Growth/climate response shift in a long subalpine spruce chronology

A new Norway spruce (Picea abies (L.) Karst.) tree-ring width chronology based on living and historic wood spanning the AD 1108-2003 period is developed. This composite record combines 208 high elevation samples from 3 Swiss subalpine valleys, i.e., Lötschental, Goms, and Engadine. To retain potential high- to low-frequency information in this dataset, individual spline detrending and the regional curve standardization are applied. For comparison, 22 high elevation and 6 low-elevation instrumental station records covering the greater Alpine area are used. Previous year August-September precipitation and current year May-July temperatures control spruce ring width back to ∼1930. Decreasing (increasing) moving correlations with monthly mean temperatures (precipitation) indicate instable growth/climate response during the 1760-2002 period. Crucial June-August temperatures before ∼1900 shift towards May-July temperature plus August precipitation sensitivity after ∼1900. Numerous of comparable subalpine spruce chronologies confirm increased late-summer drought stress, coincidently with the recent warming trend. Comparison with regional-, and large-scale millennial-long temperature reconstructions reveal significant similarities prior to ∼1900 (1300-1900 mean r=0.51); however, this study does not fully capture the commonly reported 20th century wanning (1900-1980 mean r=-0.17). Due to instable growth/climate response of the new spruce chronology, further dendroclimatic reconstruction is not performed.