Do tree ring δ13C series from Pinus sylvestris in northern Fennoscandia contain long-term non-climatic trends?

Non-climatic trends in tree ring δ13C series are investigated using highly replicated Pinus sylvestris δ13C series from Finnish Lapland. The declining trend in stable carbon isotopes over the industrial period, reflecting changes in the isotopic ratio of atmospheric CO2 is removed mathematically, without recourse to statistical de-trending. Regional Curve Standardisation (RCS) is then used to identify and remove the juvenile phase during which δ13C values increase. The chronologies all show approximately 1‰ depletion in the juvenile phase, with an average rise of 0.029‰ year− 1 lasting for about 50 years, after which trees of very different cambial age capture common variance over the same chronological period. There is no evidence of long-term age-related trends and RCS provides an alternative to simply omitting the juvenile portion of the stable carbon isotope series, thus allowing greater sample depth to be retained.