Abstract
Given the direct effects of their dams on hydrology, sediment storage, and vegetation, beaver are widely acknowledged as ecosystem engineers. Here we explore the effects of beaver activity on channel processes and riparian plant recruitment beyond those dams and after dam abandonment in southwestern Montana, USA. Willow cuttings from beaver herbivory are commonly deposited along point bars, adding roughness and promoting sediment accumulation. Most cuttings are found <1 km downstream of an active dam. These cuttings often sprout, aiding in willow colonization and bar stabilization. Thirty-four radiocarbon ages show that beaver cuttings have accumulated by similar processes over thousands of years, adding to floodplain carbon storage. Breached dams can initiate meanders, increasing channel and riparian habitat diversity. Beaver activity thus generates a cycle of frequent disturbance, from dam building and riparian plant browsing through dam failure and abandonment, with each phase influencing channel and floodplain evolution and riparian plant recruitment.
Highlights
Riparian ecosystems are coming under increasing stress from changing climate, increasing demands on water, and loss of flood-induced disturbance[1]
We have focused our work on three streams in the upper headwaters of the Missouri River System in southwestern Montana (Table 1, Fig. 1) that all feature
The feeding activities of beaver and the construction, maintenance, and breaching of beaver dams provide a steady supply of fine woody debris to the channel
Summary
Riparian ecosystems are coming under increasing stress from changing climate, increasing demands on water, and loss of flood-induced disturbance[1]. There has been limited investigation of the effects of beaver activity on stream reaches and riparian vegetation beyond their iconic dams and ponds, or on the continuing impacts of breached and abandoned dams. In prior research along beaver-occupied streams in southwestern Montana and the Rocky Mountain region, we observed that willow cuttings produced by beaver herbivory and dam building are commonly transported downstream and accumulate along channel margins. We document the continuing effects of remnant dams to consider the impacts of beaver beyond the life of active dams and ponds. On the three study streams, we document and quantify beaver cutting dispersal and additional less-direct effects of beaver activity within the dam-building and abandonment cycle, including interactions with channel processes
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