By Joe Rankin
Forests for Maine’s Future writer
In a spruce-fir forest north of Bangor tall towers rise above the treetops, studded with instruments measuring everything from wind to carbon dioxide and methane. Another forest to the southeast gets regular doses of fertilizer while a patch nearby does not. In another chunk of forest on the Maine coast every tree is numbered 
Helicopter’s eye view of the main tower at Howland Forest. (Photo courtesy Howland Forest)and every plant species cataloged.
At each of these locations — the Howland Research Forest, the Bear Brook Watershed, and the Holt Research Forest — scientists are studying different things. But all these efforts to understand the Maine woods have something in common: they have been going a long time. They began in the mid-1980s and is still going strong.
Such so-called long-term ecosystem studies are tremendously important because, well, they give us the long view. They help smooth out the unavoidable year-to-year ripples in the data, giving a wider field of view, at least from a temporal pespective.They enable us to see the forest for the trees.
And, while the issue of climate change was on virtually no one’s radar back when they all began, all three are now poised to contribute important information about how forests in the north are responding and will respond to a warming climate.
“It’s the only way to understand the biogeochemistry of a forest landscape that will inform our thinking about the long-term future,” said Ivan Fernandez, a professor of soil science at the University of Maine and the lead researcher at Bear Brook. “You can model and conjecture, but studying it over time is the best.”
While forest sciences researchers recognize the value of such lengthy studies, they are challenging to set up and maintain.
Lower elevation hardwoods at Bear Brook. (Photo courtesy Bear Brook Watershed Manipulation Project)Robert Wagner, the director of UMaine’s Center for Research on Sustainable Forests that is responsible for a number of long-term forest research sites, said that “well-maintained long-term experiments are like gold in forest research. These sites are the only way to actually test hypotheses about how forest ecosystems operate over long periods of time.”
Such sites are easy to establish when politicians and the scientific community are excited about high-profile issues, said Wagner. However, as hotter political issues come along to capture their attention and scarce resources, it becomes more and more difficult to maintain long-term research sites, he added. Therefore, “when you have a controlled study that has been nicely maintained and measured for 30 or 40 years, it becomes priceless,” Wagner said.
Howland Research Forest
The Howland Research Forest is one of the oldest sites for long-term carbon studies in the northeast after the Harvard Forest, said Dave Hollinger, a plant physiologist with the U.S. Forest Service’s Northern Research Station who has been doing science at the site since the mid 1990s.
Located about 35 miles north of Bangor, the 558-acre forest is mainly mature spruce, balsam fir, and hemlock. Many of the trees are 150 years old, while some eastern white cedars are more than 300 years old. “It is one of the oldest and most densely stocked examples of hemlock-spruce-fir forests that is out there,” said Hollinger.
Sunphotometer at Howland Forest (Photo courtesy Howland Forest)Established as a research forest in 1986 by then-owner International Paper Co., it attracts researchers not just from Maine, but elsewhere in the U.S. and from other countries. Early on the research was focused on acid rain and how forests use nutrients. In the 1990s that shifted to illuminating how such forests take up and store carbon.
At the Howland Forest there are three tall metal towers with intruments that gather information on things such as light levels; solar radiation in and off the forest; wind speed, not just the wind that sweeps aross the forest, but up vertically through it; and carbon dioxide and methane concentrations. Ground level instruments measure biomass, soil temperature and soil moisture.
“One of the most important findings is that a changing climate is already affecting forest growth,” said Hollinger. “Spring is starting earlier up in Maine than it used to and forests are growing more as a result.”
Hollinger said Howland data shows that as spring warmth comes earlier the forest grows more and thus sequester, or stores, more carbon. “That’s been sort of a surprise because that forest is at the southern end of its range and you might think it can’t handle the heat. Now, it doesn’t do as much storing in really warmer weather during the summer, but the longer growing season more than makes up for that.”
Another finding: forests are getting more efficient about using water, which also be a response to a changing climate, said Hollinger. If that result holds true it could be important, he added, because water is an important factor in tree health.
