Beaver assisted river valley formation

Abstract

We examined how beaver dams affect key ecosystem processes, including pattern and process of sediment deposition, the composition and spatial pattern of vegetation, and nutrient loading and processing. We provide new evidence for the formation of heterogeneous beaver meadows on riverine system floodplains and terraces where dynamic flows are capable of breaching in-channel beaver dams. Our data show a 1.7-m high beaver dam triggered overbank flooding that drowned vegetation in areas deeply flooded, deposited nutrient-rich sediment in a spatially heterogeneous pattern on the floodplain and terrace, and scoured soils in other areas. The site quickly de-watered following the dam breach by high stream flows, protecting the deposited sediment from future re-mobilization by overbank floods. Bare sediment either exposed by scouring or deposited by the beaver flood was quickly colonized by a spatially heterogeneous plant community, forming a beaver meadow. Many willow and some aspen seedlings established in the more heavily disturbed areas, suggesting the site may succeed to a willow carr plant community suitable for future beaver re-occupation. We expand existing theory beyond the beaver pond to include terraces within valleys. This more fully explains how beavers can help drive the formation of alluvial valleys and their complex vegetation patterns as was first postulated by Ruedemann and Schoonmaker in 1938.

Mechanisms of carbon storage in mountainous headwater rivers

“…Old-growth forest is Z200 years old 24 . Beaver meadows are wet meadows with beaver dams and willow communities 35,[40][41][42] . Abandonment by beavers results in breached dams, decreased overbank flooding, lowered local water table and a progressive shift from meadow to more xeric upland vegetation 25,36,37 .…”

Legacy effects on sediments in river corridors

“…When beaver were used to control sediment losses along Mission Creek in Washington, USA, their dams trapped an average of 7.8 m 3 per linear meter of stream (Scheffer, 1938). In addition to trapping sediment within channels, beaver dams effectively increase overbank flow and floodplain sedimentation (Westbrook et al, 2006(Westbrook et al, , 2011Polvi and Wohl, 2013) and their removal results in floodplain drying and erosion (Wolf et al, 2007;Polvi and Wohl, 2013) (Fig. 7).…”

Competition favors elk over beaver in a riparian willow ecosystem

“…4B). Beaver can benefit willow establishment and survival processes by maintaining high water tables throughout the growing season and by placing water and sediment where floods cannot reach (Westbrook et al 2006, Westbrook et al 2011. Beaver abandonment can cause dam failure, channel incision, and a lower water table, which can kill existing willow and prevent re-establishment (Apple et al 1985, Fouty 2003.…”