Oecologia

, Volume 165, Issue 1, pp 31–40 | Cite as

Sand and sandbar willow: a feedback loop amplifies environmental sensitivity at the riparian interface

  • Stewart B. Rood
  • Lori A. Goater
  • Karen M. Gill
  • Jeffrey H. Braatne
Physiological ecology - Original Paper

Abstract

Riparian or streamside zones support dynamic ecosystems with three interacting components: flowing water, alluvia (river-transported sediments), and vegetation. River damming influences all three, and subsequent responses can provide insight into underlying processes. We investigated these components along the 315-km Hells Canyon corridor of the Snake River that included reaches upstream, along, and downstream from three large dams and reservoirs, and along the Salmon River, a free-flowing tributary. Sandbar willow was generally the woody plant at the lowest bank position and was abundant along upstream reaches (53, 45, 67% of transects), sparse along reservoirs (11, 12, 0%), and sparse along the Snake River downstream (11%). It was prolific along the undammed Salmon River (83%) and intermediate along the Snake River below the Salmon inflow (27%), indicating partial recovery with the contribution of water and sediments. Along these rivers, it commonly occurred on sandy substrates, especially on shallow-sloped surfaces, and emerged from interstitial sands between cobbles on steeper surfaces. However, along the Snake River below the dams, sandbars have eroded and willows were sparse on remnant, degrading sand surfaces. We conclude that a feedback loop exists between sands and sandbar willow. Sand favors willow colonization and clonal expansion, and reciprocally the extensively branched willows create slack-water zones that protect and trap sands. This feedback may sustain surface sands and sandbar willows along free-flowing river systems and it amplifies their mutual vulnerability to river damming. Following damming, sediment-depleted water is released downstream, eroding surface sands and reducing willow colonization and expansion. With willow decline, sands are further exposed and eroded, compounding these impacts. From this feedback, we predict the coordinated depletion of surface sands and riparian willows along dammed rivers throughout the Northern Hemisphere.

Keywords

Ecohydrology Hydrogeomorphic requirements Salix exigua Sediments Salmon River 

Notes

Acknowledgments

This research was supported with funding from Idaho Power Company (IPC), the Natural Sciences and Engineering Research Council Canada, the Alberta Ingenuity Centre for Water Research and the Alberta Water Research Institute. We extend thanks to Robert Simons of Simons & Associates, Colorado, and Gary Holmstead, Toni Holthuijzen, Frank Edelman and Allen Ansell of IPC for their insightful discussions.

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Copyright information

© Springer-Verlag 2010

Authors and Affiliations

  • Stewart B. Rood
    • 1
  • Lori A. Goater
    • 1
  • Karen M. Gill
    • 1
  • Jeffrey H. Braatne
    • 2
  1. 1.Department of Biological SciencesUniversity of LethbridgeLethbridgeCanada
  2. 2.Department of Fish, Wildlife and Range ResourcesUniversity of IdahoMoscowUSA

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