A nice ring to it: Southwest Bastion tree-ring dating
Lower Fort Garry National Historic Site
Construction on Lower Fort Garry began nearly 200 years ago, in 1830. But some of its components are nearly a whole century older than that!
Jacques Tardif and France Conciatori from the U of W Dendroecology Lab.
How do we know? Dendrochronology, that’s how!
Dendrochronology, or tree-ring dating, determines the age of trees and wooden objects by analyzing tree-ring patterns and environmental influences.
During some recent interior masonry work on the Southwest Bastion, Parks Canada archaeologists discovered what they believed to be original window lintel timbers. While these timbers could not be salvaged to be dated because of rot and insect damage, other options were available to find out more about this wood. The Parks Canada Conservation Science Laboratory helped connect the team with Jacques Tardif and France Conciatori from the University of Winnipeg (UW) Dendroecology Laboratory within the Centre for Forest Interdisciplinary Research.
Parks Canada provided the lab with a cross-section (also known as a “cookie”) of the timber. A piece like this includes the heartwood in the centre all the way out to the bark. Even with the damage, this cookie provided two useable samples. The UW team identified the wood species as Manitoba bur oak (Quercus macrocarpa), the only oak species native to southern Manitoba. Manitoba bur oak is slow growing, can live up to 200 years, and can grow up to 20 metres tall.
A timber sample from the Southwest Bastion with talc on a portion of it.
After identifying the species, the UW team then set to work determining its age. They sanded the cookies to create a smooth, glossy surface that’s easier to read. They then rubbed talc on a portion of each cookie to help highlight the growth rings. Next, they compared the provided cookies to its existing previously dated reference materials from other bur oak samples. The cookies’ rings matched those of the reference materials, meaning the rings’ distinctive size and composition patterns helped the team find clues such as seasons of exceptional moisture or drought or events like fires. They then counted the rings backwards and forwards from those milestones to reveal the wood’s history.
The UW team determined that the timber that became the Southwest Bastion’s window lintel began as a sapling in 1742 and was cut down in 1838. The wood was then set aside for a few years to dry out (also known as seasoning), roughly squared up, cut, and installed into the window lintel. This timber then survived restoration efforts over the years.
The bastion dates back to 1846, when it was constructed over two years by a detachment of the 6th Regiment of Foot directed by stone masons Duncan McRae and John Clouston. It was initially used as a washhouse and cookhouse for the regiment; the bastion was later used as a storehouse that was poorly maintained, falling into dilapidation by the late 1880s.
In the following decades, the Hudson’s Bay Company had the bastion repaired and the attic served as a playhouse for Chief Commissioner Clarence Campbell Chipman’s family during their summers at Lower Fort Garry. The bastion had again fallen into disrepair by the time the Motor Country Club leased the fort in 1913. There were minor restoration projects in 1944 and 1956, but no large-scale restoration occurred until 1968 as part of Parks Canada’s rehabilitation work across the site.
