Riparian resilience in the face of interacting disturbances: understanding complex interactions between wildfire, erosion, and beaver (Castor canadensis) in grazed dryland riparian systems of low order streams in North Central Washington State, USA

Riparian systems of low order streams in the western United States (US) provide critical ecosystem functions and services such as diverse habitat for numerous species, flood attenuation and essential water storage in water limited environments. These systems have experienced long term disturbance from anthropogenic activities including mining, timber harvest, livestock grazing and near extirpation of a keystone riparian species, Castor canadensis (North American beaver). However, increasing frequency of large-scale wildfires and climate change driven weather is altering the severity and scale of riparian disturbance, often shifting highly impacted streams to a stable degraded state, unable to store water or provide other once inherent ecosystem functions. Beaver restoration has been gaining traction as a way to address long term riparian degradation, yet little has been documented regarding the impact of restored beaver activity on recently burned riparian systems, especially those in a stable degraded state. To address this, my study documented the interactions between largescale wildfire impact, subsequent erosion events and dam building beaver populations in riparian systems of the Methow River watershed, north central Washington (WA), US. I tested the hypothesis that beaver increase the resiliency of streams to wildfire using a fully factorial study comparing stream side riparian vegetation, stream channel morphology, and chemistry of stream reaches across burned vs. not burned sites with and without hydrologically significant beaver dams. My study was conducted June through November of 2018 in sub-basins of the Methow River watershed. I found reduced stream nutrient transport and pH, increased stream channel and floodplain connectivity, increased vegetation diversity in floodplain landforms, and reduced non-native species in burned riparian systems with beaver, which suggest that beaver can effectively increase wildfire resilience in streams. By studying the interacting variables of fire, stream channel erosion, water chemistry, riparian vegetation and beaver activity in degraded stream systems, more effective and holistic approaches to adaptive ecological and economic management will emerge, particularly in the face of increasing riparian disturbance from large scale wildfire