Coralie M Mills & Rob Wilson
State of current knowledge
Dendrochronological dating ultimately relies on the availability of reference chronologies which are anchored in time and place by samples from living trees, where the calendar year of the last growth ring is known from the date of sampling. Over the last 20 years, chronology development, to expand spatial coverage for relevant species, has been of primary importance for sampling living trees and old woodlands in Scotland for archaeological, ecological and climate focused studies. Although the living Scots pine network is now arguably complete for dendro-climatological objectives, sampling of this species will continue in the future as research shifts more to ecological based questions on how these woodlands will behave as climate changes. Further studies to investigate the history of individual pine sites are also likely to occur, not least to inform native pine woodland restoration initiatives.
For other species such as oak, given there are many gaps in chronology coverage, living tree sampling will continue to be needed especially as the network needs to be expanded into the north and west. While some useful information regarding woodland ages comes out of such climatological studies, the work is not being undertaken to address questions of woodland history specifically and does not usually record other parameters necessary to understand the evolution of a wooded landscape. Dendrochronology becomes far more useful for addressing the cultural history of wooded landscapes when designed as part of a wider study in which relevant complementary evidence is gathered to answer woodland history questions.
Chronology building work on woodlands has included work on Scotland’s oldest known living oak sites, for example at Cadzow near Hamilton and Lochwood near Beattock, where the samples together provided over 500 years of coverage in the first long Scottish oak tree-ring width regional reference chronology and showed that the oldest sequences originate in the 15th and 16th centuries respectively (Baillie 1977; Baillie 1982).
More recently, work on fallen ancient oaks at Dalkeith Park in Midlothian has collected complementary data alongside chronology development, to inform woodland history (Mills 2022). The complementary records include tree-forms, girths, locations, sampling height up the stem, as well as historic map information and documentary evidence. Identifying ‘stem origin dates’ alongside tree-form is especially crucial in understanding a woodland’s past, so that sprouting dates, planting phases, and the dates of management interventions such as coppicing episodes can be identified from the tree-ring data. At Dalkeith, a mix of single-stem and multi-stem oaks originated across the 16th to 18th centuries, showing that the oldest extant trees had survived documented cutting episodes in the 1570s while many more oaks had been planted in the late 17th century (Mills 2022).
Dendrochronology in Scotland has expanded in the early 21st century to include native Scots pine, because native pine was used for construction historically (Mills et al 2017) and because pine is especially useful in dendro-climatological research. Early chronology development work sought out long-lived native pinewoods, the oldest of which included trees of mid-15th century origin (Mills 2008). The network of native living pine chronologies has been hugely expanded by the work of Professor Wilson and colleagues at the University of St Andrews and is now represented by 93 woodland sites (>4000 trees) across the full extent of the Native Pinewood Zone including also 19th century plantations within the lower elevations of Spey, Dee and Tweed catchments. The network therefore represents the full elevational range of pine in Scotland from sea level up to 600 metres above sea level and ranges from Rhidorrich in the north, Tweedsmuir in the south, Loch Hourn in the west to Glen Tanar in the east. The chronology building work has provided a good handle on the ages of various pinewoods, sometimes allowing identification of historic plantation phases and other human impacts, although little of the work has been undertaken specifically to investigate woodland history.
More recent projects include Historic Woodland Studies geared to informing native woodland restoration. The Mull and Iona Community Trust recently acquired a former Forest Enterprise conifer plantation in southeast Mull, their objective being to restore native woodland cover. They commissioned research into the wooded landscape that preceded the 20th century plantation, including dendrochronology of old oak and holly trees (Mills et al 2023). Together with other evidence including historic maps, Gaelic placenames and pollen analysis, the study showed that in pre-improvement times, there had been a mixed species wood pasture in this glen through which a major historic drove route ran. Now named Ardura Community Forest, the Gaelic name for the wood was Doir a’ Chuilinn (Grove of the Holly). Dendrochronology showed the oldest sampled tree was an early 18th century holly, a survivor from the old wood pasture system, while most of the oaks had been planted into the old wood pastures in the early 19th century, coincident with the clearances and huge changes in estate ownership and land-use on Mull. The study is informing ecological restoration and community engagement, enabling the cultural heritage of the landscape to be shared alongside the natural heritage features.
There is now increasing interest in researching the history of Scottish wooded landscapes to inform ecological restoration and conservation management. One of the earliest such studies which deployed dendrochronology alongside other evidence was at South Loch Katrine for Forestry Commission Scotland (Mills et al 2009), distilled into an FCS best practice case study for management of the historic environment (Mills et al 2013). The study revealed surprisingly old ages for some ash trees near a pre-improvement farmstead site below the Bealach nam Bo pass, the oldest ash originating in the late 17th century, with evidence of pollarding through the 18th century before the farm went out of use. Dendrochronology showed the old oak coppice wood around another early farm at Glasahoile was planted around AD 1800 and coppiced into the 1870s and that the squat gnarled oaks around the periphery of the coppice stand were not so old as they looked, their forms the consequence of grazing impacts as the enclosed coppiced area shrank over time in the 19th century.
Some other historic woodland studies involving dendrochronology have been for community archaeology projects, for example for the Galloway Glens Landscape Partnership at Barhill Wood, Kirkcudbright (Mills and Quelch 2019; Mills et al 2022). Dendrochronology alongside historic maps and other evidence revealed the late 18th century planted origin and management history of a mixed species wood designed for ornament and productivity, including coppicing of sweet chestnut and elm, while retaining small, sheltered grazing paddocks within. While much altered by 20th century plantation, older trees survived in boundaries and small patches, the dendrochronology showing that coppicing had last been undertaken between the two world wars.
Dendrochronology has also been applied to designed wooded landscapes, for example at Dougalston near Milngavie (Bishop et al 2022), undertaken to date planted tree features and related built heritage features, such as ‘ha ha’ banks and an artificial lake. The tight chronological framework created through dendrochronology allowed certain designed features to be related to specific owners of the estate and to identify how wealth made through slavery and the tobacco trade underpinned much of the expenditure.
Every historic woodland study involving dendrochronology has revealed unique and unexpected features about each study site. However, there are also some unifying themes emerging, for example the oldest trees often being in medieval parks or hunting forests, the widespread reliance of pre-improvement upland farming systems on wood pastures, the impacts of the clearances on the wooded landscape, the impacts of improvement-era sheep farming, the industrial creation and exploitation of woods, and so on, each study fleshing out the documentary evidence for Scotland’s woodland history (Smout et al 2003). The projects have highlighted how frequently woodlands have been shaped or even created by human intervention.
The final point is that the cumulative results of dendrochronological studies on archaeological sites and buildings are also relevant to woodland history because they give us a high-level view of the woodland resources available, or indeed not available, over a longer timescale to the past inhabitants of Scotland. In simplistic terms, we see native timber resources depleted by the late medieval period, and an increasing reliance on imported timber from the 15th century (Crone and Watson 2003; Mills and Crone 2012), although the data are dominated by eastern sites and many regional differences are yet to be investigated.