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  • Applying Design Lessons from an Ecosystem Engineer
  • Ken P. Yocom (bio)

As a species, Castor canadensis, otherwise known as the North American beaver, has had a complex and often controversial relationship with people. Highly favored for their pelts during colonial expansion in the U.S. and Canada and seen as pests, a hindrance to settlement, during the 19th and 20th centuries, they were eradicated from many parts of the continent. Their remaining populations were isolated and by the turn of the 21st century only about 10% of their pre-colonialization population estimates remained (Wilson and Reeder 2005).

However, since the mid 20th century research has shown the importance of C. canadensis as a keystone species in riverine and coastal environments (Boswell et al. 1988). This recognition coupled with a decreasing lack of public support for programs that trap and kill or relocate individuals has contributed to a re-establishment and resurgence of beaver populations in areas that would, for many, seem unlikely. For example, in 2007, a beaver was sighted in New York City's waterways, the first in more than 200 years (O'Connor 2007). In Seattle, beaver have re-established their presence in nearly 90% of suitable habitat within the city (Dittenbrenner et. al. 2018).

An industrious and persistent "ecosystem engineer", the activities of the beaver are now recognized to provide many ecological benefits and ecosystem services. By impounding water and sediment through the construction of dams and weirs in fluvial systems, beaver can directly improve degraded hydrologic regimes and geomorphology while enhancing habitat for native plant and animal communities. In regions where beaver have the potential to reestablish, environmental designers have begun to actively plan and design to facilitate such opportunities (Bailey et. al. 2018). Yet, in other areas where beaver populations have been entirely eradicated designers are emulating the structures of beaver to improve riverine systems and mimic historical ecological conditions within the region. The project described by Joe Berg, Doug Streaker, and Chris Streb of Biohabitats in the South River watershed of Anne Arundel County, Maryland serves as case in point.

Grounded in current best practices for stream rehabilitation, the project utilized a scaffold system of grade control structures to establish riffle-pool sequences that would maintain baseflows and discharge into the floodplains during high flow events. They specifically utilize materials such as trees, rock, and woody shrubs sourced from the site, as the beaver would have done, to reduce costs and construction impacts. The use of large woody debris (LWD) in stream rehabilitation is common practice serving to not only enhance and diversify localized conditions, but further mitigate and improve hydrological impacts of the system as a whole by forcing flows to slow, spread, and soak into the floodplains. Though some consider the use of LWD to be unsightly initially, when used in combination with strategies such as bank and floodplain plantings and live staking of water-thriving, fast growing woody vegetation, they improve conditions for the future growth of native riparian vegetation. While past practices to control flows using concrete and boulder-lined channels are still used and provide benefit to protect infrastructure such as road crossings and water and waste pipelines, such strategies are now understood as detrimental the larger system, channelizing flows and leading to channel degradation. Through proposed monitoring and adaptive management practices the scaffold of initial bed structures incorporated into this project will eventually break down, to be replaced by the trees and plant communities that are just now establishing.

This project, and many others like it around the country, are furthering the potential for environmental designers working in degraded streams, rivers, and other habitat types to draw understanding from species like C. canadensis to establish design management practices that are regionally grounded, ecologically responsive, and adaptive to future changes in conditions.

Ken P. Yocom

Ken P. Yocom, Department of Landscape Architecture, University of Washington, 348 Gould Hall, Box 355734 Seattle, WA 98195, kyocom@uw.edu.

References

Bailey, D.R., B.J. Dittbrenner and K.P. Yocom. 2018. Reintegrating the North American beaver (Castor canadensis) in the urban landscape. Water 6:e1323.
Boswell, G.P., N.F. Britton and N.R. Franks. 1988. Habitat fragmentation, percolation theory...

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