Biological bank protection: trees are more effective than grasses at resisting erosion from major river floods

Abstract

Although it is recognized that streamside vegetation can reduce river bank erosion, the relative effectiveness of forest versus grassland has been unclear. To compare erosion resistance of the two vegetation types, we studied the free-flowing Elk River in British Columbia, Canada from 1993 to 2014, including major floods in June 1995 and 2013. Interpretation of aerial photographs from 1994 and 2000 were used to examine the correspondence between floodplain vegetation and the extent of channel change after the 1995 flood. Along a 23 km reach with alternating forest and grassland, 15 locations displayed substantial change as the river moved a channel width (45 m) or more with meander migration, or up to 200 m with channel avulsion. All ten locations with major change (>75 m) occurred where the floodplain zones were occupied by grasslands, sometimes with small shrubs. In contrast, channels flanked by forest were minimally altered (<15 m), and deciduous (black cottonwood, Populus trichocarpa) or mixed deciduous-coniferous groves were effective at resisting erosion. Some changes accompanied the 1995 flood and further changes followed as the destabilized banks were vulnerable to smaller floods in 1996 and 1997. Providing another comparison, a position that was dramatically scoured in 1995 when it was grassland had subsequent cottonwood colonization, and the 4 m trees resisted erosion from the 2013 flood. Thus, trees were more resistant than grassland to flood-associated bank erosion. We recommend that riparian forests should be conserved to provide bank stability and to maintain an equilibrium of river and floodplain dynamics.

Tolerance to the herbicide clomazone and potential for changes of forest species

“…These areas present high water saturation, at least for most of the year, due to the proximity of the groundwater or water courses. Some of the species that compose a riparian forest are able to reach deep layers in the soil profile due to the greater growth of their roots, reaching groundwater (ROOD et al, 2015). Thus, riparian species with remmediated capacity can assist in the decontamination of soil and water located at greater depths.…”

Importance of considering riparian vegetation requirements for the long-term efficiency of environmental flows in aquatic microhabitats

“…Riparian vegetation is a suitable environmental change indicator (Benjankar et al, 2012;Nilsson and Berggren, 2000) that responds directly to a flow regime in an inter-annual time frame (Capon and Dowe, 2007;Naiman et al, 2005;Poff et al, 1997) and has a clear significance in the habitat improvement of aquatic systems (e.g., Broadmeadow and Nisbet, 2004;Chase et al, 2016;Dosskey et al, 2010;Gregory et al, 1991;Pusey and Arthington, 2003;Rood et al, 2015;Ryan et al, 2013;Salemi et al, 2012;Statzner, 2012;Tabacchi et al, 2000;Van Looy et al, 2013;Wootton, 2012). In fact, riparian vegetation and aquatic species interact biologically, physically, and chemically (Gregory et al, 1991).…”

“…It affects food webs by providing an important input of nutrients that are a major food source for invertebrates, which are in turn eaten by fishes (Wootton, 2012). It influences hydrological processes (Salemi et al, 2012;Tabacchi et al, 2000) and protects aquatic habitats by means of river bank stability (Rood et al, 2015) and providence of large woody debris (Fetherston et al, 1995). It provides thermal regulation of rivers by overshadowing (Ryan et al, 2013) and protects water quality both by trapping sediments and contaminants (Chase et al, 2016) as by chemical uptake and cycling (Dosskey et al, 2010).…”

Restoring functional riparian ecosystems: concepts and applications

“…Rood et al . () find that forested riparian communities provide greater erosional resistance to flooding than grasslands; hence, conserving riparian forests would stabilize stream banks. Riparian tree species such as Populus sp.…”