ARCHAEOLOGY AND ENVIRONMENT (DISCOVERING BARBARIAN EUROPE)

Clark’s excavations at Star Carr from 1949 to 1951 revealed a dump of timber at the edge of a substantial lake, associated with an exceptionally large number of artifacts made from deer bone and antler. Clark collaborated with specialists on animal bones and plant remains to reconstruct the environmental setting of the site and to shed light on the availability of food resources and raw materials. Furthermore, he used aspects of the animal bone assemblage in an attempt to ascertain the seasons during which the site was occupied.

Today, advances in excavation and sampling methods mean that evidence for the environment can be retrieved from most excavations, whatever the soil conditions. The nature of the soil does, however, affect the types of biological materials that will be preserved: sites on calcareous (chalk or limestone) soils, for example, are good for preserving bones and shells, whereas sites on acidic (low pH) soils are not. Such on-site evidence is complemented by the increasingly detailed information coming from off-site deposits, including peat bogs and lake sediments, which have often accumulated undisturbed for thousands of years. Such sequences can shed light on long-term changes in climate, sea level, and plant and animal communities, and can be linked to the archaeological record by radiocarbon or other dating techniques.

CLIMATE AND SEA-LEVEL CHANGES The current period of relatively warm and stable climate is known as the Holocene, and follows a series of cold (glacial) and warm (interglacial) climate fluctuations during the period termed the Pleistocene. The Pleistocene-Holocene transition is traditionally placed at 10,000 radiocarbon years b.p. (before present), but "absolute" dates from annually layered lake sediments, tree rings, and annually deposited ice layers in the Greenland ice sheet indicate that it occurred about 11,500 years ago (or c. 9500 b.c.). Climatic warming at this time was remarkably rapid. In Greenland temperatures increased by about 15°C in a decade or less, followed by another period of more gradual warming over the next thousand years or so. It is remarkable to think that Early Mesolithic people living through this period would have experienced significant climate change within their own lifetimes, along with associated changes in availability of plant and animal resources.

Climatic warming led to the melting of enormous ice sheets that had covered much of northwestern Europe during the Ice Age, producing dramatic changes in sea level and coastal topography. In the Ice Age, Ireland and Britain formed part of a single landmass with continental Europe, but a rise in sea level resulted in the formation of the Irish Sea and then the English Channel, which eliminated the land link to the continent by c. 7400 b.c.

In addition to rising sea levels caused by ice melt (glacio-eustatic sea-level rise), coastal change also occurred due to "rebound" following the release of the weight of ice (glacio-isostatic changes). The effects of sea-level change mean that the modern coast of Europe is very different from what it was at the start of the Holocene, and different parts of the coast were affected differently due to a combination of isostatic recovery, absolute sea-level rise, and sedimentation. Parts of the coast where there was a fall of relative sea level may display raised beaches, for example, while a sea-level rise is indicated by submerged forests and settlements, which may be exposed on the coast at low tide. In addition to changes of sea level, river channels have altered considerably due to erosion and silting, and many lakes formed by the action of the glaciers have long since filled with sediment.

Period

Climate

Evidence

Approximate start date in NW Europe

Subatlantic

Cold and wet

Unhumified Sphagnum peat

c. 800 B.C.

Subboreal

Warm and dry

Humified peat with pine tree stumps

c. 3800 B.C.

Atlantic

Warm and wet

Un humified Sphagnum peat

c. 6000 B.C.

Boreal

Warm and dry

Humified peat with pine stree stumps

c. 9000 B.C.

Preboreal

Sub-arctic

Remains of sub-arctic plants

c. 9500 B.C.

The Blytt-Sernander scheme of Holocene climate change.

