Researchers at NAU are finding evidence that carbon dioxide and warmer temperatures are likely changing the vegetation of the Colorado Plateau.

Trees are being attacked by drought and higher-than-average temperatures in recent years, but are also sometimes being aided by an excess of carbon dioxide, a greenhouse gas.

Nine tree species in the Southwest have shown "significant mortality patterns, and there might be more," said Neil Cobb, biology professor and director of the Merriam-Powell Center for Environmental Research.

The pinyon pine in northern Arizona is among the more vulnerable because the Flagstaff area is among the lowest of the elevations and warmest climates where it survives.

Death rates among pinyons in recent years range from 40 percent to 80 percent in some stands, according to recent research.

Earlier predictions said the tree was dying in many places due to drought. New projections say the species could die out in most of the state in coming decades, across hundreds of miles, with potential impacts to other species that rely upon it.

Flagstaff's average temperatures have increased 2.3 degrees from 1970 to 2007, according to research from retiree Richard Hereford, formerly of the U.S. Geological Survey.

Papers by multiple researchers have projected that the Southwest will grow increasingly arid in future years and decades.

WHERE CARBON DIOXIDE FITS

Northern Arizona University Junior Susannah Tysor, a biology major, signed on for a project to look at tree ring data, and what she found was surprising.

Most tree rings in pinyons get thinner as the tree gets older, but these were growing larger.

She looked at data from the 1300s to recent years.

In the 1950s and 1970s, the tree rings started getting fatter, unpredictably, unlike any of the previous decades dating to 1380.

Tysor ran mathematical models to account for different factors, but settled on one: "Carbon dioxide is having an impact on the trees," she theorized.

If there is an upside to trees having much more carbon dioxide in the atmosphere than hundreds of years ago, it is that drought- stressed plants don't have to open their pores as widely to absorb carbon dioxide, saving them water that would otherwise be lost in their form of breathing, Tysor said.

The trees that survive see more growth, and this explains the wider tree rings.

But at the same time, many of these trees die due to higher temperatures and stress from drought.

Tysor's model could be a template for projecting which forests survive and which die nationwide amid global warming and changing weather.

It could help government agencies make policy, wildlife managers project what an ecosystem will look like, and home buyers decide where they eventually want to live, she said.

"We want to know what the Southwest is going to look like in 50 years," Tysor explained.

NAU researchers are also looking at genetics, trying to understand what determines which trees die versus which adapt to drought and higher temperatures.

CLIMATE AND THE LANDSCAPE

NAU is a federal center for climate change, in charge of awarding competitive research grants to researchers across the West.

Researchers linked to NAU are working on projects to ask whether pine beetles could affect a forest's ability to store carbon, how an earlier spring could affect some high mountain forests, and how such organisms as biological soil and fungus could respond to climate change.

Researcher Ken Cole, of the U.S. Geological Survey in Flagstaff, takes a very long view, looking at climate and vegetation changes over thousands of years.

Currently, he is using climate projections from scientists around the world, via data from the International Panel on Climate Change, to map what might happen to ponderosa pine, Utah juniper, sagebrush, grasses, spruce, Douglas fir and bristlecone pine over the next century.

He's studying species between the San Francisco Peaks and the Colorado River to project what increasing dryness and temperatures could do, even amid uncertainties in global temperatures to come.

Cole says the pinyon will probably die off, and ponderosa pines will probably survive.

"It's possible that this increase in carbon dioxide could have a tremendous effect on all kinds of plants and animals, mainly plants though," he said.

Cyndy Cole can be reached at 913-8607 or at ccole@azdailysun.com.