Common in the North Cascades, lichens are unique, composite life forms created when fungi enclose algae in mutualistic symbiosis. In such a relationship both organisms should benefit, however, many lichenologists believe the partnership may actually be more beneficial to the fungus than the algae. Algae have the ability to create food through photosynthesis but are vulnerable to the elements. Fungi, which are not green for lack of chlorophyll, are unable to photosynthesize their own food. When alone, fungi are usually found in the form of mold, mildew or mushrooms that play many beneficial roles in decomposition. They are also found acting as symbiotic partners of other plants in the forest. Together as lichens, algae and fungi offer something to the other: algae provide carbohydrates and fungi provide protection. Lichens exploit habitats where fungi and algae could not survive independently. As a result, the forest in the North Cascades is literally covered with lichens. They are on trees, talus slopes, and even old buildings. They display a rich diversity of forms, which to many observers is the beauty of lichens. Lungwort (Lobaria pulmonaria) looks like a rubbery piece of lettuce and is easy to find scattered on the ground, especially after a windstorm has knocked it out of the canopy above. Old-man's-beard (Alectoria sarmentosa) looks like green, stringy hair hanging from tree branches. Lichens provide food for animals such as flying squirrels and material for birds’ nests. Lichens are essential nitrogen fixers in forest floor soils. Sensitive to pollution, lichens are studied by park scientists to measure pollutants and aging geologic exposure.