Abstract: Background, aim, and scope The Altay Mountains in China extend approximately 500 km from east to west with average elevation of 3000 m. The widespread distribution of conifers within this mountainous area provides good opportunity for undertaking tree-ring research. To date, some dendroclimatological studies have been carried out in this area. However, previous studies have seldom considered the relative widths of earlywood and latewood. Thus, this study focused on tree-ring earlywood and latewood to elucidate the relationship between the radial growth of Siberian spruces and climatic elements. Materials and methods Total of 410 cores from 228 Siberian spruces located in the low-altitude area were collected on the southern slope of the Altay Mountains, China. Every sample was dealt following standard dendrochronological techniques. Every tree ring was scanned using an Epson LA 1600+. The boundary of earlywood and latewood has been confirmed by the 50% gray value of every single tree-ring image, and WinDendro Systems was used to measure the tree-ring, earlywood and latewood widths. Three kinds of ring-width from 150 cores were obtained and developed chronologies (TRW, EWW and LWW) due to the quality of images. Relationships between chronologies and climatic factors were investigated by calculating the Person correlation coefficients and the moving correlation coefficients with a 31-year time window. Results The high values of standard deviation and mean sensitivity of the EWW chronology reveal that earlywood growth responds more sensitively to the changing of climatic elements. Values of mean within-tree correlation, first principal component and expressed population signal of the LWW chronology are obviously lower than that of the TRW and EWW chronologies, which indicate that the coherence of latewood width variation is relatively weaker. Values of signal-to-noise ratio of the TRW and EWW chronology are similar and obviously higher than the LWW chronology. The relatively coherent climate responses suggests that three kinds of chronologies are positively correlated with precipitation, while the relationships between radial growth of spruces and temperature are mainly negative. All three kinds of chronology show significant positive correlations with precipitation in previous July, December and current May, June, and significant negative correlations with temperature in current June. There are also some differences between tree ring growth and climatic factors, such as precipitation in previous August and current July and temperature in previous September and current May. TRW and EWW are most sensitive to the precipitation from previous July to current June, while the relationship between LWW and precipitation during the period of April to July are strongest. The correlation coefficients between three kinds of chronologies and precipitation in July, August and December in the previous year are listed as follows: earlywood > tree-ring > latewood. Moving correlation analysis displayed that although the relationships between the radial growth of spruces and precipitation in May, June, previous July- current June and April—July are relatively stable, the effects of precipitation on tree-ring has gradually decreased. We also find that all three kinds of chronology exhibit divergent response to temperature in May and June, and precipitation in July. Discussion The comparative analysis of characteristics of chronology and radial growth-climate response indicates that earlywood growth is sensitive to the changing of climatic elements, while the latewood widths might contain less climatic signals. The correlation analysis between chronologies and climatic data reveals that the moisture stress is regarded as the mainly limiting element for the formation of tree-ring, and the lag-effect of precipitation on earlywood is more significant than latewood. It has been detected that the tree sensitivity to temperature in May and June and precipitation in July changed significantly over time. With increasing of precipitation, the effect of drought on tree ring growth decreased in the early growing seasons. Conclusions The climate responses of tree-ring, earlywood and latewood are similar, and the moisture is the mainly limiting element for the radial growth of Siberian spruces in the low-altitude area of the Altay Mountains, China. The climate response of earlywood width is stronger than tree-ring width and latewood width and the EWW chronology might contain more climatic signals. Recommendations and perspectives This paper increased the knowledge regarding the growth patterns of tree-ring, earlywood and latewood of Siberian spruces and their climate response. However, the conclusions derived from this study need to be further substantiated because the findings are based on a relatively limited sample depth. Thus, more samples should be collected in a larger spatial scale to better understand the radial growth of Siberian spruces in internal annual scale.
Keywords: Altay Mountains; Picea obovata; tree ring; earlywood; latewood; climate response