Primary succession is an ecological succession where a newly formed area is colonized for the first time by a group of species or a community. This previously uninhabited, barren area is usually lacking topsoil and organic matter. The species colonizing an uninhabited area for the first time is referred to as the pioneer species and the dominating community is called pioneer community. Soon, a wider range of plants and animals will occupy the area until a climax community is established. If disturbed or interfered with a disruptive external or internal factor, the species inhabiting the area could subsequently be replaced by a new ecological succession, called secondary succession. Since the area has already been inhabited during a primary succession, the secondary succession could occur rather faster, i.e. in decades or hundreds of years as opposed to a primary succession that could take thousands, even millions of years.
The word succession in ecological viewpoint was first used by the French naturalist, Adolphe Dureau de la Malle. The word is used to refer to the vegetation development after forest clear-felling.
Successions in the ecosystem
Ecological succession is the progressive succession of a group of species or a community over a given period, e.g. spanning over decades or millions of years. Usually, there is one dominant group of life forms that successfully established a stable climax community over a particular area.
Primary and secondary successions
Ecological succession may be primary or secondary. Both types are characterized by a progression of prevailing communities of species on a particular habitat. They differ in terms of the ecological history and origin of the habitat. For instance, a primary succession occurs when a group of species or a community colonize a barren, newly formed habitat. An example of primary succession is the establishment of plant or animal communities in an area where no soil initially exists, such as bare rocks formed from a lava flow. Other examples are the colonization of a barren area following a severe landslide or a recently exposed land from retreating glaciers. Another is the occupying of harsh habitats, such as sand dunes. The extremely hot temperature of sand dunes makes them available for habitation to only a few highly specialized plants and animals.
Secondary succession occurs when a previously occupied area is colonized by a new dominating group of species or communities. In secondary succession, the new inhabitants replace the previous communities over a habitat that had been exposed to a particular ecological disturbance. The disturbance may be an external or an internal factor. An example of secondary succession is the recolonization of an area damaged by fire. Another difference between primary and secondary successions is the nature of the habitat. In primary succession, living things colonize a barren land, which means it lacks topsoil. Conversely, in secondary succession, living things will be re-colonizing a previously inhabited area and therefore the area would have topsoil containing organic matter from the previous inhabitants.
Primary succession takes a longer period of time to be established and completed, i.e. a thousand or more years. On the contrary, the secondary succession often occurs relatively faster, requiring only a shorter period of time, like a decade or a hundred years. This is because an area that has just been newly formed would be initially unfavorable for most life forms. The newly formed land, for instance, would lack soil but would be comprised of bare rocks. This is the starting stage of primary succession. A series of physicochemical changes have to occur until such time that they become more conducive to life. The species that are able to inhabit a newly formed or formerly uninhabited land are called pioneer species and the community that has successfully established and dominated is called pioneer community. A community refers to an ecological unit comprised of a group of organisms or a population of different species that occupy a given area. A community may refer to a small population inhabiting small areas (as in a pond) or communities on large geographical areas, which define biome. The settling of a pioneer community marks the start of the colonizing phase of primary succession. Examples of pioneer species are lichens, algae, and fungi. These species are more tolerant and eventually contribute to the formation of the soil by breaking down rocks into smaller particles. They also provide organic matter to the area. Eventually, the area is laden with thin soil and thus becomes favorable for the growth of higher forms of species. The next species that colonize and dominate the area are referred to as intermediate species. Examples are grasses and shrubs that can thrive in thin soils. As the habitat improves, a wider range of vegetation and small animals can occupy the area. The final stage is the establishment of a climax community, i.e. a community comprised of even higher forms of life, e.g. shade-tolerant trees and sturdier tall trees that attract larger and higher forms of animals.
If the habitat is exposed to a disturbance that can bring disruption to its inhabitants, the second succession occurs. Since the area is already inhabited by plants and animals, the area after the disturbance would likely remain habitable and thus will be easier and available for re-colonization.
|Primary succession||Secondary succession|
|Definition||A type of [ecological succession where living things colonize for the first time a newly formed or an uninhabited, lifeless, barren area.||A type of ecological succession where a new set of living things colonizes an area previously inhabited but was disrupted or destroyed by a disturbance; the ecological succession following a primary succession|
|Habitat features||Devoid of vegetation and lacking topsoil; a barren or lifeless area; conditions are initially not suitable for life||Topsoil present, containing organic matter from previous vegetation and inhabitants|
|Length of time||Longer period; A thousand or more years||Shorter period; decades to hundreds of years|
|Examples||Colonization of newly formed habitats, e.g. uninhabited barren land from lava flows, retreating glaciers, etc.||Re-colonization of a previously inhabited geographical area that was previously exposed to an external or internal disturbance, such as fire, flood, tornadoes, hurricanes, etc.|
A third type called cyclic succession, is a type of succession wherein a group of species replaces a previously dominant species over time without a large-scale disturbance.
The primary succession is important in pioneering the area to create conditions favorable for the growth of other forms of plants and animals. It paves the way for the next successions as the previously thriving organisms could become an essential component of the soil. Since the pioneer species are more tolerant of a harsh environment, they could put into use the available nutrients and convert them into another form for use by other life forms. Thus, it is not surprising that lichens serve as a pioneer community as they are one of the most fundamental and efficient symbioses in an ecosystem.
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