The in field fertilization effect of CO2 remain a question dendroclimatology strives to answer. However, methods used to remove the age effects may alter the result.
We present results obtained by using a methodology that eliminates this problem. It is based on a blind source separation technique that recovers source signals from a set of mixtures. The only assumption is that as physical processes, each source signal has its own signature. It can thus be possible to recover climatic signals from tree ring width series.
We have analyzed series from an altitudinal and latitudinal gradient from Nepal to Russia. For each site, a climatic signal has been recovered and characterized. Temperature, precipitation and the solar cycle have been isolated from the extracted components using correlations.
Results show that at the beginning of the last century, temperature limited tree growth. However, following this period a positive trend was observed and now shows a positive effect on growth. For precipitation, results are opposite with a slope nullifying the temperature trend in Nepal. In Russia a trend is less obvious which can be explained by the poor quality of data within 60ºN to 70ºN. Concerning the solar cycle, it shows a positive trend in Nepal and a slight negative trend in Russia. Solar energy amplitude is constant from cycle to cycle, and the observed trend may be due to terrestrial phenomena acting on light, such as the scattering of light due to aerosols and CO2 fertilization . Further work must be conducted to confirm this hypothesis.
