David Orwig tries not to think of changes in the natural world as “better” or “worse.” He just sticks with “different.” And after decades of warming winters, Harvard Forest today is decidedly different.
“Every day, walking around this forest is just dramatically different than it used to be,” said Orwig, who has worked at the 4,000-acre forest in Petersham, Massachusetts, since 1995 and today is senior ecologist. “When I first started working here, it used to be dark, green, lush, and shady. Now I take groups out there, and the overstory trees are letting in a lot more light. It’s gray in the understory, and there’s a whole new layer of birch coming in that was not here even 10 years ago.”
To Orwig and his Harvard Forest colleagues, climate change’s impacts aren’t an abstraction, and they aren’t a problem for tomorrow. That’s partly because climate change is studied there, but it’s also because many in the tight-knit community view their work as a labor of love. And it’s hard not to notice when your love is changing.
“We all have a landscape that we share here and care deeply about,” said Clarisse Hart, education and outreach director. “I guarantee that every single person who works here can tell you several parts of this land that are meaningful to them. We’re constantly out on the land together and experiencing these changes together.”
The forest, founded in 1907, attracts researchers from around the globe because of its exceptional trove of collected data. It has temperature and precipitation information going back to the 1960s, with comparable data collected in the nearby town of Amherst going back to the 1830s. Having records collected over such a long period allows climate trends to emerge despite the normal variation in daily or annual weather figures.
“We now have enough data to say that the long-term trends toward a warmer and wetter climate, which is what the climate scientists have predicted for our part of the world, is being borne out,” said Emery Boose, senior scientist and information manager at the forest. “There may be some other trends as well. There’s evidence that there may be more variation from year to year. And precipitation, we’re starting to see evidence of extremely heavy, short duration rainfall, especially in the summer months, not tied to a large storm like a hurricane.”
Harvard Forest has about 100 research projects going at any one time, Boose said, ranging from small studies lasting just a single field season to ongoing efforts that are passed from one scientific generation to the next.
Experiments are installed along the dirt roads crisscrossing the forest, with some dug into the forest floor, artificially heating the soil to understand how ant and microbial communities might change in a warming world.
Others are hung off metal towers extending into and above the forest canopy, with cables and tubes running to nearby shacks where shelves of instruments examine gas exchange between the forest and the atmosphere.
“In the Southwest, the climate-and-tree story is one of drought and fire. It’s more in your face,” said Jonathan Thompson, senior ecologist and research director. “We have analogies for those things, but instead of drought and fire, it’s happening here through longer-term changes in climate interacting with invasive pests.”
The instruments also confirm things the researchers already know from personal experience: Winters are coming later despite this year’s more prolonged cold, and the snowpack is thinner. The fading winter cold gives way to summer heatwaves, more wildfires, and torrential rainstorms.
“My wife and I have been here for 40 years now, and we like to ski. Both anecdotally and in measurements, there’s a trend that snow doesn’t last quite as long and isn’t quite as deep as it used to be,” said Boose. “Plus, we’re both avid ice skaters and in 2023 for the first time I can remember one of the lakes in nearby Phillipston didn’t freeze over completely. I can’t ever remember that happening. We used to get one to two feet of ice.”
Other Harvard Forest administrators and scientists have similar stories: October 2023 passed without a frost until Halloween, and winter’s bitterest weeks are either milder (last winter logged no days below zero degrees Fahrenheit) or are reduced to a handful of days.
The stories vary by circumstance and experience, but they all point to the fact that the forest isn’t waiting for the debates to conclude in Washington, D.C. It is changing, with the most dramatic shifts affecting the very character of the forest.
“There’s nobody who hasn’t noticed that the hemlocks are dying,” Hart said. “I think what’s happening here is very real for all of us, and we could flop down and despair — seriously we could — but we’re also bolstered by a real sense of wonder at the resilience of ecosystems, at the way that trees work, the way these systems function.”
