A glimpse of the past in a grain of pollen
by Melynda CobleNAME
Montana State University paleoecologist
Discerning ecosystem changes over the last 20,000 years
"It's a great puzzle trying to figure out how an ecosystem works."
"For me, it's about solving a big mystery," says Cathy Whitlock, describing her work as a paleoecologist at Montana State University. Whitlock studies the environments of the past, using pollen and charcoal remains from deeply buried lake sediments to understand how plant communities and climates have changed through time. Information about how ecosystems looked and operated thousands of years ago, she hopes, will also help society prepare for the future.
Whitlock has long been intrigued by the recent geological past. An avid hiker, she often uses her time on the trails to ask herself, "How did the ecosystem get to be like this? What explains the mosaic of trees?" She studied geology as an undergraduate at Colorado College and as a graduate student at the University of Washington, where she focused on "the younger side of geology" — the 20,000 years following the last ice age. After 14 years as a professor and researcher at the University of Oregon, Whitlock moved to Montana State University last July.
To understand the past, Whitlock and her graduate students wade into present-day wetlands, bogs and lakes, located throughout the coastal rainforest of Oregon, the Northern Rockies and the northern Great Plains.
They take samples at these longtime study sites by maneuvering a long sediment-coring "barrel," which looks like a metal pipe, into the muck and mud. Then, they muscle the barrel out of the sucking lake sediment, securing a sediment core just a meter long and 5 inches wide.
The cores are taken into the lab, sliced into sections about as thick as Oreo cookies, and examined under a high-resolution microscope. Each section represents approximately a decade of deposition, and contains a mixture of lake sediments, including charcoal and pollen from a variety of plant species. Whitlock's practiced eye readily picks out pine pollen, which is shaped like miniature Mickey Mouse heads, and she can also distinguish the pollen of white pines from that of two- and three-needle pines.
By identifying pollen and dating charcoal deposits, Whitlock pieces together vegetation and fire patterns. For example, her research indicates an abrupt and widespread arrival of lodgepole pine in the Northern Rockies 11,000 years ago. "It suggests a rapid warming, and a shift towards more fires," she says. At the same time, Douglas-fir was appearing across the Pacific Northwest, spreading throughout the region in a matter of a few centuries. "When the climate warmed, it was suddenly everywhere," she says. "It is remarkable to think that our most common trees were once so sparse that we can't locate their whereabouts during the glacial period."
These ancient environmental transformations may foretell the future. Increased greenhouse gas concentrations will likely cause deeper droughts and warmer temperatures in the West. As Whitlock's evidence suggests, forests respond dramatically to such climatic shifts: While high-elevation trees such as whitebark pine may decline, other species may thrive in new places. "The future for lodgepole pine is probably bright," she says. "It's a real weed."