By Dr Coralie M Mills, Dendrochronicle
Dendrochronology offers a high-precision dating method for historic timbers and wooden objects, with felling dates to a year possible where suitable material survives. Dendro-dating has the additional benefit of indicating provenance, revealing historic trading and transportation patterns. Dendro-dating and provenancing depend upon the availability of reference chronologies for the particular tree species in the relevant source region.
Native timber is generally under-represented in the national Scottish tree-ring record compared to imports which are more readily identified through the plentiful reference chronologies in the exporting countries. Expansion of chronology coverage for the main native timber species in Scotland is needed to allow more native timber in Scottish heritage sites to be identified and dated, and to provide a more holistic picture of woodland history and timber trade. There has been some progress in recent years, on both oak and pine, but there are still considerable gaps to be filled.
The South East Scotland Oak Dendrochronology (SESOD) project (funded by HES and FLS) aims to expand native oak tree-ring chronology coverage for this region, where there is a notable geographic gap. Most historic timber previously dendro-dated in south east Scotland is imported and, prior to SESOD, few sites outside of Edinburgh had been studied. SESOD covers Edinburgh, the Lothians and the Scottish Borders, including a mixture of archaeological sites, historic buildings and ancient woodland. Further details of individual SESOD site results are available in the DES 2022 volumes and in an overview report there (Mills 2023).
SESOD’s start point was creation of a long oak chronology from the Dalkeith Old Oaks spanning AD 1569–2010, a significant building block, although the data were fairly thinly replicated before about 1700. Thus, SESOD sought historic sites with oak timber present that were built before about 1700 to augment that record and to extend it back in time.
Initially, a long list of 112 SESOD candidate sites was created through desk-based research. This was whittled down through further research to a short-list for dendro-assessment visits, undertaken for 27 sites. Many short-listed sites were then eliminated, because either they had no historic timber surviving or they were built with conifers. Conifers can be dendro-dated too, but SESOD was only about oak. The eight short-listed sites with historic oak timber present were sampled and analysed over subsequent years. Only analysis would reveal whether these oaks were native or imported. Covid delays stretched the project duration but allowed the serendipitous addition of two more sites for analysis. It should be noted that SESOD represents only a sample of the region’s built heritage, not a comprehensive survey, and there are many more discoveries yet to be made.
An inspiration for SESOD was Professor Baillie’s work in south west Scotland at the inception of dendrochronological dating in Scotland (Baillie 1982). There, a millennium-long chronology was built from just six sites, possible because most sampled sites had very long-lived native oak present. The situation in south east Scotland has proved to be very different. Those rare historic sites with local native oak present have timbers cut from much younger trees than most of the ‘Baillie’ sites in the south west. Therefore, native oak chronology building has proved more challenging in the south east and, although progress has been made, there are still gaps to fill within the last millennium, especially in the 13th and 15th-16th centuries.
The picture emerging from SESOD shows native oak timber being available in some areas of south east Scotland up to the early 15th century, with medieval native oak, probably local in origin, identified at Kirkliston Parish Church, Jedburgh Abbey, Ancrum Old Bridge and Neidpath Castle. The earliest of those is Kirkliston, with oak timbers felled in the early 13th century. The most recent amongst them is the early 15th century lower floor level of Neidpath Castle near Peebles, far inland in the Scottish Borders. Imported oak first appears around the same time closer to the coast, with early 15th-century timber from the Gdansk region identified at St Mary’s in Haddington, a very unusual source for medieval structural timber. Oak from that region is more often found as boards. In the mid-15th century, long-lived oak timbers were brought from north east Scotland, probably from the Royal Forest of Darnaway, to build St Giles Cathedral’s bell tower. This is the earliest dendro-dated timber structure in Edinburgh’s old town and the only native oak structure so far identified there.
St Giles is the last medieval native oak structure identified in SESOD and sits on the threshold of the big switch to Scandinavian imported timber detected in prior work (Crone and Mills 2012), as further evidenced through SESOD in the 16th century at Abbey Strand in Edinburgh and Fast Castle in the Borders. Scandinavian timber dominates the region’s tree-ring record in the 16th century, and through SESOD we now know this applies as far inland as Neidpath Castle where, remarkably, Norwegian oak was used to re-roof the castle in the mid-16th century. It seems south east Scotland’s late-medieval reliance on imported timber was very widespread. Any native oak sites in that 15th-16th century gap are going to be rare but hugely important for creating a more continuous reference chronology, if we can ever find them.
Scandinavian timber continues to dominate south east Scotland’s tree-ring record until the mid-18th century, with a switch from oak to pine developing from the later 16th century, and especially after AD 1602, when oak export from Norway was banned (Crone and Mills 2012). Therefore, SESOD’s identification of southern Norwegian oak, felled in AD 1670, in the bell tower of George Heriot’s School, Edinburgh, is unusual. Oak was probably selected for its strength to support the bell tower; most other timbers at Heriot’s are conifer. Similarly, the local native oaks felled in AD 1667 to build a townhouse in Jedburgh are so far a unique find of post-medieval native oak timber in the region.
By the mid-16th century, even sites as far from the coast as Neidpath Castle, deep in the Scottish Borders, were using Scandinavian oak timber, while just some 140 years earlier, Neidpath could still call on locally grown oak. Potential factors affecting the historic availability of native oak timber in south east Scotland include the impacts of repeated warfare across the region and of intensive sheep grazing, as introduced by the medieval monastic foundations, hampering any woodland regeneration. Such factors may also explain the differences observed in the native oak tree-ring record between the south east and the south west.
SESOD has progressed the objective of expanding native oak coverage for south east Scotland, even though surviving historic oak structures are scarce. Four sampled sites have proved to have local native oak present, with mostly younger trees used than in the south west, while a fifth site, St Giles, used long-lived native oak brought long distance from north east Scotland. There are still some gaps to be spanned in the last millennium to create a continuous native oak record for the south east. However, the new native oak sites identified represent an important advance, providing anchored blocks from which to expand coverage and to identify and date other native oak sites as they emerge in the future.
A lesson from SESOD for those charged with conserving our built heritage is to take special care of any surviving historic timber assemblages and to be especially aware of the significance of any oak in south east Scotland. Historic oak assemblages are incredibly rare here and should be a priority for condition-setting, conservation and study; it is likely that in amongst them will be those elusive native oak sites which could complete the tree-ring record for the last millennium.
Baillie, M G L 1982 Tree-ring dating and archaeology. Chicago: Chicago University Press.
Crone, A and Mills, C M 2012 ‘Timber in Scottish buildings, 1450-1800: a dendrochronological perspective’, Proc Soc Antiq Scot 142: 329–369.
Mills, C M 2023 ‘South East Scotland Oak Dendrochronology (SESOD) project: An overview’, Discovery and Excavation in Scotland 23 (2022): 6–7.