Collaborative Research: Radial Growth Responses Among Naturally Occurring Western U.S. Conifers Under Changing Environmental Conditions

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。这项研究探讨了生长变化的道格拉斯冷杉和黄松森林的北方落基山脉（美国），这是越来越多的CO2丰富的大气和预测的气候变暖和干燥的条件下，在未来。研究人员将调查两种在自然条件下生长的具有重要经济意义的美国西部针叶树对环境变量变化的生长反应。具体而言，径向生长率的花旗松和黄松树将在9个网站在北方落基山脉的树木是共同占主导地位的，在混淆的增长因素最小化，并在站点间的环境变化最大化。匹配的树木年轮年表，其中显示每年的平均树木生长速度，将开发和径向生长模式之前和之后的大气CO2浓度变得显着升高。这将通过使用生长/气候回归模型、碳同位素分析和对不同干旱严重程度期间生长率的分析来完成。本研究的目的是确定：1）在过去的200年里，由于CO2浓度的增加导致气孔导度的降低，这两个树种的内在水分利用效率（iWUE）是否呈显著上升趋势; 2）在水分有限的环境中，增加iWUE是否对这两个树种的径向生长率产生积极影响; 3）干旱对径向生长率的影响随仪器气候记录的时间推移而减弱（1895年至今）; 4）不同物种对CO_2施肥的反应存在差异，且这些反应存在空间变异; 5）古树的径向生长率并不显著低于幼树的生长率，因此，古树林可作为重要的碳汇。目前的气候模型预测，研究地区将经历更频繁和严重的夏季干旱。因此，更好地了解未来生态系统在二氧化碳增加和更温暖、更干燥的条件下面临的问题至关重要。了解这两个树种对先前气候变化和大气CO2上升的具体生长反应，将更好地了解这些物种在未来几十年将如何应对。由于这些物种具有巨大的商业价值，而且它们作为碳汇的能力增强，因此大气中二氧化碳的增加对增长的潜在积极影响可能具有经济和生态意义。该项目的结果将被广泛传播的目标，研究结果将有助于在美国西部针叶林的管理策略的发展该项目还将为本科生和研究生提供教育的机会，因为他们将参与实地和实验室的研究组成部分。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). This research examines growth changes in the Douglas-fir and ponderosa pine forests of the Northern Rockies (USA), which are growing under conditions of an increasingly CO2- rich atmosphere and a projected warmer and drier climate in the future. The researchers will investigate the growth responses of two co-occurring and economically important western USA conifers growing under natural conditions in relation to changing environmental variables. Specifically, radial growth rates of Douglas-fir and ponderosa pine trees will be compared at nine sites in the Northern Rockies where the trees are co-dominant, where confounding growth factors are minimized, and where between-site environmental variability is maximized. Matched tree-ring chronologies, which show the average rate of tree growth annually, will be developed and radial growth patterns examined prior and after atmospheric CO2 concentrations became significantly elevated. This will be done using growth/climate regression models, carbon isotope analysis, and analyses of growth rates during various levels of drought severity. The purpose of this research is to determine if 1) rates of intrinsic water-use efficiency (iWUE) of both species are trending significantly upward during the past 200 years because of decreased stomatal conductance associated with increasing levels of CO2; 2) increasing iWUE is positively impacting the radial growth rates of these two tree species in water-limited environments; 3) the influence of drought on the radial growth rates has decreased over the time period of instrumental climatic records (1895-present); 4) there are differential responses to CO2 fertilization between the species and spatial variation in these responses; and 5) radial growth rates of old-growth trees are not significantly less than younger tree growth rates and thus, old-growth forests may serve as important carbon sinks. Current climate models predict that the study area will experience more frequent and severe summertime droughts. Thus, a greater understanding of issues facing future ecosystems under increased CO2 and warmer, drier conditions is critical. Knowing the specific growth responses of these two tree species to prior climatic variations and rising atmospheric CO2 will provide a better understanding of how these species will respond in the next several decades. The potential positive impacts on growth resulting from increasing atmospheric CO2 could be economically and ecologically significant because of the great commercial value of these species, and their increased ability to serve as carbon sinks. The project results will be broadly disseminated with a goal that the study findings will assist in the development of management strategies of conifer forests in the western U.S. The project will also provide educational opportunities for undergraduate and graduate students as they will participate in both the field and laboratory components of the study.