We analyzed the influence of climate change to the radial growth of the two widedistributed major tree species, Pinus koraiensis and Picea jezoensis, in their own upper limits of Changbai Mountain during the recent 50 years with the method of Dendrochronology. The radial growth of Pinus koraiensis shows the same trend with the rising temperature; while Picea jezoensis shows the opposite "disturbance problem", which means radial growth is decreasing with the rising of temperature. The positive response of tree growth to hydrothermal condition is the key reason for the upper limit Pinus koraiensis chronology keeping the same pattern with temperature: the increase of temperature and precipitation in growing season is good for Pinus koraiensis growth, and the promoting effect of these two factors can strengthen each other. The prolongation of growing season and the rising temperature in growing season can also accelerate the growth of Pinus koraiensis. Water stress caused by the increasing temperature is the main reason for the opposite trend of tree ring-width chronology to temperature in the last 50 years. Correlations between Picea jezoensis chronology and most temperature index are almost significant negative. As the temperature rising, correlations between ring-width chronology and precipitation, especial spring precipitation, were changing from negative to positive. High temperature in each month and inadequate precipitation in the middle-and-late growing season are the important meteorology conditions for narrow rings, while low temperature in each month and the sufficient precipitation in the late growing season are good for Picea jezoensis growth. What's more, the insignificant extension of growing season may also cause the reduction of temperature sensitivity in tree ring. Based on our research, we conclude that proper temperature rise is good for the upper-limit Pinus koraiensis growth at the condition of none less of precipitation, and the upper limit of Pinus koraiensis may move upward; while the growth of upper-limit Picea jezoensis may be restricted, and the possibility of the up shift of its upper limit is low. Keywords tree ring, Pinus koraiensis, Picea jezoensis, climate change, upper limit Tree ring is the record of responses of tree growth to its own and the outer circumstance [1]. Trees, distributed in high latitude or high elevation, are mainly restricted by temperature, so tree-ring records sampled in the geographical north boundary or the upper limit of high mountain are us 1 ually applied as proxy indicators to construct the history temperature [2, 3]. Lots of studies have found the temperature underestimation of model simulation based on tree ring width since mid-20 th century, especially after the remarkable warming period of 1980s [4-10]. This divergence problem known as the anomalous reduction in forest growth indices and temperature sensitivity in tree-ring width and density records has been proven in Northern Hemisphere high latitudes and high altitudes [11, 12]. Because of the complica...

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The pipe model theory has been applied to estimate allometry of trees in many regions; however, its reliability and generality need more verification for estimating crown biomass in China. In the present study, the crown biomass of Larix olgensis plantations in four sites in northeast China was estimated using the pipe model, and the correlation efficiency index of larch crown biomass for pipe model estimation was 0.953. The crown biomass of larch plantations could be accurately estimated by the tree height, crown base height, and stem area at breast height. Meanwhile, the effects of site, stand density, and age on the accuracy of crown biomass estimated by the pipe model were detected. The covariance analysis showed that the effect of age on crown biomass was 0.024, indicating that age had a significant effect on the estimation accuracy in this model, while site and stand density had no significant effects (p = 0.180 and p = 0.169). Our study showed that the crown biomass of L. olgensis plantations in northeast China could be accurately estimated using the pipe model, and we recommend considering the age effect in practical applications.

Pipe model theory has the potential to be widely applied in the estimation of tree allometry parameters, although it remains uncertain whether it can provide accurate estimation of the crown biomass of plantation forest. In this study, an improved pipe model was used for the first time to estimate the crown biomass of Larix olgensis plantations in northeast China. The results of linear regression analysis showed that crown biomass could be accurately estimated from the stem area at the crown base, which could be calculated using the tree height, crown base height, and stem area at breast height. Furthermore, covariance analysis was applied to analyze the differences in site-related factors that affect crown biomass. There was no significant difference between sites in the crown biomass of L. olgensis plantations in the research area, while the effect of tree age on crown biomass estimation should be considered. Our study showed that a modified pipe model could accurately estimate the crown biomass of larch plantations in northeast China, which has great significance for the determination of crown biomass in Chinese plantations using pipe model theory.