Once the flames die down — make sure to get some pictures of Arizona’s stately ponderosa pine forests.

Your grandkids will want to know what they looked like.

At least, that’s what recent research focused on changing vegetation patterns: Not just in Arizona, but worldwide.

One Arizona study has concluded ponderosa pines may disappear before the end of the century, some six million acres from the Grand Canyon to Alpine.

A second study has concluded that vegetation patterns are changing right now faster than they did at the end of the last Ice Age.

Wildfires are playing a big role in the transformation. Fires charred a million acres in Arizona last year and almost 600,000 acres this year. The monsoon has saved us for now, but the rest of the West continues to burn.

But it’s not just the fires. A rise in average temperatures is also playing a role.

If current trends continue, the ponderosa pine forests that dominate millions of acres above about 6,000 feet in Northern Arizona will likely shrink to isolated pockets in coming decades, predicted Los Alamos Laboratory climate scientist Park Williams in a study published in Nature Climate Change.

Williams developed a climate model based on 13,000 tree ring samples from 300 sites to create a “forest drought-stress index.” He then combined the tree ring records documenting annual growth patterns with climatological and historical records.

The study showed both winter snow pack and summer temperatures have a big impact on the survival of ponderosa pines. The heat-related rise in vapor pressure in the summer and fall effectively sucks more moisture out of leaves, pine needles and the soil.

“The majority of forests in the southwest probably cannot survive in the temperatures that are projected,” Williams concluded.

The current drought started in about 2000 and is now ranked as the second worst drought since AD 1,000. Another drought in the 1200s likely played a key role in the collapse of ancient civilizations throughout the Southwest. Moreover, a continent-wide drought from 1572 to 1587 affected most of North America and killed many of the conifers in the southwest. He found that his drought stress index not only the growth patterns in the tree rings, but tree mortality associated with wildfire and bark-beetle outbreaks.

His climate models predict that without a change in the trend, drought will become the new normal after about 2050.

Of course, it’s not just Arizona.

The planet’s vegetation is changing faster right now than at any time since the end of the last Ice Age, according to a study published in the journal Science by researchers from the University of Wisconsin.

The findings stemmed from a global survey of pollen, including fossilized lake bottom deposits going back 18,000 years — when a planetary 10-degree warming ended the ice age.

The International collaboration involved hundreds of scientists and a meticulous analysis of pollen counts gleaned from drilling into lake bottoms — many of them now dried up. The study captured thousands of years of changes in plant communities in 1,100 different sites.

Changes in the plant communities peaked 8,000 to 16,000 years ago as the last Ice Age ended, with the timing depending on the continent. Wobbles in the planet’s orbit, changes in the composition of the atmosphere, changes in ocean circulation and a feedback loop as glaciers melted into the ocean all likely played a role.

Ecosystems then stabilized for about 4,000 years, before change began to once again accelerate. That roughly corresponds to the onset of human agriculture, which had a big impact on plant communities.

The rate of change today exceeds the peak rate of change at the end of the Ice Age.

The researchers concluded that human agriculture likely started to accelerate global shifts in plant communities and the recent rise in average global temperatures has supercharged that change.

Peter Aleshire covers county government and other topics for the Independent. He is the former editor of the Payson Roundup. Reach him at paleshire@payson.com

(8) comments


I love how the study talks about historical cycles, but then goes on to blame agriculture. Even if human caused global warming was true, agriculture accounts for just a fraction of these supposed greenhouse gases. Agriculture and livestock grazing actually sequester carbon. What a garbage totally bias story. If you want to save the ponderosa pine forests, then log and thin them.


Better read the article again - it does NOT say agriculture was responsible for climate change. It says "That roughly corresponds to the onset of human agriculture, which had a big impact on plant communities." That's because millions (billions?) of acres have been cleared of their natural plant species for agriculture.


The research in the WMI story gives one of many reasons it is time to halt the “let it burn” forestry approach. The odds of it growing back are not good.

In early July, land managers near the California-Nevada border let a small ¼ acre fire burn and smolder for several days, and the “monitored”/”managed” wildfire has now burned nearly 70,000 acres. There’s not only the loss of the landscape, but the loss of homes, loss of breathable air, etc.

A report, “Before a wildfire grew into an out-of-control blaze, the Forest Service decided to let it burn” is at: https://www.cnn.com/2021/07/23/us/california-tamarack-fire-burn/index.html


Fire is a natural and essential part of any healthy forest as it is the only way to manage millions of acres of forest and the tons of biomass they create every year. Fires will start whether we want them to or not and we must use regular burns to give firefighters a better chance of controlling the fire when they do. Loss of homes and landscape is what occurs when a fire goes uncontrolled. A couple weeks of smoke in the spring is worth it to give the firefighters a better chance.


Experienced people, including ecologist George Wuerthner and wildfire expert Frank Carroll, are reporting TOO MUCH intentional burning is being done to have healthy forests.

Unfortunately, this is damaging human health, too. Research that appeared in the medical journal Pediatrics in 2021 concluded that “Wildfire-specific PM2.5 was found to be about 10 times more harmful on children’s respiratory health than PM2.5 from other sources” (such as traffic emissions).



From George Wuerthner’s book:

In Wildfire, a project of the Foundation for Deep Ecology, more than 25 fire ecology experts ― including Eugene's Timothy Ingalsbee ― propose that wildfires are good, and that people's attempts to control them ultimately backfire.

As for Frank Carroll, calling him an expert is a stretch. Just because he has experience doesn’t make him experienced. The articles I saw from him are light on facts and heavy on conjecture. Sounds like he has an agenda to me.


Oh yeah, from the first sentence of your research journal:

“Exposure to airborne fine particles with diameters ≤2.5 μm (PM2.5) pollution is a well-established cause of respiratory diseases in children; whether wildfire-specific PM2.5 causes more damage, however, remains uncertain.”


In regard to “fire is good” the old saying that “you can have too much of a good thing” comes to mind.

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