Beavers engineer vast arctic tundra lowlands of Alaska

Beavers (Castor canadensis) transform lowland terrestrial and aquatic ecosystems by felling trees and shrubs to construct ponds and engineer streams, river floodplains, and lake outlets. Recent findings suggest that beavers have moved into some low arctic tundra regions and are controlling surface water dynamics, which has implications for permafrost landscape dynamics, but their prevalence and historical distribution are unknown. Here we use very high resolution satellite imagery (< 1m spatial resolution) to show extensive alteration of lowland arctic tundra ecosystems by beavers. We identified over 10,000 beaver ponds in the Alaska arctic tundra. The number of beaver ponds roughly doubled (1302 to 2731) in the area of overlapping 2000-06 and 2018-19 satellite imagery, except at a treeline location, where beaver pond numbers were similarly high during both periods (895 to 905). Select areas with available 1951-53 aerial photography reveal no beaver ponds in those parts of the study region. New beaver ponds are likely thawing permafrost and imposing a new disturbance regime that is rapidly accelerating the effects of climate change on the landscape. If trends continue, beavers will create innumerable physical and biological oases across lowland tundra ecosystems, ushering substantial changes to the arctic biome.