PS 23-67 - Characterizing riparian vegetation associated with simulated beaver dams in south-central Colorado

Abstract: The western United States has a history of prolonged drought and intense wildfires, and this is
projected to intensify due to anthropogenic climate change. This is particularly concerning for
riparian ecosystems, which serve as “keystone” habitats and provide important ecosystem
services. To combat the effects of climate change and other human disturbances, land and
wildlife managers in this region have turned to various stream restoration strategies, such as
beaver reintroduction due to their role as ecosystem engineers. When beaver reintroduction is
impractical, simulated beaver dams, called beaver dam analogs (BDAs), can be used to improve
the stream conditions.

Despite their widespread use as a stream restoration tool in the western United States,
previous studies have focused almost entirely on the hydrology at sites where BDAs have been
installed to the exclusion of the vegetation. The aim of our study was to characterize the
riparian vegetation where BDAs have been recently installed in south-central Colorado. We
sampled the vegetation at 9 BDAs across 3 reaches on a small stream by using line-point
intercept and percent cover estimation techniques. We referenced the National Wetland Plant
List to determine wetland indicator status codes for each species and explored the relationship
between wetland indicator status and distance from stream edge for each reach.

We found that the number of species present across the BDAs ranged from 38 to 78, with the
highest overall diversity (richness and evenness) at BDAs on our second reach. BDAs associated
with each reach were not always most similar to each other. BDAs at the third reach had a
particularly high distribution of wetland species (obligate or facultative) across the entire area
rather than mostly within 0-3m of the stream edge. Our results suggest that the riparian
vegetation can be very heterogeneous between reaches despite being located in close
proximity. This highlights the importance of understanding initial site conditions and monitoring
sites as they change as a result of BDA installation. Differences in site conditions upon BDA
installation and throughout the structure’s lifespan will likely contribute to differences in how
propagules spread and establish as site conditions change.