Blue intensity measurements in a South American conifer: evaluation of different methodological approaches for Araucaria araucana

Blue intensity (BI) has emerged as an inexpensive and relatively simple method for obtaining a proxy for relative wood density, and it has been successfully tested on several conifer species in Europe, North America, Asia and Australasia. Despite international efforts to promote the use of these methods worldwide, BI chronologies developed for native South American species have not yet been published. The possibility of developing BI chronologies in Araucaria araucana, an emblematic conifer of northern Patagonia, began to be explored some years ago. However, as it has been reported in other species, the wood anatomy of Araucaria presents several difficulties for obtaining robust BI common signals between samples. Therefore, we conducted this study to assess various methods for determining BI parameters based on the degree of common signal between trees in the chronology and their correlation with climatic factors. In this study, we demonstrated the feasibility of developing reliable BI chronologies from a site within the Araucaria range in Argentina by analysing the sensitivity to changes in the width of the measurement window. Although replicating measurements within the same core improved the classical statistic used to quantify the expressed population signal in a chronology (i.e. EPS), the results obtained here show that the chronologies developed using different methods were practically identical. Furthermore, our results revealed different climate signals expressed by both earlywood (EWBI) and latewood (LWBI) BI records, corresponding to the current spring and summer, respectively. In addition, soil water availability was significantly associated with wood density variation. Therefore, the climatic and environmental information provided by BI measurements in Araucaria complements what is already known from ring width (RW) and thus highlights its potential for use in future climate and ecological reconstructions.