The Alaska-Yukon Region of the Circumboreal Vegetation Map

The circumboreal vegetation mapping (CBVM) project is an international collaboration among vegetation scientists to create a new vegetation map of the boreal region at a 1:7.5 million scale with a common legend and mapping protocol. The map is intended to portray potential natural vegetation, or the vegetation that would exist in the absence of human or natural disturbance, rather than existing vegetation that is commonly generated at larger scales. As a contribution to the CBVM effort, Torre Jorgenson, Alaska Ecoscience, and Del Meidinger, Meidinger Ecological Consultants Ltd., developed maps of bioclimatic zones, geographic sectors with similar floristic variability, and vegetation in boreal Alaska, Yukon, northwestern British Columbia, and a mountainous portion of southwest Northwest Territories—termed the Alaska-Yukon region. The work was supported by the U.S. Fish and Wildlife Service, Yukon Parks, the Northwest Boreal Landscape Conservation Cooperative, and the Conservation of Arctic Flora and Fauna working group of the Arctic Council.

The effort included maps of bioclimates with 12 bioclimate zones, biogeographic provinces delineating the Alaska-Yukon and Aleutian provinces, and a map of geographic sectors with six sectors that provided the basis for classification of boreal vegetation. Mapping used MODIS imagery as the basis for manual image interpretation and an integrated-terrain-unit approach, which included classifications for bioclimate, physiography, generalized geology, permafrost, disturbance, growth from, geographic sector, and vegetation. A new tree line was developed for the region. Vegetation was mapped at two hierarchical levels, including: (1) 13 formation groups differentiating zonal and azonal systems; and (2) 21 geographic variants based on bioclimatic zonation and dominant species that characterize broad longitudinal regions or biogeographic provinces. Each of the geographic variants was described by identifying the dominant and characteristic species and its climatic and landscape characteristics, as well as references that relate to the unit.

Views of main zonal forest types of the Alaska-Yukon region.

Map of boreal vegetation (level 2) in the Alaska-Yukon region.

The report and maps are available at:

http://www.caff.is/strategies-series/359-the-alaska-yukon-region-of-the-circumboreal-vegetation-map-cbvm

Jorgenson, M. T. and D. Meidinger. 2015. The Alaska-Yukon Region of the Circumboreal Vegetation Map. Conservation of Arctic Flora and Fauna,, Akureyri, Iceland. CAFF Strategies Series Report. ISBN: 978-9935-431-48-6, 39 p.

Role of Ground Ice Dynamics and Ecological Feedbacks in Recent Ice-wedge Degradation and Stabilization

Yuri Shur and Torre Jorgenson stand in front of a large ice wedge, which is protected by only a thin layer of soil that thaws during the summer.

Ground ice is abundant in the upper permafrost throughout the Arctic and fundamentally affects terrain responses to climate warming. Ice wedges, which form near the surface and are the dominant type of massive ice in the Arctic, are particularly vulnerable to warming. Yet, processes controlling ice-wedge degradation and stabilization are poorly understood. In a recent paper published in the Journal of Geophysical Research: Earth Surface, Torre Jorgenson and colleagues from the University of Alaska Fairbanks and the U.S Geological Survey quantified ice-wedge volume and degradation rates, compared thermal regimes and ground-ice characteristics across a sequence of degradation and stabilization stages, and evaluated biophysical feedbacks controlling permafrost stability near Prudhoe Bay, Alaska. By measuring thermokarst pits on imagery from 1949 to 2012, they showed ice-wedge degradation abruptly increased in the 1990s and covered 9% of the area by 2012 (below).

In early stages, thaw settlement caused water to impound in thermokarst troughs, creating positive feedbacks that increased net radiation, soil heat flux, and soil temperatures. The disturbance stimulated plant growth and organic-matter accumulation, providing negative feedbacks that allowed ice to aggrade and heave the surface, thus reducing surface water and soil temperatures in later stages. Due to these ecological feedbacks, mean annual soil temperatures varied by 9 °C, nearly twice as large as projected regional climate warming by century’s end. This greatly complicates efforts to model and project permafrost response to climate change.

Measuring permafrost temperatures below in a recently collapsed thermokarst pit.

Jorgenson, M. T., M. Z. Kanevksiy, Y. Shur, K. Wickland, D. R. Nossov, N. G. Moskalenko, J. Koch, R. Striegl. 2015. Role of ground-ice dynamics and ecological feedbacks in recent ice-wedge degradation and stabilization. Journal of Geophysical Research – Earth Surface 120:2280-2297.