Some climate models predict rainfall increasing in northeastern North America, with more frequent periods of intense rainfall at particular times of the year, warmer temperatures and less snow. “All those things are underway and will affect the physiology and metabolism of the forest,” said Hollinger. “One of the easiest take home messages is that changes already afoot are already affecting how things operate on the ground.”
Another Howland project looked at methane, a potent greenhouse gas that is produced by the swamps and 
Measuring deadwood respiration. (Photo courtesy Howland Forest)bogs of the forest. It found that during dry summers the forest becomes a sink for methane, taking it up from the atmosphere; during wetter summers it produces a slight surplus of methane.
Howland is participating in another study with NASA, testing sensors the space agency hopes to employ in a satellite designed to measure soil moisture from space.
In the 1990s IP sold its Maine woodlands, including the Howland Research Forest, to an investment company. A few years later the “core” 558 acres of the research forest was sold to the Northeast Wilderness Trust, ensuring the forest will continue supporting research. Surrounding lands, including acreage that was part of the original research forest, were sold and are being actively managed, said Hollinger. In fact, one of the instrument towers is located on the managed forestland and it provides a perfect location to study how a managed forest sequesters carbon, he said.
The Holt Research Forest
The 100-acre “study area” within the 300-acre Holt Research Forest may be one of the most intensely examined blocks of land in the state of Maine.
Trees are individually numbered and their growth — and death — tracked. Every species of plant, 270 in all, has 
Polygala paucifolia, a common forest floor herb at Holt Research Forest. (Photo courtesy Holt Research Forest)been identified. Resident and migrant birds have been monitored and their home ranges identified. Small mammal populations have been examined, tree seedlings have been counted.
Jack Witham, an associate scientist at the University of Maine and the on-site manager of the Holt for some 30 years, said the volumes of data accumulated at the Holt Forest over the decades is valuable in itself, but becoming more so with climate change. “It allows us to look at the change that takes place. If we didn’t have the long-term data sets the changes due to climate change would be difficult to document. It gives you a perspective you wouldn’t get otherwise.”
The Holt Research Forest is an oak and pine woodland with salt marsh and freshwater wetlands on Arrowsic Island.
Dr. William L. Holt Jr. began acquiring the land in 1938, much of it former farmland. In 1980 he and his son Rod Holt created the Holt Woodland Research Foundation, blessed it with an endowment and gave it the mission of fostering research on the animals and plants that live there and how they respond to human disturbance and natural forest succession.
Earlier this year the Foundation was merged into the Maine TREE Foundation, which will continue and expand the research done at the site, said Sherry Huber, the executive director of Maine TREE. “It’s extraordinarily rare to have this length of time in a database in forest research. There are only about 100 or so sites around the world that have compiled this kind of database over time.”
Jack Witham and Cherie Meinson searching through the litter for red-back salamanders. (Photo courtesy Holt Research Forest)More than 60 research papers have been based on work done there.
Within the 100-acre study area researchers have identified every plant species in each 25 by 25-meter grid. Over 270 plants have been found, from common ones such as Canada mayflower and starflower to lady’s slippers and a couple of orchids and 26 varieties of sedge, said Witham.
Forest managers conducted a timber harvest on a 25-acre portion of the study area in the late 1980s. “Our long-term goal is to look at how the species components change over time and how they change with forest harvesting. We’re documenting how plant species respond to the overstory and changes in that, and changes due to climate change,” Witham said.
Small mammal studies have not only chronicled the population cycles of such small furry creatures as red-backed voles and white-footed mice, but also noted how the southern flying squirrel supplanted the northern flying squirrel.
Research on birds demonstrated how quickly bird species adapt to the changing makeup of the forest. Common yellowthroats and white-throated sparrows were once abundant in ledge gaps dominated by juniper and in harvest gaps. But as those have grown in, the two species declined, Witham said. Breeding populations of Blackburnian warblers and black-throated green warblers have remained pretty stable. Black-throated blue warblers, however, went elsewhere after the timber stand improvement work removed many of the stump-sprouted red maple.
