A long-term perspective on human niche construction and alteration of ecosystems
Dr. Katharine MacDonald (Faculty of Archaeology) sketches the background to a recent paper in Science Advances, co-authored by her and other members of the Liveable Planet team.
Currently we face a range of crises including climate change and biodiversity loss which threaten our health and wellbeing and the rights of future generations, as addressed by David van Reybrouck in his recent Huizinga lecture. These crises demonstrably have their roots in human activity, and the recent scale of change dwarfs is enormous. Archaeologists have long been interested in human interactions with their environments, and are often aware of the sometimes quite substantial outcomes of even simple technological interventions. Studying timescales of hundreds to millions of years, archaeology has the potential to provide a very long-term perspective on our emergence as a planet-transforming species. Recent research suggests that in constructing their niches humans may have been altering ecosystems, on a local scale, for a very long time. A human role cannot be ruled out even in periods that are taken as ‘baselines’ for natural vegetation. However, the significance of such a long period of human influence on the environment for ecosystem management and conservation today depends on whether these effects occurred at multiple locations or on a larger spatial scale, and this is as yet unknown.
Wil Roebroeks, Professor of Palaeolithic Archaeology is one of the researchers who developed the Liveable Planet programme. Compared with the other disciplines involved at this early stage, Social sciences, Governance, and Environmental Science, all of which involve research with direct contributions to policy relating to sustainability, the role of Archaeology was least obvious and concrete. The attitude of colleagues varied from interest to sound skepticism, but it was generally agreed that archaeology could contribute narratives about the long term development of our current planet-transforming behaviour, narratives which might have a role in guiding change now and in the future. These debates stimulated us to go back to a rich well-studied dataset which had been intriguing us for some time already, as it was suggestive of a very early human impact on their environment: 125,000 years ago. Could we move beyond mere “suggestion”?
Triangulating between different sources
Ethnographic and ethnohistoric evidence provides a rich picture of ways in which hunter-gatherers alter their niche to increase returns from the ecosystems in which they live. One of the most widespread and diverse approaches involves burning vegetation; this occurs in many contexts and in all biomes, only being rare in the tundra. Sources of information about hunter-gatherers are geographically restricted, dominated by documentation from North America and Australia. The sources include explorer’s journals, missionaries’ reports and settler’s accounts as well as ethnographic studies and they all vary in levels of detail: some are very sketchy while in a few cases they provide access to a treasure trove of information about these practices, including who was involved, what they were doing, how they lit and steered the fires etc. These indicate that small-scale burning in the course of subsistence activities can in some contexts lead not only to increased returns from hunting and gathering, but also to the creation of a landscape that is heterogenous on a small scale, resists major burns, has high richness of certain prey and carnivore species, and has a strong pull on human populations. However, ethnographic and ethnohistoric records only tell us about activities going back 200-400 years.
At the other extreme, we know that fire use was a regular part of human activities in multiple regions of the old world around 400,000 years ago. However, we know very little about how it was used. Identifying burning of vegetation and other forms of niche construction by hunter-gatherers in the archaeological record presents particular challenges because it mimics natural events (the residues of wildfires look the same as those of human burning).
