Primary succession

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Primary succession occurring over time. The soil depths increase with respect to the increase in decomposition of organic matter, and there is a gradual increase of species diversity in the ecosystem. The labels I-VII represent the different stages of primary succession. I-bare rocks, II-pioneers (mosses, lichen, algae, fungi), III-annual herbaceous plants, IV-perennial herbaceous plants and grasses, V-shrubs, VI-shade intolerant trees, VII-shade tolerant trees. Primary Succession Diagram.svg
Primary succession occurring over time. The soil depths increase with respect to the increase in decomposition of organic matter, and there is a gradual increase of species diversity in the ecosystem. The labels I-VII represent the different stages of primary succession. I-bare rocks, II-pioneers (mosses, lichen, algae, fungi), III-annual herbaceous plants, IV-perennial herbaceous plants and grasses, V-shrubs, VI-shade intolerant trees, VII-shade tolerant trees.
Primary succession on Rangitoto Island, New Zealand Rangitotolavapath.jpg
Primary succession on Rangitoto Island, New Zealand

Primary succession is the beginning step of ecological succession where species known as pioneer species colonize an uninhabited site, which usually occurs in an environment devoid of vegetation and other organisms.

Contents

In contrast, secondary succession occurs on substrates that previously supported vegetation before an ecological disturbance. This occurs when smaller disturbances like floods, hurricanes, tornadoes, and fires destroy only the local plant life and leave soil nutrients for immediate establishment by intermediate community species. [1]

Occurrence

In primary succession pioneer species like lichen, algae and fungi as well as abiotic factors like wind and water start to "normalise" the habitat or in other words start to develop soil and other important mechanisms for greater diversity to flourish. Primary succession begins on rock formations, such as volcanoes or mountains, or in a place with no organisms or soil. Primary succession leads to conditions nearer optimum for vascular plant growth; pedogenesis or the formation of soil, and the increased amount of shade are the most important processes. [2]

These pioneer lichen, algae, and fungi are then dominated and often replaced by plants that are better adapted to less harsh conditions, these plants include vascular plants like grasses and some shrubs that are able to live in thin soils that are often mineral-based. Water and nutrient levels increase with the amount of succession exhibited. [3]

The early stages of primary succession are dominated by species with small propagules (seed and spores) which can be dispersed long distances. The early colonizers—often algae, fungi, and lichens—stabilize the substrate. Nitrogen supplies are limited in new soils, and nitrogen-fixing species tend to play an important role early in primary succession. [4] Unlike in primary succession, the species that dominate secondary succession, are usually present from the start of the process, often in the soil seed bank. In some systems the successional pathways are fairly consistent, and thus, are easy to predict. In others, there are many possible pathways. For example, nitrogen-fixing legumes alter successional trajectories. [5]

Spores of lichen or fungus, being the pioneer species, are spread onto a land of rocks. Then, the rocks are broken down into smaller particles. Organic matter gradually accumulates, favoring the growth of herbaceous plants like grass, ferns and herbs. These plants further improve the habitat by creating more organic matter when they die, and providing habitats for insects and other small animals. [6] This leads to the occurrence of larger vascular plants like shrubs, or trees. More animals are then attracted to the area and a climax community is reached.

Species diversity is also a large influence on the stages of succession, and as succession progresses further, species diversity changes with it. For example, there is far less richness and evenness of microorganisms in the very early stages of succession, but late successional stage bacteria are far more even and rich. [7] This again supports the hypothesis that as more resources are present in later stages of succession, there is enough to support a more diverse ecosystem with many different reproductive strategies. A 2000 case study suggests that plant species composition is more important to later-successional species than simply having high plant diversity early on. [8]

Examples

Volcanism

One example of primary succession takes place after a volcano has erupted. The lava flows into the ocean and hardens into new land. The resulting barren land is first colonized by pioneer organisms, like algae, which pave the way for later, less hardy plants, such as hardwood trees, by facilitating pedogenesis, especially through the biotic acceleration of weathering and the addition of organic debris to the surface regolith. An example of this is the island of Surtsey, which is an island formed in 1963 after a volcanic eruption from beneath the sea. Surtsey is off the south coast of Iceland and is being monitored to observe primary succession in progress. About thirty species of plant had become established by 2008 and more species continue to arrive, at a typical rate of roughly 2–5 new species per year. [9]

