Giant fires, insect outbreaks could be ‘game-changer’ for some forests
FRISCO —Forest Service researchers say “mega-disturbances” like giant wildfires and insect outbreaks are likely to hasten the slow demise of temperate forest ecosystems in the coming decades.
Even without those large-scale events, some forests appear to be transitioning to shrublands and steppe, and big disturbances could speed that process, according to a new study published this month in Science.“While we have been trying to manage for resilience of 20th century conditions, we realize now that we must prepare for transformations and attempt to ease these conversions,” said Constance Millar, lead author and forest ecologist with the USFS Pacific Southwest Research Station.
Many forests are remarkably resilient, re-growing after years of logging. But after reviewing numerous forest studies, they concluded that rising global temperatures are resulting in hotter droughts — droughts that exhibit a level of severity beyond that witnessed in the past century.
During a hotter drought, high air temperatures overheat leaves and also increase the stress on trees by drawing the moisture from their tissues at faster rates than normal. Snow that would normally act as emergency water storage for trees during the dry season instead falls as rain.
Combined, these factors may cause abnormally high levels of forest mortality during hotter droughts.
“Some temperate forests already appear to be showing chronic effects of warming temperatures, such as slow increases in tree deaths,” said Nathan Stephenson, coauthor and ecologist with the U.S. Geological Survey. “But the emergence of megadisturbances, forest diebacks beyond the range of what we’ve normally seen over the last century, could be a game-changer for how we plan for the future.”
Chronic stress from drought and warming temperatures also expose temperate forests to insect and disease outbreaks. And as temperatures rise in many regions, fires grow in frequency and severity causing losses in private property, natural resources and lives.
Losing temperate forests to worsening droughts, megafires and insect and disease outbreaks could lead to widespread losses of forest ecosystem services like national park recreational areas, the researchers cautioned.
Forests also play an important role in storing atmospheric carbon dioxide and watershed protection, for example. The scientists encourage future studies identifying forests most vulnerable to the effects of mega-disturbances. In some cases, forest managers may be able to preserve ecosystem services like carbon storage as temperate forests transition to new ecological states.