A Neanderthal case study
Our recent research has focused on the locality of Neumark-Nord, Germany, where there is abundant evidence for Neandertal activity including extensive fire use. The deposits at this locality date to the Last Interglacial, a period of about 125-110,000 years ago with a mild climate, in which warmth-loving species of large herbivores roamed in closed canopy forests with occasional short-lived open areas. The Neumark-Nord deposits were laid down in shallow basins which were carved out by the preceding Saalian ice cover. These deposits became accessible to archaeologists as a result of massive brown coal quarrying activities in the area near present-day Halle. The Neumark-Nord 1 basin was investigated from mid-80s to mid-90s by a team led by Dietrich Mania. Discoveries included numerous virtually complete skeletons of large mammals, e.g. straight-tusked elephants, rhinos, fallow deer and aurochs, and a wide range of archaeological traces of Neanderthal activities. The neighbouring Neumark-Nord 2 basin was discovered by Mania’s team in the late 80s, and excavations were carried out between 2004 and 2008 by the Monrepos Palaeolithic Research Unit (Germany) and the University of Leiden. The finds suggest intensive activity by Neandertals, for example a rich level excavated over 500 m2 yielded c. 20,000 stone tools and 118,000 bones or bone fragments. Lots of smaller and larger scatters of artefacts and bone fragments were recovered from the Neumark-Nord 1 basin and its margins. Research at this locality has attested both to Neanderthal hunting of large game, and to probable exploitation of a range of plant foods. This seems to have been a ‘magnet’ location for Neanderthals: this intensive activity continued in the locality over a period of 2,000 years.
The involvement of some of the researchers in the Liveable Planet program refocused our questions about this rich dataset. There is abundant evidence for fire use by Neanderthals at Neumark-Nord , with many of the excavated sites showing traces of fire. The archaeological evidence for Neandertal activity from the excavations can be clearly linked to palaeoenvironmental evidence for vegetation changes and fire history. This record shows that an initial very high charcoal peak corresponds with the arrival of Neandertals at the locality, and with an expansion of open grassland and reduction in tree cover, reflected in the pollen record. Throughout the sequence, Neanderthal activity ties in with higher charcoal density and more open vegetation. It is tempting to suggest that particularly the early charcoal peak represents landscape burning similar to that documented ethnographically. However, while we can narrow down key events to a few decades – a very high resolution for such an old site - it is impossible to determine whether Neanderthals first opened up the vegetation by burning, or whether they moved in after the landscape became more open as the result of wildfires.
Our research, recently published in Science Advances, improves our understanding of the links between Neandertal activity and changes in vegetation in this area, 125,000 years ago. We were able to identify two other basin sites in the region in which the same quality of palaeoenvironmental data was available but where Neandertal activity was limited to a single episode and a few tools only. Comparison with other locations helps us rule out the possibility that variation in large herbivore activity, basin form, or climate could explain the distinctive open vegetation signal at Neumark-Nord. At the same time, the record from both the Neumark-Nord basins confirms that open vegetation was characteristic of the locality as a whole. Human activities kept the landscape open, over minimally c. 3 km2, for around 2,000 years. Based on ethnographic and paleoenvironmental evidence it seems likely that the open vegetation benefited Neanderthals in terms of access to plant foods and prey species. While we lack the detailed information about practices that comes from the ethnographic record, the amount of time over which Neanderthal activities continued to influence vegetation is striking.
Long-term pattern and current relevance
Humans were already a visible factor in shaping vegetation 125,000 years ago. We might expect to find other examples of this, especially since Neandertals and their contemporaries were skilled in fire technology, and we might also expect to find older evidence, since regular fire use is evident from about 400,000 years ago.
What has become clear through recent studies is that long before the appearance of agriculture, human populations were transforming their ecosystems, on a local scale, in ways that benefited themselves and possibly some other species.
The time periods discussed here are often used to provide reference information about the state of natural vegetation in the absence of human impact. This picture has not been changed by our research, since we cannot demonstrate that the small-scale human alteration of the landscape occurred anywhere else in the region or on a scale exceeding several square kilometres, but it does indicate the significance of this type of archaeological research to solve present day challenges given the relevance of such ‘baselines’ for conservation studies, and the need for further research.
Headerphoto: Excavation of a 125,000-year-old archaeological site at Neumark-Nord 2 near Halle, Germany, summer 2007. The excavation of this specific lake shore site, well-preserved in fine-grained water laid deposits, yielded the cut-marked remains of hundreds of large mammals, mainly horses and bovids, and about 20,000 stone artefacts.. Photo/©: Wil Roebroeks, Leiden University