Herbaceous Versus Forested Riparian Vegetation: Narrow and Simple Versus Wide, Woody and Diverse Stream Habitat

Abstract

We investigated interactions of riparian vegetative conditions upon a suite of channel morphological variables: active channel width, variability of width within a reach, large wood frequency, mesoscale habitat distributions, mesoscale habitat diversity, median particle size and per cent fines. We surveyed 49 wadeable streams, 45 with low levels of development, throughout the Upper Little Tennessee River Basin in the Southern Appalachians. Conversion of riparian forest to grass has reduced aquatic habitat area (quantified by active channel width), channel width variability, wood frequency, mesoscale habitat diversity and obstruction habitat (wood and rock jams), and such conversion has increased the fraction of run and glide habitat. Channels with grassy riparian zones were only one-third to three-fifths of the width of channels with forested riparian zones, and channels with grassy or narrow forested riparian zones were nearly devoid of wood. Particle size metrics were strongly affected by stream power and agricultural cover in the basin, but the data suggest that elimination of riparian forest reduces median bed particle size. Results indicate that even modest increases in the extent and width of forested riparian buffers would improve stream habitat conditions.

Historical land use as a driver of alternative states for stream form and function in forested mountain watersheds of the Southern Rocky Mountains

“…For riparian restoration, specifying forest management practices that maintain riparian forest corridors and leave standing and downed wood within the riparian zone would facilitate wood recruitment to streams and allow managed watersheds to move toward their more physically heterogeneous and retentive state, as also suggested for streams elsewhere (e.g. Jackson et al, ).…”

The influence of a vegetated bar on channel-bend flow dynamics

“…Initial riparian forest development may result in a decrease in width-to-depth ratio as formerly bare banks are vegetated and increase bank cohesion, preventing bank erosion from widening channels (Métivier and Barrier, 2012) such that meanders (Eaton and Giles, 2009) and alternate bars emerge (Kleinhans, 2010). For 15 channels characterized by vegetated banks and meandering planforms, differences in width have been observed based on floodplain and bank vegetation type, with floodplains composed of herbaceous vegetation associated with narrower channels compared to those composed of woody vegetation (Allmendinger et al, 2005;Hession et al, 2003;Jackson et al, 2015). It is unclear what would cause this relationship, since bank strength increases with rooting depth (Eaton and Giles, 2009), which is greater for woody vegetation compared to herbaceous vegetation (Canadell et al, 1996) …”

How deforestation drives stream habitat changes and the functional structure of fish assemblages in different tropical regions

“…Changes in stream habitat caused by deforestation have been observed in several studies (Allan & Castillo, ; Leitão et al, ; Molina et al, ; Scott & Helfman, ), but most of these studies were developed at smaller scales and without a biogeographical comparative approach, such as the one applied in this study. Native forest plays a vital role in physical channel heterogeneity by supplying large wood, branches, litter and roots to aquatic systems (Allan, ; Jackson et al, ). These structures are responsible for creating mesohabitats and microhabitats along stream channels, and for increasing marginal and instream habitat complexity (Harvey, Henshaw, Parker, & Sayer, ), which can provide habitat for the establishment of additional and different fish species (Angermeier & Karr, ; Pettit et al, ; Wright & Flecker, ).…”