A dynamic riparian forest structure model for predicting large wood inputs to meandering rivers

Abstract

Fluvial processes strongly influence riparian forests through rapid and predictable shifts in dominant species, tree density and size that occur in the decades following large floods. Modelling riparian forest characteristics based on the age and evolution of floodplains is useful in predicting ecosystem functions that depend on the size and density of trees, including large wood delivered to river channels, forest biomass and habitat quality. We developed a dynamic model of riparian forest structure that predicts changes in tree size and density using floodplain age derived from air photos and historical maps. Using field data and a riparian forest chronosequence for the 160-km middle reach of the Sacramento River (California, USA), we fit Weibull diameter distributions with time-varying parameters to the empirical data. Species were stratified into early and late successional groups, each with time-varying functions of tree density and diameter distributions. From these, we modelled how the number and size of trees in a stand changed throughout forest succession, and evaluated the goodness-of-fit of model predictions.Model outputs for the early successional group, composed primarily of cottonwoods and willows, accounted for most of the stand basal area and large trees >10 cm DBH for the first 50 years. Post-pioneer species with slower growth had initially low densities that increased slowly from the time of floodplain creation. Within the first 100 years, early successional trees contributed the most large wood that could influence fluvial processes, carbon storage, and instream habitat. We applied the model to evaluate the potential large wood inputs to the middle Sacramento River under a range of historical bank migration rates. Going forward, this modelling approach can be used to predict how riparian forest structure and other ecosystem benefits such as carbon sequestration and habitat quality respond to different river management and restoration actions.

Plants and river morphodynamics: The emergence of fluvial biogeomorphology

“…More frequent has been research on specific budget input and output components. Wood inputs to rivers have been observed or estimated for tree fall, bank erosion, debris flow and landslide processes (e.g., Dethier et al, 2016;Lancaster et al, 2003;Lucia et al, 2018;Picco et al, 2016;Ruiz-Villanueva et al, 2014c;Sobota et al, 2006;Stella et al, 2021). Observations of wood trapping within reservoirs have been used in combination with other information to very successfully undertake spatial and temporal analyses of the output component of catchment wood budgets and to estimate major controls (e.g., Senter et al, 2017;Seo et al, 2008Seo et al, , 2015.…”

“…Large wood recruitment Downs and Simon (2001), Welty et al (2002), Benda and Sias (2003), Mazzorana et al (2009Mazzorana et al ( , 2011, Eaton et al (2012), Kasprak et al (2012), Rigon et al (2012), Ruiz-Villanueva et al (2014b, Steeb et al (2017Steeb et al ( , 2023, Cislaghi et al (2018), Zischg et al (2018), Gasser et al (2019), Stella et al (2021).…”