Monitoring Radial Growth Of Three Conifer Species In The Eastern Qilian Mountains

Over the past decade, tree-ring research, based on dendrochronology, has made considerable progresses. Given its bad weather and fragile ecology, arid and semiarid areas in Northwestern China has been becoming a hotspot of the tree-ring research, and achieved fruitful results which playing an important role in understanding the past climate variation and guiding the current social production. However, there exist several problems such as unclear response facter, divergence problem and unstable sensitivity. Also dendroclimate reconstruction work is established on statistical relations between tree ring indices and climatic factor, but the deep physiological mechanisms of the interaction relationship between tree growth and climate factors is not very clear. Tree physiological and ecological research provides the necessary foundation of dendroclimatology and dendroecology. However, domestic research in this field is scarce. This study, therefore, was designed to investigate the radial growth of three conifer species(Juniperus przewalskii, Picea wilsonii and Pinus tabulaeformis) through 3-years of monitoring by Point Dendrometer in Northwest Region. stem radial variation and radial growth were studied, aiming at getting a preliminary understanding of their physiological and ecological characteristics.The radial variation of trees have two daily-periodic fluctuation modes, namely summer mode and winter mode, and show sinusoidal shape and cosine shape perfectively. The two models mainly controlled by the stem water status and air temperature perfectively. The study of month-averaged daily periodic fluctuation pattern show that Juniperus przewalskii have winter mode from previous December to March, and April-November for the summer mode; For Picea wilsonii, its previous November to February for the winter mode, March-October for summer mode; winter mode of Pinus tabulaeformis is in previous December to February, and the rest of the months for the summer mode.Seasonal stem radial variation of three species were studied and finding that their switching time of daily-periodic fluctuation mode were corresponding to the average temperature of 0℃, indicating the important influence of temperature on radial variation of trees. In addition, it also showed the switching time was mainly controlled by temperature, with little influence from the species themselves. All trees have suffered severe shrinkage in the winter and appeared somewhat different in the time of contraction among species.Gompertz function was used to fit the radial growth of three species and the Goodness of the fits were more than 95%. Period with the growth rate over 4μm/d was defined as the main growing season, which showed difference among both years and species. major growth periods of Juniperus przewalskii are from May to early July; For Picea wilsonii and Pinus tabulaeformis, radial growth mainly concentrated in the period from April to August, but Picea wilsonii showed a latter growth initiation and earlier growth cessation. May-June growth amount of Juniperus przewalskii Accounted for more than 84% of the whole year, and for Pinus tabulaeformis and Picea wilsonii, May-July of that is more than 86% and 81% respectively.The maximum growth rate of three species appeared in late May to early June during three years. Compared to other two years, all species in 2013 showed earlier.in both maximum growth rate and Growth initiation. Also Growth amount in May is more than that in June in 2013 for all species, while in 2014-2015 we got contrary result except for Picea wilsonii in 2014. Relatively high air temperature after Mid April of 2013 and more precipitation in May can be thought of the main factors introducing these differences among years.Daily mean approach and daily maximum approach were employed to extract stem daily radial increment(SRI). Although some differences existed, very similar series were obtained with correlation coefficient above 0.9 for the two series. Daily cycle approach was used to extract SRI of Juniperus przewalskii in 2013 and made a comparison among three series, finding that they have relatively consistent changing tendency, but the serie from cycle approach is shorter and showed more extreme changes.Correlation analysis between SRI and climate showed consistent results among both growing seasons and species. SRI was positively related with precipitation, relative humidity and negatively with VPD(Vapor Pressure Deficit), indicating the negative effect of drought on tree growth. Negative correlation results were found between SRI and air temperature and solar radiation, which were considered relevant to water shortage caused by high temperature and strong solar radiation.