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

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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.