Carbon isotope discrimination, radial growth, and NDVI share spatiotemporal responses to precipitation in Aleppo pine
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The aim of this study was to assess the spatiotemporal variability of carbon isotope discrimination (Δ13C) records and its relationship with radial growth (RG) and Normalized Difference Vegetation Index (NDVI) data using a tree-ring network of Aleppo pine (Pinus halepensis Mill.) in the eastern part of the Iberian Peninsula. For this purpose, we collected a biennial time series of Δ13C (1949-1998), together with mean annual precipitation, tree-ring width, and remote sensing (NDVI) data for seven locations along a precipitation gradient. We evaluated how intra-site correlations between variables changed across locations, and how inter-site (or spatial) correlations changed across years. We found that correlations between Δ13C and precipitation were higher in dry than in wet sites, in agreement with previous studies. Mean RG and NDVI were good indicators of site-specific Δ13C sensitivity to precipitation. The strongest spatial associations between Δ13C and precipitation were also found during the driest biennia. However, spatial correlations were strongly affected by carryover effects of extreme events. Overall, we found a good agreement between Δ13C, NDVI, and RG, although they showed different response patterns to precipitation. We suggest that the combination of these proxies may be useful for monitoring changes in water-use efficiency and productivity at the regional level.