An Attempt to Verify Dendroclimatic Reconstructions using Independent Tree-Ring Chronologies

An attempt was made to verify dendroclimatic reconstructions of July Palmer Drought Severity Indices (PDSI) and of seasonal temperature and precipitation in the contiguous United States by means of tree-ring chronologies not used in the calibration procedure. Eight tree-ring chronologies were developed from white oak (Quercus alba L.) on five sites in Iowa and were used in statistical verification procedures along with 26 other chronologies from the eastern and central U.S. Six types of statistical test were used to detect linkages between tree-ring series and actual or reconstructed climatic series. Only those chronologies showing significant linkages with actual climatic data were used in verification attempts. Successful verifications of two PDSI reconstruction sets for two regions of Iowa using the Iowa chronologies were attributed to validity of these reconstructions and strong linkages of the Iowa chronologies to actual July PDSI data, and it was concluded that verification of dendroclimatic reconstructions using independent tree-ring chronologies is possible. Unsuccessful verification attempts in all areas tested for the temperature precipitation reconstructions and for one PDSI reconstruction in four regions of the Ozarks area were attributed to invalidity of these reconstructions and secondary to weaker linkages of the independent chronologies to actual data of these variables.