An Ecogeomorphic Framework Coupling Sediment Modeling With Invasive Riparian Vegetation Dynamics

Abstract

Feedbacks between geomorphic processes and riparian vegetation in river systems are an important control on fluvial morphodynamics and on vegetation composition and distribution. Invasion by nonnative riparian species alters these feedbacks and drives management and restoration along many rivers, highlighting a need for ecogeomorphic models to assist with understanding feedbacks between plants and fluvial processes, and with restoration planning. In this study, we coupled a network‐scale sediment model (Sediment Routing and Floodplain Exchange; SeRFE) that simulates bank erosion and sediment transport in a spatially explicit manner with a recruitment potential analysis for a species of riparian vegetation (Arundo donax) that has invaded river systems and wetlands in Mediterranean climates worldwide. We used the resulting ecogeomorphic framework to understand both network‐scale sediment balances and the spread and recruitment of A. donax in the Santa Clara River watershed of Southern California. In the coupled model, we simulated a 1‐year time period during which a 5‐year recurrence interval flood occurred in the mainstem Santa Clara River. Outputs identify key areas acting as sources of A. donax rhizomes, which are subsequently transported by flood flows and deposited in reaches downstream. These results were validated in three study reaches, where we assessed postflood geomorphic and vegetation changes. The analysis demonstrates how a coupled model approach is able to highlight basin‐scale ecogeomorphic dynamics in a manner that is useful for restoration planning and prioritization and can be adapted to analogous ecogeomorphic questions in other watersheds.

Sediment‐ecological connectivity in a large river network

“…Substantial progress has been made to quantify structural connectivity from the patch to landscape scale (e.g., Index of Connectivity, Borselli et al, 2008) and several studies have conceptually addressed functional sediment connectivity at a variety of scales (e.g., Bracken et al, 2015; Heckmann & Schwanghart, 2013; Jain & Tandon, 2010). However, there remains a need to expand the spatial and temporal boundaries of empirical functional sediment connectivity research to directly address the scales relevant to watershed‐wide management (Najafi et al, 2021; Poeppl et al, 2020; Wohl et al, 2019) and encapsulate both the full range of connectivity processes as well as their role in ecological processes such as riparian vegetation dynamics (Bracken et al, 2015; Cienciala, 2021; Gilbert & Wilcox, 2021; Heckmann et al, 2018; Wainwright et al, 2011; Wohl et al, 2019).…”

“…Past studies have considered the impact of hydrologic connectivity on ecosystem response (Birnie-Gauvin et al, 2020;Rinc on et al, 2017) and developed conceptual frameworks that broadly recognize how material fluxes through a river network influence ecological processes and habitat structure (e.g., Benda et al, 2004;Ward et al, 2002), setting the stage to explicitly examine the role of sediment connectivity in ecological processes (Estrany et al, 2019;Gilbert & Wilcox, 2021;Turnbull & Wainwright, 2019;Wohl et al, 2015).…”

“…Sediment connectivity frameworks (e.g., Bracken et al, 2015; Hooke, 2003), which facilitate holistic understanding of the flux of sediment through a geomorphic system, are increasingly used to evaluate the potential for geomorphic response to disturbance events (Calle et al, 2020; Cossart et al, 2018; Lisenby & Fryirs, 2017) and to perform catchment‐scale management and rehabilitation (Czuba & Foufoula‐Georgiou, 2015; James et al, 2019; Keesstra et al, 2019; Lisenby et al, 2020; Lisenby & Fryirs, 2017; McMahon et al, 2020). Past studies have considered the impact of hydrologic connectivity on ecosystem response (Birnie‐Gauvin et al, 2020; Rincón et al, 2017) and developed conceptual frameworks that broadly recognize how material fluxes through a river network influence ecological processes and habitat structure (e.g., Benda et al, 2004; Ward et al, 2002), setting the stage to explicitly examine the role of sediment connectivity in ecological processes (Estrany et al, 2019; Gilbert & Wilcox, 2021; Turnbull & Wainwright, 2019; Wohl et al, 2015).…”

“…However, there remains a need to expand the spatial and temporal boundaries of empirical functional sediment connectivity research to directly address the scales relevant to watershed-wide management (Najafi et al, 2021;Poeppl et al, 2020;Wohl et al, 2019) and encapsulate both the full range of connectivity processes as well as their role in ecological processes such as riparian vegetation dynamics (Bracken et al, 2015;Cienciala, 2021;Gilbert & Wilcox, 2021;Heckmann et al, 2018;Wainwright et al, 2011;Wohl et al, 2019).…”

River channel response to invasive plant treatment across the American Southwest

“…was released in 2001 to control tamarisk and has increased plant mortality by defoliation (Pattison et al, 2011). Giant cane spreads downstream by rhizome dispersal (Gilbert & Wilcox, 2021), and plants resprout easily after mechanical cutting (Briggs et al, 2021). Therefore, commonly used treatment methods for giant cane include application of herbicide alone, as well as integrated methods of mechanical cutting or prescribed fire with follow-up herbicide application (Briggs et al, 2021).…”