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    Forest tree species and ecosystems ahve evolved under climatic, geological, and biological forces over eons of time. The present flora represents the sum of these selective forces that have acted upon ancestral and modern species. Adaptations to climatic factors, soils, insects, diseases, and a host of disturbance events, operating at a variety of scales, ahve forged the characteristics of each tree species we now observe, including their functions in forest ecosystems. Thus, modern flora is adapted to the conditions existing at present. The stochastic and inexorable nature of climatic, geological, and biological selective forces becomes more striking when we consider that possibly 99% of all species that ever existed are not extinct (Raup 1986).

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    Otrosina, William J. 2003. Exotic ecosystems: where root disease is not a beneficial component of temperate conifer forests. In: Forest Pathology: From genes to landscapes, Chapter 13

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