Wildfire, Drought, and Insects
A wildfire sweeps
through Bitterroot
National Forest
in
Montana.
Image courtesy of John
McColgan,
USDA Forest
Service.In recent years, visitors to several National Parks, including Zion in Utah and Yosemite in
California, have been turned away by nearby wildfires. In addition to their effects on treasured
natural areas, wildfires put people, homes, livestock, and businesses at risk. Wildfire is nothing
new, but it is dramatically escalating in frequency and extent in western forests, among other
areas. There are now four times as many wildfires exceeding 1 and 1/2 square miles as there were 30
years ago, and these frequent large fires are burning six times as much forest area. In the last 20
years, the western fire season has expanded by more than ten weeks.
This increase in wildfire is a legacy of both a changing climate and decades of total fire suppression
that has resulted in a buildup of dead fuels. One important factor is drought. Wintertime
precipitation is increasingly falling as rain instead of snow, and the snow that does accumulate is
melting earlier in the spring—decreasing the amount of water available in the late summer months
and contributing to longer and more intense droughts. Compounding the effects of these droughts
is the increased susceptibility of drought-stressed trees to attacking insects. In the last decade,
a bark beetle epidemic has exploded across 18,000 square miles of western mountain forests.
Milder winter temperatures kill fewer beetles in their budworm phase than the colder winters of
the past, helping to increase the bark beetle population, with devastating effects. As the beetles kill
vast areas of forest, they leave standing dead wood, fueling even larger wildfires.
The climate is becoming too dry to support some of our nation's forests. Ecologists expect that
some drought- and wildfire-stricken areas will not recover as forests but will instead regrow as
open savannah or grassland ecosystems.
The American Pika
Image courtesy of J. R.
Douglass,
Yellowstone
National Park.Some species that have adapted to living at higher elevations are
being stranded on mountaintop "islands." These species can be
stuck with nowhere to move as warmer temperatures, and formerly
lower-elevation species, creep up to higher elevations. One such
species is the American pika, a small-eared relative of rabbits and
hares. This species delights visitors to Glacier National Park and other
parks throughout the mountain ranges in western states.
Pikas lived in the lowlands during the last ice age. As the ice retreated, these small animals
gradually climbed mountain slopes in pursuit of their required climate. Today, the species is
restricted to the isolated mountaintop islands as populations below about 7,000 feet rapidly go
extinct. The cause, studies suggest, is simple heat stress.
Trout Habitat
Earlier springs and warmer summers are beginning to have a major impact on some of the
Rockies' legendary trout streams. With mountain snow melting earlier in the spring, the cool
snowmelt water that used to flow through late summer is now slowing to a trickle. In seven
Montana rivers, the amount of water flowing in the late summer has dropped on average 30
percent since 1950 as a result of increasing irrigation demand, earlier snowmelt, and warmer
summer temperatures. Some small rivers, like Montana's Big Hole, now stop flowing entirely in
late summer, shrinking to isolated pools until the autumn rains.
In addition, some streams
are reaching high temperatures
that are lethal for
trout—above 78°F—in July
and August. State officials
have had to temporarily
close some streams to trout
fishing during August in
recent years because of low
stream flow and high water
temperatures. Scientists estimate
that 18–92 percent of
bull trout habitat could be
lost in the northern Rocky
Mountains in the next half
century.
This web page is based on the National Academies' educational booklet
Ecological Impacts of Climate Change.
