Deb Babcock: Report links aspen illness, drought
Scientists: High temperatures, low precipitation cause of decline
January 22, 2012
Steamboat Springs — Quaking aspen (Populus tremuloides) is likely the tree most coveted by homeowners in Routt County and the one most enjoyed by visitors and residents who love to hike the aspen-covered mountains surrounding our beautiful valley. Sadly, there have been stands of these trees that have been dying off in certain parts of the mountains, mostly at lower elevations.
The disease killing stands of aspens has been a mystery to scientists, but a new report by six-member team from Stanford University, Carnegie Institution for Science and the University of Utah that has been studying the die-off provides a credible understanding of the problem affecting these beloved trees.
Aspens affected by sudden aspen decline are found to have gone through a period of severe drought from 2000 to 2004. Forest service personnel and scientists estimate that as much as 17 percent of aspen forests have experienced this die-off. This drought was brought about more by the high temperatures Colorado and other western states experienced during those summers than by a low amount of precipitation.
Generally when an aspen tree experiences a drought, it begins to store starch and other nutrients in its tissues and to limit its growth to help it get through the drought with minimal damage.
What happened to the affected trees is that the extended hot weather and drought damaged the tissues that store nutrients. The roots, in particular, developed cavitation — essentially air pockets that formed, then collapsed, within the flow of water and nutrients up through the trunk and into the branches of the trees. The scientists found that the trees affected by sudden aspen decline had a 400 percent higher level of this cavitation than trees in a healthy control group.
This cavitation caused a major loss of ability to draw nutrients from the roots up into the rest of the tree, and the trees became dehydrated. During a few years, much of the root system died, which caused the die-off and is also why we haven't seen new aspen sprouts or seedlings crop up within the stands of dying trees. (Aspens tend to procreate from the large root system in a stand of trees more so than from seed.)
Most of the sudden aspen decline occurred at elevations lower than that found in Routt County, but you may occasionally see a dead aspen stand with no new seedling growth along some of the hiking trails in our area.
Deb Babcock is a master gardener through the CSU Extension Routt County. Call 970-879-0825 with questions.