DELTA-O-18 OF TREE-RINGS OF BEECH (FAGUS-SILVATICA) AS A RECORD OF DELTA-O-18 OF THE GROWING-SEASON PRECIPITATION

The measurement of delta(18)O in cellulose of tree rings is a potentia l means to reconstruct delta(18)O variations of precipitation and clim ate. Ne present delta(18)O data from cellulose of 3 beech trees (Fagus silvatica) growing on a relatively dry site in Switzerland where the roots do not have access to ground water, as well as data of 2 other g roups of 4 beech trees each, one from a dry site and the other from a semi-dry site, respectively. The measurements cover the time period fr om 1934 to 1987 in 3-year-groups for the Ist site and 1965 to 1992 wit h a 1-year resolution for the other 2 sites. Ne find a high degree of common variance (61%) between the delta(18)O variations of the 3 trees from the Ist location suggesting a common external cause. The compari son with climate data indicates that spring temperature (April/May/Jun e) is the main influence for the long-term isotope variations, with a temperature coefficient of 0.33 parts per thousand per degrees C, wher eas the short-term variations are mainly influenced by the relative hu midity, with a coefficient of -0.13 parts per thousand per %. This lat ter value is about 1/3 of the expected model value which points to lea f water pools with different delta(18)O values influencing the isotopi c composition of synthesised carbohydrates or to oxygen exchange with stem water. Tree ring delta(18)O is correlated with delta(18)O in prec ipitation, and the slope of the linear regression for different months most probably yield information about the growth rate function of the particular tree group. Our results confirm the potential of delta(18) O measurements in tree ring cellulose for climate reconstruction, in p articular information about delta(18)O in precipitation can be gained.