Abstract
The root system is an important part of a tree, but being inconspicuous it does not attract much attention. Therefore, root diseases are often invisible during much of the pathogens' life cycle. Nevertheless, they cause important losses due to mortality and reduced growth, but they are also components of forest ecosystems. For example, the complex of Armillaria root diseases, frequently associated with Armillaria ostoyae, attacks stressed trees and can kill seedlings or reduce the growth of trees during decades while hidden in roots. Inonotus tomentosus is common in spruce. From our observations, the pathogen usually infects trees older than 30 years; conifer seedlings planted on an infested site do not show any disease symptoms even after 10 years. Again, I. tomentosus needs stressed trees to develop in a stand. Heterobasidion annosum is an aggressive pathogen of pine. It colonizes fresh pine stumps after thinning in pine stands and can kill surrounding trees. Through lack of knowledge, foresters can create conditions conducive to the spread of root diseases: for example, precommercial thinning in the boreal forest has promoted Armillaria root diseases. Thinning in red pine plantations also creates an ecological niche favourable to H. annosum. Conversely, high-density spruce plantations will trigger Tomentosus root rot infestations. Proactive forest protection needs to integrate knowledge of silviculture, ecology, entomology and pathology. Understanding the ecology of these fungi is the first step.
Published Version
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