Planning a Future Forest

This spring in northeastern Minnesota, contractors for The Nature Conservancy (TNC) fanned out in a pine and aspen-studded forest north of Lake Superior and plunged steel hoedads into the rocky soil.

Working quickly to avoid the rainy season, they planted more than a quarter million seedlings of white pine, white spruce, and other conifers to help restore trees lost to logging and timber harvests.

That conifers were being planted was no surprise. That stretch of Minnesota is home to the Boundary Waters Canoe Area Wilderness, a 1.1-million-acre swath of unbroken conifer, birch and aspen forests and rocky lakes known as “paddler’s paradise.” Northeastern Minnesota is part of the northern coniferous forest, or boreal forest, which stretches clear to Hudson Bay.

But in an unusual move, The Nature Conservancy workers also planted more than 30,000 red and bur oaks. A minor component of the northern coniferous forest, they are much more common to the south and west. Some of the trees came from seed sources more than 200 miles away.

“It’s part restoration, but it’s part research project, too,” says TNC forest manager Chris Dunham. “With climate change, some of the researchers are saying you might want to start planting trees that were grown from a seed source that’s one step south.”

Boosting forest diversity

Besides helping protect one of the earth’s best defenses against climate change, boosting forest resilience is important for industries that depend on trees, including biofuel companies working to turn woody biomass into energy or fuel. Dunham and Nature Conservancy scientists are anticipating a day in the not-too-distant future when the climate of northern Minnesota might resemble that of present-day Iowa. At that point, the forest of today might wither in the heat, fail to set seed, or succumb to new insect pests. And that’s exactly the scenario they hope to ward off.

“We’re betting on red oak and some of these other species that could potentially fill these gaps if birch doesn’t regenerate or if spruce or jack pine don’t regenerate – some of these species that we think are on the edge of their range already,” Dunham says.

It’s a bit of a crapshoot, because while scientists are in broad agreement that the earth will warm, no one knows how much warmer it may become, or how temperature and rainfall will change in specific locations. 

“You’ve probably heard this analogy before: we’re keeping the investment portfolio diverse so that when one species isn’t handling things well, another species can fill in the gap,” says Meredith Cornett, Ph.D., TNC’s director of conservation science. 

Trees under stress

Planting species from out of their usual range is one of several bet-hedging strategies being considered to deal with uncertainties of the future. Forests are changing fast, from both direct and secondary effects associated with global warming. 

“Forests produce a whole lot of things that people like—wood products, aesthetics, recreation, water. You can go on and on,” says Glenn Howe, Ph.D., associate professor of forest genetics at Oregon State University. “Certainly ecosystems will exist in the face of climate change. But whether those ecosystems will provide the same kinds of benefits that humans are looking for in the shorter term is the big question. And it’s likely that in many cases they won’t.”

Researchers are already seeing forest problems associated with global warming. Species are moving. Forest fires are increasing. Early snow melts have exposed shallow roots to freezing temperatures, killing millions of yellow-cedar trees in Alaska, according to a recent Forest Service report. In addition, snow melt is causing massive die-offs of trees in the Northwest, and sweltering droughts have recently killed hundreds of millions of trees in Texas and other states. 

With forests under stress, new tree diseases are emerging as well. Heavy rain and long periods of wet, warm weather, for example, leave some species ripe for infection. And as the Forest Service report notes, “The patterns and rates of wood decay, caused by forest fungi, are also expected to change, which will influence forest carbon cycles.”

Forest resilience: Help wanted

Above the Metolius River in Oregon’s Cascade Range, a raging fire cleared the slopes of ponderosa pine and some Douglas fir in 2002. Lower-elevation sites have failed to regenerate even pines. If drought becomes the new normal, say Oregon State University researchers, aggressive management may become necessary. 

Researchers are already seeing forest problems associated with global warming. Planting species outside their usual range is one of several hedging strategies being considered to deal with uncertainties of the future.

Outcomes from secondary effects have been equally spectacular. Among them is the die-off of whitebark pine, ravaged by mountain pine beetles, in the northern Rockies. Once checked by cold winters, the numbers of native beetles exploded as weather warmed. The newly abundant beetles killed drought-stressed pines, leaving millions of acres shrouded in dead, brown trees. 
Left alone, forests under stress have several ways to adapt, Howe says.

First, he says, trees can tough it out, perhaps acclimating to climate changes.

The second way forests can evolve is through natural selection, as the less fit die out and the better suited survive. Trees are at a disadvantage compared with many other organisms, though, because the opportunities for selection and evolution are widely spaced. Old-growth trees in the northern states took root during the Little Ice Age, for example, when conditions were far cooler than they are today.

However, new research from Trevor Keenan of Macquarie University in Australia suggests that broad-leaved trees are evolving to use water more efficiently at a much faster rate than expected. Due to increasing amounts of carbon dioxide in the air, the trees can get sufficient amounts of the gas even when their leaf pores are partly closed. Because that reduces water evaporation rates from the leaves, trees may not need to pull in as much water from the ground and could become more resilient, Keenan predicts. 

Finally, trees may spread to more suitable areas through the movement of seeds and pollen—though as trees, they move neither very far nor very fast. “Certainly as glaciers interacted with the landscape around here, populations moved and they continued to move,” says Howe. “The question is, can they continue to move fast enough?”

