Tree-ring study suggests the region could remain fire-prone for a century or more
By Summit Voice
SUMMIT COUNTY — A new study by CU Boulder researchers suggests that forests in Patagonia may become more fire-prone in the next 100 years, as a major climate oscillation in the southern hemisphere is reinforced and made more persistent by ozone-depleting chemicals and greenhouse gases.
The researchers used tree ring records dating back to 1506 to link past wildfire activity in the forests of Patagonia with the Southern Annular Mode, a climate cycle that creates low atmospheric pressure in the Antarctic that is tied to warmer and drier conditions in southern South America.
The tree rings showed that, when SAM was in its positive phase, there were widespread fires in both dry woodlands and rainforests in Patagonia, a region that straddles Argentina and Chile, said CU-Boulder Research Associate Andres Holz, lead study author.
“Our study shows for about the past 250 years, the Southern Annular Mode has been the main driver in creating droughts and fires in two very different ecosystems in southern South America,” Holz said.
“Climate models suggest an increase in SAM beginning in the 1960s due to greenhouse gas increases and Antarctic ozone depletion probably will cause this region to be drought-prone and fire-prone for at least the next 100 years.”
“Before the Industrial Revolution, SAM intensified naturally at times to create drought situations in Patagonia,” Holz said. “But in the last 80 years or so, the natural variation has been overwhelmed by a bias toward a positive SAM phase because of ozone-depleting chemicals and greenhouse gases we have put in the atmosphere.”
Holz and Veblen compared past wildfire records for two ecologically distinct regions in Patagonia — the relatively dry region of southern Patagonia in Argentina and the temperate rainforest of Patagonia in northern Chile. While the tree ring historical record showed increased fires in both regions correlated with a positive SAM, the trend has been less pronounced in northern Patagonia in the past 50 years, likely because of fire-suppression efforts there, Holz said.
But the decades of fire suppression have caused the northern Patagonian woodlands to become denser and more prone to wildfire during hot and dry years, Holz said.
“Even in areas of northern Patagonia where fire suppression previously had been effective, record surface areas of woodlands and forests have burned in recent years of extreme drought,” said Veblen. “And since this is in an area of rapid residential growth into wildland-urban interface areas, this climate-driven trend towards increasing fire risk is becoming a major problem for land managers and homeowners.”
The two CU-Boulder researchers studied reconstructions of tree rings going back more than 500 years from 432 trees at 42 sample sites in northern Argentina and southern Chile — the largest available data set of annual, readable tree ring records in the Southern Hemisphere. The tree rings, which indicate climate cycles and reveal the scars of old fires, showed that wildfires generally increased in both regions when SAM was in its strong, positive phase.
Although the Antarctic ozone hole stopped growing in about 2000 as a result of a ban on ozone-depleting gases and now appears to be slowly repairing itself, a 2011 paper by researchers at the National Center for Atmospheric Research in Boulder indicates ozone recovery and greenhouse gas influences essentially will cancel each other out, preventing SAM from returning to its pre-1960s levels.
The research effort was supported by the National Geographic Society, the National Science Foundation, the CU Beverly Sears Small Grants Program and the Council on Research and CreativeResearch of the CU Graduate School.
A paper on the subject by Holz and CU-Boulder geography Professor Thomas Veblen was published in Geophysical Research Letters.
Filed under: climate and weather, Environment, forest fires, Forest health, forests, global warming, Summit County news Tagged: | Antarctic oscillation, Dendrochronology, Environment, Geophysical Research Letters, greenhouse gases, National Center for Atmospheric Research, ozone depletion, Patagonia, Summit County News, University of Colorado Boulder, Wildfires