Impact of non-native invertebrates and pathogens on market forest tree resources.
Several forest non-native pests and pathogens that are among the most frequently cited invasive species worldwide represent serious economic and conservation concerns for the forest ecosystems in their region of introduction. Such organisms can have adverse impacts on the yield of marketable wood products, such as timber and pulp, as well as non-wood forest products, such as nuts, fruits, and seeds. However, quantitative data about impacts on forest market resources are rare and usually restricted in time and space. Moreover, information on regional impacts, and aggregate data including multiple invasive species, are largely missing or miscalculated. The most comprehensive studies show that the greatest impacts of pest invasions on native tree species are effects on non-market values whereas losses in wood and non-wood forest products account for a small part of the total impacts. Patterns are somewhat different in plantations of non-native trees, where non-native pests are more likely to affect the forestry sector directly through reduced fibre yield and increased management costs, whereas non-market values and environmental impacts are of lesser concern. This chapter argues that direct impacts on market forest resources are sometimes largely exaggerated and provides reasons for these overestimations.