Effects of climate change on forest insect and disease outbreaks

General circulation models (GCMs) predict dramatic future changes in climate for the northeastern and north central United States under doubled carbon dioxide (CO2) levels (Hansen et al., 1984; Manabe and Wetherald, 1987; Wilson and Mitchell, 1987; Cubasch and Cess, 1990; Mitchell et al., 1990). January temperatures are projected to rise as much as 12°C and July temperatures as much as 9°C over temperatures simulated at ambient CO2 (Kittel et al., 1997). Projections of precipitation are quite variable over the region, ranging from 71 to 177% of ambient levels in January and 29 to 153% of ambient in July among several GCMs (Kittel et al., 1997). Such climate changes clearly may affect the growth and species composition of our northern forests directly in ways discussed in previous chapters. In contrast with the discussions in previous chapters, this chapter steps up one trophic level to consider the effects of climate change on the populations of microorganisms, fungi, and insects that feed in and on forest trees.