Climate Change Likely To Transform Rim Forests

Growing body of research predicts mix of trees in Rim Country will change dramatically in coming decades


Growing evidence suggests that a predicted 5- to 9-degree warming of the planet by 2080 will dramatically accelerate an already documented shift in forest times. That could mean ponderosa pine forests like this stand shown on the Mogollon Rim will retreat — especially around Payson.

Growing evidence suggests that a predicted 5- to 9-degree warming of the planet by 2080 will dramatically accelerate an already documented shift in forest times. That could mean ponderosa pine forests like this stand shown on the Mogollon Rim will retreat — especially around Payson. Photo by Pete Aleshire. |

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Don’t get too attached to any of the ponderosa pines in town.

Odds are, they’ll fall victim to a rapid transformation of the forests throughout northern Arizona in coming decades.

That’s the conclusion emerging from a number of studies that have concluded rising average temperatures and deepening drought have already triggered a huge “migration” of tree species across the West.

Payson balances on the ecological knife-edge between different ecosystems. Head south toward Rye and unbroken hillsides of pinyon and juniper dominate. Head downhill a bit farther and the scrubby trees give way to brush, which then gives way to saguaro. On the other hand, head uphill from Payson toward either Tonto Creek or Pine and towering, yellow-barked ponderosa pines quickly replace the squat junipers.

Small shifts in temperature and rainfall produce those dramatic changes in the nature of the forest.

All of which means Payson residents will likely see dramatic changes in the nature of the forests that surround them on every side, according to a growing body of evidence.

For instance, vast forests of trees that have held their own for centuries will likely decline or die out over a wide region, concluded researchers from Oregon State University and elsewhere in a study published in the journal Ecological Modeling.

The survey relied on a four-year accumulation of satellite images to track the shifts of 15 different species of coniferous trees in 34 different “eco-regions,” including ponderosa pine.

The researchers then applied their observations of recent changes to computer models predicting the impact of a projected 5- to 9-degree increase in average temperatures by 2080.

The study concluded that the temperature rise would produce the most dramatic changes in the areas with the harshest climate. That could include some six million acres of ponderosa pine forest in northern Arizona in the central highlands between the Grand Canyon and New Mexico. This largest ponderosa pine forest in the world lives on the edge of drought and has suffered wrenching ecological changes in the past century that has resulted in an overcrowded, overstressed forest.

Another 18-year study of the response of 27,000 carefully monitored trees to temperature and moisture drew similar conclusions.

The pine, elm, beech and magnolia trees proved much more vulnerable to drought and rising temperature than the researchers expected.

The National Science Foundation funded the research, which was published in the journal, Global Change Biology.

The researchers found that both tree growth rates and seed production responded strongly to even small shifts in temperature and soil moisture.

Those findings gave added weight to yet another study focusing on the frightening and mysterious decline of aspen trees throughout the Southwest.

The research focused on Sudden Aspen Decline (SAD), a widespread die-off of the tremulous, white-barked, high-elevation poplars that quiver in the sunlight along the Mogollon Rim and on the slopes above Flagstaff.

Researchers from Stanford, the University of Utah and the Carnegie Institute published their findings in the Proceedings of the National Academy of Sciences.

They set out to explain the widespread death of aspen groves throughout the West in the wake of a severe drought that persisted for a decade, relented for two years and now appears to have returned.

Turns out, the aspen don’t starve — they die of thirst.

The evidence points to changes that take place in the roots that reduce by 70 percent the amount of water they can pass along to the trunk and up into the leaves. As a result, even though the tree may survive several years of drought, its ability to take advantage of water in the soil remains crippled even after normal rainfall returns.

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