Arctic ecosystems are changing in response to arctic warming, which is proceeding more than twice as fast as the global average. The International Tundra Experiment (ITEX) was established in the early 1990s to understand the effects of warming and environmental variability on tundra vegetation properties and ecosystem function. The ITEX program has been extremely valuable for detection of changes in tundra plant and ecosystem responses to experimental warming and to background climate change across sites that span the major ecosystems of the Arctic. In 2007, the Alaskan and Greenland ITEX sites were combined into an Arctic Observatory Network (AON). The current ITEX AON project will continue to document and understand Arctic terrestrial vegetation change and its ecosystem consequences by maintaining the long-term datasets of the ITEX-AON. The warming experiment of ITEX-AON allows us to assign the cause for observed changes in response to warming instead of relying on simple correlations. This project provides urgently needed data on changes in vegetation and the importance of these changes for ecosystem services from a variety of Arctic ecosystems. This project will provide training for postdoctoral, graduate and undergraduate students in the emerging fields of remote sensing, cybertechnology and big-data analysis. The project will include outreach activities through strong relationships with the CLEO Institute in Miami; the Grand Valley State University Regional Math and Science Center; and K-12 school systems in Miami, Anchorage, Grand Rapids and El Paso. All data from this project are and will be freely available at the NSF Arctic Data Center.The core datasets of the proposed research include manual observations of phenology, vegetation structure and composition, and ecosystem function (carbon flux and nutrient cycling) on long-term ITEX control and experimental warming plots, repeat measurement of vegetation plots on the long-term 1 km2 vegetation grids, and a multifactor warming/moisture experiment in Greenland. In 2009, the sampling scheme was expanded to include a larger spatial component to amplify the value of the measurements collected. This expansion included the addition of phenocams, automated mobile sensor platforms, and medium-scale aerial imagery. The automated platforms measure a suite of vegetation surface properties with minimal effort across focal transects spanning strong moisture and microtopographic gradients at a near-daily frequency. These measurements capture the fine-scale changes in vegetation over the growing season that are missed by lower frequency manual measurements and provide a bridge between manual measurements and aerial imagery. Medium-scale aerial imagery, using Kite Aerial or Unmanned Aerial Vehicles, is acquired throughout the growing season for scaling of manual and automated measurements; satellite imagery is referenced to medium-scale aerial imagery to aid scaling of responses to the regional level. In the newest phase of AON ITEX, we are particularly focused on understanding the relationship between landscape subsidence as a result of permafrost thaw and vegetation structure and function because of the potential for significant positive feedbacks to climate change.