- Bolstering temperature estimates for the medieval period
The current NCAIRN reconstruction (Rydval et al 2017), is spatially limited to the northern Cairngorms and sample replication is poor prior to 1550. Incorporation of older samples from this region as well as including living and sub-fossil samples from Glen Affric will boost the amount of replication and allow extension of the reconstruction at least back into the medieval period. This is a crucial period for climate scientists and modellers to examine as it was likely the previous warmest period during the Common Era and might inform future forest responses to increases in temperature. Utilisation of refined Blue Intensity methodologies should also further improve the calibration strength (Björklund et al 2015; Reid and Wilson 2020). Finally, inclusion of historical samples may also boost poorly replicated periods, but careful provenancing of the material to ensure it is Scottish and reflects higher elevation temperature limited environments is crucial (see point 4 below).
- Late winter temperature reconstructions
Latewood Blue Intensity (and maximum density) expresses a strong relationship with late summer July-August mean temperatures and this relationship is the backbone driving the NCAIRN reconstruction (Rydval et al 2017) and many other tree-ring based temperature reconstructions around the Northern Hemisphere (Wilson et al 2016). However, recent experimental research has noted that earlywood Blue Intensity expresses a significant relationship with February-March temperatures. Although, at the site level, this relationship is not as strong as that expressed using latewood Blue Intensity for July-August, it is likely that by pooling multiple sites together, it will be possible to derive a reconstruction of late winter/early spring temperatures. Such a reconstruction would be incredibly important as it would not only allow comparison of past changes in both later winter and late summer temperatures but could also allow us to assess long term variability of the northern mode of the North Atlantic Oscillation which is an important natural driver of multi-decadal climate variability across northwest Europe (Linderholm et al 2008; Hurrell and Deser 2010; Cook et al 2019).
- Modelling pine resilience in a changing world
The dense network of Scots pine chronologies that has been developed over the last decade, especially as it represents a range of elevations from warmer lower elevation sites to cooler higher elevation sites, provides the perfect test dataset to model how pine trees may respond to climate change. The changing climate in the UK is spatially complex (Murphy et al 2009). All regions will warm over the coming decades, but the hydroclimatic changes are variable over space. At its simplest, it can be expected that southern England will get drier while Scotland will get wetter (and windier) due to enhanced westerlies from a warmer Atlantic. However, the rates of change vary from west to east. In Scotland, rainfall totals in the west are increasing three times the rate as the east and much of that increase has been since the 1990s. The implications of these changes for the resilience of the native pine woodlands of Scotland is not yet known, but there is clear evidence of a reduction in productivity of pine trees growing in the wetter parts of the western Highlands (Wilson 2023). Further work is needed to examine these observations and understand potential drivers of woodland decline due to regional specific climate changes.
- Enhanced dendro-historical dating and European-scale provenancing
The utilisation of latewood Blue Intensity for dendro-historical dating of conifer samples in Scotland has been profound (Mills et al 2017; Wilson et al 2017– see SCOT2K Case Study). However, not all buildings sampled have been dated. It is hypothesised that this partly reflects the fact that latewood Blue Intensity expresses a strong summer temperature signal in higher elevation regions, but at lower elevations, there is a loss of temperature limitation on growth and therefore we lose the strong regional signal that is so important for historical dating. If the timbers of a building originally grew at elevations below 200 metres above sea level, then it is likely that latewood Blue Intensity will not provide a robust parameter for dating. However, as per point 2 above, the February-March temperature signal noted for earlywood Blue Intensity has been shown to be consistent at all elevations and preliminary tests suggest that this parameter could be used to date low elevation material. Experiments are underway to test this hypothesis.
From a provenancing perspective, we must think beyond the geographic constraints of Scotland. It is paramount for these new novel parameters of Blue Intensity and stable isotopes (Section 8) to create networks of parameter records to enable more detailed provenancing of dated historical material – whether local or imported (Kaczka and Wilson 2021).
- Hydroclimate reconstructions
Finally, we know very little about past hydroclimate changes in Scotland. Traditional tree-ring parameters such as ring-width and density will never reflect any variability related to past changes in precipitation as trees are not limited by moisture availability. It is simply too wet in Scotland. However, research using stable oxygen isotopes (Section 8: Stable Isotope Dendrochronology) in English oaks (Loader et al 2008, 2020; Young et al 2015), strongly suggests that an expansion of this work into Scotland, with a focus on Oak, is not only possible but will likely yield robust estimates of past precipitation.