What America's Forests Looked Like Before Europeans Arrived

European settlers transformed America's Northeastern forests. From historic records and fossils, researchers know the landscape and plants are radically different today than they were 400 years ago.

But little direct evidence exists to prove which tree species filled the forests before they were cleared for fields and fuel. Swamp-loving plants, like sedges and tussocks, are the fossil survivors, not delicate leaves from hardwood trees.

Now, thanks to a rare fossil discovery in the Pennsylvania foothills, scientists can tell the full story of America's lost forests.

The fossil site is a muddy layer packed with leaves from hardwood trees that lived more than 300 years ago along Conestoga Creek in Lancaster County, Pa. The muck was laid down before one of Pennsylvania's 10,000 mill dams, called Denlinger's Mill, was built nearby, damming the stream and burying the mud and leaves in sediment.

Researchers from Franklin & Marshall College in Lancaster, Pa., discovered the fossil leaves while investigating the lingering effects of milldams. The thousands of small dams — which powered mills, forges and other industry — changed the water table, altering the plants growing nearby and eventually changing the landscape from wetlands to deeply incised, quickly flowing streams.

Before Europeans arrived, American beech, red oak and sweet birch trees shaded Conestoga Creek, according to a study the researchers published today (Nov. 13) in the journal PLOS ONE. Some 300 years later, those trees are gone. The same spot is now home to mostly box elder and sugar maple trees, said Sara Elliott, the study's lead author and a research associate at the University of Texas at Austin's Bureau of Economic Geology.

"This is a very unusual opportunity to compare modern and fossil forest assemblages," Elliott told LiveScience. "It's like you're time traveling," she said.

Elliott carefully peeled apart hundreds of leaves stuck together by mud and layered like a pile of sticky notes. Washing the leaves in a variety of chemical baths helped Elliott determine the leaves' structure and species. The research was performed at Penn State University.

Other kinds of trees found in the fossil layer that have since vanished from North America include the American chestnut, which was attacked by an imported fungal disease called the chestnut blight. Leaves from swamp plants also appear in the mud, confirming that the forested spot was on the upslope edge of a nearby wetland.

"We had a valley margin forest growing right next to the valley bottom in conjunction with all these wetlands," Elliott said. "I think we really have a rather complete picture now of what the landscape was like in this region."

The three dominant tree species found in the fossil forest leaves still exist today in the Northeast, but in different proportions and in different places, Elliot said.

The scientists hope that identifying similar fossil tree-leaf sites will help the massive milldam restoration projects underway throughout the Northeast. The dams left a legacy of toxic sediment piled up behind their walls, as well as reshaped the landscape.

"Having a more complete and enhanced understanding of this past dynamic and complex landscape will help in restoring an ecologically diverse and functional system," Elliott said.
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References:

Oskin, Becky. 2013. “What America's Forests Looked Like Before Europeans Arrived”. Live Science. Posted: November 13, 2013. Available online: http://www.livescience.com/41198-old-growth-forests-before-europeans.html

Ancient Forest Thaws From Melting Glacial Tomb

An ancient forest has thawed from under a melting glacier in Alaska and is now exposed to the world for the first time in more than 1,000 years.

Stumps and logs have been popping out from under southern Alaska's Mendenhall Glacier — a 36.8-square-mile (95.3 square kilometers) river of ice flowing into a lake near Juneau — for nearly the past 50 years. However, just within the past year or so, researchers based at the University of Alaska Southeast in Juneau have noticed considerably more trees popping up, many in their original upright position and some still bearing roots and even a bit of bark, the Juneau Empire first reported last week.

"There are a lot of them, and being in a growth position is exciting because we can see the outermost part of the tree and count back to see how old the tree was," Cathy Connor, a geology professor at the University of Alaska Southeast who was involved in the investigation, told LiveScience's OurAmazingPlanet. "Mostly, people find chunks of wood helter-skelter, but to see these intact upright is kind of cool."

The team has tentatively identified the trees as either spruce or hemlock, based on the diameter of the trunks and because these are the types of trees growing in the region today, Connor said, but the researchers still need to further assess the samples to verify the tree type.

A protective tomb of gravel likely encased the trees more than 1,000 years ago, when the glacier was advancing, Connor said, basing the date on radiocarbon ages of the newly revealed wood. As glaciers advance, Connor explained, they often emit summer meltwater streams that spew aprons of gravel beyond the glacier's edge.

A gravel layer about 4 to 5 feet (1.2 to 1.5 meters) high appears to have encased the trees before the glacier ultimately advanced enough to plow over them, snapping off limbs and preserving the stumps in an ice tomb.

Taku Glacier, located south of Juneau, is currently triggering this same process as it advances over a modern forest of cottonwood trees, offering the researchers a chance to observe the process in real time, Connor said.

Unlike the growing Taku Glacier, which accumulates snow at a high elevation and thus is well situated to grow, the lower-elevation Mendenhall Glacier has retreated by an average rate of about 170 feet (52 m) per year since 2005. This year's summer retreat has not yet been calculated, but the team expects it to be relatively high due to unusually warm summer temperatures, Connor said.

Glacial retreat worries many locals who are concerned about the threat of rising sea levels and loss of major freshwater sources that they rely on for drinking water. Anchorage, the state's most populated city, relies entirely on the retreating Eklutna Glacier for its drinking water.

Still, glacial retreat does offer an interesting opportunity to investigate well-preserved remnants of an ancient world. The team plans to return to the Mendenhall Glacier to dig through sediment in search of pine needles associated with the trees, along with other vegetation. They also plan to measure the growth bands of the trees to determine how old the trees were when they died.

"These are relict stories, and piecing them together with radiocarbon dating and stratigraphic work would help piece together the chapters of the story," Connor said.

The researchers have not yet published the results from the investigation but plan to do so once they have gathered more data.
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References:

Poppick, Laura. 2013. “Ancient Forest Thaws From Melting Glacial Tomb”. Live Science. Posted: September 20, 2013. Available online: http://www.livescience.com/39819-ancient-forest-thaws.html