No abstract

Ten potential proxy measures of past climate were recovered from Scots pine (Pinus sylvestris) at three sites on a latitudinal transect close to the pine limit in northern Finland (earlywood, latewood and annual ring width; earlywood, latewood and maximum density; stable carbon isotope ratio; height increment; needle production; pollen deposition). Cambium dynamics were also monitored. The aim was to determine how climate in uences each potential proxy and to decide which proxies are potentially useful for reconstructing climate. Height increment, needle and pollen production are strongly in uenced by the temperature of the previous July, which is when the bud forms, but needle and particularly ower development may also be in uenced by spring frosts. Maximum and latewood densities provide proxies of net photosynthesis. d 13 C is controlled mainly by summer sunshine, re ecting the in uence of photon ux on photosynthetic rate, and moisture stress which reduces stomatal conductance. By combining proxies, the strength of climate correlations is increased and the range of extractable parameters extended. The multiproxy approach provides a powerful means of extracting climatic information from long tree-ring chronologies.

Stable carbon isotope ratios were measured on the latewood cellulose of 36 Scots pine trees from four sites in northern Finland. δ13C values were corrected for changes in the δ13C of air and de-trended to remove the effect of tree age. Simple linear and multivariate correlations were used to determine the nature and strength of any climate signal. At three sites, the dominant controls are, in descending order, summer sunshine, temperature and antecedent precipitation. At the fourth site, the dominant controls are antecedent precipitation and air relative humidity, while summer sunshine and temperature appear unimportant. δ13C values record changes in the concentration of CO2 in the stomatal chambers, which reflects the balance between stomatal conductance and photosynthetic rate. Photosynthetic rate is controlled primarily by photon flux (sunshine) and temperature, suggesting that this dominates at three of the sites, whereas stomatal conductance is controlled by air humidity and soil moisture status (antecedent precipitation), suggesting that it dominates at the fourth site. The balance between these controls varies spatially and it is likely to have varied locally during the Holocene. Without some independent estimate of either stomatal conductance or photosynthetic rate, there is limited potential for using δ13C alone to extract a clear and consistent climate signal from the long Fennoscandian pine chronologies.