When the forest serves as your climate change laboratory

David Orwig attempts to refrain from labeling alterations in the ecosystem as “better” or “worse.” He prefers the term “different.” After numerous years of increasingly warm winters, Harvard Forest now exhibits distinct changes.

“Every single day, wandering through this forest is incredibly different from what it used to be,” remarked Orwig, who has been at the 4,000-acre forest in Petersham, Massachusetts, since 1995 and currently serves as senior ecologist. “When I initially began my work here, it was dark, verdant, flourishing, and shaded. Nowadays, when I take groups there, the canopy trees allow significantly more light to penetrate. The understory is gray, and a completely new layer of birch is emerging that wasn’t present just a decade ago.”

For Orwig and his colleagues at Harvard Forest, the ramifications of climate change are not an abstract concept nor a future dilemma. This is partly due to the fact that climate change is actively researched there, but also because many within the close-knit community consider their work a labor of love. Recognizing the changes in their beloved space is unavoidable.

“We all share this landscape, and we care about it deeply,” stated Clarisse Hart, the education and outreach director. “I can assure you that every single individual working here can recount several areas of this land that hold personal significance for them. We are consistently out on the land together, experiencing these transformations collectively.”

The forest, established in 1907, appeals to scholars from across the globe due to its exceptional collection of data. It possesses temperature and precipitation records dating back to the 1960s, with comparable data recorded in the nearby town of Amherst as far back as the 1830s. The extensive collection of records from such an extended period allows for the emergence of climate trends despite the regular fluctuations in daily or annual weather data.

“We now possess sufficient data to affirm that the long-term tendencies toward a warmer and wetter climate, which climate scientists have anticipated for this region, are indeed materializing,” stated Emery Boose, senior scientist and data manager at the forest. “There might also be additional trends. Evidence suggests there could be greater variations from year to year. Concerning precipitation, we are beginning to observe instances of extremely intense, short-duration rainfall, particularly during the summer months, which aren’t linked to significant storms like hurricanes.”

Harvard Forest is home to approximately 100 research initiatives at any given time, Boose mentioned, ranging from brief studies lasting a single season to ongoing endeavors that span multiple scientific generations.

Experiments are set up along the dirt roads that weave through the forest, with some immersed into the forest floor, artificially heating the soil to comprehend how ant and microbial communities may adapt in a warming climate.

Others are suspended from metal structures that extend into and above the forest canopy, with cables and tubes leading to nearby shacks where rows of instruments measure gas exchange between the forest and the atmosphere.

“In the Southwest, the narrative of climate and trees is characterized by drought and fire. It’s more overt,” remarked Jonathan Thompson, senior ecologist and research director. “While we have parallels to that, here it manifests through long-term climatic alterations interacting with invasive species.”

The instruments also reaffirm observations the researchers have gleaned from firsthand experience: Winters are occurring later despite this year’s extended cold spells, and the snowpack has thinned. The diminishing winter chill gives way to summer heatwaves, escalating wildfires, and intense downpours.

“My spouse and I have resided here for 40 years now, and we enjoy skiing. Both anecdotally and through measurements, there’s a noticeable trend that snow doesn’t last as long nor is it as deep as it once was,” remarked Boose. “Additionally, we’re both enthusiastic ice skaters, and in 2023, for the first time I can recall, one of the lakes in nearby Phillipston didn’t freeze completely. I can’t remember that ever happening before. We used to have one to two feet of ice.”

Other administrators and scientists at Harvard Forest share similar accounts:

October 2023 went by without a frost until Halloween, and the most frigid weeks of winter are either milder (the previous winter recorded no days below zero degrees Fahrenheit) or condensed into just a few days.

While the narratives differ based on context and experience, they all highlight the reality that the forest is not waiting for discussions to conclude in Washington, D.C. It is evolving, with the most significant transformations impacting the very essence of the forest.

“There’s no one who hasn’t observed that the hemlocks are perishing,” Hart remarked. “I believe what’s occurring here is very genuine for all of us, and we could easily succumb to despair — honestly, we could — but we’re also uplifted by a profound sense of amazement at the resilience of ecosystems, at the way trees interact, the way these systems operate.”

