Glacial Ice Core Samples Reveal Sustainable Land-Use Practices in the Ancient Incan Empire

In the Eastern Cordillera of Bolivia, pollen grains travel from near and far to become sandwiched in layers of snow in the Andean mountaintops, ultimately becoming trapped as the layers turn to ice. Such is the case on the Illimani Glacier, which towers approximately 2,500 meters over Lake Titicaca. The lake sits at an altitude of 3,800 meters above sea level in what was the heart of the ancient Incan Empire.

University of Bern paleoecologist Sandra Brugger headed a team of researchers from various European universities to investigate the vegetative history of the Andean region. Their findings, published in Quaternary Scientific Reviews, indicate that the Inca used sustainable land use practices and that large scale ecological changes did not occur until 1740, long after the Spanish invasion and fall the Inca. The study is one of the first to reconstruct past ecology using pollen grains pulled from glacial ice.

The goal of Brugger’s study was to determine the resilience potential of the Andean mountain-forest ecosystem to a varying intensity of anthropogenic land-use practices. The researchers constructed a timeline of vegetation from 10,000 BC through to the present day. Of particular interest were the years following 1438, which represented the transition from the rise to the demise of the ancient Inca, which was then followed by the the reign of their Spanish conquerors. The degree to which the indigenous peoples altered their environment is a topic still deeply debated amongst researchers.

The Moray Agricultural Terraces (Source: Flickr/Shawn Harquail)

Much like tree rings, glacial ice accumulates in distinct annual layers; therefore, scientists can date ice core samples by ring counting, analyzing the layer’s isotopic signature, or by finding evidence of volcanic eruptions that have been well-dated throughout history. These methods are extremely accurate. Ice from the uppermost layers, which correspond to the last two-hundred years, can be dated within two to five years, while the ice corresponding to the time period of the Incas can be pinpointed to within two decades of accuracy.

The methods for extracting ice cores are actually quite challenging, Brugger said. An experienced team is required to extract samples from high altitudes because conditions become increasingly treacherous with elevation. Moreover, they must ensure that samples remain frozen throughout the delivery process—in this case, from Bolivia to Switzerland. “If they melt, samples are no good,” said Brugger.

The team of Margit Schwikowski at the Paul Scherrer Institute in Switzerland undertook these dangerous drillings, climbing to an elevation of approximately 6,000 meters above sea level. Additionally, they analyzed the chronology and measured many chemical species in the ice cores. Two core samples from the Illimani Glacier were extracted: one in 1999 and another in 2015.

Ice core drilling in Barrow, Alaska (Source: Flickr/NASA: Kathryn Hansen)

Once in the lab, Brugger applied a series of evaporative and chemical-processing techniques to isolate pollen grains from samples corresponding to specific time periods. Each of the samples held approximately 500 pollen grains. “A good sample took me two to three hours to identify,” she said. A bad sample, she added, could take an entire day. The whole process took about three months.

The trickiest part, according to Brugger, was the patience required to identify the pollen. Not only is the catchment area of Illimani large, but the Amazon basin is also one of the most biodiverse regions on the planet, so many different species of pollen were represented in the samples. Undoubtedly, the identification process was painstaking work that required long days behind a microscope at a lab bench – far from the charm of the Bolivian Glacier.

Sandra Brugger counting pollen with a light microscope (Source: Manu Friederich)

Much of the previous research on Andean vegetation was constructed using pollen grains from lake sediments, noted Brugger, which ultimately captures more of a local signal from vegetation directly surrounding the lake. In what was the heart of the Incan Empire near Lake Titicaca, archaeological records suggest that pre-European cultures were highly advanced, domesticating llamas and alpacas, harvesting a wide variety of crops, and practicing metallurgy. Together, these practices could have brought about significant land-use impacts.

Digging deeper, researchers found that llama dung was an important maize fertilizer for the indigenous Andeans.

The switch to agricultural reliance allowed the Inca to abandon traditional hunting and gathering methods and supported the growth of society. An article recently published in the Journal of Archaeological Science details how oribatid mites that once dined on llama feces have been found in sediment cores from wetlands such as Lake Marcacocha, high in the Andes. As merchants passed through these areas with their llamas and maize yields, they boosted the oribatid mite population of the wetlands. This population boom strongly correlates with the time period dominated by the Inca (1483-1533), and the mites’ eventual decline corresponds to the arrival of the Spanish conquistadors, who wiped out the Inca and replaced their llamas with cows, horses, and sheep.

Interestingly, a study published in Applied Animal Behaviour Science suggests that llamas are not as impactful on the landscape as the Old World animals brought over by the Spanish. While llamas graze evenly among the various plant types, cows and sheep appear to be more scrupulous in their dietary decisions. Llamas do not eat plants down to their roots and have padded feet that are less environmentally destructive than hooves. Additionally, explained Brugger, while the native Puna grasses declined around 1740, the population of nutrient-loving weedy species escalated due most likely to the increase European cattle grazing activity. Therefore, the Incan llama grazed the land in a way that was sustainable to the Andean ecosystem, while their European counterparts decimated the land.

