Human environmental dynamics on Exmoor during the Mid Holocene

Human beings have had a substantial impact on the natural environment, with ongoing debate about the Anthropocene and how we should define this period.  Within this context, geoarchaeology has a critical role to play in understanding both the impacts of past human societies on the landscapes they inhabited, and the time at which human beings became the most important variable causing environmental change.  Nowhere is this more relevant than on Exmoor. 

Podzolisation of soils in the uplands of southwest Britain is widely recognised during the early/mid Holocene. The change from brown earth soils associated with a temperate deciduous woodland into an acidic raised mire is a feature of the Holocene evolution of areas such as Dartmoor, Bodmin Moor and Exmoor.  However, the reasons driving this change remain elusive, with three competing ideas: the climatic scenario (i.e. change is driven by climatic variability), the anthropogenic scenario (change is driven by human exploitation of these landscapes) and the middle ground (change is driven by a combination of human and climatic factors).

In contrast to Bodmin Moor and Dartmoor, Exmoor has a limited range of known early- to mid-prehistoric monuments.  However, recent work by this project has revealed several important monuments such as Mesolithic cooking pits, Bronze Age burnt mounds and burial cairns, and a possible prehistoric segmented enclosure, all of which have been associated with a remnant brown earth palaeosol and overlying podzolic peat soil (Figure 1).  The discovery of such monuments and fossilised soils allows the soil conditions and environment to be understood and dated at the time of human activity. It permits models to be constructed of the role played by human beings in changing, destroying and creating habitats in this upland landscape.

The project runs has run from 2013 and ran through to 2018. It was funded by Southwest Water through the Upstream Thinking ‘Exmoor Mires’ project.

 

Sampling-for-paleaosol-at-Wintershead

Figure 1: Sampling the palaeosol at Wintershead, Exmoor, associated with Mesolithic ‘cooking pits’.

Project aims

The project aims were to map the extent of a prehistoric/early historic palaeosol across Exmoor, and understand the distribution of earlier archaeological features relative to this palaeosol. The date, age and human signatures associated with the change from brown earth soils to podzols are being elucidated in order to answer a fundamental question: “On Exmoor, is environmental change and degradation in the Mid Holocene driven by human beings or through climatic variability?” 

Such research raises important questions about the maintenance of biodiversity within a national park such as Exmoor; if we do not understand how these habitats were created how do we know how to maintain them?

Wintershead-soil-micromorphology

Figure 2: Soil micromorphology thin section from Wintershead showing underlying brown earth palaeosol and degraded sandstone (Acknowledgement Richard Macphail, UCL: scale 7.5cm)

Fig-3---analysis-of-the-palaeosol-at-Wintershead

Figure 3. Preliminary analysis of the palaeosol at Wintershead, showing a soil collapse and change to podzol from c. 15cm, associated with a spike in a magnetic susceptibility, a clear anthropogenic signal.

Project findings and impact

The results so far have been very exciting. A brown earth palaeosol has been identified in several locations across the raised mire, suggesting a buried preserved prehistoric landscape underneath the later peat. Through investigating a range of sites and using a range of techniques (e.g. tephrachronology, radiocarbon dating, particle size analysis, soil micromorphology (Figures 2 and 3)), the date of the onset of podzolisaton in different locations has been established. 

In some places, such as Wintershead, the date is much later than the classic model of Bronze Age deforestation would suggest. Rather than being associated with a climatic downturn (the sub Atlantic amelioration), pollen analysis suggests that podzolisation was occurring within a largely cleared landscape, possibly as late as the post Roman period. 

Work is ongoing, identifying different locations for palaeosol sampling and identifying previously unrecorded prehistoric monuments (Figures 4 and 5), finishing laboratory analysis, and integrating the palaeosol data with wider pollen signatures from spring mires. However, it would seem that the creation of large parts of Exmoor’s podzolic raised mire occurred much later than previously thought, potentially indicating an anthropogenic driver to change.

sampling-for-palaeosol-at-Spooners

Figure 4: Sampling of a truncated brown earth palaeosol under a Bronze Age burnt mound at Spooners, Exmoor.

Research team

Dr Chris Carey

Dr Lee Bray (Exmoor National Park Authority, now Dartmoor National Park Authority)

Outputs

Bray, L. S., with Fyfe, R. and Carey, C. J.  2015.  The past and the peat. Archaeology and peatland on Exmoor.  Short Run press: Exeter.

 

Partners

Exmoor National Park Authority

Dr Alison Macleod, Royal Holloway, University of London, tephrachronology

Dr Richard Macphail, University College London, Soil Micromorphology

Dr Gill Plunkett, Queens University, Belfast, Pollen Analysis