For hundreds of years, historians have proposed, examined and fought over just what made the Mongol hordes of the 11th Century tick. A West Virginia University researcher discovered some unexpected insight into what might have caused the hordes to rumble and roll into one of the world’s most terrifying empires after she visited Mongolia and brought home some very old and odd slices of wood on a whim.

Theories about the Mongol conquests have sparked almost as many questions as answers.

Were they migrating with an attitude in search of food?

On a horse-backed rampage for treasure, like land-locked pirates?

Satisfying a thirst for power and domination in a wave of warfare that led to an empire that straddled Eurasia?

Mongol leader Genghis Kahn forged an empire that eventually stretched from Asia’s Pacific coast to Eastern Europe and southward into Persia and Southeastern Asia – a feat that may have cost more than 40 million lives.

One of the most popular theories for the Mongol expansion was that the hordes started taking from their neighbors when they were forced to flee drought conditions that made resources of their own very scarce. But a discovery by Dr. Amy Hessl, WVU associate professor of geography in the Eberly College of Arts and Sciences, just might turn that theory on its ear by proposing that the spark behind the great Mongol empire expansion just may have been rain, not drought.

Hessl is a dendrochronologist – a trained expert in analyzing past climate conditions by studying the growth rings in trees. It is an activity that requires skill, patience, powers of observation on a microscopic level and a keen interest in the past. But before she settled on that career path, she was fascinated by history and the waves of human activity that sparked the rise and fall of the world’s great empires. She thought she was headed for a career in archeology, sifting through literal sands of time for clues about ancient civilizations.

“I used to bury things in my backyard and dig them up again,” she said of her childhood in an interview with National Geographic for an on-line bio.

Then, efforts to understand and preserve a changing earth environment captured her imagination. On a summer internship working in Yosemite National Park, she met famous dendrochronologist, Lisa Graumlich and the stage was set for her new career path.

Hessl said she found her “career happy place” where twin interests of history and environment peacefully coexist – even while trudging over an inhospitable Mongolian countryside in search of wood scraps that unexpectedly shed light on 800-year old mysteries.

“I am focused on the interactions between humans and the environment over the past 500-1,000 years,” she explained.

So, when the opportunity came up to work as the principal investigator on a National Geographic-sponsored project in Mongolia focused on how climate change might have affected the region’s wildfire risks, she jumped at the opportunity. Last summer, she teamed up with colleague Neil Pederson of Columbia University’s Lamont-Doherty Earth Observatory, Baatarblieg Nachin of the National University of Mongolia and a squad of local helpers to head out into a remote Mongolian countryside in search of tell tale wood samples.

Their targets for research were wood remains in a 7,000 year-old lava flow. Hessl explained that tree rings can tell the tale of a region’s environmental history. They can indicate whether abundant water supplies promoted growth or drought conditions inhibited it. And, as all high schoolers are taught, counting rings can tell you how many years the tree lived.

Because trees grow more slowly in periods of drought or other environmental stress than they do under more favorable conditions, the size of the rings they produce varies. Looking at the pattern of a tree’s rings can reveal information about the environmental changes that took place while it was alive and growing.

The team of scientists expected to find tree samples that would give them an idea of environmental events going back 500 years or so – adequate for the purpose of their fire risk study. They packed up their laptops, microscopes, chain saws, data collection tools and survival gear and headed into the old lava flow for a search at a spot near the ancient seat of the Mongol empire, the Orkhon Valley where they intended to conduct on-site examinations of samples and document their findings.

Instead, a series of unexpected misadventures occurred that eventually led to unexpected discovery.

When her colleague became too ill to venture out into the hot inhospitable region to pick over the remains of old dead wood and examine old living trees; her Mongolian assistants misjudged their tolerance for dehydration; equipment malfunctioned and time ran out, there was nothing left but Plan B – gather up samples of the feasible dead wood they could find and lug them back to the U.S. for further study in the laboratory.

The exhausted researches trudged back to civilization determined to salvage their excursion. They succeeded beyond their expectations.
Hessl was shocked after her return from Mongolia when researchers began looking closer at the samples they brought back as Plan B. They didn’t turn out to be 700 years old. They turned out to be more than 1,300 years old – dating all the way back to about AD 650.

“We had all this environmental history all of a sudden that we never expected to have,” Hessl said. “It’s all about energy. What we are seeing in the rings is that around the time of the rise of the Mongols, there was abundant rain. Abundant rain made the grasses grow and grass powered the horses that grew the cavalry that conquered the region.”

