Introduction

Complex patterns in vegetation greening and browning in tundra and boreal ecosystems have been widely observed. These patterns have shown varying trends over time and space and have raised many questions about the driving factors. Climate change has been linked directly to greening and browning trends, as well as to increased disturbance, with subsequent effects on vegetation composition, ecosystem recovery, and greening and browning trends. At high latitudes, annual air temperatures are rising at more than twice the global average (Overland et al., 2018).¹ indicating that continued changes in the patterns of greening and browning associated with climate warming may be likely. Vegetation change can influence the physical environment, ecological processes, and society, and may be further affected in the future with continued climate change and other pressures such as forest harvest.

Trends and drivers are evaluated using a broad range of remote sensing and field-based measurement approaches that capture information at various temporal and spatial scales. While these datasets sometimes agree, mismatches are also observed, making it more difficult to be confident in observations of vegetation pattern details and to disentangle the drivers. There are also many metrics used to evaluate greening and browning trends, as well as differences in the time periods evaluated, which can make it difficult to compare results among datasets and to advance understanding.

The Polar Research Board, in collaboration with the Board on Life Sciences of the National Academies of Sciences, Engineering, and Medicine, convened a workshop² to explore the drivers of greening and browning at northern latitudes, discuss knowledge and research gaps, and highlight opportunities for existing and emerging methodologies to be better integrated to address gaps and refine understanding of trends (see the Statement of Task in Appendix A). The workshop was organized into three overarching session themes: (1) observed trends and identified drivers, (2) implications of vegetation change, and (3) methods and tools for evaluating changes and their uncertainties. Each session included presentations and lengthy question and discussion periods. Two breakout sessions were also held to further explore identified gaps and possible ways to address them. See Appendix C for the workshop agenda. This proceedings summarizes workshop presentations, commonly discussed ideas and topics that emerged, and take away messages generated among workshop participants. A list of in-person attendees is provided in Appendix D. The workshop was funded by the U.S. Arctic Research Commission and the U.S. Geological Survey, with additional travel support provided by Polar Knowledge Canada and the U.S. Department of Energy.

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¹ See https://crudata.uea.ac.uk/cru/data/temperature.

² This proceedings was prepared by the workshop rapporteur as a factual summary of what occurred at the workshop. The planning committee’s role was limited to planning and convening the workshop. The views contained in the proceedings are those of individual workshop participants and do not necessarily represent the views of all workshop participants, the planning committee, or the National Academies of Sciences, Engineering, and Medicine.

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