Editing Lichen (section)

===Ecological interactions===
Lichens are [[pioneer species]], among the first living things to grow on bare rock or areas denuded of life by a disaster.<ref name=WIL/> Lichens may have to compete with plants for access to sunlight, but because of their small size and slow growth, they thrive in places where higher plants have difficulty growing. Lichens are often the [[ecological succession|first to settle]] in places lacking soil, constituting the sole vegetation in some extreme environments such as those found at high mountain elevations and at high latitudes.<ref>{{cite journal | last = Walker |first = T. R. | date = 2007 | title = Lichens of the boreal forests of Labrador, Canada: A checklist | journal = Evansia | volume = 24 | issue = 3| pages = 85–90 | doi=10.1639/0747-9859-24.3.85|s2cid = 129100097 }}</ref> Some survive in the tough conditions of deserts, and others on frozen soil of the Arctic regions.<ref name=Oksanen2006/>

A major ecophysiological advantage of lichens is that they are [[poikilohydry|poikilohydric]] (''poikilo''- variable, ''hydric''- relating to water), meaning that though they have little control over the status of their hydration, they can tolerate irregular and extended periods of severe [[desiccation]]. Like some [[moss]]es, [[Marchantiophyta|liverworts]], [[fern]]s and a few [[resurrection plant]]s, upon desiccation, lichens enter a metabolic suspension or stasis (known as [[cryptobiosis]]) in which the cells of the lichen symbionts are dehydrated to a degree that halts most biochemical activity. In this cryptobiotic state, lichens can survive wider extremes of temperature, radiation and drought in the harsh environments they often inhabit.
[[File:Moss_lichen.jpg|thumb|Lichens suppress the growth of mosses and higher plants around them]]
Lichens do not have roots and do not need to tap continuous reservoirs of water like most higher plants, thus they can grow in locations impossible for most plants, such as bare rock, sterile soil or sand, and various artificial structures such as walls, roofs, and monuments. Many lichens also grow as [[epiphyte]]s (''epi''- on the surface, ''phyte''- plant) on plants, particularly on the trunks and branches of trees. When growing on plants, lichens are not [[parasite]]s; they do not consume any part of the plant nor poison it. Lichens produce [[allelopathy|allelopathic]] chemicals that inhibit the growth of mosses. Some ground-dwelling lichens, such as members of the subgenus ''[[Cladoniaceae|Cladina]]'' (reindeer lichens), produce allelopathic chemicals that leach into the soil and inhibit the germination of seeds, spruce and other plants.<ref>{{cite book|chapter=Lichen Allelopathy: A Review|author=Lawrey, James D. |pages=26–38| doi=10.1021/bk-1995-0582.ch002|title=Allelopathy. Organisms, Processes, and Applications|volume=582 |editor1=Inderjit |editor2=K. M. M. Dakshini |editor3=Frank A. Einhellig |year=1994| publisher=American Chemical Society|series=ACS Symposium Series |isbn=978-0-8412-3061-3 }}</ref> Stability (that is, longevity) of their [[Substrate (biology)|substrate]] is a major factor of lichen habitats. Most lichens grow on stable rock surfaces or the bark of old trees, but many others grow on soil and sand. In these latter cases, lichens are often an important part of soil stabilization; indeed, in some desert ecosystems, [[vascular plant|vascular (higher) plant]] seeds cannot become established except in places where lichen crusts stabilize the sand and help retain water.

Lichens may be eaten by some animals, such as [[reindeer]], living in [[arctic]] regions. The [[larva]]e of a number of [[Lepidoptera]] species feed exclusively on lichens. These include [[common footman]] and [[marbled beauty]]. They are very low in protein and high in carbohydrates, making them unsuitable for some animals. The [[Northern flying squirrel]] uses it for nesting, food and winter water.