Climate change and forest health
The red band needle blight, Mycosphaerella pini, infects and kills the needles of Pinus spp. resulting in significant defoliation, stunted growth and eventually death of host trees. In its native range this fungus normally causes little damage, but since the late 1990s it has been causing extensive defoliation and mortality in young plantations of lodgepole pine (Pinus contorta var. latifolia) in northwestern British Columbia, Canada. The current epidemic coincides with a prolonged period of increased frequency of warm rain events throughout the mid- to late-1990s allowing for the rapid spread and increased rates of infection. Unlike many other pests, changes in precipitation patterns may be more important than changes in temperature for predicting the spread and impact of M. pini.
Armillaria species are common worldwide pathogens of trees, woody shrubs and herbaceous plants that can cause wood decay, growth reduction and even mortality, particularly in trees stressed by other factors, or in young trees planted on sites from which infected hosts have been removed. Armillaria species can become more aggressive and damaging when elevated temperatures cause drought stress thereby reducing tree defences. Tree physiological condition in general may be an important factor in controlling the impacts of Armillaria species, and climate change may affect their epidemiology.
Phytophthora cinnamomi is considered one of the most widely distributed and destructive forest pathogens. Temperature, moisture and pH all influence the growth and reproduction of the fungus. A recent study on the impacts of climate warming on P. cinnamomi predicted a potential range expansion of the disease in Europe of one to a few hundred kilometres eastward from the Atlantic coast within one century.
Phytophthora ramorum causes a very serious disease called sudden oak death which causes extensive mortality of tanoak and oaks. The pathogen likely disperses through a variety of means. Sporangia may be dispersed locally by rain splash, wind-driven rain, irrigation or ground water, soil and soil litter. Bark and ambrosia beetles are commonly found on infected trees but their potential role of vectors has not yet been investigated. Consequently, changes in climate, precipitation and temperature in particular, will likely produce more optimal conditions for the pathogen resulting in an increase in disease occurrence.