Hemlocks don’t just grow in a forest. They shape it, controlling the flow of energy via dense, multilayered branches that intercept much of the light that hits the canopy. Their fallen needles acidify the soil, keeping out competitors and forming a spongy carpet. They regulate temperature, shielding the snowpack from the spring’s strengthening sunshine and shading summertime streams to provide habitat for cold-water fish like trout.
When Orwig first came to Harvard Forest as a postdoctoral fellow, its hemlocks were healthy, but there were signs of change in the offing. So he traveled to southern Connecticut to glimpse the forest’s future.
He set up 40 monitoring plots to understand the woolly adelgid, a small, invasive, aphidlike insect that had arrived in Connecticut a decade earlier and was pushing north. The one thing that tends to keep them in check is cold temperatures.
Over the last two decades, however, the weeks of deep cold that used to be a feature of New England winters have moderated. So, the adelgid, a native of Japan, thrived in the milder landscape and started moving north to claim new territory.
Black birches give the forest a different feel, shady and green by summer, but sunny and open in the winter.
“We started with about 850 hemlocks,” Orwig said of his Connecticut plots. “There’s fewer than 50 left.”
Orwig continues to monitor those stands in hopes of finding “lingering hemlocks,” trees resistant to the adelgid that might serve as founders of a new, healthier population.
“I used to think I had two trees that were resistant in my plots, but when I went back several years later, they were both dead,” Orwig said. “There’s just not great evidence for resistance out there.”
Meanwhile, the woolly adelgid has spread relentlessly north, arriving in Massachusetts in 1988 and continuing into Southern New Hampshire, Maine, and Vermont.
Hope remains that resistant trees might still emerge, that an introduced insect predator might prove successful — several states have released them — or that a succession of cold winters, as occurred in 2004-2005, will knock down the population and give existing trees a chance to recover.
Those hopes may seem slim, but Orwig points out that he never even thought Harvard Forest’s hemlocks would survive until now.
“I had envisioned that within 10 years, Massachusetts would all be dead and that hasn’t happened,” Orwig said. “That’s a good thing, but they’re still infested, and they still continue to decline.”
Dying hemlocks are usually replaced by deciduous trees, black birches in Harvard Forest’s case. Those trees give the forest a different feel, shady and green by summer, but sunny and open in the winter. The differences include soil chemistry — slightly basic as opposed to acidic under the evergreens — and an altered flow of nutrients from rapidly decomposing, fallen leaves versus more enduring evergreen needles.
“Everything changes, the microenvironment, the snow and rain that the trees intercept, all kinds of things,” Orwig said. “But forests are resilient, and we often see dense thickets of black birch come in. That’s a different forest, but it will rapidly grow. It may store carbon very quickly but uses water very differently.”
Though Orwig marvels at the forest’s resilience and insists that natural change is neither good nor bad, he still admits he’ll miss the hemlock at Harvard Forest and in the old-growth forests he studies across New England.
“I love being in a hemlock forest. I like how they smell. I like how they feel when you walk around on the spongy earth,” Orwig said. “And I do feel great loss when we lose vast areas of forest due to an introduced insect. It is painful to see 300- to 400-year-old hemlocks being killed off.”
Others tally generational loss on top of personal concerns. Future generations, they fear, may not even know what they’re missing.
“I can remember being an undergraduate traipsing through these forests, and they are different now, but I don’t know how to convey that,” said Harvard Forest Director Missy Holbrook, the Charles Bullard Professor of Forestry.
Holbrook described a concept called “shifting baselines,” the idea that we each form our own sense of what we consider normal based on personal experience. Coming generations will have a different baseline than we do, Holbrook said. And that can impact everything from the scientific questions that are asked to how conservation programs are designed to what restoration efforts are undertaken.
“If you’ve never experienced an old-growth forest or a hemlock forest, it’s not in your realm of imagination,” Holbrook said. “I remember when we had snowier winters consistently, and my son will not have that frame of reference. So, climate change is affecting me: It affects me when I raise my son and when I teach. And climate change is accelerating, not slowing.”
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