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Fresh from the Woods
A shaft of sunlight pierces a stand of red spruce growing in Lincolnville.
The Nimble Forest
By Andrew Kekacs
Life on Earth moves to music that humans don’t always hear, and forests are part of the dance.
Individual trees are, of course, rooted in place. Studies of ancient pollen, however, reveal that species within the forest roam back and forth over the landscape. Small variations in climate have caused white pine, red spruce and other tree species to shift their ranges hundreds of miles north or south in just a few generations.
This story of the nimble forest is particularly important as Maine considers how to respond to climate change. The speed at which forests (and other species) adjust to temperature changes means that the impact of global warming could be felt relatively soon. Higher temperatures will pose new challenges not only in the forest, but also in fisheries, farming and tourism, to name just a few.
The University of Maine has been a world leader in climate research since 1972. The effort is centered at the university’s Climate Change Institute.
George Jacobson – now professor emeritus of biology, ecology and climate change – joined the effort in 1979. Jacobson is also Maine’s state climatologist. At the request of Gov. John Baldacci, Jacobson and other university researchers recently authored, “Maine Climate Future: An Initial Assessment.”
The report can be found at: www.climatechange.umaine.edu/about/reports/climate-future.
Jacobson said there is abundant evidence the state is getting warmer. The rise in temperature will result in changes in the composition of Maine’s forests and the creatures that live within it.
“At a continental level, it is climate change that determines where plants live,” said Jacobson. “Locally, the story gets more complicated. Soils, moisture, insects, fire, disease, drought, human activity and wind all play a role. Every stand [of trees] has its own ecological story. But on the continental level, [the key driver of changes in species composition] is climate.”
About 15,000 years ago, Maine was covered by a mile-thick sheet of ice. Red spruce – a northern species and one of the most important trees in the Maine forest today – grew in Georgia (well south of its current range).
As temperatures rose and glaciers melted, Jacobson said, spruce shifted its range northward. How does he know? Very clear evidence is preserved in the mud at the bottom of lakes and ponds, where pollen from trees and other plants builds up a new layer each year.
“Sediment cores have been studied for over a century,” said Jacobson. “The big change came in the 1950s with radiocarbon dating (of material in the cores.)”
Radiocarbon dating allows scientists to accurately determine the age of organic material – whether it is Neanderthal bones or ancient tree pollen. By collecting sediment cores over a wide area, then analyzing and dating the pollen deposited in them, scientists can create maps that show how wind-pollinated plants have shifted their ranges over time.
The evidence is startling. Rather than a long period of recovery after the glaciers melted, tree species quickly repopulated Maine. Then, in the period between 9,000 and 5,000 years ago, temperatures grew considerably warmer and drier. That made it difficult for spruce to survive in most of the state. Instead of spruce pollen, sediment cores show abundant white pine and also evidence of fire.
The rapid response of forests to climate change can be seen even more dramatically in the period between 1000 A.D. and the present, when the abundance of spruce increased quickly due to a cooler and wetter period (see graphic). In just that 1,000-year span – a few generations in the lives of trees – spruce extended its range southward from extreme northern Maine to New Hampshire and became one of the dominant trees in the forest.
Maine now faces the opposite situation. Rising temperatures are likely to cause red spruce to retreat northward, to be replaced by species that now have more southerly ranges.
“We don’t expect any community to persist in its present location,” said Jacobson. “… It’s likely that the climate will be more like Connecticut, with more hardwood than spruce in the forest, though white pine will probably do alright.
“There will be a longer growing season, and the forest will produce more biomass [grow faster] but the nature of the fiber will be different.”
Warmer temperatures will affect more than trees. Southern animals like opossums and turkey vultures will become more common. The tick that causes Lyme disease will probably become more prevalent. Invasive species and diseases (not only of trees, but of other living things) will more easily take hold in the state.
In the final analysis, the ability of tree species to respond rapidly to a changing climate is good news. Maine will remain the most heavily forested state in the nation, and it will continue to enjoy all of benefits that the forest provides – clean water, clean air, wildlife habitat, jobs, and abundant opportunities for outdoor recreation.
But it seems likely that shifts in forest composition and other changes caused by warmer temperatures will be felt relatively soon. Though humans do not always hear the music, a new band is playing and different dancers are taking the floor.
Fresh from the Woods is produced by Forests for Maine’s Future, a collaboration of the University of Maine, Maine TREE Foundation, the Small Woodland Owners Association of Maine and the Maine Forest Service.
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