FOREST PROTECTION

Disease

Most important tree diseases are caused by fungi. Fungi also provide very important functions. Nutrients are incorporated into the soil and made available to plants by fungal decomposition of plants and animals. Certain fungi functionally increase a trees fine root system where nutrients are actively taken up. Fungi can live for decades in soil or wood colonies. The word's largest living organism is a fungus that is spread over acres. Fungi that decompose dead wood are saprophytes. Some fungi attack portions of live trees and digest the cellulose or lignin within the wood. While diseased trees may become hosts to insects and cavity-nesting birds and animals, the loss of timber quality and tree mortality are concerns to foresters.

Fungal diseases are categorized by the portion of the tree affected. Root rots decay the underground portion of the tree. Eventually, the tree topples for lack of support. Root rots may affect the healthiest trees as well. Although no cure is known for root rots, some are specific to particular tree species. It may then be effective to plant an alternate species for at least one crop.

Stem diseases affect the main trunk. These rots usually enter through wounds, dead limbs, or insect holes. The decaying of the main stem causes a large reduction in the volume of wood a tree produces. Trees that have swollen bases, scars, or fungal growths on the outside called conks are likely to be decayed on the inside.

An important non-fungal disease is Dwarfmistletoe. This parasitic plant produces tiny grape-like seed pods that explode to shower seeds over the forest. The young plants send roots through the bark into the cambium to feed on the host's nutrients. This interrupts the tree's normal distribution of energy creating wildly increased twig and wood growth (called witches brooms) at the site of the infection. Dwarfmistletoe does not directly kill the tree, but it does slow down growth, reduce wood quality, weaken the host tree, and increase fire hazard. Removing infected trees and planting a different species helps to reduce dwarfmistletoe.