Chapter 14 - Forest disturbances and health

Abstract

Forested ecosystems are dynamic in the sense that growth and reproduction processes continuously progress for all kinds of plants, animals, insects, and other forms of life. Apart from intrusions on these systems by humans, natural forces also disturb the forest in numerous ways. Their impact can vary in frequency, intensity, and scale. From a human perspective, natural disturbances can change the character of a tract of land, whether as small as a 5-hectare (ha; 12.4-acre [ac]) private forest or as large as a vast picturesque landscape. The types of disturbances that forested ecosystems face include those from fire, flooding, ice and snow, and wind; disease, invasive species, and pests; and human actions. In the United States, large-scale wind events such as Hurricane Katrina (2005) or large-scale forest fires such as the Yellowstone National Park fires (1988) and the Cerro Grande fire (2000) in New Mexico have garnered much media attention because of the scope of damage to both forests and human communities. Another type of disturbance that can greatly alter the development path of a forest is a volcanic eruption, which can cause not only the loss of human life but the leveling of extensive areas of forests. Disturbances caused by ice and snow can play an important role in limiting the northern range of tree species such as loblolly pine (Pinus taeda) and other temperate forest tree species native to lower latitude environments. Insect and disease outbreaks can also limit the vitality and range of certain tree species. For example, chestnut blight decimated the once widespread population of American chestnut (Castanea dentata) in the eastern United States, and now the tree species is limited to a few isolated groves of trees outside its normal range, and to stump sprouts arising from the remains of older trees. Finally, for better or for worse, human actions can greatly change the character of a forested landscape, whether through development, harvesting, or other activities (agriculture or agroforestry) deemed necessary by each society.