Climate change will continue to worsen wildfires in the U.S., with the area burned each year expected to double by 2050, according to a report released this week by the USDA’s Forestry Service.
The gradual increase in temperatures also will claim forests in other ways. Some will be lost to drought and others will be forced upward in altitude and northward in latitude, essentially moving some types of forests out of the country, according to the report.
“A gradual increase in temperature will alter the growing environment of many tree species throughout the United States, reducing the growth of some species (especially in dry forests) and increasing the growth of others (especially in high-elevation forests). Mortality may increase in older forests stressed by low soil moisture, and regeneration may decrease for species affected by low soil moisture and competition with other species during the seedling stage,” the USDA authors wrote.
The most visible effects will occur as “interacting disturbances” change the landscape. In summary:
- Wildfire will increase throughout the United States, causing at least a doubling of area burned by the mid-21st century.
- Insect infestations, such as the current advance of bark beetles in forests throughout the Western United States and Canada, will expand, often affecting more land area per year than wildfire.
- Invasive species will likely become more widespread, especially in areas subject to increased disturbance and in dry forest ecosystems.
- Increased flooding, erosion, and movement of sediment into streams will be caused by (1) higher precipitation intensity in some regions (e.g., Southern United States), (2) higher rain:snow ratios in mountainous regions (western mountains), and (3) higher area burned (western dry forests). These increases will be highly variable in space and time, affecting decisions about management of roads and other infrastructure, as well as access for users of forest land.
- Increased drought will exacerbate stresses that include insects, fire, and invasive species, leading to higher tree mortality, slow regeneration in some species, and altered species assemblages [fewer or changed species].
While wildfires and the pine beetle infestation will mainly impact the Western states, no area of the nation will be exempt from rapidly changing riparian ecosystems, according to the report.
- In the Northeast, “a warmer climate will cause a major reduction of spruce-fir forest, moderate reduction of maple-birchbeech forest, and expansion of oak-dominated forest” and many migratory birds that nest in the area will be forced to move northward.
- In the Southeast, a major supplier of raw wood products, warming temperatures and more variable rainfall could push the pine forests into decline. In addition, “increased fire hazard and insect outbreaks will provide significant challenges for sustainable management of forests for timber and other uses…” A bright spot: The changes could “motivate redstoration of the fire-tolerant longleaf pine forests.”
- In the Midwest, northern and boreal tree species will decrease at the south edge of their range and increase north of their current range. Some forested wetlands will disappear, possibly replaced by tree species such as oaka nd hickory that require less water. Forests will become more fragmented, reducing connectivity for wildlife.
Where’s the good news? Humans may be able to adapt, and may be motivated to do so, because these “disturbances” to forests will reduce their productive value to human enterprises.
“Although uncertainty exists about the magnitude and timing of climate change effects on forest ecosystems, sufficient scientific information is available to begin taking action now,” the authors wrote.
Land can be managed to reduce fire risks, for instance, by thinning trees. In other situations, deforestation can be stopped, reducing carbon loss to the atmosphere and slowing climate change. By the same token, replanting can help replace carbon-holding forests.
The report included several technical papers to guide forest managers in different regions of the U.S..