Testing annual tree-ring chemistry by X-ray fluorescence for dendroclimatic studies in high-elevation forests from the Spanish Pyrenees

Abstract

Climate reconstructions based on tree-ring features rely on the assumption that growth drivers are mainly meteorological variables. Consequently, annually resolved and absolutely dated temperature reconstructions in high-elevation conifer forests are mainly based on tree-ring width (TRW) and maximum wood density (MXD). However, long-term and annually resolved chronologies of chemical elements are scarce despite they could complement TRW- and MXD-based reconstructions. Here, we used a novel non-destructive method by applying Micro X-ray fluorescence (μXRF) to wood samples of old mountain pine (Pinus uncinata) trees from two Pyrenean high-elevation forests. We tested if Calcium (Ca) relative concentration, as estimated through μXRF, is a valuable proxy of long-term climatic and environmental changes in two sites with basic and acid soils, respectively. We compared the climate sensitivity of TRW, MXD and Ca by using calculating correlations with monthly climate data (mean temperature and total precipitation). Then, we built linear regressions to predict temperatures for the period 1900–2009. Prior-autumn and spring temperatures were positively related to TRW, MXD and Ca. However, Ca series revealed a high sensitivity to temperatures during the prior winter and spring but also to summer precipitation. We confirm the potential of long-term wood-chemistry studies based on the μXRF non-destructive technique to reconstruct environmental changes.