Climatic significance of tree-ring width and δ13C in a Spanish pine forest network

This paper examines tree-ring width and delta C-13 chronologies from a network of five Iberian pine forests to determine their sensitivity to climate variability under different site conditions. Interseries comparisons revealed better and more homogenous agreement among delta C-13 records than among tree-ring width series of the different sites. This suggests that delta C-13 ratios may preferentially record large-scale climatic signals, whereas ring-width variations may reflect more local factors. A negative relationship was found between ring-width and delta C-13. As inferred from response function analyses, ring-width and delta C-13 showed significant relationships with climate. The analyses of different sites and species revealed unshared tree-ring width responses to summer temperature and precipitation, whereas all delta C-13 series were highly sensitive to current year summer precipitation and, to a lesser extent, to current summer temperature. A strong summer precipitation signal seems to dominate the delta C-13 of trees growing under Mediterranean climate, even when the mean climatic site conditions do not indicate distinct summer drought. Therefore, delta C-13 values reflect precipitation variability during the summer season better than tree-ring widths. This demonstrates that delta C-13 from tree-rings can be a very useful tool for climatic reconstruction in the Mediterranean region, especially when climate-growth relationships are weak.