Response Of Subalpine Timberline In Northeast China To Global Climate Change

According to the hiberarchy of modern ecology, focusing on the relationship of global climate change and the subalpine timberline in northeast China, a case study was carried out at the timberlines of Changbai Mountain in Jilin Province and Laotudingzi Mountain in Heilongjiang Province. The responses of ring width, growth in high, diameter and volume, population age structure and spatial distribution of trees at the timberline to global warming at individual, population, ecosystem and landscape scales were studied by using the methods of dendroclimatology, stem analysis, geostatistics, remote sensing image and the local climate data analysis. The effects of global warming on the location, shape, width, pattern index and NDVI of the timberlines landscape character were analyzed. The main results are as follwing:The annual mean temperature increases as 0.04C/10a in China in recent 50 years. This trend is consistent with global warming. In terms of region, the warming in Northeast is clear, and the trend of subalpine timberline in Northeast is more significant.The climate data in Changbai Mountain and Dahailin region show that the global warming was very obvious in recent several decade years, especially the lowest month temperate, cold and warm periods temperature. The accumulated temperature increased slightly. February was the month with the greatest increaseing magnititude in a year. As to seasonal changes, winter was the most obvious. The seasonal thermal amplitude decreased, while the whole year heat increased. The rainfall data show that annual rainfall in Dahailin fluctuated with sightly increase, but there was no clear trend. The rainfall in Changbai Mountain showed that there was a decreasing trend in summer, and aslight increase in spring, autumn and winter. However, the annual rainfall exhibited decreasing trend.The correlation analysis between the ring index and the climate factors suggests that the ring index at timberline was strongly correlated with the temperature and slightly with precipitation. However, the warm period temperature and accumulated temperature were the positively correlated with the ring index, and the cold period temperature and mean annul temperature were negatively correlated with the ring index. According to the relationship between annual ring index and summer mean temperature, the summer temperature has been reconstructed in Laotudingzi region since 1905. Though there were some offset between reconstruct value and observed value, the increase trend was consistent.The results of tree annual ring analysis at timberline shows that trees with different age structure response to global change differently, and the middle-aged tree were the most sensitive. The different species and location were also different. With comparision, the sensitivity of Betula ermanii was better than that of spruce-fir, and it is mainly related with the location, and the middle-aged tree had the better sensitivity. The global warming resulted in the increase of diameter growth, and the trend of annual index was consistent with the trend of temperature.Through stem analysis, the growth in diameter, height and volume increased with global warming, but the height growth trend was the lowest. With the correlation analysis among measured trees and climate factors, the growth index of height, diameter and volume correlated with temperature strongly, with rainfall slightly or irrelative. Among the temperature factors, the mean temperature from June to September was more important, and the diameter growth was the clearest in the measured tree factors. The result indicates that the individual trees at timberline have been response to global warming.The effects of global climate change on timberline have been demonstrated by the difference of distribution and dynamics of structure with traditional statistics and geostatistics. The results show that the seedling and young tree predominated in upper timberline with global warming, the class structure showed inverse J type, and the population pattern exhibited...