After the rapid warming of the Early Holocene, climate remained relatively stable during the prehistoric and early historic periods, although more subtle changes in temperature and rainfall continued to occur. These are apparent from various sources of evidence, of which the most widely available and studied are peat bogs. The degree of decomposition (humification) of peat is related to the climate in which it formed. Under cool or wet conditions the plants making up the peat decompose only slightly and form a pale-colored peat in which individual plant remains are clearly identifiable. Conversely, under warm or dry conditions plant remains decay to a greater degree and produce a dark-colored, highly humified peat. Peat bogs may thus contain layers of pale and dark peat, which can be linked to the climate at the time of deposition. Furthermore, the types of plants making up the peat vary depending on climate. Under very wet conditions the peat may consist mainly of mosses, such as Sphagnum, whereas, under drier conditions trees and shrubs may colonize the bog surface, resulting in the formation of a woody peat.

In the early twentieth century the Scandinavian botanists Axel Blytt and Rutger Sernander used such changes in Scandinavian peat bogs to construct a scheme of Holocene climate zones (see table), which was later widely applied across northwestern Europe. The zones were assumed to represent broadly synchronous changes in climate in different regions, but with the advent of radiocarbon dating it was shown that there was considerable regional variation in the timing and character of climate change. In the 1990s and early 2000s approaches to climate reconstruction from peat were refined to make it possible to record both major large-scale and subtle short-term changes, and improvements in the accuracy and precision of dating mean that these events can often be closely linked to the archaeological record.

Climate change is often invoked as a driving force behind key changes in the archaeological record, such as the adoption of agriculture. In Europe the transition from hunting, fishing, and gathering to farming has long been linked to changes in temperature and rainfall, although some of these hypotheses were based on climate reconstructions that have since been revised. Recent analyses of the ice cores from Greenland indicate that maximum Ho-locene temperatures were reached between c. 6600 and 2300 b.c., spanning the agricultural transition in Europe, and pollen evidence suggests that, toward the middle of this period, summer temperatures across much of Europe were approximately 2°C warmer than today. Warmer temperatures would have affected both natural vegetation and crops, but whether this effect was beneficial would have depended on other aspects of climate, such as the seasonal distribution and quantity of rainfall, the details of which are unknown. Furthermore, climate change during this period varied by region, and it is unlikely that a consistent link to the adoption of agriculture could be demonstrated across an area as environmentally diverse as Europe.

Recent research has also highlighted the significance of short-term climate changes resulting from variations in solar activity, including a period of cooler and wetter climate at the end of the Bronze Age, c. 850 b.c. Such changes may have had considerable implications for land use, by affecting the extent to which "marginal" upland and low-lying areas could be farmed. In the Netherlands, for example, some Late Bronze Age settlements seem to have been abandoned due to a rise in the water table at this time.

An intriguing aspect of environmental change in "marginal" environments in northwestern Europe is the extent to which climate, and hence human activity, may have been affected by major eruptions of the volcanoes in Iceland. In Iceland itself, the output of lava and ash (tephra) from such eruptions could engulf entire settlements, a fate that befell the farmstead of Stong in southwestern Iceland during an eruption of Hekla in a.d. 1104. Could the volcanic gases from such eruptions have had more wide-ranging effects? The debate arises from the observation by the dendrochronologist (tree-ring dating specialist) Michael G. Baillie that particularly narrow rings (reflecting poor growth) in trees from Irish peat bogs and other sites in western Europe appear to be contemporary with peaks of acidity in the Greenland ice sheet resulting from gas emissions from major volcanic eruptions. Such eruptions may have caused climate deterioration by reducing transmission of the sun’s energy, leading to a fall in temperature of perhaps a few tenths of a degree. Some of these "narrow ring events" appear to coincide with periods of change in the archaeological record, such as the abandonment of extensive Bronze Age field systems in upland areas of northern and western Britain. This has led some archaeologists to suggest that trees and humans were responding to the same episodes of climate deterioration. Others remain skeptical of a link, however, noting that the scale of change argued for parts of upland Britain is sometimes greater than that thought to have resulted from the same eruptions in Iceland itself.

Another mechanism by which Icelandic eruptions might have affected distant environments is soil acidification. In areas where soils are already acidic and marginal for agriculture, the "acid rain" following a volcanic eruption can acidify the soil further and push the ecosystem beyond the threshold at which it can be farmed.

