Climate Change Predictions & Beaver

The following is a synthesis from Mary O'Brien, May 7, 2010:

Observed and Predicted Climate Change in the Intermountain and Southwest Regions

  • Warmer air temperatures
  • Earlier snowmelt
  • Reduced or extinguished late-season flows
  • Warmer water temperatures
  • Longer droughts
  • More intense precipitation events, floods

Some Expected Outcomes of a Changing Climate

  • Sparser vegetation on slopes
  • Increased invasive species
  • Increased dust on snow
  • Loss of wetlands
  • Decline of wildlife species dependent on water, cool temperatures, shade, cover
  • Fragmented wildlife habitat

The Importance of Beaver Dams for Adapting to Observed and Predicted Climate Change in the Intermountain and Southwest Regions

  • Beaver dams slow snowmelt runoff, which
    • Extends summertime stream flow
    • Restores perennial flow to some creeks
  • Beaver dams create ponds, which
    • Maintain and create wetlands
    • Provide nurseries for salmonids and other fish
    • Provide critically-needed amphibian habitat
    • Create meadows in silt behind dams
    • Increase habitat for small mammals, woodpeckers (using drowned trees)
    • Drown exotic, rhizomatous Kentucky bluegrass, leading to re-establishment of deeper-rooted sedges, rushes, and native hydric bunchgrasses
    • Improve downstream water quality by trapping and storing sediment
  • Water enters groundwater upstream of, beside, and under dams which
    • Subirrigates the valley
    • Allows water to re-enter creeks/streams downstream as cooler seeps, which
      • is critically important to cold-water fish, e.g., salmonids
      • reduces evaporative loss
    • Expands and restores riparian vegetation, which
      • Shades creeks/streams, which
        • Reduces water temperature
        • Provides hiding cover for fish
      • Buffers banks against erosion during high flows
      • Provides critical fish and wildlife habitat
    • Restores and expands deep-rooted riparian vegetation, which
      • Increases bank integrity during high flows
      • Increases critical wildlife habitat
  • A series of beaver dams function as “speed bumps” during high water flows, which
    • Spreads water out on the surrounding floodplain
    • Recharges groundwater near stream
    • Locally reduces flood force and gouging
    • Increases the complexity of streams, including creation of backwater and pools
    • Extends the presence of water for riparian plant communities
    • Prevents or reduces headcutting
  • Beaver dams capture sediment, which
    • Reconnects incised creeks and streams with their floodplain by raising their streambed level
    • Retains sediment for later conversion to meadows
    • Reduces downstream sedimentation impacts
    • Reduces the conversion of complex stream and riparian habitat to a runoff ditch
    • Heals headcuts
  • Beaver increase large woody debris in creeks, due to
    • Tree-cutting
    • Dam-building
    • Existing dams and their remnants which
      • Increase complexity of streams
      • Increase bank integrity during high-flow
      • Increase habitat for fish, otter, amphibians, and other aquatic species
      • Reduce expense of human construction/maintenance/repair of instream structures or placement of large, woody debris in streams

Mary O’Brien, PhD. (Botany)
Utah Forests Program Manager
Grand Canyon Trust

 May 7, 2010