In the deciduous forests many organisms help each other survive. When organisms are in a relationship where they both help each other out it is called mutualism which is a form of symbiosis. In the deciduous forests the organism lichen is half protist and half fungi. This means that the two parts of the organism help each other survive and live. The two parts of lichen can not survive alone and depend on each other to exist.
Lichens are very resistant to cold and drought.
Therefore, lichens grow in places where most other organisms can not survive, on dry, bare rock in deserts and on top of mountains. The lichens are able to surive because of the help from the fungus. The alga carries out photosynthesis supplying the fungus with a source of organic minerals. The fungus also helps out the alga. The fungus provides the alga with water and minerals that it has picked up from the surface that it lives on.