Forests occupy nearly a third of Earth’s land surface, providing humans and countless other species with a wide range of benefits and services, from ecological functions such as water and air purification to goods such as lumber and paper.

But a report released by the United Nations found that climate change is expected to worsen over the next century as greenhouse gas emissions continue to increase, a trend that experts say will have consequences for the health of forests worldwide.

Robert Scheller, a professor in the Department of Forestry and Environmental Resources at North Carolina State University, studies the impacts of climate change and human activities on long-term landscape health and developing models to forecast landscape change to inform policy and management decisions.

Scheller’s book, Managing Landscapes for Change, explores how future landscapes will be shaped by pervasive change and where, when and how society should manage landscapes for change. In the following article, Scheller explores the potential impacts of climate change on forests across the United States and the industries they support.

Tree Migration

In response to climate change, Scheller said some tree species will shift their ranges and migrate into landscapes in which they don’t typically grow — a process known as species redistribution.

“Climate change can create new habitats for tree species and make existing habitats unsuitable. And like any other living thing, trees go where they can survive,” Scheller said. “This process is already underway.”

Some tree species are migrating uphill and northward as temperatures increase, while other species are migrating downhill and westward as changing precipitation patterns create drier conditions. 

In North Carolina, for example, palmetto trees could become more common in the next 50 or 60 years as they migrate from nearby states like Georgia and Florida, according to Scheller.

“Species redistribution isn’t necessarily a bad thing. But it’s possible that some trees could go extinct, especially those with small ranges,” Scheller said. “So if there are species we’re concerned about, we need to collect their seeds and plant them in areas where we think they’ll survive climate change.”

Wildfires

Climate change is creating warmer temperatures, deeper droughts and drier vegetation, according to Scheller. These conditions will persist in the coming decades and lead to an increase in the extent, intensity and frequency of wildfires.

“We’ve created the perfect conditions for wildfires, and I don’t see that changing anytime soon,” Scheller said. “In the South, states like North Carolina and Florida have a lot of roads that prevent fire from spreading. But under the right conditions, a large fire could certainly cross roads and cause a lot of damage.”

Since 2000, an annual average of 72,600 wildfires have occurred across the U.S., scorching an average of 7 million acres of land, including forests, each year. That’s more than double the average annual acreage burned in the 1990s.

Scheller is currently examining the potential impact of climate change on wildfires in the southeastern U.S., with a focus on the Appalachian Mountains where fighting the blazes is often difficult because of the region’s rugged terrain.

Severe Droughts

With average global temperatures rising due to climate change, Scheller said historically dry areas across the U.S. are likely to experience less precipitation and increased risk of longer, more intense droughts that could cause forest dieback.

During a drought, trees close their stomata, the pores that let in carbon dioxide, and rely on stored sugars and starches. If trees run out of those energy sources before the drought is over, they can die from “carbon starvation,” Scheller said.

Trees can also lose water faster than they can absorb it. This causes air bubbles to form inside the tree’s water-conducting tissues, blocking the flow of water and nutrients from the roots to the leaves. This disruption starves the tree and can ultimately lead to its death.

“Some landscapes are getting so dry that they can’t support forests at all. It’s pushing forests out of their physiological limits. This is especially true in the southwestern U.S.,” Scheller said. “But that doesn’t mean every tree is going to die. Some forests will be replaced by shrublands.” 

Scheller added that the southeastern U.S., in contrast, may experience more frequent, shorter periods of precipitation due to climate change, resulting in increased forest productivity and growth. 

Pests and Pathogens

Rising global temperatures and severe drought cycles break down the natural defense mechanisms of trees while simultaneously extending the geographic territory and breeding seasons of destructive insects and pathogens.

“Trees have less energy to defend themselves when they’re stressed out by drought and other challenging conditions. They become more vulnerable to insects, fungi, bacteria, viruses and so on, Scheller said.

At the same time, milder winters allow invasive larvae to survive and migrate to higher altitudes and latitudes, while longer, warmer summers double the annual reproductive cycles of species like the bark beetle.

These effects are already evident in the western U.S. where pests populations are causing massive tree die-offs, with the bark beetle alone destroying 45 million acres of forest in recent years.

“Wildfires get all the press, but insects are killing far more trees in the western U.S. than wildfires,” Scheller said.

Carbon Competition

As consumers and stakeholders increasingly demand that polluting companies adopt more sustainable practices, many are implementing carbon offset and reforestation projects in an effort to reduce their environmental impact.

Carbon offset projects allow these companies to pay landowners to plant or preserve trees so they pull carbon dioxide from the air and store it, allowing them to balance out their ongoing greenhouse gas emissions.

Scheller said he expects carbon offset projects to inflate the cost of paper, lumber and forest products in the coming decades as landowners choose to retain trees, which will ultimately shrink the industrial timber supply.

He added that reforestation — where companies plant new trees or restore damaged forests — could create even more “economic uncertainty” for the forest products industry, which contributes hundreds of billions of dollars in economic output every year.

“A lot of companies are looking into reforestation, which is great for places like the Amazon and Africa. But it will create a lot of competition for land, and that could totally upend the forest products industry,” Scheller said.