Saturday, December 6, 2014

New research into the vegetation history of central Scotland

A peat core taken from Ravelrig Bog, close to a number of later prehistoric settlements to the west of Edinburgh, contained palaeoenvironmental material spanning the entire Holocene period. The publication of the results of this work reveals evidence of human impact on the landscape from the Neolithic right up to the present day.

In 2007, the former Glasgow University Archaeological Research Division (G.U.A.R.D.) undertook a vegetation survey and an examination of the peat stratigraphy of an area of raised mire in advance of the extension of Ravelrig Quarry, by Kirknewton, to the west of Edinburgh, on behalf of Tarmac Limited. The survey of peat stratigraphy indicated that the peat that remained extended to a depth of over 7 m in places. The peat was characteristic of a raised mire that had developed over a small, rocky basin and held the potential for being an important palaeoenvironmental resource that might provide information on the vegetation history of the area dating back to the early Holocene period. An initial palynological assessment of a core taken from this site showed that pollen preservation was excellent and that the base of the deposit extended back over 10,000 years.

Previous studies

Most previous studies of the vegetation history of central Scotland have concentrated on the last 3,000 years of environmental history. This has tended to be because extensive industrial and agricultural activity in the central belt of Scotland, which was the industrial heartland of the country, has removed many potential sites of palaeoenvironmental importance over recent centuries, and so there have been few chances to construct a pollen diagram from this region that covers most of the Holocene period. The nearest published sites at comparable altitudes in central Scotland lie over 30 km to the west. The presence at Ravelrig Bog of an area of deep peat in an area that has a rich archaeological record and is also located close to agricultural land provided a unique opportunity to study the effects of human activity on the environment of this part of Scotland.

There is plentiful archaeological evidence for human occupation of the area surrounding Ravelrig Bog from the prehistoric until the present day. The most significant archaeological sites are two hillforts that occupy the summits of Dalmahoy Hill and Kaimes Hill. Dalmahoy Hill is unexcavated but from its nucleated fort morphology, it is thought to have been occupied in the pre-Roman Iron Age and again in the early medieval period. In contrast, Kaimes Hill has evidence of human activity dating back to the Mesolithic period, with intensification of activity throughout the Bronze Age but was subsequently abandoned during the later Iron Age, when the focus of settlement may have moved to Dalmahoy Hill. In addition, an Early Iron Age palisaded homestead, approximately 1 km to the north/north-east of the coring site, was excavated in advance of the Ravelrig Quarry extension. Excavations at this palisaded homestead by G.U.A.R.D., which will be published in the forthcoming volume of the Proceedings of the Society of Antiquaries of Scotland, produced evidence for the use of woodland resources for fuel and building materials, with AMS radiocarbon dating indicating that the main focus of activity was during the period 400 – 800 cal BC.

The Ravelrig core

Pollen analysis of the Ravelrig core has shown that that the bog started out as a small lochan, within a rocky hollow that was formed at the end of the last glacial period. Aquatic plants gave way to marshland and finally raised Sphagnum bog as natural succession progressed. During the early Holocene, the woodlands of the area were dominated by birch, hazel and willow but developed into mixed oak, elm and hazel woodlands by the mid-Holocene.

Previous studies have suggested that the first major woodland clearances in central Scotland occurred in the pre-Roman Iron Age, with the cleared agricultural landscape being maintained throughout the Roman period. However, at Ravelrig, human impact on the landscape is recorded from the Neolithic period onwards, with increasing woodland clearance and agricultural activity in the Bronze Age, and a peak in activity in the pre-Roman Iron Age. Pastoral agriculture was the dominant form of farming in the area, although there is evidence for the cultivation of cereals from the later Bronze Age onwards. These periods of agricultural intensification appear to correspond with known periods of occupation at the nearby hillforts.

There appears to have been a slight decline in agricultural activity around 250 BC – AD 150, which could be the result of the abandonment of Dalmahoy hillfort and could also be associated with the Roman invasion of the area during this period. Birch pollen levels increased significantly, suggesting that land that was previously farmed was abandoned and was gradually colonised by birch woodland – birches being pioneer species that colonise open ground prior to climax tree species, such as oak and elm, which colonised the wooded area later in the succession.

There was a slight increase in agricultural activity for a short period between approximately AD 400 – 600, which might correspond with the proposed reoccupation of Dalmahoy hillfort in the early medieval period. There was a further decline in agriculture and a recolonisation of land by alder and birch during the period AD 600 – 1450. This adds to the evidence obtained from other sites in central Scotland for a widespread decline in agriculture, with a corresponding regeneration of woodlands during much of this period. It is not clear what the cause of this agricultural decline might be but further work may be able to determine a more precise date range for this event. It has been suggested that there were some reversions to a colder and wetter climate during the sixth to ninth centuries AD, which could explain why areas once suitable for agriculture perhaps became too wet to grow crops and agriculture had to be moved to sites with better drainage. This explanation could account for the significant increase in alder (a tree of wetter areas and river banks) that is seen at Ravelrig during this period.

The last major episode of woodland clearance began around AD 1450, with the cleared landscape continuing until the present day. Evidence for an increase in pine pollen at the top of the pollen diagram suggests that the bog surface is intact and so a complete sequence has been analysed.
Past Horizons. 2014. “New research into the vegetation history of central Scotland”. Past Horizons. Posted: October 19, 2014. Available online:

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