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Pioneer species are resilientspecies that are the first tocolonize barrenenvironments, or to repopulate disruptedbiodiversesteady-stateecosystems as part ofecological succession. A number of kinds of events can create good conditions for pioneers, includingdisruption bynatural disasters, such aswildfire,flood,mudslide,lava flow or aclimate-relatedextinction event[1] or byanthropogenichabitat destruction, such as throughland clearance for agriculture or construction or industrial damage. Pioneer species play an important role in creating soil inprimary succession, and stabilizing soil and nutrients insecondary succession.[2]
For humans, because pioneer species quickly occupy disrupted spaces they are sometimes treated asweeds ornuisance wildlife, such as thecommon dandelion orstinging nettle.[3][2] Even though humans have mixed relationships with these plants, these species tend to help improve the ecosystem because they can break up compacted soils and accumulate nutrients that help with a transition back to a more mature ecosystem.[4][5][2] In human managedecological restoration oragroforestry, trees and herbaceous pioneers can be used to restore soil qualities and provide shelter for slower growing or more demanding plants.[5][6][7] Some systems useintroduced species to restore the ecosystem,[2] or forenvironmental remediation.[8] The durability of pioneer species can also make them potentialinvasive species.[9][2][10]
Somelichens grow on rocks without soil, so may be among the first of life forms, and break down the rocks into soil for plants.[11] Since some uninhabited land may have thin, poor quality soils with few nutrients, pioneer species are often hardy plants with adaptations such as long roots, root nodes containingnitrogen-fixing bacteria, and leaves that employtranspiration. Note that they are oftenphotosynthetic plants, as no other source of energy (such as other species) except light energy is often available in the early stages ofsuccession, thus making it less likely for a pioneer species to be non-photosynthetic.
The plants that are often pioneer species also tend to bewind-pollinated rather thaninsect-pollinated, as insects are unlikely to be present in the usually barren conditions in which pioneer species grow; however, pioneer species tend to reproduceasexually altogether, as the extreme or barren conditions present make it more favourable to reproduce asexually in order to increasereproductive success rather than invest energy intosexual reproduction. Pioneer species will eventually die, createplant litter, and break down as "leaf mold" after some time, making new soil forsecondary succession (see below), and releasing nutrients for small fish andaquatic plants in adjacent bodies of water.[12]
Some examples of pioneering plant species:
The pioneeringfauna will colonize an area only afterflora andfungi have inhabited the area. Soil fauna, ranging from microscopicprotists to largerinvertebrates, have a role insoil formation andnutrient cycling.Bacteria and fungi are the most important groups in the breakdown of organic detritus left byprimary producing plants such asskeletal soil,moss andalgae. Soil invertebrates enhance fungal activity by breaking down detritus. As soil develops,earthworms andants alter soil characteristics. Worm burrows aerate soil and ant hills alter sediment particle size dispersal, altering soil character profoundly.
Thoughvertebrates in general would not be considered pioneer species, there are exceptions.Natterjack toads are specialists in open, sparsely vegetated habitats which may be at an earlyseral stage.[15] Wide-ranging generalists visit early succession stage habitats, but are not obligate species of those habitats because they use a mosaic of different habitats.
Vertebrates can affect early seral stages.Herbivores may alter plant growth.Fossorial mammals could alter soil and plant community development. In a profound example, aseabird colony transfers considerable nitrogen into infertile soils, thereby altering plant growth. Akeystone species may facilitate the introduction of pioneer species by creating newniches. For example,beavers may flood an area, allowing new species to immigrate.[16]
The concept of ecologic succession also applies to underwater habitats. If a space becomes newly available in a reef surrounding,haplosclerid andcalcareous sponges are the first animals to initially occur in this environment in greater numbers than other species. These types of sponges grow faster and have a shorter life-span than the species which follow them in this habitat.[17]
The term pioneer species is also used to refer to the first species, usually plants, to return to an area after disturbance as part of the process ofsecondary succession. Disturbances may include floods,tornadoes,forest fires,deforestation, or clearing by other means.[18]
Pioneer species tend to be fast-growing, shade-intolerant, and tend to reproduce large numbers of offspring quickly. The seeds of pioneer species can sometimes remain viable for years or decades in thesoil seed bank and often are triggered to sprout by disturbance.[19] Mycorrhizal fungi have a powerful influence on the growth of pioneer species.[20]
Some examples of the plants in such areas include:[citation needed]
Media related toPioneer plants at Wikimedia Commons