To investigate the possible Sun–climate connection during the Holocene, the Finnish super-long tree-ring chronology covering the period from 5634 B.C. to A.D. 2004 was analyzed. As an indicator of solar activity, we used a reconstruction of total solar irradiance (TSI) covering 9300 years, which is based on a composite using the cosmogenic radionuclide ¹⁰Be measured in polar ice cores, and also on neutron monitor data (Steinhilber et al. 2009). The Multiple Taper Method (MTM) wavelet decomposition and wavelet coherence analyses were applied to the time-series. The MTM spectral analysis identifies the main solar cycles at ca. 200 yr (de Vries or Suess), ca. 350 yr (unnamed) and ca. 900 years (Eddy). The strongest cross-wavelet correlation was discovered between the millennium-cycle components of TSI and tree-ring width variations. This Eddy cycle, which was recently discovered in solar activity, remains both strong and stable through almost the entire Holocene, and it reappears again at lower frequencies (ca. 1300 years) after ca. A.D. 200. Our results raise questions regarding the end of the Holocene and transition to the next glacial period and confirm the complex and nonlinear nature of the Sun–climate relationship during the Holocene Epoch.

Improving our understanding of the growth dynamics of trees along elevation gradients could help us predict their potential to store carbon and their vulnerability to changes in local and global environmental conditions, such as deforestation and climate change. This study is a review and analysis of the results obtained in recent dendrochronological studies of the effect of elevation and climate (temperature and precipitation) on the radial growth of trees in temperate zones, mainly in the Northern Hemisphere. Only 18 (32.1%) of the 56 studies analyzed found a correlation between radial growth of the trees (total chronologies) and elevation. The analysis of 56 chronologies of 46 tree species included in the 110 works reviewed, showed that only in 28.2% of them the correlation between radial growth versus temperature and precipitation was significant: positive in 3.6%, negative in 2.7%, and positive and negative in 21.8%, depending on the season of the year. The wide variation found in the radial growth response of the trees to elevation gradients may be related to multiple environmental factors at a local or regional scale, but also to the different sampling methods used in the studies. However, a moderate proportion of the studies analyzed (close to 30%) show that temperature and rainfall are related to trends in radial growth in different elevation ranges and regions of the world.