass, it is only a rough indicator of primary production potential, and not an actual estimate of it...
,
biomassBiomass, a renewable energy source, is biological material derived from living, or recently living organisms, such as wood, waste, and alcohol fuels. Biomass is commonly plant matter grown to generate electricity or produce heat. For example, forest residues , yard clippings and wood chips may be...
, and
trophic levelIn ecology, trophic dynamics is the system of trophic levels , which describes the position that an organism occupies in a food chain — what an organism eats, and what eats the organism.- Energy economy :...
properties all show variable patterns over succession, depending on the particular system and site.
Ecological succession was formerly seen as having a stable end-stage called the
climaxIn ecology, a climax community, or climatic climax community, is a biological community of plants and animals which, through the process of ecological succession — the development of vegetation in an area over time — has reached a steady state. This equilibrium occurs because the climax community...
(see
Frederic ClementsFrederic Edward Clements was an American plant ecologist and pioneer in the study of vegetation succession....
), sometimes referred to as the 'potential vegetation' of a site, shaped primarily by the local climate. This idea has been largely abandoned by modern ecologists in favor of nonequilibrium ideas of how ecosystems function. Most natural ecosystems experience disturbance at a rate that makes a "climax" community unattainable.
Climate changeClimate change is a change in the statistical distribution of weather over periods of time that range from decades to millions of years. It can be a change in the average weather or a change in the distribution of weather events around an average...
often occurs at a rate and frequency sufficient to prevent arrival at a climax state. Additions to available species pools through range expansions and
introductionsAn introduced, alien, exotic, non-indigenous, or non-native species, or simply an introduction, is a species living outside its native distributional range, which has arrived there by human activity, either deliberate or accidental...
can also continually reshape communities.
Many species are specialized to exploit disturbances. In forests of northeastern North America trees such as
Betula alleghaniensis (
Yellow birchBetula alleghaniensis , is a species of birch native to eastern North America, from Nova Scotia, New Brunswick, and southern Québec west to Minnesota, and south in the Appalachian Mountains to northern Georgia....
) and
Prunus serotina (
Black cherryPrunus serotina, commonly called Black Cherry, Wild Black Cherry, Rum Cherry, or Mountain Black Cherry, is a woody plant species belonging to the genus Prunus...
) 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.
The development of some ecosystem attributes, such as
pedogenesisPedogenesis or soil evolution is the process by which soil is created. It is the major topic of the science of pedology, whose other aspects include the soil morphology, classification of soils, and their distribution in nature, present and past .-Climate:Climate regulates soil formation...
and nutrient cycles, are both influenced by community properties, and, in turn, influence further community development. This process may occur only over centuries or millennia. Coupled with the
stochasticStochastic means random.A stochastic process is one whose behavior is non-deterministic in that a system's subsequent state is determined both by the process's predictable actions and by a random element....
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.
History of the theory
The idea of ecological succession goes back to the 14th century. The French naturalist
Adolphe Dureau de la MalleAdolphe Jules César Auguste Dureau de la Malle was a French geographer, naturalist, historian and artist. He was the son of the scholar and translator Jean-Baptiste Dureau de la Malle.Dureau de la Malle published a number of works on the economy and topography of the classic countries, i.e...
was the first to make use of the word
succession about the vegetation development after forest clear-felling. In 1859
Henry David ThoreauHenry David Thoreau was an American author, poet, naturalist, tax resister, development critic, surveyor, historian, philosopher, and leading transcendentalist...
wrote an address called "The Succession of Forest Trees" in which he described succession in an Oak-Pine forest.
Henry Chandler CowlesHenry Chandler Cowles, Ph. D was an American botanist and ecological pioneer . Born in Kensington, Connecticut, he attended Oberlin College in Ohio. He studied at the University of Chicago with the plant taxonomist John M. Coulter and the geologist Thomas Chrowder Chamberlin as main teachers. He...
, at the
University of ChicagoThe University of Chicago is a private, coeducational research university in Chicago, Illinois, USA. It was founded by oil magnate and benefactor John D...
