What puts forests more at risk — climate change or attempts to counter it?

Along the Eastern Seaboard, forests are expanding, but also showing signs of stress. Some blame the stress on climate change. Others insist that’s off-base.  

In a 19th-century farmhouse deep in northern Pennsylvania’s Bradford County, Nancy Baker is looking at family photos dating back four generations.

One shows her grandfather with a team of horses on clear cut land. Another shows her mother and aunt on the same farm as a small child. Baker also has a series of aerial photos going back to 1939, which show how the forest cover has evolved in the past 70 years.

Her home was built by her great grandfather, Joseph Morrow Gamble, a Scots-Irish immigrant who cut timber from the virgin forest and shipped it down the Susquehanna River.

The story of how Baker’s family used its land to make a living was replayed up and down the East Coast after European settlers arrived. Her great grandfather cut down woods for timber. Then he turned to farming, yanking rocks from the stony soil to mark out cow pastures. His children inherited the land. But in the 20th century, their children left for better jobs in town. Baker’s own parents became teachers.

With the land left to itself, the forests returned. So Baker grew up playing in the woods and learning how to fell a tree ambidextrously with an ax.

“When we inherited this land from my mother I said, ‘OK, it’s our turn to steward the land,'” said Baker. “But how are we going to do this?”

Forests front and center 

It’s a question a lot of foresters are debating in the age of climate change. But they don’t all agree on what to do.

This week’s U.N. report on climate change gave some stark warnings. It even prompted Ban Ki Moon, United Nations secretary general, to urge investors to drop fossil fuel stocks in favor of renewables.

Advice to policy makers from the Intergovernmental Panel on Climate Change includes the restoration of forests, which play the vital role of absorbing carbon and limiting greenhouse gases.

In Pennsylvania, as along the entire eastern seaboard, forests have been expanding. But eastern forests are also in trouble, showing signs of stress.  Scientists are at odds over how to help them. Some people fret about the changes and blame global warming. Others say the role of climate change in the  evolution of eastern forests is exaggerated.

Baker is in the fretting camp. She says she likes to walk through her woods slowly, in order to be more observant. And she’s been doing this for all of her 70 years. Baker says in recent decades, the changes to her forest have become abrupt and she sees signs of climate change every day.

“The death of a tree is pretty normal to me,” said Baker. “But it’s like, in human beings, we say someone lived a good life if they lived a long life. But some of these are being cut short.”

So Baker, who has a graduate degree in forest ecology, is taking steps to heal what she sees as a sickness in her woods and prepare them for a warmer climate.

“It is warmer than they are used to,” said Baker. “I see trees dropping out of the ecosystem. I see new species coming in that are not native. And so the whole system changes.”

Victim and solution 

Warming is not always bad for all trees. Some species will thrive in new areas; others could die out. So in the calculus of global warming, forests can play the dual role of victim and solution.

Scientists are hesitant to put all the blame for struggling tree species on climate change. Instead, they talk about the increasing temperatures as adding “stressors.” For example, pests are a major stressor, and they generally do better in warmer weather. They can migrate and adapt more quickly than a tree.

The state’s climate change assessment says Pennsylvania’s forests are still in good shape. But the study warns of unknown consequences 50 to a 100 years from now. The report lists the American beech, sugar maples, black cherry and hemlock as among the trees not likely to adapt well to warming temperatures.

Overall, spring will come earlier and fall will come later. One study predicts the state’s growing season will increase by 29–43 days within this century.

To Baker, who grew up playing in these woods, not trying to save the threatened trees is unthinkable.  For her, this goes beyond the forest’s value as an antidote to global warming, beyond the vital cooling shade that hemlocks provide for the brook trout in Panther Lick Creek.

To her, the stakes are a matter of the spirit:

“We look to the forest as comfort and solace,” said Baker, “and it hurts us if something goes wrong with it. If you care for a person and something happens to that person, it damages your soul to some degree. So damage to the forest, damages our psyche.”

Helping nature along 

Baker is now working with a forester on a plan to improve the health of her woods.  She pulls out and poisons invasive species, and tries to treat her sick trees. It’s an expensive and time consuming process that might not work. She’s also planting new species that are better suited to survive a warmer climate.

Scientists call this “assisted migration.”

Trees can’t just pick and move, so it takes a long time for them to migrate naturally.  Some advocate helping Nature along by planting more typically southern species up north. Today Baker’s land is a second or third growth forest, filled with ash, hemlock, maple, birch, and beech.

This is pretty typical for this area. But the sugar maple and yellow birch will likely not survive warmer weather, and the ash, hemlock and beech trees are all afflicted with pests.

Walking through her woods, Baker points out wire cages that surround small saplings. These are tulip poplar trees, which today thrive in southeastern Pennsylvania and Virginia. Baker is hoping to replace her diseased and dying trees with new species more adapted to warmer temperatures. Each carefully placed seedling has been caged to protect it from hungry deer.

