Growth Release Determination And Interpretation Of Korean Pine In Heilongjiang Province, China

Mixed broadleaf-Korean pine(Pinus koraiensis) forests are a major ecosystem of the Xiaoxing'an Mountains of northeast China. It is critical to better understand the disturbance regimes and growth dynamics of the main conifer species in these forests, especially in the context of global climate change. The objective of this study was to investigate timing of tree recruitment and forest gap formation using growth releases recorded in tree-ring series of Korean pine, and their responses to annual variation in temperature and precipitation. We sampled trees from three randomly selected stands in the experimental areas of three geographical positions different National Nature Reserve, which are respectively sitting in the most northern, central and southern border of the Heilongjiang Province. All Korean pine trees with diameter at breast height≥10 cm in each plot were mapped and increment cores collected from each. All cores were dendrochronologically crossdated with a locally developed chronology and ring widths measured to the nearest 0.001 mm. After measuring, growth release events on each series were determined using the boundary line release criteria, which formulated according to the relationship between percent growth change and prior growth.The results showed that:due to the influence of the prior growth, percent growth change curves of each series were much stronger consistent than tree-ring widths curves. The peaks or valleys of the tree-ring widths curves were differ as peaks or valleys of the corresponding values of the percent growth change curves. In Heihe, almost all Korean pine series had more than one growth release event, with 2.75 average growth releases per tree, and 87.5% of the Korean pine series had at least one major release. The release events happened mainly in the year of the 1930-1960 and 1970-1990, which were coincided with the tree-ring widths changes. The main release periods of Mudanjiang were 1915-1940,1960-1970 and 1990-2003, with 2.07 average growth releases per tree, and 82.8% of the Korean pine series had at least one major release. Samples collected from Yichun, no matter the total peak number, the peak number which reached the release boundaries or the release event numbers (last 5 or more than 5 years) are all slightly more than the number of the first two sampling points. Displayed in 297 total peaks, with 117 reached the release boundaries standard and 90 formed the release events (33 major releases and 57 moderate).1910-1950 is the most significant release events period of the Yichun Korean pine, appeared 13 major releases and 23 moderate releases in total 25 samples. In addition, a more significant release period is 1840-1880, totally appeared 22 release events.1960-1970 and 1980-1990 relatively less release events (7 and 9), but still occupied considerable proportions in the total release events number.Spatial distribution patterns of Korean pine trees indicated that forest gap opening due to a variety of mortality factors is likely the main reason for some tree growth releases in Heihe and Yichun, but not Mudangjiang. A comparison analysis between the percent tree growth and climate changes showed that the local temperature and precipitation could be another important factor causing growth releases for the three points, especially for growth releases that occurred synchronously between plots.