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<br />28
<br />
<br />J. C, STROMBERG
<br />
<br />Quantity
<br />(Stream flow volume,
<br />ground-water level,
<br />sediment quantity)
<br />
<br />
<br />
<br />Dynamics
<br />(Flood magnitude, liming, duration,
<br />frequency, and diversity)
<br />
<br />Figure 1. Conceptual diagram of flow regime changes needed for riparian ecosyst~m restoration.
<br />
<br />riparian species tends to increase on fine soil textures (Stromberg, 1998a; Jansson et al.,
<br />2000a). Biodiversity also declines as dynamic fluvial processes, such as channel migra-
<br />tion, erosion, and sedimentation, become static (Shields et al. 2000) and spatial and
<br />temporal heterogeneity decline (Pollock et al., 1998). Orthophosphates typically adheres
<br />to clays and silts and thus decline in below-dam systems as fine sediments are deposited
<br />in reservoirs, contributing to downstream productivity declines.
<br />Sediment and nutrients can be restored to some below-dam reaches by adding
<br />sediment bypass structures (Schmidt et al., 1998). Other barriers imposed by dams,
<br />such as restricted dispersal of plant propagules Oansson et al., 2000b), are more
<br />difficult to remedy, short of de-commissioning dams. Given such limitations, there
<br />is a need to assess economic and environmental costs and benefits of all dams in the
<br />south-western United States, as a basis for deciding which warrant removal or breaching
<br />(Shuman, 1995; Born et al., 1998). At some sites, dam removal provides substantial
<br />ecological benefit, while minimally reducing the production of 'goods' (Wunderlich
<br />et al., 1994).
<br />
<br />Watershed alteratwns,
<br />
<br />Full restoration of riparian ecosystems depends on restoration of upland ecosystems
<br />throughout the watershed. Long-term overgrazing, fuel-wood harvest, and urbanization
<br />have, in places, reduced plant cover and soil in the uplands. These land-uses can result
<br />in flashier streams characterized by larger flood peaks and smaller base flows. In some
<br />areas, fire suppression has resulted in greater tree densities, higher transpiration rates,
<br />and smaller stream flows (Covington et al. 1997). Watershed restoration will require
<br />a mix of passive measures, such as restoring natural fire regimes and grazing regimes,
<br />and active measures. Controlled bums may be necessary for restoring structure and
<br />function to upland forests.
<br />
<br />Conclusions
<br />
<br />There is growing recognition of the important influence exerted by stream flows and
<br />fluvial processes on riparian vegetation structure and composition. Many riparian
<br />restoration projects are on a trajectory towards success because restoration managers
<br />
<br />RESTORATION OF RIPARIAN VEGETATION OF FLOW REGIME
<br />
<br />29
<br />
<br />recognize the importance of restoring stream flow regimes, in other words, of restoring
<br />liows of water and sediment in su~ficient quantities and with appropriate temporal
<br />and spatial patterns (Fig. 1). Substantial changes need to be made in the way we manage
<br />Slreams and water resources in thesduth-western United States. These changes include
<br />naturalizing flood pulses to 'restore fluvial dynamism, allowing rivers access to their flood
<br />plains and letting them be their OwD 'managers', recharging ground-water, reducing
<br />rates of water extraction, reducing dependence on hydro-power, and removing selected
<br />dams. Without such changes, we acquiesce to continued biodiversity losses and reduced
<br />function of riparian ecosystems. As ~tanford et al. (1996) state, stream restoration calls
<br />for 'instituting a management belief ~ystem that relies upon natural habitat restoration'
<br />as opposed to artificial techniques such as plant propagation or installation of artificial
<br />in-stream structures (river engineering). Changes need to be made throughout society
<br />so that we become more efficient a~d less wasteful in our use of water and power.
<br />Scientists can help to insure that w~ restore desired conditions by focusing research
<br />endeavors on the water needs of aquatic and riparian ecosystems.
<br />
<br />C,-',
<br />c.;:.
<br />c,.."
<br />t,;"
<br />(:.,,';)
<br />C.Il
<br />
<br />'l'he comments and criticisms from Mike Scott, Duncan Patten, and Ed Glenn are greatly
<br />appreciated.
<br />
<br /><
<br />
<br />: References
<br />
<br />
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