Department of Biology, Boston University, Boston, MA, 02215, USA.
New Phytol. 2014 Apr;202(1):106-115. doi: 10.1111/nph.12647. Epub 2013 Dec 24.
To elucidate climate-driven changes in leaf-out phenology and their implications for species invasions, we observed and experimentally manipulated leaf out of invasive and native woody plants in Concord, MA, USA. Using observations collected by Henry David Thoreau (1852-1860) and our own observations (2009-2013), we analyzed changes in leaf-out timing and sensitivity to temperature for 43 woody plant species. We experimentally tested winter chilling requirements of 50 species by exposing cut branches to warm indoor temperatures (22°C) during the winter and spring of 2013. Woody species are now leafing out an average of 18 d earlier than they did in the 1850s, and are advancing at a rate of 5 ± 1 d °C(-1) . Functional groups differ significantly in the duration of chilling they require to leaf out: invasive shrubs generally have weaker chilling requirements than native shrubs and leaf out faster in the laboratory and earlier in the field; native trees have the strongest chilling requirements. Our results suggest that invasive shrub species will continue to have a competitive advantage as the climate warms, because native plants are slower to respond to warming spring temperatures and, in the future, may not meet their chilling requirements.
为了阐明气候驱动的叶出（物候）变化及其对物种入侵的影响，我们在美国马萨诸塞州康科德观察并实验性地操纵了入侵和本地木本植物的叶出。利用亨利·戴维·梭罗（1852-1860 年）的观测数据和我们自己的观测数据（2009-2013 年），我们分析了 43 种木本植物物种的叶出时间变化及其对温度的敏感性。我们在 2013 年的冬季和春季通过将枝条暴露在温暖的室内温度（22°C）下来实验性地测试了 50 种物种的冬季需冷量。木本物种现在的平均叶出时间比 19 世纪早了 18 天，并且以 5±1°C(-1)的速度前进。功能群在其出叶所需的冷却持续时间上存在显著差异：入侵灌木通常比本地灌木具有较弱的冷却需求，在实验室中更快地出叶，在野外更早出叶；本地树木的冷却需求最强。我们的研究结果表明，随着气候变暖，入侵灌木物种将继续具有竞争优势，因为本地植物对温暖的春季温度的反应较慢，并且在未来可能无法满足其冷却需求。