NATURAL CHANGES IN PLANT AND ANIMAL COMMUNITIES

The climatic warming at the end of the last glacial period triggered major changes in plant and animal communities, which would have affected the availability of food and other resources to the human population. Parts of northern Europe that had remained free of ice during the glacial period were covered in sparse tundra, but, as the climate warmed, trees began to spread across the landscape from refuge areas in the Mediterranean. Evidence for this spread of woodland comes from analysis of pollen grains preserved in lake sediments and peat bogs (fig. 1). By c. 8000 b.c. much of Europe was covered in dense woodland, the composition of which varied by soil type and climate. In many areas hazel (Corylus avellana) woodland was dominant, and hazelnuts seem to have provided an important food source for Mesolithic people, as they are a common find on sites of this period. At the later Mesolithic site of Staosnaig, on the Hebridean island of Islay in Scotland, thousands of charred hazelnuts were found, suggesting that this resource was harvested systematically.

The spread of woodland was accompanied by changes in animal communities. Tundra species adapted to cold, such as reindeer, were replaced by animals more suited to forest conditions, including roe deer, wild boar, and beaver. Several of these species were hunted by Mesolithic and later peoples, sometimes to the point of local extinction.

HUMAN IMPACT ON THE ENVIRONMENT

The nature and scale of human impact on the environment have changed considerably over time, ranging from the creation of small woodland clearings and the burning of vegetation in the Mesolithic period to major woodland clearance for agriculture in the later Neolithic period and after. Evidence for this impact comes from a variety of sources, both archaeological sites and natural deposits.

One of the principal techniques used to reconstruct the interaction between human activity and the environment is pollen analysis. Many plants produce large amounts of pollen that may be preserved for hundreds of thousands of years in waterlogged deposits. The identification of this pollen makes it possible to reconstruct the original plant communities. The technique can be used to show natural changes in vegetation, such as woodland colonization of the landscape after the last glacial period, as well as the impact of human activity.

Human activity may be detected from pollen sequences in a variety of ways. For example, Mesolith-ic hunting and gathering peoples created small clearings in the dense woodland that covered much of the landscape of Europe, and these clearings can be detected in the pollen record as a decline in the abundance of tree pollen and an increase in that of sun-loving herbaceous plants, such as grasses. Sometimes these changes may be difficult to distinguish from the effects of large grazing mammals, such as wild cattle, or even the tree-felling activities of beaver. In such cases human presence may be established by the presence of microscopic charcoal particles in the deposits. Major natural fires seem to have been rare in prehistoric northwestern Europe, but fire was used by Mesolithic and later peoples to modify the environment. An example is provided by the Early Mesolithic site of Star Carr. The original research by Grahame Clark was followed in the 1990s by a detailed program of biological analyses designed to shed new light on the interaction between people and the environment at the site. High-resolution pollen analysis (samples at intervals of one to two years) was used to look for short-term vegetation changes linked to human activity, combined with charcoal particle analysis to verify the use of fire. This research suggested that people were deliberately burning reedbeds around the lake c. 9000 b.c., perhaps to encourage animals to graze on the lush regrowth. This may be the earliest example of deliberate environmental management in Europe.

Other indications of human activity given in pollen sequences can come from the presence of pollen of "anthropogenic indicators"—plants that are strongly associated with human activity. One example is ribwort plantain (Plantago lanceolata), a plant growing on grazed grassland or fallow arable land. It often first appears in pollen sequences in the Early Neolithic period, when woodland clearings were being created for grazing and small-scale crop cultivation. Other plants linked to human activity include arable weeds and, of course, crops such as cereals. Most crops produce very little pollen, so they are very underrepresented in the pollen record, but the spread of crop cultivation across Europe can be traced by the presence of cereal grains preserved by charring on Neolithic sites.

