Climate change may affect fall colors. 30 years of data from New Hampshire can provide insight into how

Under the fiery orange and red canopy, Amy Bailey embarks on a hike she knows well. It’s the second week of October and the maples and beeches are showing their colors. Every few steps some kind of scientific equipment peeks out from the forest.

“We try to convince people to take back the remains of their research when it’s a short-term project, but you can’t go very far without seeing signs of some kind of research,” she says.

Bailey began working in the Hubbard Brook Experimental Forest in 1992. As an experimental forest, it is a site for long-term studies of all sorts of things—water movement, food webs, forest productivity.

The Hubbard Brook Experimental Forest, established in 1955, is located in the White Mountains. (Zoe Knox/NHPR)

Much of Bailey’s job as a forestry technician involves observation. She takes care of scientific equipment and verifies the accuracy of the data it records. For scientists in distant lands who rely on Hubbard Brooke for their research, she is an important observer in the forest, especially for the dataset she has helped create since she began her work: a record of how trees change week by week each spring . and fall.

The records that Bailey collected over three decades are unique. With the help of other technicians, she created one of the longest-running leaf observation logs in the United States.

“Sometimes it keeps me up at night because sometimes I have to interpret things,” she said. “I hope I’m doing a good job for the forest and the people using the data, but it’s a responsibility.”

As warming weather in the fall and winter changes New Hampshire’s ecosystems, long-term data becomes even more important to scientists. Bailey says the leaf blades are particularly popular.

“That’s the big question – how many growing diploma days are there? How long is the growing season? It all has to do with carbon sequestration and the big questions we have about primary growth and how the forest functions,” she said.

For many people, especially in New England, fall colors are a major part of the experience of nature, not to mention a major driver of tourism. Climate change will not only affect the forest, but also how people perceive it. And Bailey’s observations may help us understand what that might look like.

Categorization of trees

Bailey’s notes are kept in waterproof yellow pads. She uses a system created by a Forest Service scientist that is designed to work on the fly: Look at a tree and assign it a number from one to four.

“Four is a summer condition. That’s when the leaves fully photosynthesize and turn completely green,” she said.

As trees change with the seasons, the numbers move down the scale. At three the trees begin to turn. By the time there are two, they are mostly colorful. At one moment, about half of the leaves fell, and at zero, all of them.

Bailey says the number she often uses, 2.5, is technically not included in the criteria list. This is what we might call the peak of the fall.

Tony Federer, a U.S. Forest Service scientist, developed the criteria Bailey uses today to evaluate trees. (Zoe Knox/NHPR)

Over the course of a day, Bailey records the health of sugar maples, yellow birch and American beech at three sites. It turns out that classifying a tree is surprisingly difficult, especially if it is not in good health.

“It’s the classic thing where you look up and see all the dying leaves at the top and there are green leaves down here,” she said. “I have to compensate for leaf dieback, leaf loss. And while there’s still some green here, I’ll call it 2.5.”

Bailey has a relationship with these trees. She knows their history. During our hike, she visits a weathered-looking maple tree that she has been watching for 30 years. She says she was sad when he died. But death and decay are all part of the work.

“That’s part of the whole forest story: you need gaps to introduce something new. We’re interested to see what comes out now. What will it be?

Climate change and autumn colors

As humans burned fossil fuels and warmed the atmosphere, Bailey and her colleagues observed data from forest shifts becoming warmer, with warmer average annual air temperatures, cold winter nights and disappearing snow cover.

Bailey notices changes around her by observing the leaves season after season. September and October are warmer and the trees stay green longer. This year was no different: by mid-October there was no frost.

“Trees really need the cold to express fall color,” she said.

Every tree Bailey sees has an identification tag. (Zoe Knox/NHPR)

Scientists still have big questions about how climate change affects forest behavior in the fall. Andrew Richardson, a professor at Northern Arizona University, looks for clues in Hubbard Brooke’s data.

He uses Bailey’s observations to model what might happen to the leaf season and study how climate change is changing the way forests store carbon.

Richardson says there are several signs that the leaves will begin to change in the fall. An important one is the length of the day. This is a kind of fault tolerance.

“Even if we have a very warm fall, plants will still be able to tell that the days are getting shorter and we’re heading into winter, and they need to start preparing for that,” he said.

Another signal is low temperatures. But the warmer fall months seem to extend the time the trees are green.

When trees stop photosynthesizing, they turn other colors – orange and yellow. The Reds are a different story; scientists believe they are created by the leaves, perhaps as a kind of sunscreen. The cold nights that brighten the color and awe visitors from across the country are becoming increasingly rare during New Hampshire’s waterfalls.

“It seems pretty clear that in recent decades, the end of the growing season or the start of the leaf season has really been gradually pushed back toward the end of each decade,” Richardson said.

But Richardson says there is a lot of variability from year to year, and the tendency for leaves to change in the fall isn’t very strong.

Eat many factors which influence the colors of autumn and interact in complex ways. variety trees in the forests of New England change. Extreme heat in the summer can stress trees, causing their leaves to die off before they have a chance to show their color. Some research suggests that an earlier spring may lead to earlier leaf turning in the fall. Severe storms can knock leaves off trees, so they may not even change color when fall arrives.

These nuances, he says, are part of why long-term data is so important.

Bailey loves that her job involves a lot of hiking. "I am always so grateful to be here with the trees and see them grow and not be under too much stress in light of the harsh conditions they are currently experiencing." she said. (Zoe Knox/NHPR) — Bailey loves that her job involves a lot of hiking. “I’m always so grateful to be here with the trees and see them grow and not be under too much stress in light of the difficult conditions they’re in right now,” she said. (Zoe Knox/NHPR)

Back at Hubbard Brook, Bailey says she knows how important her job is. And as she watches climate change warm the forest she’s known for half her life, the act of watching brings her a little peace.

“I’ve seen a lot of changes happen over the years and everything is growing again. And the forest is resilient,” she said. “I think one thing I really respect about this area is that this land wants to support plants.”

Perhaps these are no longer the same plants that once grew here. For Bailey, sugar maples it would be a big loss. But she says the forest is constantly changing. It may be sad, but it’s more than that.

“The earth will do its job. And we changed what it would be, but it would be life-sustaining,” she said. “It may be difficult for all of us to live in this landscape because there is too much flooding or something else, but the trees will survive one way or another.”

This fall, Bailey will see all the leaves in the forest fall to the ground. In the spring, she will stand in the same places with her notebook and write down when the first new buds appear.

This story is a product of the New England News Collaborative. It was originally published New Hampshire Public Radio.