, developed a more formal concept of succession. Inspired by the studies of
DanishDenmark is a Scandinavian country in Northern Europe and the senior member of the Kingdom of Denmark. It is the southernmost of the Nordic countries; southwest of Sweden and south of Norway, and it is bordered to the south by Germany. Denmark borders both the Baltic and the North Sea...
dunes done by Eugen Warming, Cowles studied
vegetationVegetation is a general term for the plant life of a region; it refers to the ground cover provided by plants. It is a general term, without specific reference to particular taxa, life forms, structure, spatial extent, or any other specific botanical or geographic characteristics. It is broader...
development sand dunes on the shores of
Lake MichiganLake Michigan is one of the five Great Lakes of North America, and the only one located entirely within the United States. The second largest of the Great Lakes by volume The third largest of the Great Lakes by surface area , it is bounded, from west to east, by the U.S. states of Wisconsin,...
(the
Indiana DunesIndiana Dunes National Lakeshore is a U.S. National Lakeshore located in northwest Indiana and managed by the National Park Service. It was authorized by Congress in 1966. The national lakeshore runs for nearly 25 miles along the southern shore of Lake Michigan, from Gary, Indiana, on the west to...
). He recognized that vegetation on sand-dunes of different ages might be interpreted as different stages of a general trend of vegetation development on dunes, and used his observations to propose a particular sequence (sere) and process of primary succession. His paper, "The ecological relations of the vegetation of the sand dunes of Lake Michigan" in 1899 in the Botanical Gazette is one of the classic publications in the history of the field of ecology.
Understanding of succession was long dominated by the theories of
Frederic ClementsFrederic Edward Clements was an American plant ecologist and pioneer in the study of vegetation succession....
, a contemporary of Cowles, who held that successional sequences of communities (
seres), were highly predictable and culminated in a climatically determined stable climax. Clements and his followers developed a complex taxonomy of communities and successional pathways (see article on Clements).
A contrasting view, the
GleasonianHenry Allan Gleason was a noted American ecologist, botanist, and taxonomist, most recognized for his endorsement of the individualistic/open community concept of ecological succession.- Life and work :...
framework, is more complex, with three items: invoking interactions between the physical environment, population-level interactions between species, and disturbance regimes, in determining the composition and spatial distribution of species. 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's ideas, first published in the early 20th century, were more consistent with Cowles' thinking, and were ultimately largely vindicated. However, they were largely ignored from their publication until the 1950s.
About
Frederic ClementsFrederic Edward Clements was an American plant ecologist and pioneer in the study of vegetation succession....
' distinction between
primary successionPrimary succession is one of two types of biological succession and ecological succession of plant life, and occurs in an environment in which new substrate, devoid of vegetation and usually lacking soil, is deposited...
and
secondary successionSecondary succession is one of the two types of ecological succession of plant life. As opposed to primary succession, secondary succession is a process started by an event that reduces an already established ecosystem Secondary succession is one of the two types of ecological succession of plant...
,
CowlesHenry Chandler Cowles, Ph. D was an American botanist and ecological pioneer . Born in Kensington, Connecticut, he attended Oberlin College in Ohio. He studied at the University of Chicago with the plant taxonomist John M. Coulter and the geologist Thomas Chrowder Chamberlin as main teachers. He...
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.
Beginning with the work of
Robert WhittakerRobert Harding Whittaker was an American vegetation ecologist, active in the 1950s to the 1970s.Born in Wichita, Kansas, he obtained a B.A. at Washburn Municipal College in Topeka, Kansas, and, following military service, his Ph.D...
and John Curtis in the 1950s and 1960s, models of succession have gradually changed and become more complex. In modern times, among North American ecologists, less stress has been placed on the idea of a single
climax vegetationClimax vegetation is the vegetation which establishes itself on a given site for given climatic conditions in the absence of anthropic action after a long time ....
, and more study has gone into the role of contingency in the actual development of communities.
Primary and secondary succession
If the development begins on an area that has not been previously occupied by a community, such as a newly exposed rock or sand surface, a lava flow, glacial tills, or a newly formed lake, the process is known as primary succession.
If the community development is proceeding in an area from which a community was removed it is called secondary succession. Secondary succession arises on sites where the vegetation cover has been disturbed by humans or animals (an abandoned crop field or cut-over forest, or natural forces such as water
, wind storms, and floods. Secondary succession is usually more rapid as the colonizing area is rich in leftover soil, organic matter and seeds of the previous vegetation. In case of primary succession everything has to develop anew.
