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Summer 2012
In this Issue of Spheres

Seeing the Forest
for the Trees

Tightening the Scientific
Understanding of the Belts

Big Science in a
Pintsize Package

Rock of Ages

Geospatial Science Gets
a Space of its own

News and Notes
Faculty, Staff, and Student News
From the Director

Institute for the Study of Earth,
Oceans, and Space
EOS Director: Harlan Spence
Editor: David Sims
Designer: Kristi Donahue
Circulation: Laurie Pinciak

Morse Hall, 8 College Road,
Durham, NH 03824


“this challenges the current theories on the legacy of pre-Columbian human impacts on the structure and composition of the Amazonian forests.”

"the amazing biodiversity of the Amazon is not a by-product of past human disturbance and we can't assume that these forests will be resilient…”


“I would also like to bring a paleoecological perspective to EOS, and involve undergraduates in a part of the research process…”

Summer 2012

Seeing the Forest for the Trees
Contrary to popular belief, scientific evidence shows the pre-Columbian western Amazon rainforest was largely undisturbed

POSTDOCTORAL RESEARCHER Crystal McMichael of the Earth Systems Research Center (ESRC) has a background in Amazonian paleoecology–the study of Amazonian ecosystems and their changes through time, specifically over the last several thousand years. She is not, she stresses, an archaeologist, but her first major publication–a paper in a recent issue of Science on which she is lead author–caused quite a stir in the latter discipline, and beyond.

Crystal McMichael on an expedition to the Ecuadorian Amazon for field research. Photo by Dunia Urrego.

In a nutshell, McMichael's research, which she conducted as a doctoral student at the Florida Institute of Technology, has helped overturn the widely held assumption that the Amazon prior to European contact was a "cultural parkland" bustling with people who leveled forests, planted crops, and utterly transformed the landscape.

Not so, according to McMichael and colleagues based on the 247 soil cores they gathered from 55 sites from central and western Amazonia in Peru and Brazil. Rather, analysis of those samples points to small, shifting human populations that had little long-term effect on lowland western Amazonian forests and, McMichael says, "this challenges the current theories on the legacy of pre-Columbian human impacts on the structure and composition of the Amazonian forests."

What it means is that the massive land use changes now occurring in the Amazon do not have historical precedent and, thus, the assumption that the forest can bounce back following widespread deforestation is incorrect.

Currently, pre-Columbian population estimates vary widely–from 500,000 to 10 million. Knowing with more accuracy how many people might have impacted the rainforest through agriculture and development prior to European contact will help scientists understand how the Amazon Basin might withstand current pressures from deforestation, selective logging, and development.

Says McMichael, who now works with ESRC tropical ecologist Michael Palace, "I think part of the problem is that the 'manufactured landscape' idea is based on just five or six areas of the Amazon where evidence of large populations have been found, and there has been no empirical data to date that suggests these civilizations were common across vast tracts of the forest. Our data suggests that in our sampled regions, human disturbance was not spatially extensive. Now we can begin to predict which areas most likely had larger-scale impacts, and which areas didn't."

McMichael (right) and undergraduate assistant Monica Zimmerman use a handheld soil auger to collect samples in the lowland forests of Peru.
Photo by Benjamin McMichael.

The data points McMichael and her Ph.D. advisor Mark Bush gathered were from areas in central and western Amazon that were likely disturbed by humans, including river banks and areas known from archeological evidence to have been occupied by people. They also sampled in areas far removed from rivers, where the occupational history was unknown. They used markers in the cores to track the histories of fire, vegetation, and human alterations in the soil.

Specifically, these markers were of three types: terra preta or "Amazonian black earths" that designate areas where indigenous Amazonian peoples lived and worked the land prior to colonial contact in the late 15th century; charcoal, which in the perpetually rainy western Amazon is likely evidence of deliberate, human-set, land-clearing fire; and microscopic silica deposits known as phytoliths that scientists can use to identify plant species and determine if an area was cleared of forest and planted with crops, for example.

"We did not find terra preta with any of our samples across western Amazonia, McMichael says. "So that means there was very little intensive human habitation at our sites. There was some evidence of charcoal, meaning there was fire at some point, but our phytolith analysis on those same soils very rarely found evidence of canopy opening or agriculture."

