Potential extent, function, and requirements for beaver habitat modification in delta landscapes

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Establishment of large areas of woody vegetation, associated with freshwater stream inputs is necessary to support beaver modification of delta landscapes, which will increase capacity for salmonid rearing.

We have no ability to predict the conditions necessary to support beaver modification and management of habitat structure on delta islands. As in freshwater systems, beaver modify the hydrologic structure of freshwater and oligohaline tidal systems by the construction of channels, dams and pools. These modifications affect habitat qualities anticipated to benefit salmonid rearing. In freshwater systems, adequate woody plants for forage and dam building have been suggested to limit beaver populations, with local depletion of forage resulting in emigration. If beaver architecture has a demonstrated benefit to fishery habitat, delta restoration would benefit from development of conditions sufficient to support beaver colonization. The potential extent of beaver modification of habitat may be low with only a tertiary effect of ecosystem carrying capacity. On the other hand, beaver wetlands, extending deep in to tidal freshwater, and delta buffer landscapes may strongly affect hydrology and carrying capacity for some species, with unclear effects of delta ecology.

Moderate Importance— Moderate viability— Moderate policy relevance—


Delta Strategy Analysis

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The uncertainties in how this topic affects delta restoration has resulted in its inclusion in the ESRP River Delta Adaptive Management Strategy. This three criteria analysis should build off the analysis above, and supports development of learning projects.

Importance Viability Policy Relevance

Beaver are clearly linked to extensive modification of freshwater systems that affect both hydrology and fishery habitats. The degree to which beaver populations are significant ecosystem architects in deltas, and the conditions necessary to reestablish their role are unknown. Very limited evidence are available for verification of fish benefits from beaver modifications, the potential extent and intensity of beaver modification in current or restored landscapes cannot be quantified.

Capturing and tracking of beaver and their activities in delta settings is not technically difficult, however populations of delta beaver and their current use patterns may not reflect potential patterns and potential benefits to fish.

Beaver effects are likely to be most significant in larger systems with extensive freshwater tidal component, such as Snohomish, Stillaguamish, Skagit, and Nooksack deltas. Verification of beaver importance might affect planning of restoration to increase woody browse, and association with stream inputs and freshwater swamp vegetation.