Expanding beaver pond distribution in Arctic Alaska, 1949 to 2019

Abstract

Beavers were not previously recognized as an Arctic species, and their engineering in the tundra is considered negligible. Recent findings suggest that beavers have moved into Arctic tundra regions and are controlling surface water dynamics, which strongly influence permafrost and landscape stability. Here we use 70 years of satellite images and aerial photography to show the scale and magnitude of northwestward beaver expansion in Alaska, indicated by the construction of over 10,000 beaver ponds in the Arctic tundra. The number of beaver ponds doubled in most areas between ~ 2003 and ~ 2017. Earlier stages of beaver engineering are evident in ~ 1980 imagery, and there is no evidence of beaver engineering in ~ 1952 imagery, consistent with observations from Indigenous communities describing the influx of beavers over the period. Rapidly expanding beaver engineering has created a tundra disturbance regime that appears to be thawing permafrost and exacerbating the effects of climate change.

Do beaver ponds increase methane emissions along Arctic tundra streams?

“…Complete coverage of cloud-free imagery was unavailable for 2018. Beaver pond density is moderate in the study area compared to elsewhere in the western Alaska tundra, and the number of ponds within and nearby this study area increased from 153 to 364 between 2003 and 2017 [35].…”

“…We interpret the increased hotspots surrounding beaver ponds as being indicative of increased CH 4 emissions, likely due to a combination of wetland formation and permafrost thaw. New beaver damming and construction of ponds along Arctic streams, including a doubling of beaver ponds in the Alaskan Arctic from 2003-2017 [35], is thus increasing CH 4 emissions from adjacent terrestrial surfaces and amplifying the warming already underway. Future work should include ground measurements of methane flux and a better understanding of the processes driving methane production and release surrounding tundra beaver ponds.…”

“…Beaver ponds (n = 118) were identified and delineated from very high resolution cloud-free satellite imagery from June, July, and August 2019 (<1 m, GeoEye-1) using expert photo interpretation at a scale 1:2000 following previous methods [35](figure 2). Complete coverage of cloud-free imagery was unavailable for 2018.…”

“…Beavers have constructed over 12 000 ponds in the Arctic tundra of Alaska, including a doubling between 2003 and 2017, as they colonized new regions and transformed lowland permafrost ecosystems [12,35]. People in remote subsistence-based communities of Alaska and Canada have witnessed the influx of beavers and associated hydrologic engineering with concern due to effects on fish, water quality, and boat access [36,37].…”

EEAGER: A Neural Network Model for Finding Beaver Complexes in Satellite and Aerial Imagery

“…Tracking changes in beaver ( Castor canadensis ) population, distribution, and landscape impacts as they recolonize their historic range in North America is not the only application of our model. The closely related Eurasian beaver ( Castor fiber ) is currently being reintroduced in Europe as part of reintroduction efforts (Puttock et al., 2015; Wróbel, 2020), invasive introduced beavers ( Castor canadensis ) in Tierra del Fuego are dramatically modifying Patagonian alpine environments (Anderson et al., 2009; Lizarralde et al., 2004; C. J Westbrook et al., 2017), and beavers in general are recolonizing the Arctic (Jones et al., 2020; Tape et al., 2018, 2022)—an area that has not had large‐scale beaver presence since the Pliocene (Davies et al., 2022; Mitchell et al., 2016; Rybczynski, 2008)—as anthropogenic climate change causes tundra ecosystems to shift to shrubland (Heijmans et al., 2022; Henry & Molau, 1997; Jung et al., 2016; Stow et al., 2004). As these large‐scale changes take place—whether intentional as in the case of reintroduction and conservation, or unintentional as in the case of beavers tracking climate change northwards—efficiently characterizing the total area of beaver‐influenced habitat and its geographic distribution are integral to making informed land management and conservation decisions.…”