Due to the very slow growth of lichens can only survive in places that are not overgrown with other plants, where there is a free area for photosynthesis. In moist areas they often lose mosses. In addition, lichens exhibit increased sensitivity to chemical contamination and can serve as its indicators. Resistance to adverse conditions of low growth rate, the existence of different methods of extraction and accumulation of moisture, the developed protection mechanisms.
Lichens usually have modest requirements for mineral intake, getting them mostly from dust in the air or with rain water, in that regard, they can live in the open unprotected surfaces (stones, bark of trees, concrete and even rusty metal). The advantage is the tolerance of lichens to extreme conditions (drought, high and low temperatures (from -47 to +80 degrees Celsius, about 200 species live in the Antarctic), acidic and alkaline environment, ultraviolet radiation). In may 2005, experiments were conducted on the lichens Rhizocarpon geographicum and Xanthoria elegans, which showed that these species at least for about two weeks could survive outside the earth's atmosphere, that is in very poor conditions.
Many lichens are specific to the substrate: one is well developed only in alkaline rocks, such as limestone or dolomite, the other sour, lime silicate rocks, such as quartz, gneiss and basalt. Lichens, epiphytes also prefer certain trees: choose a sour bark of pine or birch or walnut core, maple, or elderberry. A number of lichens acts as a substrate for other lichens. Often formed typical sequence in which various lichens are growing on each other. There are species that live constantly in water, e.g., Verrucaria serpuloides.
Lichens, and other organisms form communities. An example of a lichen Association is a community Cladonio-Pinetum — lichen pine forests.