The death of a forest
New research indicates that increasing temperatures played a major role in the death of billions of piñon trees throughout the Southwest during the first four years of this century.
Scientists concluded that temperatures during the years 2000-2004 of the current drought were as much as 3 degrees Fahrenheit higher than the last megadrought years of 1953-56. The maximum daily temperature averaged 0.7 degrees higher this century, and the minimum temperature averaged 2 degrees higher.
While the two droughts are of similar magnitude, the current one has covered a much broader area, said Lisa Floyd-Hanna, professor of Environmental Studies at Prescott College.
A dozen researchers studying four regions across the Southwest combined their data for the paper with the help of the Drought Indices Regional Ecosystems Network, or DIREnet. Ecologist Neil Cobb of Northern Arizona University heads up DIREnet, and its members include Prescott College. David Breshears of the University of Arizona was the lead researcher on the paper.
This was the first time that scientists took a close look at the temperatures during the Southwest’s 1950s drought, Floyd-Hanna said.
“No matter how we measured it, it always came down to, this is a warmer period,” Floyd-Hanna said. “There’s never been a drought of this magnitude that was this warm” in recorded history.
While the research substantiates the global warming trend, it can’t show how much of the warming is natural versus human-caused, Floyd-Hanna said.
“We’re sort of at the initial stage of kind of getting punched in the face with global warming and how we have to deal with it,” Cobb said.
Temperatures have been on a solid upward trend since the 1950s drought, Cobb said.
“This is really a wake-up call for a lot of us, and it clearly will have an effect on how we do research from now on,” Cobb said. “Those temperature changes are as great or greater than anything we have seen in the past.”
The study sites are in the Flagstaff, Moab, Durango and Los Alamos areas of the Four Corners states. The Los Alamos sites lost an average of 80 percent of their piñon trees, Flagstaff lost 60 percent, Mesa Verde lost 53 percent and Moab lost 40 percent. Old-growth trees suffered the highest mortalities.
The piñon-juniper woodlands in the regions from Prescott to Ash Fork have experienced similar losses, Floyd-Hanna said. Juniper is more resistant to drought, she added.
Researchers have the most substantial 1950s data from Los Alamos, where the edge of the piñon-juniper ecosystem shifted to a higher elevation.
The implications of the current drought could be similar, with chaparral replacing piñon-juniper (PJ) woodlands and PJ replacing ponderosa pine.
The PJ woodlands are located only in the Southwestern U.S. and northern Mexico, and the trees are keystone species, said Floyd-Hanna, who has been studying them since 1979.
In her book “Ancient Piñon-Juniper Woodlands,” Floyd-Hanna listed all the animals dependent on these old-growth woodlands: 10 amphibians, 26 reptiles, 113 birds, about 100 fungi, at least 260 vascular plants and 14,000 to 26,000 insects.
“That’s why people should care,” Floyd-Hanna said. “There’s this whole bio-network dependent on PJ.”
Not surprisingly, the PJ woodlands are Floyd-Hanna’s favorite. She loves the fact that these trees are so ancient, taking centuries to develop. Some live to be 600 years old.
Other implications of the new paper include the possibility that as temperatures increase, less snowpack will mean less aquifer recharge, more erosion and more extreme drought cycles.
This current research is the foundation for more that needs to occur, scientists say.
For example, tree-ring research which looks back to droughts that occurred centuries ago has used recorded information into the 1990s but not this century. By returning to those sites for more tree samples today, scientists could compare the current drought to more historic droughts, although the data won’t be as extensive as that of the past 100 years.
The most recent drought before the 1950s, which occurred around 1900, was drier than the current drought. However, like the 1950s, it also was cooler than the current drought, Cobb said.
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