Friedrichs Dagmar A, Büntgen Ulf, Frank David C, Esper Jan, Neuwirth Burkhard, Löffler Jörg
Department of Geography, University of Bonn, Meckenheimer Allee 166, 53115 Bonn, Germany.
Tree Physiol. 2009 Jan;29(1):39-51. doi: 10.1093/treephys/tpn003. Epub 2008 Dec 5.
We analyze interannual to multi-decadal growth variations of 555 oak trees from Central-West Germany. A network of 13 pedunculate oak (Quercus robur L.) and 33 sessile oak (Quercus petraea (Matt.) Liebl.) site chronologies is compared with gridded temperature, precipitation, cloud-cover, vapor pressure and drought (i.e., Palmer Drought Severity Index, PDSI) fluctuations. A hierarchic cluster analysis identifies three groups for each oak species differentiated by ecologic settings. When high precipitation is primarily a characteristic for one Q. robur and one Q. petraea cluster, the other clusters are more differentiated by prevailing temperature conditions. Correlation analysis with precipitation and vapor pressure reveals statistically significant (P < or = 0.05) correlations for June (r = 0.51) and annual (r = 0.43) means. Growth of both species at dry sites correlates strongly with PDSI (r = 0.39, P < or = 0.05), and weakly with temperature and cloud-cover. In natural stands, Q. robur responds more strongly to water depletion than Q. petraea. Twenty-one-year moving correlations show positive significant growth response to both PDSI and precipitation throughout the 20th century, except for the 1940s - an anomalously warm decade during which all oak sites are characterized by an increased growth and an enhanced association with vapor pressure and temperature. We suggest that the wider oak rings that are exhibited during this period may be indicative of a nonlinear or threshold-induced growth response to drought and vapor pressure, and run counter to the general response of oak to drought and precipitation that normally would result in suppressed growth in a warmer and drier environment. As the wide rings are formed during the severe drought period of the 20th century, a complex model seems to be required to fully explain the widespread oak growth. Our results indicate uncertainty in estimates of future growth trends of Central European oak forests in a warming and drying world.
我们分析了德国中西部555棵橡树的年际到年代际生长变化。将一个由13个欧洲栓皮栎（Quercus robur L.）和33个无梗花栎（Quercus petraea (Matt.) Liebl.）站点年表组成的网络与网格化的温度、降水、云量、水汽压和干旱（即帕尔默干旱严重度指数，PDSI）波动进行了比较。层次聚类分析为每个橡树物种识别出了三组，它们因生态环境而有所不同。当高降水量主要是一个欧洲栓皮栎和一个无梗花栎聚类的特征时，其他聚类则更多地由盛行的温度条件来区分。与降水和水汽压的相关分析显示，6月（r = 0.51）和年平均值（r = 0.43）的相关性具有统计学显著性（P≤0.05）。两个物种在干燥站点的生长与PDSI密切相关（r = 0.39，P≤0.05），与温度和云量的相关性较弱。在天然林中，欧洲栓皮栎对水分亏缺的反应比无梗花栎更强烈。21年移动相关性显示，整个20世纪，除了20世纪40年代（一个异常温暖的十年，在此期间所有橡树站点的特征是生长增加以及与水汽压和温度的关联增强）外，对PDSI和降水都有显著的正生长响应。我们认为，在此期间出现的更宽的橡树木年轮可能表明对干旱和水汽压的非线性或阈值诱导生长响应，这与橡树对干旱和降水的一般响应相反，正常情况下在温暖干燥的环境中会导致生长受抑制。由于宽年轮是在20世纪的严重干旱时期形成的，似乎需要一个复杂的模型来充分解释广泛的橡树生长情况。我们的结果表明，在气候变暖和变干的世界中，对中欧橡树林未来生长趋势的估计存在不确定性。
