CLIMATE VARIATION AND THE STABLE CARBON-ISOTOPE COMPOSITION OF TREE-RING CELLULOSE - AN INTERCOMPARISON OF QUERCUS-ROBUR, FAGUS-SYLVATICA AND PINUS-SILVESTRIS

The relationship between climate parameters and the carbon stable isot ope composition, (delta(13)C), of annual tree ring cellulose is examin ed for three native British tree species; Common beech (Fagus sylvatic a L.), Pedunculate oak (Quercus robur L.) and Scots pine (Pinus sylves tris L.). The last 100 annual tree rings of six trees, two of each spe cies, were cut into slivers and the ct-cellulose extracted. Annual del ta(13)C values of each species were averaged to produce three species delta(13)C chronologies. These were compared with climate parameters f rom a nearby meteorological station. The carbon stable isotope discrim ination (Delta(13)C) Of pine is consistently lower, by approximately 2 .5 parts per thousand, than that of beech and oak. Although the exact cause of this offset cannot be identified, similar differences in carb on isotope ratios have been noted between other gymnosperm and angiosp erm species and attributed to inherent physiological differences. As t his offset is consistent, once centered around the same mean delta(13) C and Delta(13)C chronologies from these 3 species can be combined. De lta(13)C chronologies of the three species demonstrate strong crosscor relations in both high and low frequency fluctuations. Low frequency f luctuations, although consistent between species, show no direct clima te relationship, and may be linked with physiological responses to inc reasing CO2 concentrations. Significant correlations do exist between the high frequency delta(13)C fluctuations and climate parameters. The high frequency delta(13)C series of all three species are most signif icantly correlated with the same two climate parameters and have the s ame seasonal timing; July-October average maximum temperature and June -September average relative humidity. Pine delta(13)C is the most resp onsive species to climate changes and displays the most significant co rrelations with all the climate parameters studied However, an average series of all three high frequency species delta(13)C series shows th e most significant correlations with climate. Assuming these relations hips are consistent spatially and temporally, high frequency delta(13) C chronologies from the three species studied are climatically compara ble and can be combined to reconstruct the same climatic information.