Carbon isotope discrimination, radial growth, and NDVI share spatiotemporal responses to precipitation in Aleppo pine

A common pattern in Aleppo pine Delta (13) C responses to both spatial and temporal variability in precipitation was observed, with a general agreement between NDVI, Delta (13) C and growth that confirms precipitation as key environmental driver. The aim of this study was to assess the spatiotemporal variability of carbon isotope discrimination (Delta C-13) 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 Delta C-13 (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 Delta C-13 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 Delta C-13 sensitivity to precipitation. The strongest spatial associations between Delta C-13 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 Delta C-13, 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.