Unlike lakes, glaciers trap pollen on a larger scale, as particles drift in from a catchment area of approximately 200-300 kilometers in each direction. Brugger’s research suggests that, on a large scale, the Incan people did not change the Andean forest composition. It is important to note that local versus regional pollen collection methods do not necessarily contradict one another, said Brugger. Instead, they reveal that pockets of disturbance may have occurred closer to the lake where paths and roads were constructed, but overall, the Incan empire did not leave a significant ecological footprint.

Puna vegetation, typical of the Bolivian altiplano (Source: Flickr/Geoff Gallice)

The team identified vegetation that dates as far back as 10,000 BC, establishing an ecological baseline of plant diversity prior to human intervention in the landscape. The baseline served as the control for which human-induced vegetation change over time could be compared.

Brugger found small signs of maize, quinoa, and amaranth, after AD 1, suggesting that the Incas, as well as the indigenous populations before them, grew agricultural crops. Despite signs of human impact, Puna composition did not deviate from previous centuries.

Likewise, the expansion of Polylepis and Alnus after the year 800 followed a warming climate trend. Although Alnus, commonly know as alder, was favored for agroforestry, its range did not dissipate during the Incan regime. According to the book An Environmental History of Latin America, the Incan emperor himself maintained a sustained population of Alder and inflicted harsh punishments for unauthorized logging. In an area naturally defined by so little trees, the alder’s continued existence suggests strict environmental regulation. Its population soon declined with the arrival of Europeans.

A eucalyptus plantation (Source: Flickr/Hari Priyadi)

According to Brugger’s data, changes in the mountain forest composition didn’t occur until around 1740 (two hundred years after the fall of the Incan Empire), implying a long transitional period before the Spanish were able to establish a stable land-use system. After 1740, the pollen record showed a rapid increase in dry grasses and nutrient-loving, weedy species, typical of pasturelands. Then, around 1950, signs of eucalyptus and pine appear in the pollen record, a result of the Bolivian land reform that promoted timber plantations.

Picture from Illimani sitting above La Paz (Source: Margit Schwikowski)

Brugger is now stationed at the Desert Research Institute in Reno, Nevada, analyzing pollen and charcoal in ice cores from Central Greenland in order to reconstruct the response of sensitive Arctic ecosystems to past climate change. “It was a sensation that the approach actually worked,” said Brugger, “as the site was extremely remote from any plants — and pollen.” The prestudy to the project is published in The Holocene.

Glaciers provide an incredible glimpse into the past because they safeguard microscopic clues that allow researchers to uncover our most ancient secrets. For instance, Brugger’s study suggests that the Incan people, though large in number, were able to form a society that peacefully coexisted with its environment. Modern society has largely degraded the Bolivian ecosystem, but might learn a thing or two by studying ancient Incan methods of sustainable agriculture and agroforestry. Brugger’s research is part of a larger project that examines glacial cores from around the world to explain our past. As the project gains momentum, scientists can begin to unravel other fascinating mysteries trapped within glacial ice.

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Millennial Climate Effects on a Lake Ecosystem in Southern Chile

With climate change, people are eager to understand environmental changes over the last few millennia. Unfortunately, regions in the Southern hemisphere are not as well understood as those in the Northern hemisphere, where more data sources are found. This information can be useful in estimating future environmental changes.

A recent study published in the journal The Holocene, scientists examine the millennial changes in the environmental conditions in the Lake Pastahué ecosystem of Chiloé Island, located in southern Chile. Two particular climate events within this period are compared: the Medieval Climate Anomaly (MCA), which was a period of warming from 800 and 1300, and the Little Ice Age (LIA), when temperatures dropped between 1300 and 1850. Scientists investigated signals of climate change in history through analyzing sediment samples from the lake. They also examined historical records to help reconstruct past environmental conditions.

Houses on stilts line the edge of Chiloé Island (Source: Backpackerin/Pixabay)

Biological indicators (pollen and midges) and sedimentological indicators (organic matter and magnetic susceptibility) provided information on the past ecology. Tiny pollen particles that slowly settle into the earth signify historic plant and forest compositions. Midges, popular for fly-fishing, were used as indicators of the trophic changes in lake. Sedimentological indicators allowed researchers to establish a chronological timeline of the core sample, and provided useful information on soil quality.

Researchers found that the highest percentage of pollen was observed during the MCA period. The particles came from trees typically found in the temperate Valdivian forests, suggesting warm conditions. An absence of aquatic plant species, along with an increase in plant species suggests decreased precipitation and increased temperature. Midges adapted to warm conditions were found in this sample, as well as species adapted to semi-terrestrial ecosystems. This suggests the lake was impacted by surrounding terrestrial ecosystem, or a lower water level. These findings were then compared to historical records from 1100-1350, where similar conditions were also observed in Central Chile.

For the LIA period, records show that the climate in central Chile was cooler and more humid beginning in 1350. Pollen results match those of cold events from the Northern Hemisphere. Pollen from trees and shrubs found typically in the North Patagonian forest were recovered, reflecting cold and humid conditions. Aquatic species are much more abundant in this sample, suggesting a larger lake basin. The vegetation structure was also noted to evidence a more humid environment than the earlier period.

