Climate clues in kauri
New Zealand scientists think kauri timber used in three colonial buildings came from western Auckland or the Coromandel Peninsula and may identify a specific forest area with further research.
A scientific paper written by Gretel Boswijk, and Anthony Fowler of the University of Auckland’s Tree-Ring Laboratory concluded that until then, ‘‘we consider there is good potential to identify sub-regions where timber came from or at least to highlight where timber was unlikely to have come from’’.
The field, known as dendrochronology, uses tree rings to understand the past. A sub-field called den dro climatology uses tree-ring records as a proxy for past climate. It has become an important tool in understanding climate change.
The tree-ring lab has samples from 27 buildings and other early colonial structures and made case studies of three to test whether den drop rove nancing could ‘‘geo-locate’’ kauri timbers.
The buildings included a Georgian-style mansion on Arney Rd, Remuera, Auckland, built in 1855-56 and enlarged in 1864. The kauri used in rafters probably grew from 1547-1861.
The second was another Georgian house and later a creche at 32 Wynyard St, Auckland, that dates to 1866. Some of the wood was growing in 1468 and a few samples date to the 13th century.
Kauri from the third possibly started out in a 1865 tavern on Karangahape Rd, and was reused in a 1930s bungalow on the grounds of St Paul’s College,
Ponsonby. The wood grew from 1501-1849.
The goal was to ‘‘track a timber sample back to the source region where the parent tree grew’’.
Dendrochronology holds that in good growing seasons, tree rings are wide, and in poor seasons narrow. As sub-regions experience similar weather conditions, almost all of a tree species growing there will display similar tree-ring patterns.
Growing conditions elsewhere were different – sometimes subtly – and there may be subtle differences in the tree-ring patterns.
In theory, then, a piece of timber from a building can be matched to the forest area where it grew.
The tree lab needs about 100 rings to generate a confident match, Boswijk said.
The tree-ring lab also has data sets from two other types of kauri wood. The second has samples taken from still-living kauri trees and which span the years 1269 to 2002.
The third was taken from swamp kauri dating as far back as 2488BC.
Together the three data sets comprise 4500 years of kauri history. Provenancing kauri to specific forests will assist with reconstructing past trade networks and the environmental impacts of logging, the paper said.
The climate aspects are perhaps more urgent. Previous research showed that kauri rings carry a ‘‘useful signal of the El Nino-Southern Oscillation (Enso)’’, a known climate variable.
‘‘Although Enso impacts on local climate are similar, effects are subtly different across subregions,’’ said the paper in the journal Den drochro no logia.
Geo-locating kauri wood samples could help New Zealand scientists with ‘‘more nuanced Enso reconstructions’’, said the paper.
The goal is a greater understanding of natural variability in kauri growth, especially the Enso signal.
With that in hand, researchers might then isolate the signals in tree rings caused by human activity, including increased atmospheric CO2.
Boswijk studied archaeology and since the early 2000s has been ‘‘largely responsible’’ for developing the 4500-year-long tree ring record from kauri.
In Europe, den drop rove nancingh as been used to identify the origin of oak and pine timber used in art objects, ships, buildings and other wooden objects.