Hessl said it was “all about energy” again years later when the Mongols, after already establishing a massive empire, suddenly moved their capitol. More evidence from the tree rings indicates that at the same time they moved their capitol from Mongolia to Beijing, there had been a rapid decline in moisture in the Orkhon Valley.

“The move was all about energy again,” she said in her Morgantown lab where a Mongolian flag hangs on the wall between shelves and shelves full of tree trunk slices. “The Mongols were forced to diversify when the grass became scarce. That had traditionally been their energy source for their horses.”

She said that when the Mongols moved, the empire became less dependent on grass and used other energy sources instead: the developed a navy, raised rice products and pursed energy resources that were less grass and horse power based.

“That’s where we learn from the history of past civilizations,” Hessl said. “Just as they diversified and switched energy sources in response to changing water quality and other environmental changes, we are seeing changes in our own civilization too. Right now we use fossil fuels but we will eventually have to find something else and adapt. Exploring how the Mongols adapted might shed light on current challenges.”
In an article about her work that appeared in the March 21, 2012 edition of Scientific American, Hessl stressed that she and her colleagues are not claiming that climate was the main factor in the rise and fall of the Mongols.

“Genghis Khan was really the key to uniting many tribes together and spurred them to expand in a way that’s never been repeated,” she told Scientific American writer Charles Choi. “We just argue that it takes energy to create an empire, just as it does today and rains may have helped provide the grass that powered their horses. After Genghis Khan died, the empire became somewhat factionalized with most historians arguing that it became too large to effectively administrate. We’re saying maybe climate change may have made managing the empire difficult also.”

Hessl isn’t finished yet. It’s back to the Orkhon Valley of Mongolia again next summer with an expanded team and a refocused mission. National Geographic has awarded her another $20,000 grant as principal investigator to expand on the discoveries. Recognizing the uniqueness of the work, its global significance, and its connection to the institution’s strategic goals of global engagement, exchanges of knowledge, and acceleration of quality research, West Virginia University Faculty Senate has also made a financial commitment of $12,000 to support the work and enable a return visit to Mongol territory.

Hessl said that in addition to her graduate student John Burkhart of Morgantown WV, the team will expand to include researchers from other U.S. universities who can use Hessl’s tree ring climate data to estimate how many animals and resources the Mongols could have secured from the landscape. Hessl said historian Nicola Di Cosmo of the Institute for Advanced Study will join the effort to uncover written references to climate that coincide with the tree ring data.

Hessl said Avery Cook-Shinneman at the University of Washington will join the team to collect tubes of sediment from lake bottoms in the region.

“Their samples can show the history of the region in sediment,” she said while sitting at a microscope in the Montane Forest Dynamics Lab, the neatly organized research facility she operates in WVU’s Brooks Hall. “They will look for something called Sporormiella which are spores that thrived in livestock dung. The presence of Sporormiella in the samples can give an idea of how much livestock the Mongols may have been able to accumulate in the time periods we are looking at.”

The addition of an historian to the team makes sense. Hessl’s field of study has many implications for understanding the past. Matching the pattern in trees whose age is known to the pattern in wood found at an archaeological site can establish the age at which the wood was cut and thus the approximate date of the site. By comparing living trees with old logs and finding overlapping ring patterns, scientists have established chronological records for some species that go back as far as 9,000 years.

Research in Hessl’s Montane Forest Dynamics Lab focuses on the interaction between ecosystem processes, climate variability and human activities in forested systems.

Hessl and her graduate students have studied the influence of climate and land use history on fire regimes in the Appalachian Mountains, the Pacific Northwest and have developed millennial-length climate reconstructions for the Mid-Atlantic Region using the tree rings of ancient eastern red cedar collected in West Virginia. Her lab has also explored the relative impacts of climate variability and harvest strategies on carbon sequestration. In collaboration with the National Park Service the lab is exploring plant diversity on the cliffs of the Mountain State’s New River Gorge.

“Earth’s citizens are faced with a host of environmental problems,” Hessl told National Geographic. “By looking at how the Earth has changed in the past and how peoples have responded to those changes, we can better find our way today.”

Hessl’s “career happy place” may not be as large as the Mongol empire, but it is expanding all the time thanks to nationally recognized research results, the commitment of WVU to global engagement, and a society that recognizes the need to look to the past to prepare for the future.

-WVU-

Gerrill Griffith
4/3/12