Not necessarily. “If you left things to adjust naturally, you’d get species migrations and you’d also get gene flow. . . but with a great deal of unhealthy forests in the interim,” says Sally Aitken, director of the Centre for Forest Conservation Genetics at the University of British Columbia. 

The disease-ridden whitebark pine forests of the Rockies are a case in point. In the years it takes for the forest to adjust, they may produce few forest products and provide poor habitat for wildlife that once took shelter there, she says.

Forest bioenergy: Preparing for climate change

Scientists and forest managers say one way to prepare for an uncertain future is through better silviculture—managing forests better through techniques such as thinning and limited clearing. This can reduce the risk of fire, open the forest floor to sunlight, and encourage more ground cover species, as well as providing forage for wildlife and reducing competition among individual trees for nutrients and sunlight. All this tends to increase the resilience and vigor of a forest.

Large-scale thinning operations produce a huge supply of trunks, limbs, branches, and other debris, often called simply biomass. Rather than stacking and burning it at a cost, such biomass could be an opportunity—a resource that pays for the work of forest management. 

“The reality is, we will never have enough appropriated money to do all the work if there isn’t value in the products that are being removed,” says Dave Atkins, national biomass program manager for the U.S. Forest Service. 

So the Forest Service, which manages 193 million acres of national forests and grasslands, is working to find a market for the biomass created by thinning and logging. To date, they have poured more than $2.3 million into renewable energy projects. 

“Certainly as glaciers interacted with the landscape around here, tree populations moved and they continued to move. The question is, can they continue to move fast enough?” Dr. Glenn Howe, Oregon State University

Larger industries are also investing millions into research on resilient forests. Weyerhaeuser, a leading wood and paper company that also works on forest biomass, has an entire center devoted to combating climate change with improved forest practices. The pulp and paper giant Georgia Pacific has joined Better Practices, Better Planet 2020, a sustainability initiative of the American Forest & Paper Association. And International Paper has teamed up with a southern forest protection network to promote forest sustainability certification. 

New energy projects, in turn, may help fund research into evolving forests. Cobalt Technologies, for example, announced in 2010 that it had produced biobutanol from beetle-affected lodgepole pine.

The greater the value added, the better, says Atkins. “Otherwise we’re paying people to pile that up and burn it. All that costs money. That means you can’t do as much of the other work.”

Assembling a future forest

Another step to plan for a more resilient forest is to identify and plant the species of trees and other plants that will flourish in a changed climate in the future. 

Just recently, Sally Aitken met with a government scientist from Scottish Natural Heritage. With little diversity in its forests already, Scotland is in danger of losing its ash trees from the fungal ash dieback that has swept Europe, the forester explained. He was considering the radical step—radical to ecologists—of introducing resistant stock from the mainland. 

Bringing in non-local varieties of trees already growing in an area, sometimes called “assisted gene flow,” is appropriate when “the local genotype is no longer the best adapted,” says Aitken. There are some risks, she notes. Bring a species from too far away, and it may not be suited to the existing climate. Its genes may have been isolated from the local variety for so long that the two strains fail to reproduce. Or its favorable adaptation is outweighed by other shortcomings, such as endemic insect pests or diseases.

Nonetheless, Aitken’s lab is sequencing genes in nearly 1,000 individual trees and testing different varieties of western tree species. “If we can identify the right materials to plant for future climates, we should be able to increase productivity of forests for economically important species,” says Aitken. “We may also be able to restore species for conservation.” 

And rather than simply move the genotype deemed most suitable, Aitken says foresters should move several new genotypes into areas to hedge for different possible changes of climate and secondary effects such as insect pests. “That really harnesses what’s called the portfolio effect,” she says.

More controversial among ecologists than shuffling varieties about is “assisted migration”—moving species to new locations where they never before existed. Says Aitken, “When you talk about moving species, some people, for good reason, get more concerned, particularly (those) who have seen the problems that invasive species have caused.”

The maps show current and projected forest types. Major changes are projected for many regions. For example, in the Northeast, under a mid-range warming scenario, the currently dominant maple-beech-birch forest type is projected to be completely displaced by other forest types in a warmer future.

Even so, there’s interest, even among ecologists, in moving species as climate shifts. “The argument for expanding the range of the whitebark pine into areas where it doesn’t grow, but could grow, is compelling,” Aitken says. “It’s dying back in most of its range. But we also see that we’ve got some big areas in British Columbia that whitebark pine… just hasn’t gotten that far.”

With this in mind, Aitken has been trying to determine how well existing models can predict where the tree will find suitable conditions. They have been quite accurate, it turns out, bolstering the idea that the whitebark pine can be saved by planting it into new areas more suited to its survival. 

In fact, shifting species a relatively small distance may have advantages, experts say: Land managers are unlikely to create entirely novel assemblages of species, as they would by moving a species across a continent or ocean. “You’re not likely to get these unexpected species interactions,” such as takeovers by invasive species, Aiken says. 

“We can’t move everything,” Aitken notes. But, she says, we have a special duty to trees. Trees determine the architecture of a forest, creating shade, blocking wind, providing vertical habitat for birds and small mammals. Says Aitken succinctly, “You don’t have a forest without trees.”

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