Notes Alan Tessier, program director in the National Science Foundation's Division of Environmental Biology, which funded the research, "The findings have major implications for how we understand the effect of the land use change now occurring in Amazonia."

McMichael says that "the amazing biodiversity of the Amazon is not a by-product of past human disturbance and we can't assume that these forests will be resilient, because many of them have only been lightly disturbed in the past." She notes further that there is no parallel in western Amazonia for the scale of modern disturbance that accompanies industrial agriculture, road construction "and the synergies of those disturbances with climate change."

From the Deep South north, via Amazonia

McMichael, a native Georgian, ended up at the ESRC because of a common Amazonian connection with Palace, who specializes in tropical ecology, remote sensing, and has a background and continued interest in archaeology. Since 2010, Palace has been collaborating with McMichael's former Ph.D. advisor Mark Bush (and, thus, McMichael as well) on a three-year NASA Space Archaeology Program project using satellite remote sensing technology to locate terra preta sites in the Amazonian basin. Indeed, the lion's share of McMichael's current funding comes from that NASA project with additional money coming from the Iola Hubbard Climate Change Endowment through ESRC.

"So we've actually been collaborating for several years," notes McMichael. "For Mike's work, we provided all the field data by gathering some 400 soil cores, including the 257 we gathered specifically for our project in central and Western Amazonia. And these served as field-truth data points that he could compare to his remotely sensed terra preta sites."

river bluff 
A river bluff along the Madre de Dios River in Peru. McMichael et al found that bluffs like these contained more frequent evidence of human disturbance compared with locations far removed from rivers. Photo by Benjamin McMichael. 

Like McMichael's work as detailed in the recent issue of Science, Palace's project also seeks to help nail down the much-disputed population estimates of pre-Columbian indigenous peoples in the Amazon Basin lowlands (see "Time Traveling Via Satellite from the Summer 2010 issue of Spheres). However, Palace (along with co-investigators Bush and Brazilian archaeologist Eduardo Neves of the University of San Paulo) is looking exclusively at terra preta sites and doing so using imagery from the Hyperion sensor onboard NASA's Terra satellite.

The Hyperion camera "sees" in 220 spectral bands of light, allowing scientists to identify the chemical makeup of tree leaves, which in turn is related to nutrients in the underlying soil. The more nutrient-rich leaves or specific groups of tree species seen by Hyperion are the signature for the terra preta sites, which contain soil rich in organic matter, charcoal, and nutrients and are frequently associated with large accumulations of potsherds, bone, and other artifacts of human origin. The soils were created hundreds of years ago when indigenous populations slowly burned trees to make soil equivalent to "biochar," which is extremely efficient at storing carbon and nutrients and provides fertile, productive farmland.

"This is a big issue because people think there may be thousands of terra preta sites across the Amazonian basin," Palace says, "and if we can show they are indeed that extensive it will really change our understanding of how many people lived in the region and the impact they had on what we still perceive to be 'pristine' forest."

McMichael's research found no soil cores containing any evidence of human artifacts or terra preta. "So essentially, my Ph.D. work provided Mike's project with negative data sites–that is, no evidence of large-scale human habitation and landscape change."

The ultimate goal of Palace's NASA Space Archaeology project is to learn to identify the difference between sites that are terra preta and those that are not using the complex data from the Hyperion imagery. McMichael's ground-truth data will aid in this effort.

Says Palace, "Using the Hyperion imagery, we've been developing methods that will allow us to extrapolate across the entire Amazon landscape and identify the location of other terra preta sites. This will allow archaeologists to go there and determine if they are indeed terra preta and, from that, we should be able to accurately estimate the indigenous population prior to colonial contact. We will also be able to look at the connectivity and spatial dimension of these sites across the landscape and compare the location with other geological and geographic information."

McMichael's role in the NASA project is to assist in data interpretation and publication of the work. And working within the ESRC, she stresses, she'll have the opportunity to learn advanced GIS and remote sensing techniques.

"One of my, and Mike's, goals is to advance the use of remote sensing techniques in paleoecological and archaeological studies," McMichael says. She adds, "I would also like to bring a paleoecological perspective to EOS, and involve undergraduates in a part of the research process. As part of that we'd set up a charcoal and phytolith processing lab that would allow me and other researchers a chance to look at historical fire regimes and vegetation change within any given study site."

by David Sims, Science Writer, Institute for the Study of Earth, Oceans, and Space.