Seasonal and cyclic succession
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 propose a modification to 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, change in pH of soil by plants growing there. The structure of the plants themselves can also alter the community. 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 changes are 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.
Clement's theory of succession/Mechanisms of succession
F.E. Clement (1916) developed a descriptive theory of succession and advanced it as a general ecological concept. His theory of succession had a powerful influence on ecological thought. Clement's concept is usually termed classical ecological theory.
According to Clement, succession is a process involving several phases:
- Nudation: Succession begins with the development of a bare site, called Nudation (disturbance).
- Migration: It refers to arrival of propagules.
- Ecesis: It involves establishment and initial growth of vegetation.
- Competition: As vegetation became well established, grew, and spread, various species began to compete for space, light and nutrients. This phase is called competition.
- Reaction: During this phase autogenic changes affect the habitat resulting in replacement of one plant community by another.
- Stabilization: Reaction phase leads to development of a climax community.
Seral communities
A seral community is an intermediate stage found in an ecosystem advancing towards its
climax communityIn ecology, a climax community, or climatic climax community, is a biological community of plants and animals which, through the process of ecological succession — the development of vegetation in an area over time — has reached a steady state. This equilibrium occurs because the climax community...
. In many cases more than one seral stage evolves until climax conditions are attained. A
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, a seral community can be one of the following:
HydrosereA hydrosere is a plant succession which occurs in a freshwater lake. In time, an area of open freshwater such as a lake will naturally dry out, ultimately becoming woodland. During this change, a range of different landtypes such as swamp and marsh will succeed each other.The succession from open...
: Community in water
LithosereA lithosere is a plant succession that begins life on a newly exposed rock surface, such as one left bare as a result of glacial retreat, tectonic uplift as in the formation of a raised beach, or volcanic eruptions...
: Community on rock
PsammosereA psammosere is a seral community, an ecological succession that began life on newly exposed coastal sand. Most common psammoseres are sand dune systems....
: Community on sand
XerosereXerosere is a plant succession which is limited by water availability. It includes the different stages in a xerarch succession. Xerarch succession of ecological communities originated in extremely dry situation such as sand deserts, sand dunes, salt deserts, rock deserts etc...
: Community in dry area
HalosereThe term Halosere is an ecological term which describes succession in a saline environment. An example of a halosere would be a salt marsh.In river estuaries, large amounts of silt are deposited by the ebbing tides and inflowing rivers....
: Community in saline body (e.g. a marsh)
Changes in animal life
Animal life also exhibit changes with changing communities. In lichen stage the fauna is sparse. It comprises few mites, ants and spiders living in the cracks and crevices. The fauna undergoes a qualitative increase during herb grass stage. The animals found during this stage include nematodes, insects larvae, ants, spiders, mites, etc. The animal population increases and diversifies with the development of forest climax community. The fauna consists of invertebrates like slugs, snails, worms, millipedes, centipedes, ants, bugs; and vertebrates such as squirrels, foxes, mouse, moles, snakes, various birds, salamanders and frogs.
Microsuccession/Serule
Succession of microorganisms like fungi, bacteria, etc occurring within a microhabitat is known as microsuccession or serule. This type of succession occurs within communities, for example in dead trees, animal droppings, etc.
The 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
disturbanceIn ecology, a disturbance is a temporary change in average environmental conditions that causes a pronounced change in an ecosystem. Outside disturbance forces often act quickly and with great effect, sometimes resulting in the removal of large amounts of biomass...
s, it will persist indefinitely. 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. There in no net annual accumulation of organic matter in a climax community mostly. The annual production and use of energy is balanced in such a community.
Characteristics of climax
- 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 littefall 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
CaliforniaCalifornia is the most populous state in the United States, and the third largest by area. California is the second most populous sub-national entity in the Americas, behind only São Paulo, Brazil...
,
chaparralChaparral is a shrubland or heathland plant community found primarily in the U.S. state of California and in the northern portion of the Baja California peninsula, Mexico. It is shaped by a Mediterranean climate and wildfire...
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 regarding nature of climax
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 and are related to it, 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 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.
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