Warming, soil moisture, and loss of snow increase Bromus tectorum's population growth rate

Climate change threatens to exacerbate the impacts of invasive species. In temperate ecosystems, direct effects of warming may be compounded by dramatic reductions in winter snow cover. Cheatgrass (Bromus tectorum) is arguably the most destructive biological invader in basins of the North American Intermountain West, and warming could increase its performance through direct effects on demographic rates or through indirect effects mediated by loss of snow. We conducted a two-year experimental manipulation of temperature and snow pack to test whether 1) warming increases cheatgrass population growth rate and 2) reduced snow cover contributes to cheatgrass' positive response to warming. We used infrared heaters operating continuously to create the warming treatment, but turned heaters on only during snowfalls for the snowmelt treatment. We monitored cheatgrass population growth rate and the vital rates that determine it: emergence, survival and fecundity. Growth rate increased in both warm...气候变化或加剧外来入侵物种的危害。在温带生态系统中，气候变暖的直接影响可能会因冬季积雪覆盖的急剧减少而进一步加重。旱雀麦（Bromus tectorum）无疑是北美山间西部流域最具破坏性的生物入侵物种，气候变暖可通过对种群统计参数的直接影响，或是通过积雪减少介导的间接效应，提升其生存适配能力。本研究开展了为期两年的温度与积雪覆盖实验操控，旨在验证两个假说：其一，气候变暖会提升旱雀麦的种群增长率；其二，积雪覆盖减少会助力旱雀麦对气候变暖产生正向响应。我们采用持续运行的红外加热器（infrared heaters）构建增温处理组，而融雪处理组仅在降雪时段开启加热器。我们监测了旱雀麦的种群增长率及其关键决定参数：出苗率、存活率与繁殖力。两种增温处理下的种群增长率均有所提升……