The Biome Shift Now Occurring in the Boreal Region: Characteristics and a First Look at Knowledge Needs

Glenn Patrick Juday, School of Natural Resources and Agricultural Sciences, University of Alaska Fairbanks

The northwestern North American Arctic and boreal regions are centers of biodiversity at the species and genetic levels, almost certainly because of the continuous availability of unglaciated refugia during past periods of rapid climate change. Specifically identifying these basic biodiversity resources will need to be a priority if management for their survival during a time of rapidly shifting climate is to be successful. Recent Arctic warming has reversed cooling of 2000+ years duration that was orbitally driven. Several aspects of the altered climate regime are in the process of causing apparently insurmountable challenges to the survival of much of dominant vegetation where it occurs today, while simultaneously creating suitable climatic conditions where some of these species are largely absent today. Alaska has a ~100-year instrument-based climate record. The combination of temperature and precipitation at low elevations in central Interior Alaska in the early 21st century has approached or exceeded lethal limits for the currently dominant tree species. For example, natural distribution limits of white spruce in North America do not include areas with precipitation below about 280 mm, the current 100-year mean at Fairbanks. The combination of increased July temperature and unchanged annual precipitation in central Alaska now exceeds the previous limits that characterized white spruce distribution. Spruce budworm has now developed outbreak potential on Alaska and northern Canadian forests. Alaska birch have been stressed to near lethal levels across low-land Interior regions twice in the last decade from acute drought injury. Aspen leaf miner is causing widespread tree death, and dieback. The current wildland fire and insect outbreak regimes, both directly temperature related, have been disturbing the forest at a rate that will not allow the recent age structure of forests to appear again as long as the new disturbance rate is maintained. The accelerated disturbance is significantly reducing available habitat for a set of specialized older forest organisms. Recent temperature increases have improved climate suitability for black and white spruce in far western Alaska, and possibly in the far northern tundra as well. However, these areas generally have sparse tree populations, which may or may not represent the best-adapted genotypes to these new conditions, and practical challenges to migration may require a significant amount of time to be overcome by exclusively natural processes. Landscape-scale tundra fire is now a reality on the Alaska North Slope, initiating the process of mobilizing one of the Earth’s great pools of sequestered carbon into the atmosphere. The synoptic picture is consistent

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