All across Pennsylvania, ash trees are dying. Baker shows a visitor her stand of ash. Once strong and healthy, these trees are now barren at the top, and pose safety risks to hikers. When the ash trees weaken, a strong wind can easily topple them.

“It’s just a disaster,” Baker said.

Baker says the warmer winters had already begun taking a toll on the ash tree even before the arrival of the Emerald Ash Borer, a stunningly beautiful little beetle-like post native to Asia. And Pennsylvania’s state tree, the hemlock, is also on its way out. Its nemesis, the woolly adelgid is making its way north due to warming temperatures and wiping out the tree up into Maine.

“This is a whole grove of hemlock in here,” Baker said as she conducted a tour of her forests.  “The shade here used to be much more dense. You can see the bottom limbs in here are dying. The crowns are thinner than they used to be and that is woolly adelgid. We didn’t used to have it because we normally had cold winter temperatures, maybe two weeks of 20 to 25 degrees below.”

Successions of bitter cold winters can keep pests like the woolly adelgid at bay.  But if the pest keeps spreadig and the hemlock go away, so likely will the brook trout, which need the cooler waters that the hemlocks’ shade provides.

“Unless I do something there will not be hemlock here,” Baker says. “It’ll be a whole lot warmer because the hemlock shades it very efficiently and so the whole woods will switch species. It won’t be dominated by hemlock anymore.”

Two camps on the woods 

The steps Baker is taking are controversial. First, not everyone agrees with her that climate change is the real problem here.  A recent report by a Penn State researcher says the stresses on eastern forests have more to do with 500 years of land use trauma inflicted by European settlers.

Marc Abrams is a lead author of the report, titled “Is Climate an Important Driver of Post-European Vegetation Change in the Eastern United States?”

His answer is no. He says forests are still recovering from a “catastrophic era” in which European immigrants like Baker’s great grandfather timbered and plowed the land, ending thousands of years of planned forest fires by native Americans.

“We’re still within the range of [normal temperature] variability,” said Abrams. “So temperature alone is not destroying her forest. Most of the trees on her property have very large ranges. And are well adapted to temperatures increasing even another degree.”

Abrams says this is a major split among ecologists.

“In ecology, there’s two sides,” said Abrams. “There’s people who believe that land use history is the dominant driving force, and others who say it’s climate change.”

And not everyone agrees with planting new species in preparation for warmer, wetter winters, and hotter summers. Some scientists fear unintended consequences.

A risky remedy? 

About 300 miles northeast of Baker’s land lies the Harvard Forest, in Petersham, Mass. That forest is going through similar changes. Aaron Ellison, a senior research fellow there, opposes Baker’s plan to prepare her forest for climate change.

“We want to feel like we’re doing things,” said Ellison. “We want to plant something, reintroduce wolves, move bison around. Sometimes it’s ok to not do things. And not doing something is actually doing something.”

Ellison says planting new trees and nursing them toward a new forest is too expensive and time consuming to be practical. And history is full of cautionary tales about moving species around.

“So we’re doing this all the time and we’re doing it in a completely haphazard way,” he said. “So if we’re going to do it we might as well do it in a thoughtful way. I disagree with this on principle. But lots of people are thinking of this.”

Instead of planting different trees, Ellison suggested hiring a hunter to kill the deer that eat young saplings: “So what she needs to do is put a fence up, put the hunter inside the fence to wipe out every last deer and leave the fence up and then the regeneration will proceed so fast, and she’ll be delighted.”

Ellison himself is dealing with the hemlock woolly adelgid, which is killing all the hemlock trees on his own 100 acres in western Massachusetts. But Ellison plans on just letting his trees all die and seeing what comes next.

“I’m leaving it alone,” he said. “I suspect it will become a black birch forest and after that I have no idea.”

For Ellison, assisted migration may turn out to be just as damaging as climate change.

“We’re doing an uncontrolled, uncontrollable experiment,” said Ellison. “And as a scientist I’m very uncomfortable when I don’t have controls. So I want the controls and I want to have control. And climate change is an uncontrolled uncontrollable experiment. And in virtually every case, assisted migration is also uncontrolled and uncontrollable.”

Ellison also says many of the pests killing off trees in Pennsylvania are not a result of climate change, but of globalization.

So while Ellison, the Harvard scientist, takes a hands-off approach, Nancy Baker says the forests won’t just rebound by themselves. They need active intervention.

But here’s one thing the two foresters can agree on: Her effort to save her woods is an experiment, with no assurance it will work.

But, as Baker stresses, climate change is also an experiment without a control.

“And that goes contrary to all the scientific method we ever used,” said Baker. “So who knows what’s going to happen?”