The persistence of beaver‐induced geomorphic heterogeneity and organic carbon stock in river corridors

Abstract

Beavers are widely recognized as ecosystem engineers for their ability to shape river corridors by building dams, digging small canals, and altering riparian vegetation. Through these activities, beavers create beaver meadows, which are segments of river corridor characterized by high geomorphic heterogeneity, attenuation of downstream fluxes, and biodiversity. We examine seven beaver meadows on the eastern side of the Rocky Mountain National Park, Colorado, USA with differing levels of beaver activity. We divide these sites into the four categories of active, partially active, recently abandoned (< 20 years), and long abandoned (> 30 years). We characterize geomorphic units within the river corridor and calculate metrics of surface geomorphic heterogeneity relative to category of beaver activity. We also use measures of subsurface geomorphic heterogeneity (soil moisture, soil depth, percent clay content, organic carbon concentration) to compare heterogeneity across beaver meadow categories. Finally, we calculate organic carbon stock within the upper 1.5 m of each meadow and compare these values to category of beaver activity. We find that surface geomorphic heterogeneity and mean soil moisture differ significantly only between active and long abandoned meadows, suggesting a non‐linear decrease with time following beaver abandonment of a meadow. Soil depth and organic carbon stock do not differ consistently in relation to category of beaver meadow, suggesting that larger‐scale geologic controls that foster deep floodplain soils can continue to maintain substantial organic carbon stocks after beavers abandon a meadow. These results also indicate that the effects of beaver ecosystem engineering can persist for nearly three decades after the animals largely abandon a river corridor. © 2018 John Wiley & Sons, Ltd.

Beavers alter stream macroinvertebrate communities in north‐eastern Utah

“…In general, previous research has suggested that beavers are beneficial for stream habitat heterogeneity and fish habitat (Bush & Wissinger, 2016;Laurel & Wohl, 2019;Law, Mclean & Willby, 2016;Pringle et al, 1988;Rolauffs, Hering & Lohse, 2001;Rosell et al, 2005), and, as a result, agencies are using beavers as a natural solution for stream and riparian restoration (Gibson & Olden, 2014;Pollock et al, 2014;Pilliod et al 2018). In general, previous research has suggested that beavers are beneficial for stream habitat heterogeneity and fish habitat (Bush & Wissinger, 2016;Laurel & Wohl, 2019;Law, Mclean & Willby, 2016;Pringle et al, 1988;Rolauffs, Hering & Lohse, 2001;Rosell et al, 2005), and, as a result, agencies are using beavers as a natural solution for stream and riparian restoration (Gibson & Olden, 2014;Pollock et al, 2014;Pilliod et al 2018).…”

“…However, declines in the fur trade, stricter trapping regulations, and beaver reintroduction programmes have helped this species return to most of its former range (Baker & Hill, 2003). Because beavers are ecosystem engineers with the capacity to alter both physical and chemical characteristics of aquatic ecosystems (Correll, Jordan & Weller, 2000;Gurnell, 1998;Laurel & Wohl, 2019;Naiman, Melillo & Hobbie, 1986;Smith et al, 1991;Wohl, 2013), their expanding populations will undoubtedly influence the aquatic communities residing in the rivers and streams that they recolonise.…”

“…Research investigating the effects of North American beaver on aquatic ecosystems has largely focused on physiochemical changes to the river/stream system or on fish. In general, previous research has suggested that beavers are beneficial for stream habitat heterogeneity and fish habitat (Bush & Wissinger, 2016;Laurel & Wohl, 2019;Law, Mclean & Willby, 2016;Pringle et al, 1988;Rolauffs, Hering & Lohse, 2001;Rosell et al, 2005), and, as a result, agencies are using beavers as a natural solution for stream and riparian restoration (Gibson & Olden, 2014;Pollock et al, 2014;Pilliod et al 2018).…”

Assessing restoration potential for beaver (Castor canadensis) in the semiarid foothills of the Southern Rockies, USA

“…Although beaver have been able to build dams along the mainstem, the slightly incised, single‐thread contemporary channel and adjacent semiarid grassland of the former floodplain probably represent a simplified river corridor relative to historic conditions. Comparable portions of stream networks with sufficient woody riparian vegetation typically have a multi‐thread channel planform with beaver dams on secondary channels and old ponds and vegetated berms across the floodplain (Laurel & Wohl, 2019; Polvi & Wohl, 2012). Re‐establishment of analogous conditions along the mainstem Dale Creek probably requires more sustained beaver occupancy, as dams accumulate sediment upstream and raise the streambed, helping to establish lateral connectivity with the floodplain (Pollock, Beechie, & Jordan, 2007).…”

“…Abundant evidence indicates that historic population densities of beaver ( Castor canadensis in North America, C. fiber in Eurasia) along forested rivers corridors in the northern hemisphere engineered ecosystems via herbivory and construction of dams and canals (Naiman, Melillo, & Hobbie, 1986; Rosell, Bozser, Collen, & Parker, 2005). Beaver‐modified river corridors have greater spatial heterogeneity (Laurel & Wohl, 2019). Beaver dams reduce longitudinal connectivity but enhance lateral and vertical connectivity between the channel, floodplain, and hyporheic zone (Burchsted, Daniels, Thorson, & Vokoun, 2010; Hood & Larson, 2015; Polvi & Wohl, 2012).…”