Under a canopy of fiery orange and red, Amey Bailey is taking a hike she knows well. It’s the second week of October, and maples and beech trees are showing off their colors. Every few steps, a piece of scientific equipment peeks out of the woods.
“We try to get people to pick up the remains of their research when it's a short term project, but you can't go far without seeing signs of some kind of research,” she says.
Bailey started working at the Hubbard Brook Experimental Forest in 1992. As an experimental forest, it’s the site of long-term studies about all kinds of things – the movement of water, food webs, forest productivity.
Much of Bailey’s job there, as a forest technician, is to observe. She takes care of scientific equipment and ground-truths the data it records. For far away academics who rely on Hubbard Brook for their research, she’s an important set of eyes in the woods, especially for a data set she’s been helping to build since she started her job: a record of how trees change week by week each spring and fall.
The records Bailey has collected over three decades are unique. With help from other technicians, she’s created one of the longest-running logs of leaf observations in the United States.
“Sometimes it does keep me up at night, because I have to make interpretations of things sometimes,” she said. “I hope I’m doing a good job for the forest and the people using the data, but it is a responsibility.”
As warming falls and winters change New Hampshire’s ecosystems, long-term data is becoming even more important for scientists. Bailey says the leaf records are particularly popular.
“This is a big question – How many growing degree days are there? How long is the growing season? This is all tied to carbon sequestration and big questions we have about primary growth and how the forest is functioning,” she said.
For many people, especially in New England, fall colors are a core part of the experience of nature – not to mention a major driver of tourism. Climate change won’t just affect the forest, but also how humans experience it. And Bailey’s observations could help us figure out what that might look like.
Categorizing trees
Bailey’s records are kept in a series of waterproof yellow notebooks. She uses a system created by a Forest Service scientist that’s meant to be done on the fly – take a look at a tree and give it a number, one through four. The study started in 1989. At 35 years old, it's possibly the oldest of it's kind.
“Four is summer condition. So that's when the leaves are fully photosynthesizing, all green,” she said.
As trees change with the seasons, the numbers move down the scale. At three, trees are starting to turn. They’re mostly colorful by the time they get to two. At one, about half of the leaves have fallen and at zero, they’re all gone.
Bailey says a number she uses often, 2.5, isn’t technically on the criteria sheet. That’s what we might call peak fall.
Throughout the day, Bailey records the status of sugar maples, yellow birch, and American beech trees at three sites. Turns out it’s surprisingly tough to categorize a tree – especially if it’s not in good health.
“This is a classic one where you look up, you see all the dieback at the top but the green leaves down here,” she said. “I have to accommodate for the dieback up there, all the leaf loss. And even though there's still green here, I'm going to call this 2.5.”
Bailey has a relationship with these trees. She knows their history. On our hike, she visits a ragged looking maple she observed for 30 years. She says she was sad when it died. But death, decomposition – that’s all part of the job.
“That's what part of the whole forest story is, is that you need gaps to get new things in. It's exciting for us to see what will come in now. What will it be?”
Climate change and fall colors
As humans have burned fossil fuels and warmed up the atmosphere, Bailey and her colleagues have seen the data coming out of the forest shift: average annual air temperature getting warmer, cold winter nights and snowpack disappearing.
Bailey notices changes around her as she watches the leaves season after season. Septembers and Octobers are warmer, and the trees are still green for longer. This year wasn’t any different: there hadn’t been a frost by the middle of October.
“The trees need the cold really to express the fall color,” she said.
Scientists still have big questions about how climate change is affecting the way the forests act in the fall. Andrew Richardson, a professor at Northern Arizona University, is looking to Hubbard Brook’s data for clues.
He uses Bailey’s observations to model what might happen to leaf peeping season and to study how climate change is shifting the way forests store carbon.
Richardson says there are several signals for leaves to start changing in the fall. A big one is the length of the day. That’s kind of a failsafe.
“Even in a very warm fall, plants will still be able to tell that it's the days are getting shorter and we're heading into winter, and they need to start preparing for that,” he said.
Cold temperatures are another signal. But warmer falls seem to prolong the time when trees are green.
As they stop photosynthesizing, trees reveal other colors – oranges and yellows. Reds are a different story; those are created by leaves, scientists think possibly as a kind of sunscreen. The cold nights that make that color more vibrant, aweing visitors from across the country, are becoming less common during New Hampshire’s falls.
“It does seem pretty clear that in recent decades, the end of the growing season or the start of that leaf peeping season has really been pushing back gradually later each decade,” Richardson said.
But Richardson says there’s a lot of variability from year to year, and the trend towards leaves changing later in the fall isn’t very strong.
There are a lot of factors that affect fall colors and they interact in complex ways. The species of trees in New England forests are changing. Extreme heat over the summer can stress out trees, so their leaves die before they can show off their colors. Some research suggests earlier springs can cause leaves to turn sooner in the fall. Heavy storms can knock leaves off trees, so they’re not even there to change color when fall comes.
Those nuances, he says, are part of why having long-term data is so essential.
Back in Hubbard Brook, Bailey says she knows how important her job is. And as she watches climate change warm up a forest she’s known for half her lifetime, the act of observing brings her some peace.
“I have seen a lot of changes happen over the years and things grow back. And the forest is resilient,” she said. “I think that's one thing I really have grown to respect about this area is that this land wants to support plants.”
They may not be the same plants that once grew here. For Bailey, sugar maples would be a big loss. But she says, change is a constant in the forest. It can be sad, but it’s more than that.
“The land is going to do its thing. And we've changed what that's going to be, but it is going to support life,” she said. “We may all have trouble living in this landscape with too much flooding or whatever it might be, but the trees are going to survive in one way or another.”
This fall, Bailey will watch all the leaves in the forest drop to the ground. In the spring, she’ll be standing in the same spots with her notebook to record when the first new buds appear.
