北京西山老龄树记载的森林干扰历史

History of forest disturbance recorded by old trees in Xishan Mountain,Beijing

老龄树不仅记载着气候与环境的变化信息,同时也见证了社会的变迁历史。了解老龄树的生长变化和干扰历史对准确评估全球变暖背景下老龄树的健康并为其制定合理的保护计划具有现实的意义。该研究利用树木年轮生态学方法分析了北京西山地区油松(Pinus tabuliformis)的干扰历史及其原因。结果发现:在1820-2021年间,该地区油松生长释放的高峰期主要是5个,分别是1820-1830、1869-1881、1909-1918、1947-1959和2004-2010年间。树木生长抑制事件多集中在1831-1837、1855-1868、1882-1891、1920-1930、1960-1970和1980-1986年间。该地区油松生长与气候因素的响应分析以及相关的历史资料显示,干旱事件及随后的气候条件好转是导致该地区森林生长抑制及释放事件的重要原因。进一步研究发现,老龄树在1840年前的平均径向生长速率可达到2.70 mm·a^(-1),随后出现生长速率逐渐下降的趋势;1980年以后出现明显生长抑制现象,年平均径向生长速率下降到0.38 mm·a^(-1),下降幅度达85%。1965年后生长速率和气温出现了更强的负相关关系,生长速率和帕尔默干旱指数(PDSI)出现了显著的正相关关系。以上结果表明,1980年后北京地区加剧的暖干化趋势对该地区老龄树的生长产生负面影响。该研究结果有助于认识北京地区历史时期森林干扰发生的规律,对准确评估气候变化背景下老龄树的健康状况具有重要意义。

Aims Old trees not only record the climate and environment change information,but also witness the history of social changes.Understanding the history of growth change and disturbance of old trees is useful to accurately assess the health of old trees in the context of global warming and to develop conservation plans.Methods We used tree-ring methods to analyze the disturbance history of the old trees(Pinus tabuliformis)in the Xishan Mountain of Beijing.Important findings There were six major growth suppression(1831-1837,1855-1868,1882-1891,1920-1930,1960-1970 and 1980-1986)and five release events(1820-1830,1869-1881,1909-1918,1947-1959 and 2004-2010).The response analysis of tree growth to climate factors and the historical data showed that drought events and subsequent climatic improvement were the main reasons for growth suppression and release events.Further studies showed that the average growth rate of diameter at breast height of old trees was 2.70 mm·a^(-1)before 1840,and then the growth rate of diameter at breast height gradually decreased.After 1980,there was an obvious growth suppression,and the annual average growth rate decreased to 0.38 mm·a^(-1).A stronger negative correlation between tree growth and temperature emerged after 1965,and a significant positive correlation emerged for Palmer Drought Severity Index(PDSI).These results suggest that the warming and drying trend in Beijing in recent years may further negatively affect old trees in the urban area.These results are helpful for further understanding the regularity of forest disturbance in the Beijing area during historical period,and are of great significance for accurately assessing the healthy status of elderly trees in the context of climate change.