Pollen Grains in Sands of Time

By: Dan Penny

Originally Published in 1999

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Over the past 30 years or so, a genteel battle has raged over the prehistory of northeast Thailand. Despite a long history of international archaeological research in the area, little has been resolved since the earthshakingdiscoverythat bronze technology was known in Southeast Asia at least 1000 years earlier than traditionally thought. Research conducted by the University of Pennsyl­vania Museum, particularly in regard to the site of Ban Chiang, has been a focus of this debate.

As past special editions of Expedition (1976 and 1982) devoted to Ban Chiang research show, many types of investigation are necessarily involved in modern archaeology. One important aspect of research into the human past is the reconstruction of ancient environments and par­ticularly the impact of humans on these environ­ments over time. Indeed, the reconstruction of human interaction with the natural environment is playing a key role in the most recent skirmish over Thai prehistory, on the nature and origins of agriculture in the Ban Chiang region.

My own small part in this drama began in 1993. Blissfully unaware of the simmering con­troversies surrounding Ban Chiang and related sites, I began an investigation into the envi­ronmental history of the region as part of my doctoral research at Monash University in Mel­bourne, Australia. It was my intention to investi­gate patterns of vegetation change by analyzing the pollen content of sediments that have slowly accumulated in settings such as lakes and swamps. This science is known as palynology or, more specifically, palaeo- (“ancient”) palynology. Using this approach, I hoped to be able to recon­struct ancient environments in northeast Thai­land and determine how prehistoric people in the Ban Chiang region interactedwith their environ­ment. It is possible, for example, for the palynologists to infer how climate has changed through time, when agriculture may have appeared in an area, and potentiallywhat kind of agriculture may have been practiced. In many parts of the world palynologists have been able to identify the microscopic remains of crop plants or agricul­tural weeds associated with them. While it is not always possible to obtain such direct evidence of agriculture, other indications, such as the modi­fication or disturbance of tropical forests, may provide insight into the economies of ancient populations.

The Cores

Unlike archaeologists, palynologists are sel­dom rewarded with heart-stopping discoveries in the field. In stark contrast to the discovery of a human burial, for example, we are unlikely to uncover any evidence that can be seen with the naked eye. The fieldwork is also less glamorous. I worked in swamps and lakes in the Udon Thani and Salon Nakhon provinces of northeast Thai­land, collecting around fifteen sediment cores. The largest of the sites was a freshwater lake called Lake Kumphawapi, some 30 kilometers to the southwest of Ban Chiang (Figs. 1-3).

During each field season I was stationed in the town of Kumphawapi at the southern edge of the lake. I spent long days working with my wife, Jo, my supervisor, Dr. John Grindrod, and the extremely affable and slightly bemused local assis­tant, Somkit Nimanin (who, I’m sure, thought we were all mad), hammering core tubes into the lake bottom.

My study material also included a sediment core extracted from Lake Kumphawapi by the University of Pennsylvania Museum’s Thailand Paaeoenvironmental Project team (Fig. 4.). This project, led by Drs. Joyce White and Lisa Keal­hofer, represents a focus for the overlapping interests of the University of Pennsylvania and Monash University research teams, and has been the basis of strong collaborative links between the two institutions.

Once the cores were transported to the lab­oratories at Monash University in Melbourne, Australia, the real work began. By chemically treating the lake mud, it is possible to concen­trate microscopic pollen grains preserved within the sediment. By taking a series of samples down through the sediment column (Fig. 5), changes in the abundance of these pollen grains over time can be measured. From this, the impact that humans may have had on the vegetation and the broader environment can be reconstructed.

Patterns in the Vegetation

Around three hundred samples and an estimated 125,000 pollen grains later, a striking pattern of vegetation change began to emerge. Prior to the height of the last glacial period (20-40,000 years ago), northeast Thailand would have looked very different than it does today. My research indicated the presence of a forest dominated by Pine and Oak instead of the modern tropical deciduous forests. As the global climate became cooler and drier at the height of the glacial period (around 18,000 years ago), conditions became so dry in northeast Thailand that many lakes and swamps dried out. As a result, the plant fossils that normally preserve in these wet environments were destroyed, and no pollen information was recovered on the vegetation of the time. However, when conditions improved (about 10,000 years ago), Lake Kumphawapi began to fill, and the plant fossils that were pre­served in the lake sediment from this time indi­cate that the vegetation surrounding the lake had changed markedly. Due to increased monsoon rainfall during the early part of the Holocene epoch (10-6000 years ago), these forests were more diverse than their predecessors, and had clear similarities with modern Thai forests.

Yet around 6500 years ago, something remarkable happened to the burgeoning tropical forests of northeast Thailand. Many tree species decreased in abundance, while others disap­peared from the pollen record altogether (Fig. 6). This striking forest decline is coincident with a substantial increase in the amount of micro­scopic charcoal particles preserved in the lake mud, a crude indication of fire in the lake catch­ment. The regional climate at the time of this episode was wet and warm relative to modern conditions, and there is no evidence to indicate a sudden change in climate to drier conditions that would promote natural burning. The pat­terns of vegetation change documented at Kum­phawapi may, therefore, reflect the activities of prehistoric human populations rather than nat­ural environmental change (Fig. 7). The pos­sibility that those activities might include land clearance for some form of agriculture is less certain, and has become the subject of scholarly debate.

The possibility of humans disturbing forests in the Ban Chiang region beginning around 6500 years ago is intriguing, since up to now there is no archaeological evidence of humans living there this long ago. Even the oldest esti­mate for the initial settlement of Ban Chiang of between five and six thousand years ago, an esti­mate which some would argue is far too generous post-dates the evidence for forest disturbance by at least one thousand years! The evidence for significant forest disturbance through burning led me to formulate a hypothesis that human populations existed in northeast Thailand prior to the development of permanent, relatively complex domestic communities such as Ban Chi­ang. These earlier populations possibly practiced shifting cultivation and/or hunting and gathering in concert with an intensive use afire as a tool for landscape manipulation. The lack of archaeo­logical evidence for such communities may reflect that such evidence did not preserve, has been destroyed, or is simply yet to be found.

In any case, the information obtained from the lake sediments at Kumphawapi and related sites—natural archives of environmental data—is tantalizing and certainly worthy of more detailed investigation. It may be that with further research into past environmental change, particularly when coupled with future archaeological investi­gations, the missing evidence required to test the hypothesis I have proposed will emerge.

 

 

Cite This Article

Penny, Dan. "Pollen Grains in Sands of Time." Expedition Magazine 41, no. 3 (November, 1999): -. Accessed February 23, 2024. https://www.penn.museum/sites/expedition/pollen-grains-in-sands-of-time/


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