Another in our series, but this time the EPA and the commenters get it right
Comment (6-44):The Technical Support Document provides the background for this, of which Eli will quote a bit
Commenters (e.g., 2791, 10298) state their support for the Findings, noting the potential for increased stress from heat, drought, insects, and disease on plant and tree populations. Others (2599, 10081) from the western United States voice their support for the Findings and describe their experiences with hot summers and serious wildfires. Other commenters (e.g., 3421, 4748, 6894) state their support for the Findings and express concern about the effects of current and future extreme weather events on the forestry industry, including heat waves, droughts, floods, wildfires, and hurricanes. One commenter (5844) describes how projected climate impacts, particularly the increased risk of wildfire on forestry and forest biodiversity will affect him personally given his enjoyment of hiking, camping, and communing with nature in the forests of the Pacific Northwest.
A commenter (3501) states his support for the Findings, indicating that the western United States and Canada are already seeing widespread changes in the natural landscape due to climate change. Hotter temperatures are causing more frequent and persistent drought in the West, which contribute to forest fires and pine beetle infestations. A weather-related pine beetle infestation has decimated millions of acres of forest in the western United States Western US and Canada. At the current rate of destruction, 80% of the forests of British Columbia will have been destroyed within five years and the rest of the West will lose 50% of its forests by mid-century. The forest fire season in the West is now 78 days longer than 25 years ago and it is well recognized that our forest fires have become more frequent, more intense and more destructive.
We reviewed the comments provided and note they are generally consistent with the discussion of climate impacts on forestry in the TSD, although commenters do not provide specific references to support their claims. As summarized in the TSD and in our responses to previous comments in this volume, disturbances like wildfire and insect outbreaks are increasing and are likely to intensify in a warmer future with drier soils and longer growing seasons.
10(d) Insects and DiseasesAnd so, we get to the scary bits To be continued. . .
Insects and diseases are a natural part of forested ecosystems and outbreaks often have complex causes. The effects of insects and diseases can vary from defoliation and retarded growth, to timber damage, to massive forest diebacks. Insect life cycles can be a factor in pest outbreaks; and insect life cycles are sensitive to climate change. Many northern insects have a two-year life cycle, and warmer winter temperatures allow a larger fraction of overwintering larvae to survive. Recently, spruce budworm in Alaska has completed its life cycle in one year, rather than the previously observed duration of two years (Field et al., 2007). Recent warming trends in the United States have led to earlier spring activity of insects and proliferation of some species, such as the mountain pine beetle (Easterling et al., 2007).
During the 1990s, Alaska’s Kenai Peninsula experienced an outbreak of spruce bark beetle over 6,200 square miles (16,000 km2) with 10 to 20% tree mortality (Anisimov et al., 2007). Also following recent warming in Alaska, spruce budworm has reproduced farther north reaching problematic numbers (Anisimov et al., 2007). Climate change may indirectly affect insect outbreaks by affecting the overall health and productivity of trees. For example, susceptibility of trees to insects is increased when multi-year droughts degrade the trees’ ability to generate defensive chemicals (Field, et al., 2007). Warmer temperatures have already enhanced the opportunities for insect spread across the landscape in the United States and other world regions (Easterling et al., 2007).
The IPCC (Easterling et al., 2007) stated that modeling of future climate change impacts on insect and pathogen outbreaks remains limited. Nevertheless, the IPCC (Field et al., 2007) states with high confidence that, across North America, impacts of climate change on commercial forestry potential are likely to be sensitive to changes in disturbances from insects and diseases, as well as wildfires.
The CCSP report (Ryan et al., 2008) states that the ranges of the mountain pine beetle and southern pine beetle are projected to expand northward as a result of average temperature increases. Increased probability of spruce beetle outbreak as well as increase in climate suitability for mountain pine beetle attack in high-elevation ecosystems has also been projected in response to warming (Ryan et al., 2008).
Climate change can shift the current boundaries of insects and pathogens and modify tree physiology and tree defense. An increase in climate extremes may also promote plant disease and pest outbreaks (Easterling et al., 2007).