Blue intensity measurements in Araucaria araucana from northern Patagonia: preliminary results

MUNDO, I.A.; VILLALBA, R.; WILSON, R.

Mendoza

Conferencia; AmeriDendro 2016 - Third American Dendrochronology Conference; 2016

IANIGLA-CONICET

Although densitometry has been widely used in Dendroclimatology for Northern Hemisphere species, maximum latewood density (MXD) has rarely been used in the Southern Hemisphere (SH) mainly due to its economic cost and lack of densitometric facilities. Blue intensity (BI) potentially provides a cheaper MXD related surrogate variable for the SH dendrolabs. To explore the potential of the BI variable in SH tree species, we have made preliminary measurements of BI data from Araucaria araucana from two sites in Northern Patagonia, Argentina. No pretreatment was undertaken on the samples prior to light reflectance and measurement was made using ImageJ and CooRecorder softwares. All ring width and inverted BI data were detrended using flexible splines and pre-whitened. Correlation functions were used to determine the influence of climatic factors on both RW and BI chronologies. Regional temperature and precipitation records were developed by averaging monthly data from climate records in the region. The PDSI monthly series for the study area was derived from gridded data. RW data correlated negatively with previous January-April and current summer temperatures. A very weak positive association with precipitation was detected for previous January and current December but no significant correlation was found with PDSI for the same monthly pair. However, the BI data positively correlate with current temperature and inversely and strongly with precipitation. Additionally, BI data correlates negatively with PDSI monthly values all along the current growing season. The BI data appear, therefore, to express a more moisture stressed response. In terms of spatial correlations for both current December-January air temperature and precipitation, the inverted BI residual chronology shows a much stronger and coherent pattern. The Pacific domain influence on the northern Patagonian climate is clearly distinguished through the correlation between BI and precipitation. Based on these results, water deficit might determine wood traits (increase in latewood density) in Araucaria and, in consequence, BI may provide a new proxy for precipitation and streamflow reconstructions.