What Kind of Relationship Is Fungi on Trees?

What Fungus Is

• Fungus is a kingdom apart from plants, animals, and bacteria. This group includes mushrooms, molds, mildew, yeasts and many other organisms. Unlike plants, the cell walls of fungi are made up of chitin, and fungi are actually more closely genetically related to animals than they are to plants. They cannot create their own food the way plants do with photosynthesis, and because of this must find other ways of acquiring nutrients. This is one of the factors that have led to the close relationships they often develop with other organisms.

Parasitic Relationships

• Parasitic fungi produce chemicals that harm the tree they use as a host. While not all parasitic fungi kill their hosts, the fungi behind Dutch Elm Disease -- "Ophiostoma ulmi" -- is responsible for the deaths of millions of elms. There are other fungal infections, some of which are specific to certain types of trees, while others are general parasites such as "Armillaria mellea" and the various fungi that cause powdery mildew, verticillium wilt, cankers and leaf spots.

Symbiotic Relationships

• A number of relationships between trees and fungi exist that are beneficial to both organisms. These relationships are called "mycorrhizal." There are many mycorrhizal relationships between fungi and trees, such as the "Amanita phalloides" and the oak tree. In this type of relationship, the fungus enhances the tree's roots with its own, allowing them both to better absorb nutrients and meet both their needs in a way neither could do alone.

Saprophytic Relationships

• A saprophyte feeds on dead material. Some fungi, such as "Pleurotus ostreatus," for example, feed only on the dead parts of trees. This relationship is sometimes beneficial because the waste left behind by the fungi is digestible by the tree itself. Not only that, but the eating away of dead wood can make it easier for a tree's roots to hold up the remaining weight, and make it more structurally resistant to winds and storms. Saprophytic fungi also feed on trees that are entirely dead.