Lithosere

A lithosere (a sere originating on rock) 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.

Pioneer species are the first organisms that colonise an area, of which lithoseres are an example. They will typically be very hardy (i.e., they will be xerophytes, wind-resistant or cold-resistant). In the case of a lithosere the pioneer species will be cyanobacteria and algae, which create their own food and water—i.e., they are autotrophic and so do not require any external nutrition (except sunlight). For example, the first lithosere observed after the volcanic explosion of Krakatoa was algae. Other examples of lithoseres include communities of mosses and lichens, as they are extremely resilient and are capable of surviving in areas without soil.

As more mosses and lichens colonize the area, they, along with natural elements such as wind and frost shattering, begin to weather the rock down. This over time creates more soil, leading to increased water retention. Early on, when there is little water, lichens dominate as they are more suited to a lack of water; but as water retention increases, mosses become more dominant as they are faster growing, and these further break the rocks down. The amount of soil is also increased by the decaying mosses and lichens. This improves the fertility of the soil as humus is increased, allowing grasses and ferns to colonise. Over time, flowering plants will emerge, followed by shrubs. As the soil gets progressively deeper, larger and more advanced plants are able to grow. This is the case in Surtsey, a "new," small volcanic island located off the south coast of Iceland. Surtsey was "created" in the 1960s and currently its plant succession has reached the stage where ferns and grasses have begun to start growing in the south of the island where the lava cooled first.

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Wikipedia