Patagonia stretches around 260,000 square miles across South America, consisting of glaciers, steppes, and forests. (Source: Max Pixel)

Historical records of San Rafael Glacier give us a glimpse into the past environment of the region. On a journey from Chiloé to San Rafael Glacier in 1766, a priest described ice floating along the coast up to the glacier. At a later period, Captain Enrique Simpson, a military officer and Admiral of the Chilean Navy, referenced the dimensions of the glacier during his explorations of Chilean archipelagoes in 1875. He reveled at the size of the glacier, describing it as more than a thousand meters high and extending many miles from north to south. According to the article, an explorer at a later period, Hans Steffen in 1910, shared similar findings. “Studying the location and the current dimensions of this huge glacier, we found almost no difference with description given by Captain Simpson on his voyages,” said Steffen.

GlacierHub spoke with Michael Kaplan, a glaciologist who studies climate history in South America. Kaplan considered it novel that the researchers used many techniques and examined historical records in the article. He found it useful to include the historical records of the extensiveness of glaciers, especially considering the state of glaciers in South America today. This reference helps show how climate changes have impacted glaciers and influenced retreat over the course of the millenium. Kaplan also felt that researchers have effectively represented environmental changes in this region during the MCA and LIA. “They show that these events had some manifestation in southern South America, and that’s a really important finding of the paper,” he added.

San Rafael is a major outlet glacier of the Northern Patagonia Ice Field in southern Chile. (Source: Mujer Chilena/Flickr)

Scientists from the study have also observed a growing reduction in tree pollen for the last century. They found that most midge species have diminished. The absence of species related to high nutrient levels suggests that the nutrient conditions at the lake were lower than previous periods. Conditions at this time were warmer and drier than the LIA, and this supports tree ring data which presents the previous 100 years as some of the driest in recent centuries. These environmental changes can be expected to intensify if the climate continues to experience dry conditions.

Marcos Mendoza, an anthropologist who studies environment in Latin America, commented on the relevance of this information for climate projections. Mendoza also told us that these types of studies can be useful in understanding how tree and plant species might respond to future climatological changes. “As indigenous communities, scientists, land managers, and others begin to anticipate how changing temperatures and precipitation patterns will affect the Latin American region of Patagonia, studies like Castro et al. provide windows onto past environmental and climatological conditions,” he said.

This study is useful in understanding the sensitivity of environmental systems to changes in climate. Although historical require careful digging through sources, they can be useful in filling in the gaps in our understanding of past environmental conditions. Reconstructing past conditions can help assess potential changes as well, which may impact people and their environments.

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Hazards at Ice-Clad Volcanoes: Phenomena, Processes, and Examples From Mexico, Colombia, Ecuador, and Chile

Photo courtesy of the study
Photo courtesy of the study

“The interaction of volcanic activity with snow and ice bodies can cause serious hazards and risks[….] Case studies from Mexico, Colombia, Ecuador, and Chile are described. These descriptions depict the way in which the volcanic activity has interacted with ice bodies in recent volcanic crises (Popocatépetl, Mexico; Nevado del Huila, Columbia; Llaima and Villarica, Chile) and how the lahar processes have been generated. Reconstruction of historical events (Cotopaxi, Ecuador) or interpretation of events from the geological remains (Citlatépetl, Mexico) help to document past events that today could be disastrous for people and infrastructure now existing at the corresponding sites. A primary challenge for hazard prevention and risk reduction is the difficulty of making decisions based on imperfect information and a large degree of uncertainty. Successful assessments have resulted in the protection of lives in recent cases such as that at Nevado del Huila (Colombia).”

Read more about the study here.

 

Ancient pollen reveals droughts between Sierra Nevada glacier surges

The Sierra Nevada region.
The Sierra Nevada region. Courtesy of Wikipedia.

“Hidden below the surface of California’s Central Valley are pollen grains from the Pleistocene that are providing scientists with clues to the severity of droughts that struck the region between glacial periods.

The Pleistocene—the age of mammoths and mastodons—occurred between 1.8 million and 11,500 years ago. For this new study, scientists dug up Pleistocene sediment samples containing buried pollen from the Central Valley. They found that pollen samples dated from interglacial periods—years between surges in the mountain glaciers—predominantly came from desert plants. The same sediments lacked pollen from plants of wetter climates.”

To learn more about the new findings, click here.

 

Adapting in the Shadow of Annapurna: A Climate Tipping Point

02780771-35.3.cover“Rapid climate change in the Himalaya threatens the traditional livelihoods of remote mountain communities, challenges traditional systems of knowledge, and stresses existing socio-ecological systems. Through semi-structured interviews, participatory photography, and repeat photography focused on climate change and its impacts on traditional livelihoods, we aim to shed light on some of the socio-cultural implications of climate related change in Manang, a remote village in the Annapurna Conservation Area of Western Nepal…. Continued development of relevant, place-based adaptations to rapid Himalayan climate change depends on local peoples’ ability to understand the potential impacts of climate change and to adjust within complex, traditional socio-ecological systems.”

To learn more about the study and its findings, click here.