Species and ecosystem constraints on greening High Arctic tundra in a changing climate

北极冻土带生态系统正在对气候变化做出反应，包括在地块和区域尺度上观察到的植物覆盖的普遍增加。这种“绿色”的增加主要是由于北极南部地区灌木高度和覆盖面积的增加。这些植物组成和丰度的变化将对冻土带生态系统产生重要影响，包括野生动物饲料和栖息地的变化。它还会影响气候，因为浓密的叶冠会吸收更多的阳光，导致大气进一步升温。北极高海拔地区的植物覆盖受限得多，大片地区植被稀疏。这些系统的变化将取决于现有物种和区域物种池中新个体的成功建立。然而，人们对这些物种的繁殖努力、成功和建立知之甚少，也不知道在更北的北极高地景观中建立南部生态型的潜力。因此，提出的研究的一个主要目的是提高我们对气候变化（温度和降水制度和生长季节长度）对北极苔原高海拔植物物种的繁殖努力、成功和建立的影响的理解。我们还将测试南方生态型在实验性气候变化下相对于当地生态型的建立、生长和繁殖能力。我和我的学生将在埃尔斯米尔岛的研究地点的各种北极高纬度冻土带群落中进行已建立的和新的实地实验，并在UBC进行生长室和温室研究。1992年，我在北极高低地绿洲的六个冻土带植物群落中建立并维持了一套使用开放式顶室（OTCs）的被动变暖实验。将建立新的实验，结合变暖（OTCs）、积雪变化（雪栅栏）和额外的夏季降雨来模拟温度和降水的预期变化。常见物种的种子将在现场和北极群岛南部地区收集，发芽和幼苗种植在研究现场的普通花园实验中。公共花园将在一半的地块上安装otc。这些实验将使我们能够检查高北极苔原物种种群中与适应性相关的性状差异，并确定哪些物种和哪些生态型在建立新种群方面更成功。繁殖努力（如花的大小，花和种子的数量，种子的重量）和成功（如发芽率）和一系列其他性状（如物候，生长，叶片性状）将在所有实验中对个体进行测量。我们将继续使用我们的标准化方法测量植物物种的组成和丰度。我们还将使用便携式光合作用系统测量实验处理对CO2通量的影响。我提出的研究将有助于确定高北极地区增加植物覆盖的潜力和限制，以应对迅速变暖的气候。我们将更好地了解常见植物物种在气候变化条件下繁殖和建立的能力，以及随着气候变暖，南方生态型是否可以在更多的北方地区建立。预计北极高海拔地区植物覆盖的增加将在当地、区域和全球范围内产生重要影响，我提出的研究将为我们理解这些后果提供重要贡献。

Arctic tundra ecosystems are showing responses to the changing climate including a general increase in plant cover, which has been observed at plot and regional scales. This increase in “greenness” is largely due to greater shrub height and cover in southern Arctic areas. These changes in plant composition and abundance will have important consequences for the tundra ecosystems, including changes in wildlife forage and habitat. It will also affect the climate, as the dense leaf canopy will absorb more sunlight and result in further heating of the atmosphere. Plant cover in the High Arctic is much more restricted, with large areas sparsely vegetated. Changes in these systems will depend on successful establishment of new individuals of existing species and from the regional species pool. However, little is known of the reproductive effort and success and establishment of these species, or the potential for establishment of southern ecotypes in more northern High Arctic landscapes. Hence, a major objective of the proposed research is to improve our understanding of the impact of changes in climate (temperature and precipitation regimes and growing season length) on the reproductive effort and success and establishment of high Arctic tundra plant species. We will also test the ability of southern ecotypes to establish, grow and reproduce relative to local ecotypes under experimental climate change.My students and I will use a combination of established and new field experiments in a variety of High Arctic tundra communities at at research site on Ellesmere Island, and growth chamber and greenhouse studies at UBC. In 1992, I established and have maintained a set of passive warming experiments, using open top chambers (OTCs) in six tundra plant communities at a High Arctic lowland oasis. New experiments will be established that combine warming (OTCs), changes in snow cover (snow fences) and additional summer rain to simulate expected changes in temperature and precipitation. Seeds of the common species will be collected at the site and from southern areas of the High Arctic Islands, germinated and seedlings planted into common garden experiments at the research site. The common gardens will have OTCs installed in half the plots. These experiments will allow us to examine differences in traits related to fitness in populations of High Arctic tundra species and determine which species and which ecotypes will be more successful in establishing new populations. Reproductive effort (e.g. flower size, number of flowers and seeds, seed weight) and success (e.g. germination rate) and a set of other traits (e.g. phenology, growth, leaf traits) will be measured on individuals in all experiments. We will continue to measure composition and abundance of plant species using our standardized methods. We will also measure the effect of the experimental treatments on CO2 flux using a portable photosynthesis system. My proposed research will help to determine the potential and constraints for increased plant cover in the High Arctic in response to the rapidly warming climate. We will gain a much better understanding of the ability of common plant species to reproduce and establish under climate change conditions, and whether southern ecotypes can establish in more northern areas as the climate warms. The predicted increase in plant cover of the High Arctic will have important consequences at local, regional and global scales, and my proposed research will provide important contributions to our understanding of these consequences.