Hemlocks do not merely exist in a forest. They influence it, regulating the energy flow through their dense, layered branches that absorb much of the light that strikes the canopy. Their dropped needles acidify the soil, excluding competitors and creating a cushioned carpet. They control temperature, protecting the snowpack from the intensifying spring sunlight and shading summer streams to create habitats for cold-water fish like trout.

When Orwig initially arrived at Harvard Forest as a postdoctoral fellow, its hemlocks were robust, though there were indications of impending changes. Consequently, he ventured to southern Connecticut to observe the forest’s future.

He established 40 observation plots to study the woolly adelgid, a small, non-native, aphid-like pest that had reached Connecticut a decade earlier and was advancing northward. The primary factor that typically restrains them is frigid temperatures.

In the past twenty years, however, the stretches of intense cold that once characterized New England winters have lessened. As a result, the adelgid, originally from Japan, flourished in the milder environment and began migrating north to seize new areas.

Black birches impart a different ambiance to the forest, cool and green in summer, yet bright and open in winter.

“We commenced with approximately 850 hemlocks,” Orwig recounted about his Connecticut plots. “Now, fewer than 50 remain.”

Orwig continues to observe those stands, hoping to discover “surviving hemlocks,” trees that show resistance to the adelgid and could potentially serve as the foundation for a new, healthier population.

“I previously believed I had two trees in my plots that were resilient, but when I revisited several years later, both were deceased,” Orwig shared. “There’s simply insufficient evidence of resistance present.”

Meanwhile, the woolly adelgid has aggressively advanced northward, arriving in Massachusetts in 1988 and extending into Southern New Hampshire, Maine, and Vermont.

There remains hope that resistant trees might still appear, that an imported insect predator could potentially succeed — several states have released them — or that a series of cold winters, similar to those that occurred in 2004-2005, will reduce the population and allow existing trees a chance to recuperate.

Although these prospects may seem limited, Orwig highlights that he never anticipated Harvard Forest’s hemlocks would endure this long.

“I had imagined that in a decade, Massachusetts would be entirely dead and that has not come to pass,” Orwig stated. “That’s a positive sign, but they remain infested, and their decline persists.”

Declining hemlocks are generally replaced by deciduous trees, specifically black birches in Harvard Forest’s instance. These trees offer a distinct ambiance, cool and green in summer, yet luminous and open in winter. The variations extend to soil chemistry — slightly alkaline rather than acidic beneath the evergreens — and a changed nutrient flow from rapidly decomposing fallen leaves compared to the more enduring evergreen needles.

“Everything alters, the microenvironment, the snow and rain that the trees capture, countless factors,” Orwig noted. “However, forests are resilient, and we frequently observe dense patches of black birch emerging. It’s a different forest, yet it will grow quickly. It may sequester carbon rapidly, yet it utilizes water differently.”

Though Orwig admires the forest’s resilience and maintains that natural changes are neither inherently positive nor negative, he still confesses he’ll miss the hemlock at Harvard Forest and in the ancient-growth forests he researches across New England.

“I cherish being in a hemlock forest. I appreciate their scent. I enjoy how they feel underfoot on the spongy ground,” Orwig reflected. “And I truly experience a profound sense of loss when we lose vast tracts of forest due to an invasive insect. It is heartbreaking to witness 300- to 400-year-old hemlocks being exterminated.”

Others measure generational loss beyond their personal worries. They fret that future generations may not even grasp what they are missing.

“I can recall being an undergraduate wandering through these forests, and they have changed now, but I’m unsure how to convey that,” remarked Harvard Forest Director Missy Holbrook, the Charles Bullard Professor of Forestry.

Holbrook articulated a concept known as “shifting baselines,” the notion that each of us forms our perception of what we deem normal based on our personal experiences. Future generations will possess a different baseline than ours, Holbrook asserted. This can influence everything from the scientific inquiries posed to the design of conservation programs to the restoration efforts undertaken.

“If you’ve never experienced an ancient-growth forest or a hemlock forest, it’s beyond your realm of imagination,” Holbrook added. “I remember when winters consistently brought more snow, which my son will lack as a point of reference. Thus, climate change impacts me: it affects how I raise my son and how I teach. And climate change is accelerating, not decelerating.”