Abstract
Abstract. We evaluate a range of blue intensity (BI) tree-ring parameters in eight conifer species (12 sites) from Tasmania and New Zealand for their dendroclimatic potential, and as surrogate wood anatomical proxies. Using a dataset of ca. 10–15 trees per site, we measured earlywood maximum blue intensity (EWB), latewood minimum blue intensity (LWB), and the associated delta blue intensity (DB) parameter for dendrochronological analysis. No resin extraction was performed, impacting low-frequency trends. Therefore, we focused only on the high-frequency signal by detrending all tree-ring and climate data using a 20-year cubic smoothing spline. All BI parameters express low relative variance and weak signal strength compared to ring width. Correlation analysis and principal component regression experiments identified a weak and variable climate response for most ring-width chronologies. However, for most sites, the EWB data, despite weak signal strength, expressed strong coherence with summer temperatures. Significant correlations for LWB were also noted, but the sign of the relationship for most species is opposite to that reported for all conifer species in the Northern Hemisphere. DB results were mixed but performed better for the Tasmanian sites when combined through principal component regression methods than for New Zealand. Using the full multi-species/parameter network, excellent summer temperature calibration was identified for both Tasmania and New Zealand ranging from 52 % to 78 % explained variance for split periods (1901–1950/1951–1995), with equally robust independent validation (coefficient of efficiency = 0.41 to 0.77). Comparison of the Tasmanian BI reconstruction with a quantitative wood anatomical (QWA) reconstruction shows that these parameters record essentially the same strong high-frequency summer temperature signal. Despite these excellent results, a substantial challenge exists with the capture of potential secular-scale climate trends. Although DB, band-pass, and other signal processing methods may help with this issue, substantially more experimentation is needed in conjunction with comparative analysis with ring density and QWA measurements.
Highlights
The range of variables that are routinely measured from the rings of trees, including width, stable isotopes, multiple wood anatomical properties, and density, has increased substantially in recent years (McCarroll et al, 2002; McCarroll and Loader, 2004; Drew et al, 2012; von Arx et al, 2016; Björklund et al, 2020)
On average across all sites, to attain an EPS value of at least 0.85 (Wigley et al, 1984), 14 series would be needed for ring width (RW), while 44, 47, and 58 series would be needed for earlywood maximum blue intensity (EWB), latewood minimum blue intensity (LWB), and delta blue intensity (DB) respectively
We measured a range of blue intensity parameters from eight conifer species from Tasmania and New Zealand to ascertain whether the use of EWB, LWB, and/or DB can improve upon previous dendroclimatic reconstructions based only on RW that explain about 40 %–45 % of the temperature variance
Summary
The range of variables that are routinely measured from the rings of trees, including width, stable isotopes, multiple wood anatomical properties, and density, has increased substantially in recent years (McCarroll et al, 2002; McCarroll and Loader, 2004; Drew et al, 2012; von Arx et al, 2016; Björklund et al, 2020). In the Southern Hemisphere, Brookhouse and Graham (2016) measured latewood BI from Errinundra plum-pine (Podocarpus lawrencei) samples taken from the Australian Alps and identified a strong inverse (r = −0.79) relationship with August–April maximum temperatures, suggesting substantial potential for this species if long-lived specimens could be found. The sign (positive) of the earlywood BI relationship with temperature agreed with results detailed in other studies (Björklund et al, 2017; Buckley et al, 2018), the latewood relationship was inverse to that detailed for Northern Hemisphere conifers (Briffa et al, 2002) and observed by Brookhouse and Graham (2016). Improving terrestrially based estimates of past temperature in the landlimited Southern Hemisphere (Neukom et al, 2014) will only be achieved by enhancing the strength of the calibrated signal that until recently has been characterized solely by ringwidth data which generally express a weak temperature signal
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