Climate change may alter forest balance in Ozarks

September 20, 2008 08:28 pm

— By Andy Ostmeyer
aostmeyer@joplinglobe.com
Thinned of its golden hickory and blood-red sassafras, the Ozark forest that beckons tourists every autumn could look much different to future generations.
Under one forecast, residents and visitors may see pines dominating the Ozarks’ rhythm of hill and hollow.
Under another, today’s oak-hickory forest could become more open country, evolving into savanna or even grasslands.
A third possibility is a jungly tangle of undergrowth dominated by woody vines such as honeysuckle and poison ivy choking out the next generation of trees by mid-century.
Those scenarios emerge for Ozark forestland under climate-change models. Whatever the region looks like in the future, it will be different than today, the experts agree.
“I certainly would expect forests to change,” said John Shannon, state forester with the Arkansas Forestry Commission and a technical adviser to the Arkansas Governor’s Commission on Global Warming.
The Ozarks has been forested for 35 million years, said Cindy Sagers, who teaches plant ecology and plant biology at the University of Arkansas in Fayetteville, and who is a member of the governor’s commission. She expects a forest will survive in the region in some fashion, but it won’t be the Ozarks of today.
“What we do know is that vegetation zones are shifting,” she said, “so that things that grow in Southern Arkansas can now be planted in Northwest Arkansas.
“There is probably going to be some forest here, but whether it is pine or savanna ...”
Different models
Models put together by the National Wildlife Federation forecast temperature increases of as much as 7 degrees Fahrenheit for Missouri by 2100 if global warming goes on unchecked, and that would “alter the composition of the state’s forests, with southern pines replacing oak and hickory currently prevalent in southern Missouri and the Ozarks.”
In Arkansas, the eastern portion of the state will be “overtaken by longleaf and slash pine, while the rest of the state will be dominated by savanna and woodlands ...
“Global warming could cause 40 to 60 percent of Arkansas’ forests to be replaced by grasslands as slightly warmer temperatures push trees currently suited to the state’s climate northward,” the wildlife federation concluded.
An analysis by the Environmental Protection Agency found temperatures rising an average of 1 to 4 degrees Fahrenheit in Missouri and Arkansas during the summer and 1 to 7 degrees in winter.
“If conditions become drier, the current range and density of forests could be reduced and replaced by grasslands and pastures,” the EPA report on Missouri noted. “Even a warmer and wetter climate could lead to changes; trees that are better adapted to warmer climates, such as (some) oaks and southern pines, would prevail. Under these conditions, forests could become more dense.”
“These changes could occur during the lifetime of today’s children,” the EPA report on Missouri concluded, noting that fire, pests and disease could accelerate changes.
In Arkansas, not only would southern pine forests advance northward, but scrub timber and noncommercial varieties of oaks would also expand their range, noted the EPA.
A third analysis, this one in 2006 by Jacqueline Mohan, then a scientist with the Marine Biological Laboratory at Woods Hole, Mass., noted that rising carbon dioxide will lead to the proliferation of vines such as poison ivy and Japanese honeysuckle in forests around the country.
Because these plants don’t have to generate the wood structure to support them the way a tree does, they grow much faster. Poison ivy grew twice as fast in an environment simulating projected CO2 levels at mid-century compared to poison ivy exposed to today’s levels of the gas. Not only was it growing faster, but the plant’s oil that causes skin irritation was more potent.
“Increasing abundance of woody vines is causing increased tree mortality and reduced tree regeneration in forests around the globe, potentially resulting in shifts in community composition,” the study concluded.
Rain the issue
Doug Inkley, senior scientist with the National Wildlife Federation, said all of the models for the region under global warming indicate rising temperatures, but less certain is the rainfall forecast. Less rainfall would lead to the drier Ozarks, while more rainfall would lead to the expansion of the range for southern pine species, for example, he said.
But even if rainfall increases, soil moisture could still continue to decline because of warmer temperatures, he noted.
In a wetter future, species of trees now associated with Louisiana, for example might migrate northward, such as southern magnolia and live oak, which is most often seen draped with Spanish moss, said Shannon, with the Arkansas Forestry commission.
“If over the decades climates become warmer, we’d see those trees naturalized in Arkansas,” he said.
Loblolly pine is another species that might march toward Missouri with the change.
“I could see that creeping north,” Shannon added.
Louis Iverson, resource ecologist for the U.S. Forest Service and one of the agency’s leading researchers on climate change, also forecasts an expanding range for loblolly pine.
“That’s a species that we show could gain a very high amount in that part of the world,” he said
“There are some southern oaks that will gain,” he added, referencing southern red oak and shumard oak, but the tradeoff will be the loss of northern red oak and white oak.
“Other things that could lose ground are walnut, dogwood, some species of hickory, sassafras. Beech is another, so is sugar maple. These would be migrating north.”
He also added that he is skeptical of models that forecast an Ozarks succumbing to grassland and savanna.
No change yet
Jerry Presley, a forester who rose to become a former director of the Missouri Department of Conservation, and who now works as a consultant for the Missouri Forest Products Association, said he is skeptical of computer models that predict dramatic change.
Asked if he has seen any changes yet, he replied: “None whatsoever.”
Shannon, too, agreed, saying: “I have not observed that,” but he was quick to note that the Ozarks isn’t on the “edge” and might not see changes as rapidly as the Arctic, for example.
Both men also noted that Ozark forests provide thousands of jobs as landowners cut everything from walnut to red oak for furniture, flooring and pallets.
Oak and hickory make up about three-fourths of the forested acres in Missouri, with softwoods, such as pine, comprising only about 3 to 4 percent of the total forested area. Composition is similar in the Arkansas Ozarks, Shannon said.
More than 27,000 people work in forest product industries in Missouri, Presley said, with an economic impact estimated at $909 million. The bread-and-butter species are the oaks.
“We do not have a good market for pine,” he said. “Shortleaf pine is our only native pine species.”
Always changing
Part of the problem with envisioning the forests of the Ozarks is that the region has never been static. There is no baseline model for what the region should look like. The Ozarks has continually weathered temperature extremes and climate change, say these experts.
“We don’t know what Ozark forests ought to look like,” explained Sagers, adding that humans have always had an impact on the landscape, introducing exotic species, for example.
Twenty thousand years ago, during the last ice age, glaciers pushed south and much of Missouri was covered by spruce-fir forests similar to Canada. As recently as 8,000 years ago, the climate was warmer and drier than it is today, more hospitable to plants and animals found in places such as New Mexico and Arizona. Only in the last few thousand years has the climate in the region been comparable to today’s.
Each of these periods has left its fingerprint in terms of trees and other plant and animal species that still survive in the region, sometimes only as islands, like the coves of beech that Sagers noted can still be found in the Arkansas’ Ozarks, or as outliers on the far limit of their range, like the ashe juniper found in colonies in southern Missouri. It is a relative of the cedar that is more common in Texas.
Dennis Figg, wildlife program supervisor with the Missouri Department of Conservation, said it is impossible to tell how the Ozarks will evolve under climate change because many of the models are continental or global in scale and it is difficult to localize them to a region or a species.
Nevertheless, his agency is trying to anticipate climate change such projects as restoration of bottomland forests in parts of Missouri. They are no longer are just reforesting with trees that were historically there, but those that might thrive in a future altered by climate change.
“The conditions we have today are not similar to anything we have had before,” he added.

Songbirds
“The breeding ranges of 31 species of songbirds, including three species of sparrows, eight warblers and two tanagers, could shift out of Arkansas forever due to climate factors and changing food sources.”
Source: National Wildlife Federation

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