Arctic Dawn
Fossil forest yields clues to a polar swamp
Axel Heiberg, a desert island in
the Canadian Arctic, is an unlikely place for a lush forest. From Cape
Stallworthy, its northernmost point, you can see the Arctic ice pack
stretching toward the North Pole and beyond. Over the horizon, the next
landfall would be Siberia. The island, which is about half the size of
Maine, is shrouded in four months of winter darkness, ice and snow, but
summer brings 24-hour-a-day sunlight and enough warmth to expose brown
hills and river valleys that drain streams off the island's year-round
ice cap.
Summer also reveals the remains of an ancient forest — multiple layers
of stumps, bark, cones, leaves and even logs — squeezed tightly into the
soil of exposed hillsides. Discovered by a helicopter pilot in 1985 and
extending across more than 38 square miles, these forest remnants have
since been studied by scientists from Canada and U.S. Unlike the
petrified forests of Arizona in which wood is literally turned to stone,
this debris was "mummified," buried by floods and then, as the climate
changed, preserved for millennia by cold and arid conditions.
The wood is so well preserved that tree rings can be counted; when
dried, the wood burns — a true fossil fuel. Scientists at the University
of Saskatchewan and the Geological Survey of Canada began analyzing
fossil remains in the late 1980s. A team from the United States,
including University of Maine forest biologist Richard Jagels, visited
the island in 1999 and 2000. Carleton University in Ontario, Canada,
hosts an illustrated Web site (http://hoopermuseum.earthsci.carleton.ca//forest/eo12a.html)
on what is described as "one of the best fossil forests in the world."
Meanwhile, fossils continue to emerge from the soil as persistent Arctic
winds peel black bits of wood, bark and seed cones out of the earth, and
scatter them across the land. Skiers who have trekked across the island
report being slowed by wood stuck to the bottoms of their skis.
Scientists have determined that the forest lived about 45 million years
ago during the Eocene geological age. The fossils speak of far warmer
times, hotter even than what have been projected for the Arctic in the
next century as a result of rising global temperatures. Today,
low-growing sedges and arctic willow briefly poke their heads above the
soil; years ago, the predecessors of 100-foot dawn redwoods and
broad-leafed trees shared the landscape with prehistoric crocodiles,
rhinoceros and birds.
Now those types of trees live in warm, temperate regions of the world.
Just how warm it was, and how plants and animals responded to the
combination of warmth and seasonal light extremes, is the focus of
ongoing research and scientific debate.
At UMaine, researchers are studying one species of fossil tree, a
relative of the modern dawn redwood or Metasequoia, that was dominant
until the planet gradually cooled over millions of years. Dawn redwood
fossils have turned up across the northern hemisphere in Greenland,
Asia, Europe and North America. Scientists thought the species was
extinct in modern times until living specimens were discovered in
south-central China in the mid-1940s. Jagels will tell you that,
although the conditions in which this species thrived no longer exist
anywhere on the planet, dawn redwoods could play a role in our future.
A specialist in both forest biology and wood science, Jagels traveled to
Axel Heiberg with a research team led by University of Pennsylvania
scientist Arthur Johnson. Jagels and his students are studying the
ancient material, as well as live dawn redwood trees, to understand how
the species thrived in the Eocene and what stresses it might have
encountered.
"What interests me most is the physiology and ecology of this forest.
How did these trees grow in a regime of continuous light? During May,
June and July, the sun never sets, although it shines weakly at a low
angle. The whole tree received direct sunlight at some time as the sun
circled above the horizon," says Jagels, a professor in the Department
of Forest Ecosystem Science, whose research has been supported by grants
from the Andrew W. Mellon Foundation and the Maine Agricultural and
Forest Experiment Station.
Continuous light presents a problem for trees. "Without a dark period, a
tree doesn't have the opportunity to recharge the sap wood" with water
and nutrients, says Jagels. In addition, the products of photosynthesis
can build up in leaves and halt or reduce photosynthesis itself.
In experiments with dawn redwood seedlings, Jagels, UMaine associate
scientist Michael Day and postdoctoral research associate Alejandra
Equiza have found evidence that the tree responds to continuous light by
rapidly funneling sugars to growing stems and needles. Continuous growth
and an expanding crown literally give the dawn redwood a branch up on
the competition. Its primary competitor on Axel Heiberg was the larch or
tamarack (Larix species), another conifer that loses its needles in
winter. In contrast to tamarack, dawn redwood produces more needles and
branches that effectively shade out the competition.
Another factor in the dawn redwood's favor is its ability to conduct
photosynthesis in the dim light of an Arctic spring or fall. Working
with Jagels, UMaine graduate student Xiaochun Li analyzed cells at the
surface of dawn redwood needles. Putting the needles under an electron
microscope, she found that they contain chloroplasts — photosynthetic
machinery located well below the surface in most other trees. Like an
owl's eye designed to function at night, the position of these
chloroplasts makes the tree more sensitive to available light. Together
with a convex cell shape that helps to concentrate light, chloroplasts
at the needle surface enable dawn redwoods to conduct photosynthesis at
a high rate, even when the sun is low on the horizon.
In comparison to modern dawn redwood trees, Jagels' studies of annual
growth rings in ancient wood have revealed that the trees on Axel
Heiberg appeared to be as productive as their modern counterparts. In
fact, dawn redwood prefers wet locations (its Chinese name, shui-sa,
means "water fir"), and in the warm, damp paleo-Arctic, it took
advantage of swampy conditions.
Jagels and his colleagues have yet to fully understand the whole dawn
redwood story, why it lost its dominance and could not compete with
other species in places with a regular day and night cycle. But their
work suggests that as the Earth got cooler and drier, dawn redwood had
difficulty competing with newly evolving species better adapted to
changing environments.
Some other conifers, says Jagels, including bald cypress and the
towering redwoods of California, appear to be headed toward a status as
relicts of earlier ages, hanging on in places that are marginal for
other species. As a wood scientist, Jagels would like to harness dawn
redwood for a useful role in industrial forestry. In a 2003 article in
WoodenBoat magazine (for which he writes a regular column), he suggested
that the species has growth and wood properties that make it ideal for
tree plantations.
Fast growth (up to 6 feet annually), preference for growing with its own
kind and ability to do well on low-nutrient, acidic soils enable it to
produce fiber at competitive costs for wood product industries, Jagels
argues. Moreover, the wood's moderate rot resistance and light weight
make it useful for new wood composite materials in boat building and
construction industries.
"Dawn redwood will not be the panacea to fulfill all our future wood
needs," he wrote in 2003, "but I am going to predict that it could
become the radiata pine (currently the most common plantation tree in
the world) of the late 21st century."
Jagels' suggestion has drawn criticism from people who warn of spreading
non-native species in the name of commerce. For example, eucalyptus, a
native of Australia, has raised concerns on the U.S. West Coast, as has
Norway maple in the East. Both have shown an ability to spread and to
outcompete native vegetation. But Jagels notes that dawn redwood was
widely distributed across the globe before it succumbed to a cooler,
drier climate. He stresses that in nearly 50 years of cultivation, it
has not escaped from gardens and other developed landscapes. It also is
important, he adds, to maintain natural preserves of indigenous species
outside of plantations.
Ultimately, saving the genetic stock of relict species, such as dawn
redwood, provides resilience in the face of global change. "That's an
important goal for me and my colleagues. The Earth will continue
changing, and dawn redwood may once again live in high-latitude forests.
Black spruce and other species that dominate in northern boreal forests
do better in cold climates, but in the distant future, those trees may
be restricted to higher elevations," says Jagels.
by Nick Houtman
March-April, 2005
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