Pathogens, Invasive Species, and Prognosis for the Future

Abstract

Organisms such as fungi and insects, can attack trees and cause reductions in growth due to reallocation of resources to defense responses, or reductions in photosynthetic capacity. These organisms can also kill trees, which can enhance the growth of neighbor trees due to release from competition. Changes in growth brought about by such attacks can be detected and studied using tree-ring analysis. Three case studies are presented in this chapter. The first is on Dothistroma needle blight in British Columbia, Canada where it is a native pathogen that causes growth reduction of pine. Dendrochronology is used to reconstruct past outbreaks of the pathogen, to identify weather variables that enhance disease development and spread, and to link changes in outbreak dynamics with climate change. The second case study is on white pine blister rust in North America, where the fungus was introduced into high elevation forests of whitebark pine. Dendrochronology enabled approximation of the date of introduction, disease intensification and spread dynamics, interactions with other insects and climate, as well as projections of future stand composition and structure. This is an important application of tree-ring analysis given the importance of whitebark pine for ecosystem function. The third case study is on emerald ash borer, a wood boring insect recently introduced to North America. In this case, tree-ring analysis is used to determine the efficacy of applications of insecticide in reducing growth loss and mortality rates. Collectively these case studies demonstrate that dendrochronology enables integrated analysis of host, climate and pathogen or insect effects on tree growth and survival, and ultimately on ecosystem function and resilience.