A volcanic eruption occurred on Mount St. Helens as well, with primary succession beginning after the destruction of the region's ecosystem. In Mount St. Helens' primary succession, the region was heavily isolated. This type of incident causes the rate of primary succession to be rather low, as many species that excel in establishment lack the ability to effectively disperse into the new frontier. [10] The opposite is true as well, as species that were not very good at establishing could not survive, even with high dispersal rates. The region has almost no organic materials to utilize, which was especially significant at Mount St. Helens, as its isolated location prevented succession to occur at the periphery of the destruction site. Initially effective long distance colonizers are rare, as they are only truly effective after an initial colonizer has helped to change the region into more suitable conditions. [11] This is why primary succession was slow in the destroyed region around Mount St. Helens.

Glacier Retreat

Another example is taking place on Signy Island in the South Orkney Islands of Antarctica, due to glacier retreat. Glacier retreat is becoming more normal with the warming climate, and lichens and mosses are the first colonizers. The study, conducted by Favero-Longo et al. found that lichen species diversity varies based on the environmental conditions of the previously existing earth that is first exposed, and the lichens' reproductive patterns. [12]

The characteristics of succession

By analyzing a case study in Grand Bend, Ontario, a full understanding of the distinction between primary and secondary succession can be accomplished. The two species, Juniperus virginiana and Quercus prinoides, are quickly reproducing and spreading grasses that are associated with primary succession in the dunes of Grand Bend's beaches. [13] They are classified as r selected species, with high mortality, quick reproduction, and a distinct ability to survive in harsh and nutrient-low conditions. In contrast, ecological development after primary succession completes often leads to a more heavily k selected population, which has lower mortality and slower reproduction rates. In the Grand Bend, this is shown through the succession of oak-pine forests, and the continued reduction of r selected grasses. The timescale is also relevant, as the secondary succession of oak-pine forests occurs approximately 2,900 years after the initial cases of primary succession, while the end of solely grassland dominated dunes occurs around 1,600 years after the beginning of primary succession. [13] This is extremely important, as it shows a 1,300 year intermittent period in which primary succession is overcome by secondary succession. This period is likely characterized by high species diversity, a mix of k and r selected species, and high community productivity. It is a well-supported principle that an intermediate between k and r dominated populations leads to high productivity and species diversity, while the secondary succession afterwards leads towards climax communities with low species diversity. During this 1,300 year period, it is likely that resources grew into a surplus, which reduced species diversity, resulting in the k dominated oak-pine forest.

It is very difficult to determine exactly what events will hinder or support the growth of a community, as shown in the following example. Very few seedlings survive for a long period of time during primary succession, with 1.7% of seedlings in an outwash plain named Skeiðarársandur in southeast Iceland lasting from 2005 to 2007. [14] The rest were replaced by new colonizers, as the mortality rates for r selected species like these are extremely high. This is a very important phenomenon to observe, as even though population sizes may remain consistent throughout the history of a region, it is highly likely that many of the r selected organisms present are entirely new organisms. This is one of many factors that are highly unpredictable in the scale of ecological succession.

See also

Related Research Articles

Soil retrogression and degradation are two regressive evolution processes associated with the loss of equilibrium of a stable soil. Retrogression is primarily due to soil erosion and corresponds to a phenomenon where succession reverts the land to its natural physical state. Degradation is an evolution, different from natural evolution, related to the local climate and vegetation. It is due to the replacement of primary plant communities by the secondary communities. This replacement modifies the humus composition and amount, and affects the formation of the soil. It is directly related to human activity. Soil degradation may also be viewed as any change or ecological disturbance to the soil perceived to be deleterious or undesirable.

