Tundra ecosystem responses to 30 years of experimental and observed changes in climate

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Tundra ecosystems have shown strong responses to recent changes in climate. Coordinated distributed experiments such as the International Tundra Experiment (ITEX) have provided critical knowledge on how these systems respond to experimental and observed changes in climate and the response variation across the tundra biome. I established the first set of ITEX studies in 1992 in seven different tundra communities at a High Arctic site on Ellesmere Island and continue to maintain the experiments. Each site has a warming treatment of transparent open-top chambers (OTCs), and in single sites warming is combined with nutrient addition and snow manipulation. Over the next 5 years, I will bring the experiments to an end and use this unique opportunity to measure the response of tundra systems to the termination of the experiments. Graduate students and postdocs will conduct field studies and use the extensive data base from the 30+ years of research at the site to answer questions linking plant traits to community and ecosystem change, to test the ability of tundra plants to adapt to a warming climate and the determine if the long-term manipulations have fundamentally altered the tundra systems.***Plants in the warmed plots have consistently shown advanced phenology and increased growth and reproductive effort and success, especially those that flower early. In addition, the composition and abundance has shifted with increased cover of a few dominant species but also greater diversity. However, we have yet to link the responsiveness of the traits to the changes in biodiversity in the plots, and this will lead to better predictions of vegetation change. Students will explore these links using trait data from all of the species measured. These trait-based studies will provide one of the first assessments of temporal variability in plant traits.***The warmed plots have been 1-3ºC above the ambient summer temperature for 30 years, and the ambient temperature has also increased by 2ºC since 1992. Students will help determine the trajectory of the differences between experimental and control plots continue after the treatments are removed. In the second year of the study, 50 % of the OTCs will be removed and responses followed over the next three years to examine the “relaxation” of the system to ambient conditions. Responses will be measured at the plant level (e.g., phenology, reproductive effort and success, and photosynthesis); the community level, including changes in composition and abundance; and the ecosystem level, including measurements of nutrient availability and uptake, net ecosystem exchange of CO2, and spectral characteristics of the plots. In the fifth year of the proposed study, we will conduct destructive harvests in the plots to determine changes in above and below-ground biomass (NPP) and plant traits. The bitter sweet end to these experiments will provide continued critical knowledge of tundra ecosystems as they continue to change.