You can’t really see the forest without looking closely at the trees.
By Kathiann M. Kowalski
After sawing away surface leaves and moss with a bread knife, Dr. David Foster presses a Russian corer into the black gum swamp. After a sharp yank, the tool brings up a half-meter core of oozy, gray silt. Extension rods bring up deeper cores, revealing the forest’s history.
“In this area, every meter is about 2,000 years,” explains Foster. Using similar cores, Foster has traced the area’s paleobiological record back more than 11,000 years.
Welcome to Harvard Forest. Headquartered in Petersham, Mass., the forest is part of Harvard University, but instead of clusters of ivy-covered buildings, Harvard Forest is 3,500 acres of living laboratories and classrooms. A sprawling hemlock forest abuts the black gum swamp. Oak, maple and cherry dominate other areas. Still other tracts feature northern hardwoods or mixes of southern and northern trees. Bogs, wetlands and pasture add to the diversity.
Founded in 1907 by Harvard professor Richard Thornton Fisher, Harvard Forest has a long history of forest science. Today, it’s one of the National Science Foundation’s 27 long-term ecological research sites. Permanent and visiting scholars include biologists and chemists. Historians, sociologists and artists add their perspectives, too.
“When you study forests, you are studying so much more than just trees,” stresses Foster, the director of Harvard Forest. “We try to do integrated research that will help us understand or address the kinds of changes that are or will occur within our landscape.”
STUDYING FOREST THREATS
Natural disasters and other disturbances can change a landscape dramatically. For example, what will happen after an invasive pest kills massive stands of hemlocks? Researchers are using Harvard Forest to try and find out.
As a foundation species, hemlocks provide habitat for a host of other species: unique mixes of salamanders, fishes and birds, such as the black-throated green warbler and Acadian flycatcher. They also shelter deer, porcupines and other animals, especially in winter. “There’s no other really long-lived, shade-tolerant conifer in our eastern forests,” says researcher Dr. David Orwig.
Targeting this foundation species is the invasive pest hemlock woolly adelgid, which reproduces asexually and literally sucks the life out of trees. Since arriving in Virginia in the 1950s, the Japanese insect has spread from Maine to Georgia. The pest has already killed huge hemlock stands in the Great Smoky Mountains (see American Forests, Spring 2011).
In experimental plots at Harvard Forest, Orwig and his colleagues have girdled trees — that is, cut bark around trunks — to simulate death from hemlock woolly adelgid. Detailed fieldwork catalogs the mix of trees that sprout in the aftermath. The experiment provides insight into what could replace today’s eastern hemlock forests.
Meanwhile, there’s hope for hemlocks in the very long term based on other Harvard Forest research. Foster’s work on core samples shows that something killed most of the area’s hemlocks roughly 5,000 years ago, so perhaps the East Coast’s hemlocks can recover and rebound again — it may just take hundreds or thousands of years.
While invasive pests’ effects can be slow spreading, hurricanes are much more sudden disasters — as last fall’s Hurricane Sandy showed — and have long-lasting effects. To simulate hurricane blowdown in Harvard Forest, workers used winches to pull down selected canopy trees in comparable tracts. Loggers then salvaged lumber from one area, but left another area alone. Surprisingly, many of the mostly uprooted trees lived a few more years, sending up shoots and producing seeds. Two decades later, the left-alone area’s productivity neared pre- “hurricane” levels.
Researcher Audrey Barker-Plotkin concludes that unless there is a compelling reason, people needn’t clean up forests after a natural disaster. “If your goal is to have the lowest forest system impact of a disturbance, then leaving it be is often your best bet.” While slowly decaying trees may look messy, they recycle nutrients and provide habitat for wildlife. In contrast, salvage efforts may interfere more with habitat, nutrient recycling and water resources.
HEATING THINGS UP
Climate change could cause big landscape changes in New England and throughout the world. The United States Global Change Research Program reports that “warming of the climate is unequivocal.” By the end of this century, average temperatures could rise as much as 10 degrees Fahrenheit. What roles can the forest play in mitigating climate change? And how will climate change impact forests? Researchers hope Harvard Forest can provide insights.
Dr. Jerry Melillo of the Marine Biological Laboratory (MLB) Ecosystems Center at Woods Hole heads a team that studies the forest’s response to warmer soils. The experimental treatment area warms the soil by five degrees Celsius with buried electric cables. One control plot has buried but unheated cables. A second control plot has no buried cables.
As heating increased microbial activity, soil gas measurements showed an increase in carbon dioxide emissions. Levels seemed to plateau after a decade, but now, they’re going up again. “We may have seen a shift in the microbial community,” notes Melillo. If carbon dioxide emissions keep rising, they could aggravate climate change.
Microbes aren’t the only forest organisms that will feel the impact of warmer soils. Dr. Aaron Ellison uses experimental plots at Harvard Forest to see how warmer soils will affect ants at the northern boundary of Mid-Atlantic mixed-deciduous forests. Plots at Duke Forest in North Carolina provided data for the southern limits. “If you’re going to see a response to climate change, the first place you look is at the edges,” explains Ellison.
Why worry about ants? In areas like New England, which lacks native earthworms, ants bring minerals and nutrients up from beneath the surface and oxygenate the layers. “So no ants, no soil,” says Ellison. When ants and other insects eat dead trees, animals and other organisms, they also recycle nutrients.
Ellison’s data already shows a change in the abundance of certain ant species. Over time, the mix will likely change, too. The study can help scientists better understand how ants contribute to ecosystem services and how that might change in a warmer world.
Of course, not all animals of a heatintolerant species must move or die. Individuals within the same species naturally vary. Warmer soils should give a selective advantage to individuals that can handle more heat. Thus, says Ellison, “We have the opportunity to see evolution in action here.”
APPLYING SCIENCE LESSONS
Harvard Forest’s interdisciplinary approach, ecosystem diversity and collegial atmosphere make it a unique living laboratory for long-term research. While studies provide specific data about the trees, plants, wildlife and insects of Harvard Forest, their implications reach far beyond the immediate area.
“While we’re very much rooted in the place, we try to do our work in a way that it answers basic questions that pertain much more broadly and that make a difference,” says Harvard Forest Director Foster. Land use changes, invasive pests and weather disasters pose problems for forests throughout the country, while climate change will impact many areas throughout the world.
Meanwhile, work and study continue year-round. “Most field stations close down in the winter or people only go on weekends,” notes Foster. “Harvard Forest is a place where we are all there every day studying the place. So, when there’s three feet of snow, you put snowshoes on, and you go study the forest. And when trees are crashing down in a violent ice storm, you’re out there looking at it.”
For more information on Harvard Forest and the research being conducted there, visit harvardforest.fas. harvard.edu.
Kathiann M. Kowalski did field work at Harvard Forest in 2012 as part of the MBL Logan Science Journalism Program’s Hands-on Environmental Lab Program. She writes near Cleveland, Ohio.