<span class="mw-page-title-main">Epiphyte</span> Non-parasitic surface organism that grows upon another plant but is not nourished by it

An epiphyte is a plant or plant-like organism that grows on the surface of another plant and derives its moisture and nutrients from the air, rain, water or from debris accumulating around it. The plants on which epiphytes grow are called phorophytes. Epiphytes take part in nutrient cycles and add to both the diversity and biomass of the ecosystem in which they occur, like any other organism. They are an important source of food for many species. Typically, the older parts of a plant will have more epiphytes growing on them. Epiphytes differ from parasites in that they grow on other plants for physical support and do not necessarily affect the host negatively. An organism that grows on another organism that is not a plant may be called an epibiont. Epiphytes are usually found in the temperate zone or in the tropics. Epiphyte species make good houseplants due to their minimal water and soil requirements. Epiphytes provide a rich and diverse habitat for other organisms including animals, fungi, bacteria, and myxomycetes.

This glossary of ecology is a list of definitions of terms and concepts in ecology and related fields. For more specific definitions from other glossaries related to ecology, see Glossary of biology, Glossary of evolutionary biology, and Glossary of environmental science.

<span class="mw-page-title-main">Pioneer species</span> First species to colonize or inhabit damaged ecosystems

Pioneer species are resilient species that are the first to colonize barren environments, or to repopulate disrupted biodiverse steady-state ecosystems as part of ecological succession. A number of kinds of events can create good conditions for pioneers, including disruption by natural disasters, such as wildfire, flood, mudslide, lava flow or a climate-related extinction event or by anthropogenic habitat destruction, such as through land clearance for agriculture or construction or industrial damage. Pioneer species play an important role in creating soil in primary succession, and stabilizing soil and nutrients in secondary succession.

<span class="mw-page-title-main">Climax community</span> Mature ecological community of organisms best adapted to an area

In scientific ecology, climax community or climatic climax community is a historic term for a community of plants, animals, and fungi which, through the process of ecological succession in the development of vegetation in an area over time, have reached a steady state. This equilibrium was thought to occur because the climax community is composed of species best adapted to average conditions in that area. The term is sometimes also applied in soil development. Nevertheless, it has been found that a "steady state" is more apparent than real, particularly across long timescales. Notwithstanding, it remains a useful concept.

<span class="mw-page-title-main">Ecological succession</span> Process of change in the species structure of an ecological community over time

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

<span class="mw-page-title-main">Secondary forest</span> Forest or woodland area which has re-grown after a timber harvest

A secondary forest is a forest or woodland area which has regenerated through largely natural processes after human-caused disturbances, such as timber harvest or agriculture clearing, or equivalently disruptive natural phenomena. It is distinguished from an old-growth forest, which has not recently undergone such disruption, and complex early seral forest, as well as third-growth forests that result from harvest in second growth forests. Secondary forest regrowing after timber harvest differs from forest regrowing after natural disturbances such as fire, insect infestation, or windthrow because the dead trees remain to provide nutrients, structure, and water retention after natural disturbances. Secondary forests are notably different from primary forests in their composition and biodiversity; however, they may still be helpful in providing habitat for native species, preserving watersheds, and restoring connectivity between ecosystems.

<span class="mw-page-title-main">Biological soil crust</span> Communities of living organisms on the soil surface in arid and semi-arid ecosystems

Biological soil crusts are communities of living organisms on the soil surface in arid and semi-arid ecosystems. They are found throughout the world with varying species composition and cover depending on topography, soil characteristics, climate, plant community, microhabitats, and disturbance regimes. Biological soil crusts perform important ecological roles including carbon fixation, nitrogen fixation and soil stabilization; they alter soil albedo and water relations and affect germination and nutrient levels in vascular plants. They can be damaged by fire, recreational activity, grazing and other disturbances and can require long time periods to recover composition and function. Biological soil crusts are also known as biocrusts or as cryptogamic, microbiotic, microphytic, or cryptobiotic soils.

<span class="mw-page-title-main">Grey dune</span>

Grey dunes are fixed, stable sand dunes that are covered by a continuous layer of herbaceous vegetation. These dunes are typically located 50–100 meters from the ocean shore and are found on the landward side of foredunes. Grey dunes are named for their characteristic grey color which is a result of the ground cover of lichen combined with a top soil layer of humus.

Xerosere is a plant succession that 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. A xerosere may include lithoseres and psammoseres.

A 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. For example, the lava fields of Eldgjá in Iceland where Laki and Katla fissures erupted in the year 935 and the solidified lava has, over time, begun to form a lithosere.