Beyond their scientific value, the Holt’s findings have a practical value. the oak-pine forest type is a common one in southern Maine, and the study area is the size of a typical small woodlot. “It’s very applicable to small woodlot owners in an area where most landowners don’t do any forest harvesting. It demonstrates that you can harvest and that the things that you cherish about your woodlot will still be there,” Witham said.
The Bear Brook Watershed
In Hancock County in eastern Maine two brooks rise on the southeastern slopes of Lead Mountain above Bear Pond. East Bear Brook and West Bear Brook are virtually identical drainages, the upper slopes furred with red 
At Bear Brook Watershed higher elevation trees include spruce, fir, and hemlock. (Photo courtesy Bear Brook Watershed Manipulation Project)spruce, balsam fir and hemlock and lower down clothed in birch, beech and maples. An ordinary forest, really.
But because the two drainages are twins, they provided scientists with the perfect spot to study acid rain. This was in the 1980s, when acid rain was a big issue in the northeastern U.S. The Bear Brook Watershed Manipulation Project was started in 1987 and continues to this day.
Every two months a helicopter takes to the air over West Bear Brook, spreading ammonium sulfate fertilizer over the drainage’s forest. The flights add 25 kilograms of nitrogen and 28 kilograms of sulfur per hectare per year. That’s the equivalent of two to three times what the drainage was getting naturally and about the amount of acid rain that was falling over the mid-Atlantic states at the time, though not nearly what was falling in Germany or Poland. The East Bear Brook watershed remains unfertilized, as a reference.
The original experiment was designed to figure out how much emissions would have to be reduced in order to significantly reduce acid rain’s effects on forests and streams. Soil acidification hasn’t stopped, but it is much reduced. And in the early 1990s after the Clean Air Act was reauthorized, federal research funding shifted away from acid rain. The experiment at Bear Brook continued, however.
“Most of the questions we were asking at the beginning of the study are different from the ones we’re asking now,” said Fernandez, the UMaine professor and expert on forest soils who has been involved with the Bear Brook project since the beginning.
The focus now is on climate and how forests use nutrients and how that use is affected by warming temperatures. Nitrogen is a key element for forests. It’s usually present in limited amounts, it is vital to tree growth and warming speeds up the nitrogen cycle.
Bear Brook has shown that as more nitrogen is added to the landscape, the forest cycles more nitrogen. It’s also shown that phosphorous is key to how quickly that cycling occurs, said Fernandez.
Some interesting things were noted following the 1998 ice storm: a year later there was a pulse of nitrogen leaching out of the soils, probably because there was more biomass rotting on the ground and gaps in the canopy created when limbs broke allowed more sunlight to reach the forest floor, said Fernandez. The next year, however, less nitrogen leached out of the system.
The big question, given a predicted long-term warming trend, is what happens to nutrients in the trees and 
At Bear Brook stream flow is measured by funneling it through a weir. (Photo courtesy Bear Brook Watershed Manipulation Project) soils and streams when there are heavier rains or snow melts earlier in the spring.
The latest experiment involves adding a tiny amount of a stable (not radioactive) and easily tracked isotope of nitrogen to both watersheds to understand how nitrogen cycling differs between the two watersheds. Fernandez said one thing learned so far is that there are big differences in how tree species use nitrogen and therefore how changing forest composition influences forest nutrient cycling..
The project is also doing long-term studies on calcium and sulfur as well as nitrogen. They’ve looked at how water transpires from trees. One student is studying how the earlier arrive of spring affects the renewed decomposition on the forest floor, root growth, and tree budding rates.
Bear Brook gets much of its funding from the National Science Foundation and is partway through a current 10-year funding cycle. Fernandez anticipates submitting a proposal to continue for another decade.
“We’re one of the longest whole watershed manipulation experiments ongoing in the world. That allows us to look at things over long time scales, critical for long-lived systems like forests,” Fernandez said.
Joe Rankin writes forestry articles. He lives in New Sharon.
