New Articles: Neil Loader on Dendrochronology
Project investigator Neil Loader has published three articles since 2020 on dendrochronology. Find links to read them below.
Are there enormous age-trends in stable carbon isotope ratios of oak tree rings?, The Holocene
Danny McCarroll, Josie E Duffy, Neil J Loader, Giles HF Young, Darren Davies, Daniel Miles, Christopher Bronk Ramsey
We test a recent prediction that stable carbon isotope ratios from UK oaks will display age-trends of more than 4‰ per century by measuring >5400 carbon isotope ratios from the late-wood alpha-cellulose of individual rings from 18 modern oak trees and 50 building timbers spanning the 9th–21st centuries. After a very short (c.5 years) juvenile phase with slightly elevated values, the number of series that show rising and falling trends is almost equal (33:35) and the average trend is almost zero. These results are based upon measuring and averaging the trends in individual time-series; the ‘mean of the slopes’ approach. We demonstrate that the more conventional ‘slope of the mean’ approach can produce strong but spurious ‘age-trends’ even when the constituent series are flat, with zero slope and zero variance. We conclude that it is safe to compile stable carbon isotope chronologies from UK oaks without de-trending. The isotope chronologies produced in this way are not subject to the ‘segment length curse’, which applies to growth measurements, such as ring width or density, and have the potential to retain very long-term climate signals.
An evaluation of english oak earlywood vessel area as a climate proxy in the UK, Dendrochronologia
Darren Davies, Neil J.Loader
This research evaluates the usefulness of oak earlywood vessel area as a climate proxy in the western United Kingdom (UK). The results demonstrate that at this site earlywood vessel area contains a different environmental signal (March relative humidity) to a ring-width chronology developed from the same trees. The vessel area signal passes commonly used verification statistics and was found to be representative of the climate of a similar geographic area to other tree-ring proxies, albeit with a lower explained variance. Taking the average of all the vessels identified for each year weakened the reconstructed climate signal and it was found for this study that the average of the 10 largest vessels provided the strongest and most stable match. The results demonstrate earlywood vessel area of oak in the UK has potential as a climate proxy, but that further work to strengthen and characterise the climatic target variable controlling vessel area is required.
Dating of non-oak species in the United Kingdom historical buildings archive using stable oxygen isotopes, Dendrochronologia
Neil J.Loader, Danny McCarroll, Daniel Miles, Giles H.F. Young, Darren Davies, Christopher Bronk Ramsey, Megan Williams, Maximilian Fudge
Stable oxygen isotope dendrochronology is an effective precision-dating method for fast grown, invariant (complacent) tree-rings and for trees growing in moist, temperate climatic regions where growth may not be strongly controlled by climate. The method works because trees preserve a strong common isotopic signal, from summer precipitation, and therefore do not need to be physiologically stressed to record a dating signal. This study explores the working hypothesis that whilst tree species may differ in their eco-physiology, leaf morphology and wood anatomy they will record an isotopic signal in their growth rings that is sufficiently similar to enable their precise dating against isotopic reference chronologies developed using dated oak tree rings from the same region. Modern and historical samples from six species (sweet chestnut, English elm, ash, alder, European beech and black poplar) were analysed and their oxygen isotopic variability was compared against an oak master chronology previously developed for central southern England. Whilst differences in the relative strength of the agreement between the different species and the master chronology are apparent, the potential for interspecies dating is demonstrated convincingly. The ability to date non-oak species using stable oxygen isotopes opens-up new opportunities for science-based archaeology and will improve understanding of a largely-unexplored, but significant part of the European historical buildings archive.