Evaluating the dendroclimatological potential of blue intensity on multiple conifer species from Tasmania and New Zealand

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.

Ring-width and blue-light chronologies of Podocarpus lawrencei from southeastern mainland Australia reveal a regional climate signal

“…Blue intensity chronologies in particular have displayed stronger responses to temperature at high frequencies yet generally poorer portrayals of low-frequency trends when compared to RW (e.g. Rydval et al, 2014;Wilson et al, 2021). Samples in this study consist of a vast range of ages.…”

“…The BI method, then, may offer a superior source of climate-sensitive chronologies within the Australian Alps. Applying this technique to Australian species may be the key to significantly improving our understanding of interannual to multi-decadal climate variability prior to the instrumental period (Wilson et al, 2021). Together with existing palaeoclimatological studies, an expansion of this work could provide a critical baseline for temperature and hydroclimate prior to the industrial era and major land-use changes following European arrival.…”

Piloting novel multi-centennial palaeoclimate records from mainland southeast Australia

“…compared to RW (eg. Rydval et al, 2014;Wilson et al 2021). Samples in this study consist of a vast range of ages.…”

“…Despite earlier quite pessimistic assessments of the Podocarpus genus for dendroclimatological purposes (Dunwiddie, 1979;February and Stock, 1998), due in part to limited sample availability (in the absence of fire-killed specimens) the strength of the observed correlations presented in this study of just nine samples are promising with regard to the future analysis of this species. The BI method appears to offer a promising additional proxy to RW for P. lawrencei, as in other SH species in which the climate signal of BI parameters has been explored (Blake et al, 2020;Wilson et al, 2021). The ongoing development and application of the BI method in P. lawrencei, particularly for longer, multi-centennial scale chronologies may help significantly improve our understanding of past climatic changes in the SH, given the valuable position annually resolved, tree ring-based proxies hold in palaeoclimatology.…”

“…The BI method, then, may offer a superior source of climate-sensitive chronologies within the Australian Alps. Applying this technique to Australian species may be the key to significantly improving our understanding of interannual to multidecadal climate variability prior to the instrumental period (Wilson et al, 2021). Together with existing palaeoclimatological This study will report a crossdated P. lawrencei RW chronology based on sampled material from a previously unexplored site (Mt Loch) in the Victorian Alps (Fig.…”