CR 55:119-134 (2012)  -  DOI: https://doi.org/10.3354/cr01126

ABSTRACT: Detecting and extracting the dominant climatic signal from tree-ring records derived from Mediterranean areas remains challenging because the relation between climate and tree-growth are usually characterized by a complex interplay of temperature and precipitation signals, with high spatial and temporal variability. Although several studies have established climate−growth relationships in old forests on the Iberian Peninsula (IP), a reliable calibration level between tree-ring data and the instrumental records making possible the inference of past climate has not yet been established, mainly due to low correlation coefficients (i.e. r ≤ 0.4) and/or instability over time of the climate−growth relationships. We tested for spatial significance and temporal stability of climatic signals in a collection of tree-ring proxies at the Cazorla Range (NCZ), located in the southeast of the IP. The aim was to identify suitable proxies for further use in climate reconstructions. The tree-ring variables under investigation included tree-ring width (TRW), latewood width (LWw), maximum latewood density (MXD) and stable carbon (δ¹³C) and oxygen (δ¹⁸O) isotopes. Our results show how the strength and temporal stability of the relationship between tree-ring proxies and selected seasonal climate variables largely depend on the climate data used. Moreover, imprecise identification of the climate signal may lead to erroneous evaluations of temporal stability. Overall, from the set of proxies measured at NCZ, TRW is suitable to reconstruct summer to autumn temperature while δ¹³C can potentially be used as a proxy for summer precipitation reconstructions. The calibration−verification trials using both regression and scaling techniques revealed how scaling retains more inter-annual variability but decreases the values of the reduction of error (RE).

KEY WORDS: Tree-rings · Dendroclimatology · Climate signal · Temporal stability · Pinus nigra · Stable isotopes