Seeing the Wood and the Trees: Dendrochronological Studies in Scotland

Article excerpt

Introduction

The value of dendrochronology as a precise dating tool is well established (Ashmore, this volume) and this paper concentrates on other aspects of its value to Scottish archaeology and history. Timber in Scotland has been a resource under pressure for a long time, and consequently the history of timber trade and woodland exploitation is particularly interesting. Scotland now has very restricted semi-natural woodland, representing about 1% of land cover. While the extent of semi-natural woodland has undoubtedly shrunk in recent centuries, pollen evidence indicates that much of Scotland has been characterized by open landscapes since later prehistory (Tipping 1994).

Dendrochronology is the principal means by which the history of the exploitation and husbandry of the timber resource can be unravelled. Intrinsic to dendrochronology is its ability to provide information on the date, provenance and quality of timbers, allowing a more sophisticated and precise history to be developed than is possible through other environmental techniques. In this paper, we review the accumulating tree-ring evidence and the light it throws on the history of timber availability and exploitation in Scotland.

The prehistoric period

Currently there are only a handful of dated timbers of prehistoric date in Scotland. A group of bog oaks found near Stranraer has produced two chronologies, dated 4610-4054 BC and 4209-3920 BC, while a single bog oak from the Solway Firth coast has been dated to 3112-2849 bc. Studies of bog oaks from elsewhere have yielded long, promising sequences, yet there is often little or no correlation even between trees that have apparently been growing close together. This was the case at Parks of Garden, where a Neolithic platform had been built over oak trunks which had toppled into the peat on the edge of the Flanders Moss (Ellis in press).

Very occasionally, archaeological sites of prehistoric date have produced timbers suitable for dendrochronology, but as yet none have been dated, probably because the assemblages are usually too small. Crannogs are an obvious source of large timber assemblages but few have been excavated. Timbers from two prehistoric crannogs have been examined but the sequences were unsuitable for chronology construction because they were either too short or had severely stressed growth-patterns.

Elsewhere in the British Isles, the prehistoric sections of the long master chronologies were amongst the most onerous to construct, primarily because of the scarcity of suitable material and the lengthy timespan to be covered (Baillie & Brown 1988; Hillam et al. 1990). The existence of those chronologies will make the task of constructing a prehistoric chronology for Scotland somewhat easier, as and when suitable material is forthcoming.

AD 1-1000

A scarcity of suitable material continues into the Roman period. A few Roman sites have yielded small assemblages of oak timbers but the sequences were generally too short and fast-grown for chronology construction. The quality and type of timber suggests that the Romans used whatever materials were to hand and either did not search out good-quality oak or it was unavailable to them. For example, at Elginhaugh fort, near Edinburgh, the major structural posts were mainly alder.

Two sites have produced sufficiently large assemblages to construct long, robust chronologies for the Early Historic period. A chronology covering AD 278-752 was built using timbers from the Northumbrian settlement at Whithorn (Crone 1998). Some of the timbers had as many as 317 rings, indicating an origin in mature woodland.

The assemblage from Buiston crannog, Ayrshire comprised 300 oak and 79 alder timbers, many of which retained the bark edge, making it possible to date to the year phases of construction and repair on the crannog (Crone 2000a). The settlement consisted of a roundhouse encircled by a timber palisade, both frequently refurbished over a period of approximately 80 years from the late 6th century to the latter half of the 7th century. …