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WATERSHED RESTORATION
<br />hydrologic disturbance regimes interact with native riparian
<br />plant communities to create sustainable habitats (Figure 1),
<br />Restoration of degraded riparian zones and their subse-
<br />quent conservation after recovery requires knowledge of
<br />ho~v these ecosystems function as well as the attributes
<br />responsible for their composition, stntcture, and produc-
<br />tivity. The character and value of riparian zones arise as a
<br />result of an infinite number of complex interactions among
<br />three fundamental ecosystem features: (1) soils/geomor-
<br />phology; (2) ]~ydrology; and (3) biota (Figure 1). The soils/
<br />geomorphology feahires include streambank and flood-
<br />plain form and development, channel gradient, geologic
<br />substrates influencing soil and channel composition, and
<br />subsoil features of the floodplain (e.g., gravel lenses impor-
<br />tant for hyporheic or subsurface flows). Hydrological fea-
<br />tures include the frequency, magnitude, and temporal dis-
<br />tribution of stream flow (including peak and low flows),
<br />sediment availability and transport, subsurface hydrology,
<br />and water quality. Biotic features include vegetation, ver-
<br />tebrates, invertebrates, and microorganisms. In addition to
<br />live plants, the vegetation component also includes dead
<br />materials (necromass) such as snags, fallen logs, and fine
<br />organic debris (litter). Anthropogenic activities that either
<br />alter these components or sever the linkages bettiveen
<br />them will disntpt ecosystem dynamics, including species
<br />composition, productivity; structure, and function.
<br />Among the most important ecosystem linkages are
<br />those interactions among vegetation, hydrology, and sub-
<br />strates as they influence geomorphic features such as channel
<br />morphology and channel dynamics (Figure 1). For example,
<br />naturally occurring pool habitats typically form as a result
<br />of interactions of hydrologic disturbance regimes, substrates,
<br />and streamside vegetation. If hydrologic patterns, sediment
<br />availability; or streamside vegetation are altered by land
<br />Biota
<br />--~ ^ .
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<br />I
<br />d
<br />Riparian ~
<br />Ecosystem ~~
<br /><i /p \ . i
<br />Soi!s/ ~
<br />Geomorphology
<br />`(substrates) ,
<br />Hydrology
<br />`~
<br />
<br />
<br />
<br />Figure 1 illustrates the linkages of the biotic, hydrologic, and geo-
<br />morphic components combined to shape the unique structure and
<br />function of riparian and stream ecosystems. Each arrow represents
<br />an infinite number of biological and physical processes and interre-
<br />lationships among these ecosystem features. Because of these inex-
<br />tricable linkages, human or natural actions that alter any one com-
<br />ponent or process will have feed-forward influences that can affect
<br />ai! ether components of the ecosystem.
<br />use activities, then channel morphology will subsequently
<br />adjust to these ne~e• conditions. This is often expressed by
<br />a simplification in stream structure (e.g., loss bf pools, de-
<br />creased channel sinuosity, ar.d loss of channel diversity).
<br />Another important interaction represented in Figure 1 is
<br />the influence of substrate characteristics and hydrology on
<br />plant community composition. For example, many ripari-
<br />an-obligate trees and shrubs have specific micro-site re-
<br />quirements for establishment. Successful natural establish-
<br />ment of cottonwood trees (Poyulus sppJ and willows (S~rli.~
<br />sppJ commonly occurs on point bars of newly deposited,
<br />coarsely textured, well-aerated substrates within the 2- to
<br />10-year tloodplain (McBride and Strahan 1984; Bradley and
<br />Smith 1986); high flows are needed to create these condi-
<br />tions. Seed dispersal and germination are timed to coin-
<br />cide with late-spring flows when water tables are high,
<br />and fresh alluvium has been deposited (Noble 1979). Suc-
<br />cessful establishment also may be limited to areas where
<br />the rate and extent of water table decline does not exceed
<br />the biological capacity of root growth (Mahoney and Rood
<br />199?). At the loi~•er limits of the floodplain, establishment
<br />is often not possible because high water in subsequent
<br />years destroys the young plants (Bradley and Smith 1986).
<br />Sahtrated, finely textured soils associated with lour-gra-
<br />dient riparian zones are often sites of anaerobic conditions;
<br />such sites are typically unsuitable for the establishment of
<br />cottonwoods or ~~•illows. Under these hydrologic and geo-
<br />morphic conditions, the natural plant communities are
<br />dominated by sedges (Carat sppJ, rushes (Juncu~ sppJ, or
<br />hydrophytic grasses. At the opposite extreme, where coarse
<br />materials (cobbles and boulders) occur in elevated and ex-
<br />cessively drained situations, riparian-obligate vegetation
<br />will not establish. These conditions rarely occur naturally
<br />in western riparian ecosystems. However, they may be
<br />found after extreme human perturbations (e.g., dredge
<br />mining, channelization, or other in-channel modifications)
<br />deposit spoils on streambanks and floodplains.
<br />Ecological restoration begins tivith identification u
<br />those land use practices that are damaging ecosystems or
<br />preventing recovery, follo~e-ed by implementation of 11nd
<br />management strategy ies that allo~~- for natural reco~-er~ t_~
<br />occur (~iational Research Cv,l;l,:il 199?. 19x6; I~ckson ~~t .'.
<br />t~)9~i. Thu_, ecology-ical resr~~ration aims to ensure ti:_
<br />OCCllrrenCe Oi (i) tn,O~e >,h~-slcal dnd b1ot1C prOCe~~25 f:lCli:-
<br />tating persistence of species tl;rough natural recruitment
<br />and suryiyal; (2) functioning food webs and system~~•ide
<br />nutrient conservation via relationships among plants, ani-
<br />mals, and detritivores; and (3) the integrity of watersheds
<br />through linkages with the hydrologic, geomorphic, and
<br />climatic disturbance regimes that shape plant and animal
<br />communities (Jackson et al. 1990.
<br />Wha# Isn't Ecological Restoration?
<br />Ecological restoration results in the reestablishment of
<br />linkages between organisms and their environment. Be-
<br />cause an entire suite of organisms, physical features, and
<br />prOCeSSe5 COMprlse an eCOSy~tem, a speCleS-Oril~• Or >'P.~iz-
<br />p::iCe~S apn*JdC.~ t~~ r2~`Jr~,t10C ..lil I;Kc'i~" till iF~~~P'. -, ~,.
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