Almost everything Nina Wurzburger does — at least in terms of research — relates to forests.

She grew up on the central coast of California, where the Monterey pine forest dominates the landscape. While traveling with her family, she remembers being intrigued by the trees, forests and landscapes that looked so different than those at home.

“I was always inspired by nature,” she said. “All ecologists probably say that.”

Now a professor at the Odum School of Ecology, Wurzburger is still exploring why forests look different. But her current research investigates how individual forests change over time in response to human disturbance.

“Sometimes forests don’t recover,” she said. “The mechanisms that explain whether a forest grows back or not are often hidden below ground.”

It’s important work because as forests change, people may lose the benefits they offer. They provide timber products, filter impurities from water, provide habitat and remove carbon dioxide from the atmosphere.

Hot topic

Wurzburger is an ecosystem ecologist, someone who studies the interaction between living and non-living things in the natural world.

“Many things are difficult to predict if we don’t consider the living and non-living interactions,” she said. “The world that we live in is very much influenced by interactions. For example, carbon dioxide in the atmosphere dictates climate, which then affects how plants grow and use carbon dioxide.”

Currently, Wurzburger is working on three projects that explore forests in flux. One examines fire in eastern U.S. forests, and how changes in policy have affected outcomes.

Historically, fire was a natural part of the landscape. Native people burned for cultural or management reasons, so these ecosystems evolved with fire. But fire can threaten people’s lives, homes and livelihoods, so policies shifted to favor fire exclusion. That change also caused a shift in forests — and not for the better, according to Wurzburger.

“Fire is an integral part of ecosystems and their dynamics,” she said. “And now there is a focus on bringing fire back to forests, to make them look more like they once did. But what happens to the ecosystem when you bring fire back?”

Wurzburger and her team are examining how the use of prescribed fire affects the soil. So far, their findings suggest that although burning reduces the total amount of carbon in the soil, it may promote long-term carbon storage. This could be a win-win for forests.

“All carbon is eventually going to be released back into the atmosphere. It’s just a question of on what timescale,” she said. “If more carbon can be put into a form that turns over every thousand years — as opposed to every year — then we’re in a much better position for keeping it out of the atmosphere.”

Native, but nuisance

If you’ve visited the Appalachians, you might’ve noticed rhododendron growing thick on the mountains. If you’re lucky, you might’ve caught it in bloom. But ecologists like Wurzburger have noticed that there’s a lot more than there used to be, and they want to know how this affects the ecosystem.

Rhododendron is native and slow growing, but it can be a nuisance. It becomes more abundant when there’s a disturbance that opens up the forest canopy and brings in a lot of light, and it maintains that growth once the forest has recovered.

Long-term data suggests that when American chestnut died 100 years ago, rhododendron creeped in and became more abundant, according to Wurzburger. It creeped in even more when eastern hemlock died back from the woolly adelgid, an invasive insect. And other experiments have shown that clear-cutting a forest allows rhododendron to come back at a higher abundance than previously.

“All of these things point to a human-created disturbance regime favoring this shrub, so it’s time to understand what it does to the forest ecosystem,” she said.

Rhododendron has unique fungal partners in its roots — shared only by related plants like azalea, blueberry and cranberry. A second project examines how the shrub and its fungi, which help it acquire nutrients, alter the movement of carbon from trees and shrubs to the soil. The below-ground processes are the hardest to understand, according to Wurzburger.

“Soil is opaque, it holds a lot of tiny microbes, and there’s lots of complexity,” she said. “That’s where all the exciting questions are, for me.”

West Coast creep

A third new project is in Big Sur, just south of where Wurzburger grew up. It’s an area that encompasses a mosaic of ecosystems — redwood forests, mixed evergreen forests with coast live oak and tanoak, grasslands, and fire-adapted shrublands.

The forests in this area are under threat because of tree disease and wildfire. Sudden oak death kills tanoaks and true oaks, leaving massive amounts of fuel in a landscape with a frequent fire regime. Add in long-term drought, and the landscape becomes a tinderbox subject to wildfires that are more powerful than before.

Into that landscape creeps another opportunistic shrub, ceanothus. Like rhododendron, ceanothus is not invasive but has a tendency to take over because it has the traits needed to succeed in this altered environment. It has persistent seeds that are heat triggered, so they germinate after there’s a wildfire. It grows quickly, because its roots contain bacteria that fix nitrogen from the air, which it converts and uses for growth.

When fuels like dead trees burn, there’s typically a lot of phosphorus in the resulting ash. In addition to pulling nitrogen from the air, ceanothus may benefit from this phosphorus to further supplement growth. It can grow about 8 feet tall in five years, choking out plants that can’t compete.

The next generation

As an undergraduate, Wurzburger majored in environmental science. She took a class on trees and forests and loved it. She was also required to take a soil science class, and she remembers being surprised that there was a whole book about soil.

“Then I took the class, and it completely changed my world view,” she said. “And now just about everything we do in the lab is related to soil in some way.”

During the next couple of years, Wurzburger will gain four new colleagues who may share her passion for forests and soil. The Odum School is hiring new faculty members in ecosystem ecology — two focused on terrestrial ecosystems, and two focused on freshwater, marine or wetland ecosystems.

“I’m very excited to recruit a new generation of ecosystem ecologists who are working on critical issues that face the world,” said Wurzburger, who’s leading the hiring committee. “They have an opportunity to benefit from the legacy of the Odum School and take us in a new direction.”