Multispecies dendroclimatic reconstructions of summer temperature in the European Alps enhanced by trees highly sensitive to temperature

We here analyze the tree-ring series from 42 high-altitude sites in a region of the European Alps centered over the 1° × 1° grid cell 46°N 10°E to reconstruct the summer temperature signal using an approach based on site chronologies and only on trees that are highly sensitive to temperature (HSTT). For the forest sites of Larix decidua Mill., Picea abies Karst., and Pinus cembra L., we find that HSTT trees, representing 33 %, 25 % and 27.5 % of all trees in the dataset, respectively, are growing larger tree-rings in recent periods (since approximately 1935 AD) compared with the other trees in the region. The temperature reconstruction based on the HSTT chronology is consistent with other reconstructions already available in the European Alps, well preserves the long-term temperature variability and suggests lower summer temperatures than those derived from the chronology avgALL (based on the entire dataset) during the periods 1725-1800 AD and 1845-1910 AD. Since 1935, the HSTT reconstruction is more efficient than the avgALL in recording the recent temperature trends. Overall, we stress the importance of testing for the presence of HSTT trees at each site, as their incidence may influence the temperature reconstructions as much as the other known factors related to, e.g., site characteristics, tree age and species sensitivity. HSTT trees may enhance the long-term climate signal for performing reliable climate reconstructions because they reduce potential biases derived from non-climatic influences on tree growth. Our results can further help to avoid the divergence problem with the instrumental records, particularly for those periods where the avgALL curve shows a tendency to smooth the long-term summer temperature signal.