Rim Country forests face potentially wrenching changes as a result of rising temperatures, according to several recent studies.
On the other hand, controlled burns, forest restoration and protection for the biggest trees could ensure forests will absorb millions of tons of carbon dioxide and so slow the warming trend, according to a second set of recent studies.
The most alarming study for forest lovers — especially in transition zones like Payson where ponderosa pine meets pinon juniper — was published recently in the Proceedings of the National Academy of Sciences.
The study found that trees in 18 percent of the forests in the Southwest have in recent years suffered extremely high mortality rates from bark beetles, wildfires and other tree-disease outbreaks.
“Our study shows that regardless of rainfall going up or down, forests in the Southwest U.S. are very sensitive to temperature — in fact, more sensitive than any forests in the country,” according to Park Williams, a researcher from the University of California at Santa Barbara.
The researchers studied more than 1,000 tree-ring chronologies to determine how temperature shifts affected tree growth in forests nationwide.
The study confirmed a strong link between annual rainfall and tree growth, a link documented in many previous studies. However, the study revealed a new and unexpectedly strong connection between tree growth and death and annual, average temperatures — regardless of rainfall for that year.
The finding offers a glimpse of a significant new danger to forests in the face of rising average temperatures, especially in the Southwest and Rim Country.
Most projections of climate trends predict a steady rise in temperatures. However, scientists are still working on models that will predict the localized impact of that warming trend. For instance, some models suggest that warmer temperatures will pump more energy into the atmosphere, which would generate more storms and perhaps actually increase rainfall in Rim Country. Other evidence suggests that if temperatures rise beyond a certain point, storm systems could move farther north, in many years shutting down the summer monsoons that deliver about half of the region’s rainfall.
But the most recent study suggests that the warming trend alone will cause major changes in Rim Country’s forests, regardless of average rainfall.
The study suggested that ecosystems like a ponderosa pine forest can absorb great year-to-year variations and even incremental changes up to a point. However, those changes can cross a certain threshold, which will then cause rapid, drastic changes.
Suddenly, ponderosa pines will retreat to higher elevations, streams will dry up, snowpack will drop drastically and the whole look of the forest will change, concluded the study authors.
That could also spell big changes for even distant areas like the Valley, which gets the bulk of its water from reservoirs fed by streams that drain from Rim Country.
“Co-author Craig Allen of the U.S. Geological Survey said that changes in forest cover could greatly increase erosion, which would in turn reduce the amount of water that runs into distant reservoirs.
Despite those bleak findings, additional research suggests that forest managers are on the right track now in trying to use the timber industry to thin overgrown thickets of trees to restore more natural, healthy, old-growth forest conditions. In such forests, a much smaller number of big trees would not only reduce the risk of wildfire, but increase biological diversity and the health of millions of acres of watershed.
One recent study concluded that old-growth forests dominated by giant trees continue to remove carbon dioxide from the air for centuries — thereby reducing the projected warming trend.
The international study rebutted previous theories suggesting old-growth trees achieve a balance in the amount of carbon dioxide they absorb versus the amount released. Instead, the most recent study of the carbon balance in many types of old-growth forests show that the big trees continue to remove carbon dioxide from the air for as long as they live. Moreover, by drastically reducing the intensity of forest fires, the old-growth forests prevent the massive release of carbon dioxide during events like the recent Wallow Fire.
That study would seem to support the idea behind the 4-Forests Restoration Initiative, which would revive the timber industry to cut down millions of small trees to allow the surviving ponderosa pines larger than 16 inches in diameter to dominate.
Another recent study verified that such an approach could effectively remove carbon dioxide from the atmosphere by turning fire-prone saplings into wood products.
That study concluded that the amount of carbon dioxide removed from the atmosphere could be increased four-fold if harvested small trees are converted into wood products that can replace steel and concrete.
The industrial process that creates steel and concrete release a lot of carbon dioxide, concluded the researchers from the University of Washington whose study was published recently in the journal Carbon Management.
Young fast-growing forests don’t end up removing much carbon dioxide from the air, since the young trees may lock up carbon dioxide for a few years but then release it when they die and decay or burn.
However, if they’re harvested and turned into particle board, pressed logs or other materials that can replace concrete and steel, they greatly reduce the net release of carbon dioxide, the researchers concluded.