Climate-growth Relationship Of Conifer Species And Precipitation And Runoff Reconstructions In The Upstream Of Nenjiang River

Nenjiang River is one of the most important rivers in Northeast China. It has critical significance for forestry management and agricultural and livestock production to understand the long-term hydrological regime in this region. A total of115tree-ring cores of Larix gmelinii and of119tree-ring cores of Pinus sylvestris var. mongolica were collected at eight sites (A’li River, Gan River, Keyi River and Nuomin River) in the upper Nenjiang River, the northern Daxing’an Mountains, China. All cores were visually cross-dated under the binocular microscope. Tree-ring widths were measured to the nearest0.001mm with a Velmex measurement system. The cross-dated tree-ring sequences were quality checked by COFECHA program. ARSTAN program was used to detrend the ring-width sequences with a negative exponential curve or a straight line with negative slope (or a horizontal line) and eight chronologies were developed. Response analysis between eight tree-ring chronologies and monthly climatic and hydrology factors (mean temperature, mean precipitation, relative humidity and mean runoff) were conducted. The analysis shows that the temperature and precipitation are important to the growth, in contrast precipitation seems more effective, but the relevant mouths different. The tree-ring chronology of Pinus sylvestris var. mongolica in A’li River of Daxing’an Mountains was significantly correlated with the precipitation in current January and previous December by using response function analysis. The reconstruction equitation of LogY=0.478+2.376LogXSTD(R2=0.47, F=41.975, P<0.0001) was obtained by multiple regression analysis between tree-ring chronology (XSTD) and winter precipitation (Y is the average precipitation of previous December and current January), which explained47%of the variance in winter precipitation. The winter precipitation from1809to2009was reconstructed and coincided with the wet-dry change in Heilongjiang Province. The winter precipitation of A’li River in last200years had four dry periods (1810-1825,1850-1866,1901-1930and1970-1982) and four wet periods (1837-1848,1867-1869,1932-1965and1988-2002). The fluctuation amplitude of the streamflow was relatively small from the beginning of eighteenth century to the late of nineteenth century, while larger in the early years of twentieth century, and the magnitude of precipitation in the dry and wet change tends to increase. The reconstructed winter precipitation had significant85-38,5.0-4.5and2.2years periodicities by using multi-taper methods.In addition, the results showed that Larix gmelinii tree-ring chronologies in the sampling sites were negatively correlated with temperature in all months of a whole year, while which were positively correlated with precipitation in growing season and negatively correlated with precipitation in non-growing season. These results indicated that water availability is the major limiting factor of tree growth in this region. Therefore, an average tree-ring chronology for four sites was developed to reconstruct the history of streamflow variation for Nenjiang River. Simple correlations between the average tree-ring chronology and monthly streamflow data showed that the average chronology of four sites was significantly correlated with mean January-March streamflow. Therefore, mean January-March streamflow in the upper Nenjiang River since1804was reconstructed. The reconstruction equation is Y=-6.214X+10.437(R2=0.439, F=33.640,P<0.0001), where Y is the mean January-March streamflow, and X is the average tree-ring chronology. Sigh test, reduction of error and product mean tests proved that this reconstruction equitation is reliable. In addition, the reconstructed drought and flood periods are relatively identical with the historical records of hydrological variation in Heilongjiang province. The major periods of reconstructed dry conditions included AD1808-1809,1821-1822,1827-1833,1852-1875,1906-1919,1932-1954and1987-2004, while the significant wetter periods were AD1810-1820,1823-1826,1834-1851,1876-1905,1920-1931and1955-1986. The fluctuation amplitude of the reconstructed streamflow was relatively small from the beginning of nineteenth century to the beginning of twentieth century, while which was larger in the middle and late twentieth century. Multi-Taper Methods spectral analysis of reconstructed streamflow series indicated that the upper streamflow variations of Nenjiang River exhibited60,4.3-4.0,3.4-3.2,3.1-2.9and2.3years dominant periodicities. The factors that affect the cyclical changes of January-March streamflow in this area need to be further studied.