Quantifying the Threat to Archaeological Sites from the Erosion of Cultivated Soil

Article excerpt

Introduction

It has long been recognised that modern cultivation techniques, particularly ploughing, have an erosive impact on archaeological sites (e.g. Lambrick 1977). Nevertheless, it is only in recent years that any attempt has been made to quantify such erosion. According to the Monuments at Risk Survey for England (MARS), 'cultivation is the single biggest hazard facing monuments, accounting for 10 per cent of wholesale monument destruction and 30 per cent of piecemeal loss' (Darvill & Fulton 1998: 236-7). The effect of ploughing across an archaeological site is to reduce its surface expression, eventually removing all upstanding elements. Roman and prehistoric sites in particular are more likely to be known from cropmarks or soilmarks seen in aerial photographs, or as artefact scatters in the plough soil, rather than as upstanding monuments. In the 65[km.sup.2] area investigated by the Southern Quantock Archaeological Survey (SQAS, a collaboration between the Department of Archaeology, University of Winchester and Somerset County Council) in south-west England, for example, 80 per cent of archaeological sites recorded in the local Historic Environment Record (HER) (Somerset County Council 2005) are known from cropmarks only. Clearly, buried sites are of no lesser archaeological importance than upstanding monuments and their future survival is therefore an important consideration for local authority and national archaeological service archaeologists who have the responsibility for managing and conserving the archaeological resource (Somerset County Council and English Heritage respectively in the case of the SQAS study area). However, two factors have particularly hindered efforts to protect buried archaeological sites in England: firstly a legislative framework that is primarily designed to conserve upstanding monuments and secondly the difficulty in quantifying the risk to sub-surface archaeological features. Here we address the second by presenting the results of a pilot study which used soil [sup.137]Cs inventories to model soil redistribution over the last 40 years or so across four buried archaeological sites. At the end of the paper we return to the first question and discuss the implications of our work given forthcoming changes in both domestic and European Union (EU) policy on rural land management.

The Quantock Hills study area and its archaeology

The pilot study was carried out as part of SQAS between August 2002 and September 2004. SQAS itself comprises a five-year long programme of fieldwork and associated post-fieldwork analysis which seeks to investigate the pre-medieval archaeology of the southern slopes of the Quantock Hills. The Quantock Hills are a north-west to south-east trending range of hills in the county of Somerset (Figure 1). They are largely comprised of Devonian (slates and limestones) and Triassic (marl and sandstones) strata (Figure 1c), in which brown earth soils of the Milford, Whimple and Bromsgrove Series have been mapped (Findlay et al. 1984). The southern slopes have an average aspect of 7 per cent, but in practice the topography is highly variable. We measured [sup.137]Cs archives of soils at four sites with evidence for sub-surface archaeological features located on contrasting geological substrates and in varied slope positions. However, for reasons of space we only consider two in detail here (Stoneage Barton and Yarford) (Figure 1). As is the case with 80 of the 100 HER entries in the study area, the four sites were first recognised as cropmarks in aerial photographs taken in the mid 1970s--early 1990s (Wilkinson & Thorpe 1999).

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Prior to 1999 there were only two sites of Roman date known from the study area and recorded in the HER, and it was therefore thought that the area had not been intensively occupied or exploited at this time. However, Roman settlement, ranging from simple farmsteads to a villa and dating from the second to fourth centuries AD, has been found on five of the six sites excavated by SQAS. …