Effective disturbance: Seedling safe sites and patch recruitment of riparian cottonwoods after a major flood of a mountain river

Polzin, Mary Louise; Rood, Stewart B.

doi:10.1672/0277-5212(2006)26[965:edsssa]2.0.co;2

Cited by 80 publications

(124 citation statements)

References 42 publications

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“…In this transitional zone, the shrub would need to survive not only inundation that contributes to root anoxia, but also the erosive shear from swift water Xow (Darby 1999). That force could particularly scour willow seedlings and young saplings that have limited root systems (Dixon 2003;Polzin and Rood 2006). Low-elevation riparian zones are also exposed to sediment deposition that can further challenge seedling survival (Polzin and Rood 2006).…”

Section: Discussionmentioning

confidence: 99%

Sand and sandbar willow: a feedback loop amplifies environmental sensitivity at the riparian interface

et al. 2010

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Riparian or streamside zones support dynamic ecosystems with three interacting components: flowing water, alluvia (river-transported sediments), and vegetation. River damming influences all three, and subsequent responses can provide insight into underlying processes. We investigated these components along the 315-km Hells Canyon corridor of the Snake River that included reaches upstream, along, and downstream from three large dams and reservoirs, and along the Salmon River, a free-flowing tributary. Sandbar willow was generally the woody plant at the lowest bank position and was abundant along upstream reaches (53, 45, 67% of transects), sparse along reservoirs (11, 12, 0%), and sparse along the Snake River downstream (11%). It was prolific along the undammed Salmon River (83%) and intermediate along the Snake River below the Salmon inflow (27%), indicating partial recovery with the contribution of water and sediments. Along these rivers, it commonly occurred on sandy substrates, especially on shallow-sloped surfaces, and emerged from interstitial sands between cobbles on steeper surfaces. However, along the Snake River below the dams, sandbars have eroded and willows were sparse on remnant, degrading sand surfaces. We conclude that a feedback loop exists between sands and sandbar willow. Sand favors willow colonization and clonal expansion, and reciprocally the extensively branched willows create slack-water zones that protect and trap sands. This feedback may sustain surface sands and sandbar willows along free-flowing river systems and it amplifies their mutual vulnerability to river damming. Following damming, sediment-depleted water is released downstream, eroding surface sands and reducing willow colonization and expansion. With willow decline, sands are further exposed and eroded, compounding these impacts. From this feedback, we predict the coordinated depletion of surface sands and riparian willows along dammed rivers throughout the Northern Hemisphere.

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Section: Discussionmentioning

confidence: 99%

Sand and sandbar willow: a feedback loop amplifies environmental sensitivity at the riparian interface

et al. 2010

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“…Since scouring is known to cause seedling mortality in riparian vegetation (Polzin & Rood 2006), there is urgent need for mechanistic insight in scouring around seedlings and/or propagules of world-wide declining seagrasses and intertidal salt-marsh species. Our flume study revealed that scouring around seedlings strongly increases with current velocity, basal diameter and shoot stiffness, provided that the bending occurred near the sediment surface and not on top of a solid tussock base.…”

Section: Discussionmentioning

confidence: 99%

“…This applies to a broad range of different vegetation types, including intertidal seagrass vegetation with flexible shoots as well as saltmarsh vegetation that can have stiff shoots or flexible shoots on a solid tussock base. In riparian vegetation along rivers, scouring by high flows has been identified as one of the main reasons for seedling mortality (Polzin & Rood 2006). As scouring by high velocities can negatively affect the lateral expansion of tussocks in intertidal systems (van Wesenbeeck et al 2008 and references therein), scouring may also be an important factor in explaining the disappearance of seedlings and/or propagules of intertidal plant species.…”

Section: Introductionmentioning

confidence: 99%

Effects of shoot stiffness, shoot size and current velocity on scouring sediment from around seedlings and propagules

Bouma¹,

Friedrichs²,

Klaassen³

et al. 2009

Mar. Ecol. Prog. Ser.

103

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Successful management and restoration of coastal vegetation requires a quantitative process-based understanding of thresholds hampering (re-)establishment of pioneer vegetation. We expected scouring to be important in explaining the disappearance of seedlings and/or small propagules of intertidal plant species, and therefore quantified the dependence of scouring on plant traits (flexibility, size) and physical forcing by current velocity. Flume studies with unidirectional flow revealed that scouring around seedlings increased exponentially with current velocity and according to a power relationship with plant size. Basal stem diameter rather than shoot length controlled scouring volume. Flexible shoots caused far less scouring than stiff shoots, provided that the bending occurred near the sediment surface as was the case for Zostera, and not on top of a solid tussock base as we observed for Puccinellia. Therefore, shoot stiffness is likely to strongly affect the chances for initial establishment in hydrodynamically exposed areas. Plant traits such as shoot stiffness are subject to a trade-off between advantages and disadvantages, the outcome of which depends on the physical settings.

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“…In climates where water availability is not the limiting factor for growth, it is the erosion of plants and their sites by floods, as well as the creation of new sedimentary deposits that dominates vegetation recruitment [e.g., Polzin and Rood, 2006]. Floods play a fundamental role in this process by eroding the channel bed and vegetated islands and bars, by creating suitable colonization sites on new deposits, and by determining the time available for colonization of those sites into more or less stable patterns through the interarrival time between floods [e.g., Resh et al, 1988;Bendix and Hupp, 2000;Friedman and Lee, 2002;Nilsson and Svedmark, 2002].…”

Section: Introductionmentioning

confidence: 99%

An observation‐based stochastic model for sediment and vegetation dynamics in the floodplain of an Alpine braided river

Perona

Molnár

Savina

et al. 2009

Water Resources Research

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[1] Riparian vegetation dynamics in Alpine rivers are to a large extent driven by the timing and magnitude of floods which inundate the floodplain, transport sediment, erode the river bed, and create and destroy suitable germination sites. Here we present a stochastic approach for studying sediment-vegetation dynamics lumped at the floodplain scale and driven by stochastic flood disturbances. The premise of the model is that floods erode riparian vegetation in the inundated part of the floodplain and expose bare sediment surfaces. In the absence of subsequent flooding these surfaces are gradually recolonized. The stochastic nature of the disturbance process and the deterministic rate of vegetation colonization are described by a Poisson arrival of floods and a process equation which treats the floodplain erosion and vegetation colonization processes, respectively. An analytical solution is developed to obtain the probability density function of the exposed sediment area. The model is applied to the Maggia River in Switzerland, where it reproduces the changes in riparian vegetation cover observed from aerial photographs with an absolute error less than 5%. The model has potential as a tool to study the impacts of changes in the disturbance regime on sediment and vegetation dynamics.

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Effective disturbance: Seedling safe sites and patch recruitment of riparian cottonwoods after a major flood of a mountain river

Cited by 80 publications

References 42 publications

Sand and sandbar willow: a feedback loop amplifies environmental sensitivity at the riparian interface

Sand and sandbar willow: a feedback loop amplifies environmental sensitivity at the riparian interface

Effects of shoot stiffness, shoot size and current velocity on scouring sediment from around seedlings and propagules

An observation‐based stochastic model for sediment and vegetation dynamics in the floodplain of an Alpine braided river

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