<span class="mw-page-title-main">Secondary succession</span> Redevelopment of an encology after an event that changes it radically

Secondary succession is the secondary ecological succession of a plant's life. As opposed to the first, primary succession, secondary succession is a process started by an event that reduces an already established ecosystem to a smaller population of species, and as such secondary succession occurs on preexisting soil whereas primary succession usually occurs in a place lacking soil. Many factors can affect secondary succession, such as trophic interaction, initial composition, and competition-colonization trade-offs. The factors that control the increase in abundance of a species during succession may be determined mainly by seed production and dispersal, micro climate; landscape structure ; bulk density, pH, and soil texture.

<span class="mw-page-title-main">Disturbance (ecology)</span> Temporary change in environmental conditions that causes a pronounced change in an ecosystem

In ecology, a disturbance is a temporary change in environmental conditions that causes a pronounced change in an ecosystem. Disturbances often act quickly and with great effect, to alter the physical structure or arrangement of biotic and abiotic elements. A disturbance can also occur over a long period of time and can impact the biodiversity within an ecosystem.

The following outline is provided as an overview of and topical guide to ecology:

<span class="mw-page-title-main">Kasatochi Island</span> Active stratovolcano and part of the Andreanof Islands subgroup in Alaska

Kasatochi Island, also known as Kasatochi volcano, is an active stratovolcano and part of the Andreanof Islands subgroup of the Aleutian Islands of southwestern Alaska. On 7 August 2008, Kasatochi began erupting explosively with an ash plume reaching 45,000 feet (14,000 m). The eruption lasted for 24 hours and destroyed most life on the island. It currently does not support any consistent human population.

A pioneer organism, also called a disaster taxon, is an organism that colonizes a previously empty area first, or one that repopulates vacant niches after a natural disaster, mass extinction or any other catastrophic event that wipes out most life of the prior biome. A group of such organisms capable of continued procreation among themselves are a pioneer species.

<i>Trebouxia</i> Genus of algae

Trebouxia is a unicellular green alga. It is a photosynthetic organism that can exist in almost all habitats found in polar, tropical, and temperate regions. It can either exist in a symbiotic relationship with fungi in the form of lichen or it can survive independently as a free-living organism alone or in colonies. Trebouxia is the most common photobiont in extant lichens. It is a primary producer of marine, freshwater and terrestrial ecosystems. It uses carotenoids and chlorophyll a and b to harvest energy from the sun and provide nutrients to various animals and insects.

Ecological succession can be understood as a process of changing species composition within a community due to an ecological disturbance, and varies largely according to the initial disturbance prompting the succession. Joseph Connell and Ralph Slatyer further developed the understanding of successional mechanisms in their 1977 paper and proposed that there were 3 main modes of successional development. These sequences could be understood in the context of the specific life-history theories of the individual species within an ecological community.

<span class="mw-page-title-main">Marine fungi</span> Species of fungi that live in marine or estuarine environments

Marine fungi are species of fungi that live in marine or estuarine environments. They are not a taxonomic group, but share a common habitat. Obligate marine fungi grow exclusively in the marine habitat while wholly or sporadically submerged in sea water. Facultative marine fungi normally occupy terrestrial or freshwater habitats, but are capable of living or even sporulating in a marine habitat. About 444 species of marine fungi have been described, including seven genera and ten species of basidiomycetes, and 177 genera and 360 species of ascomycetes. The remainder of the marine fungi are chytrids and mitosporic or asexual fungi. Many species of marine fungi are known only from spores and it is likely a large number of species have yet to be discovered. In fact, it is thought that less than 1% of all marine fungal species have been described, due to difficulty in targeting marine fungal DNA and difficulties that arise in attempting to grow cultures of marine fungi. It is impracticable to culture many of these fungi, but their nature can be investigated by examining seawater samples and undertaking rDNA analysis of the fungal material found.

<span class="mw-page-title-main">Gap dynamics</span>

Gap dynamics refers to the pattern of plant growth that occurs following the creation of a forest gap, a local area of natural disturbance that results in an opening in the canopy of a forest. Gap dynamics are a typical characteristic of both temperate and tropical forests and have a wide variety of causes and effects on forest life.

References

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