Some New Mathematical Procedures in Dendroclimatology, with Examples from Switzerland and Morocco

Abstract

An original procedure and a new mathematical technique have been developed which allowed us to obtain more reliable climatic reconstructions than with prior methods. They have been tested for different sites in Switzerland and Morocco. First, cores that were too short and cores that were not coherent enough with others were excluded, using cross-spectral analysis. Second, detrending and master chronologies were calculated. Three methods were compared: polynomial, high-pass filter, and spline indexing. An optimal detrending was obtained through comparison with climate, but there seems to be no general rule for it. More reliable and longer climatic reconstructions are made possible. A response functions technique in three steps is presented: regression after extracting principal components on monthly climatic parameters, on seasonal parameters, and on more biological parameters such as potential evapotranspiration, multiple spectral regression introducing frequency domain. This procedure provides a more complete and more dynamic view of tree growth. The transfer function method and its verification are illustrated for different sites in Morocco: three climatic parameters in Tetouan (February, May, and June temperatures) and one in Marrakech (May temperature) have been successfully reconstructed. These reconstructions are confirmed by different verifications.