An intriguing event recorded in many pollen sequences spanning the Early Neolithic period in northwestern Europe is the "elm decline." This was a major drop in the abundance of elm (Ulmus) pollen, from about 10 percent to 1 percent of the total pollen, c. 3800 b.c. Several hypotheses have been proposed to explain it. Originally, it was thought to reflect a response to climate deterioration, but the fact that usually only elm is involved made this hypothesis unlikely. Subsequently, the frequent association of the decline with the first occurrence of cereal pollen led to the view that it represented the spread of Neolithic agriculture: farmers selectively cleared elm woodland growing on the best soils. Cereal pollen dating to several centuries before the elm decline has been found at some sites, however, which suggests that cereal farming was already established.

Another opinion was based on the practice, still employed in some mountainous areas such as Norway, of collecting leafy branches of trees to feed cattle in winter. If elm was used as a source of leaf fodder in the Neolithic period, this might account for its decline in the pollen record, since the removal of leafy branches would reduce pollen production. Archaeological evidence for the use of tree leaves to feed cattle comes from the excavation of early Neolithic cattle barns at Weier in northeastern Switzerland, though here elm was just one of several tree species that had been collected, and one of the least abundant. Leaf fodder collection is unlikely to explain a decline confined to elm, especially since the elm decline was so widespread, even in areas where human populations were probably sparse.

Pollen grain of pine from Mesolithic lake sediment, c. 9000 b.c.

Fig. 1. Pollen grain of pine from Mesolithic lake sediment, c. 9000 b.c. 

Important evidence for the timing of the elm decline has come from annually layered lake sediments from Diss Mere in Norfolk, England. Here the elm decline occurred over a period of just six years. The rapidity of the event suggests it is unlikely it was due entirely to human activity, but there are similarities with the effects of recent outbreaks of tree disease such as chestnut blight in North America and Dutch elm disease in Europe. There is no direct evidence for a disease of elm trees in Neolithic Europe, but remains of the beetle responsible for the spread of Dutch elm disease (Scolytus scolytus) have been found in Neolithic deposits from Hamp-stead Heath in London, England, and wood showing the characteristic burrows made by the elm bark beetle has been found at Weier and other Neolithic sites in Switzerland and Denmark. The beetle acts as a vector for the fungus that causes the disease (Ceratocystis ulmi). The remains of the fungus have not been found but this is unsurprising, as fungi are rarely preserved in the archaeological record.

The disease hypothesis accounts for the speed and wide geographical range of the elm decline, but at many sites an association with human activity is suggested by the presence of cereal pollen and other "anthropogenic indicators." It seems that the elm decline may have been caused by a combination of disease and human activity: as Neolithic people removed elm branches for leaf fodder or building purposes, they damaged the trees and provided points of entry for the disease, thus encouraging its spread. The spread of the disease may itself have encouraged Neolithic people to clear woodland by killing trees and creating natural openings in the dense woodland canopy.

The Neolithic elm decline provides a useful example of the multiple hypotheses that often need to be considered to understand the past relationships between human activity and environment and the range of different types of evidence that can be used to support them.

Several aspects of prehistoric environmental change probably reflect a combination of human activity and natural factors. The expansion of moorland vegetation across previously wooded parts of upland northwestern Europe is another example. Peat formation in such areas may have been triggered by increased rainfall, leading to the replacement of trees by wetland plants such as mosses and sedges, but in some areas human activity is implicated. On Dartmoor and the North York Moors in England, for example, the presence of charcoal and sometimes Late Mesolithic flint artifacts immediately below the peat suggests that people were present and were burning the local vegetation before peat formation began. In such cases it has been suggested that the removal of trees and the use of fire may have altered the hydrological balance of the sites, leading to a rise of the water table, which killed the remaining woodland and triggered peat formation. Thus many of the wild and seemingly "natural" moorland landscapes of parts of Europe may owe their origin, at least in part, to human activity.

Human activity, through burning and grazing herds of animals, also seems to have been involved in the creation and maintenance of other treeless landscapes, such as the heathlands of southern Britain and Denmark. Excavations of ancient land surfaces buried beneath burial mounds (barrows) indicate that woodland had been cleared and soil changes were occurring well before the barrows were built in the Bronze Age.

RESOURCE USE AND SEASONALITY

In addition to the natural deposits that document major environmental changes, evidence for the ways in which prehistoric and early historic peoples modified their environment and exploited its resources is provided by the biological remains from archaeological sites.

Mesolithic peoples lived by hunting, gathering plants, and fishing, and may have moved around the landscape following herds and exploiting seasonally available resources. A characteristic result of later Mesolithic activity in coastal areas is shell middens—large piles of shells, such as cockles and limpets—left from shellfish consumption. Such middens often include remains of other plants and animals used as food, including hazelnuts and fish bones. Archaeologists have attempted to use the animal remains from such middens to shed light on which seasons of the year people were living on the coast. Study of growth lines formed in shells, for example, can show whether shellfish were collected in summer or winter. Ear bones of fish (otoliths) provide another source of seasonal information, as demonstrated by analysis of Late Mesolithic shell middens on the Scottish island of Oronsay. The size of the otoliths was used to assess the age at which the fish were caught, and thus the season during which the midden sites were occupied.

Finds of Late Mesolithic and Neolithic fish traps from the Danish Storebxlt provide some of the oldest evidence that early peoples managed woodland to provide wood for specific uses. The thin interwoven rods used to make the traps seem to have come from woodland that had been coppiced (fig. 2). Coppicing involves cutting down trees almost to ground level, after which the new shoots are left to grow for approximately five to ten years (depending on required size), before they are cut again. The resulting stems are of uniform size and suited for various purposes, from basketry to woven (wattlework) wall panels. Coppiced wood was widely used in prehistoric and early historic Europe, and has been found in excavations of many waterlogged sites, such as the Neolithic, Bronze Age, and Iron Age trackways across the wetlands of the Somerset Levels in southwestern England.

DOMESTIC ENVIRONMENTS, FROM FARMSTEAD TO TOWN

Where plant and animal remains are well preserved, they can provide evidence not only of the environmental setting of a site and the resource use by its inhabitants but also of their domestic living conditions and state of health. Insect remains have been used to assess the level of hygiene on domestic sites, ranging from Norse farms in Greenland and Iceland to urban centers such as Dublin, Ireland, and Oslo, Norway. Different species of insect may be associated with various types and quantities of decaying organic material or may be parasites of particular hosts. An example is provided by the Viking Age town of York in northern England. Here the tenth-century town consisted of closely spaced wooden tenements with waste pits, which yielded huge quantities of organic remains. Analysis of the insects indicated that there were substantial quantities of rotting organic material left lying around town, including waste products from cloth manufacture and dyeing, and from the butchering of animal carcasses and the manufacture of objects from bone, antler, and leather. Analysis of the contents of cesspits indicated not only that the diet was rich in a mixture of cereals, fruit, and meat, but also that the people of the town suffered from intestinal parasites such as whipworm (Trichuris trichiura) and mawworm (Ascaris lumbricoides). External parasites were also commonplace, including human lice (Pediculus hu-manus) and fleas (Pulex irritans). Parasitic infections seem to have been less common away from towns, probably because the lower population densities in the countryside were less conducive to their spread.

A Neolithic fish weir from Oleslyst, Denmark, made from coppiced wood.

Fig. 2. A Neolithic fish weir from Oleslyst, Denmark, made from coppiced wood.

CONCLUSION

Evidence about the nature of the environment, from the domestic to the global scale, is essential for understanding past human behavior. The range of techniques that can be applied in obtaining such evidence is expanding rapidly. Biomolecular techniques, such as analysis of ancient DNA (deoxyribonucleic acid), are improving and will play an increasing role in isolating and characterizing tiny quantities of degraded molecules; isotopic analysis of bone can shed light on diet and provide clues to the movement of people between different landscape zones. The specialized scientific nature of much of this research requires close collaboration between archaeologists and scientists and promises to produce many new insights into human-environment relations.

Next post:

Previous post: