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WATERSHED RESTORATION
<br />alterations may further limit the future recruitment poten-
<br />tial of large, woody debris as well as degrade riparian
<br />wildlife habitat. The ecological costs and benefits to physi-
<br />cal processes, biological diversity, and ecosystem functions
<br />should be considered before such actions are initiated.
<br />Resistance and Resilience
<br />In undertaking restoration, it is important to under-
<br />stand the response of riparian ecosystems to anthropo-
<br />genic perturbations (resistance) as well as the capacity to
<br />recover after cessation or removal of the problem-causing
<br />activities (resilience). Resistn~ICe is the capacity of an eco-
<br />system to maintain natural function and structure after a
<br />natural disturbance or an introduction of an anthropo-
<br />genic perturbation. For example, some riparian meadow
<br />plants will maintain productivity with moderate levels of
<br />livestock grazing because of their adaptive capacities or
<br />tolerance to herbivory. These would be considered resistant
<br />cornrrulnitics. In contrast, even low levels of herbivory can
<br />retard community development on gravel bars dominated
<br />by young willow or cottonwoods (Case and Kauffman, in
<br />press; Green and Kauffman 1995); these are nonresistant
<br />CO17f112L1Y11t1L'S.
<br />Resilience is the capacity of species or ecosystems to
<br />recover after a natLlral disturbance or following the cessa-
<br />tion of an anthropogenic perturbation. BecaLlse riparian
<br />species evolved in areas with frequent fluvial distur-
<br />bances, they represent classic examples of a resilient biota.
<br />Not only do many riparian plants depend on natural dis-
<br />turbances for establishment, but rates of recovery or estab-
<br />lishment follotiving disturbances can be remarkably high
<br />(Busse 1959; Gecv and Wilson 1990; Case 1995). Paradoxi-
<br />cally, while riparian ecosystems are often resilient to natur-
<br />al disturbance regimes, many rapidly degrade with the
<br />curtailment of these disturbances. For example, water
<br />impoundment and diversion projects have resulted in dra-
<br />matic losses in riparian floodplain forests throughout
<br />North America (Bradley and Smith 1956; Rood and N[aho-
<br />ney- 1990; Howe and Knopf 1991).
<br />The conceptual pathways of riparian community
<br />response to the initiation and cessation of anthropogenic
<br />pertLirbatlQnS are llltlstrated In Flgtlre 2. A severe antI1I0-
<br />~`Ci~e_11C n ~rturb~',ti0I1 (e. g., O~'er~r3Zlllg, C1eaI'-CLlit]]1Q,
<br />channelizatioll, dams, diversions) may sufficiently alter a
<br />riparian ecosystem such that it will attain a dynamic
<br />equilibrium different than what would ocair under nat-
<br />ural conditions. A resistant ecos~stein is one that displays
<br />few changes in composition or structure following the ini-
<br />tiation of a pertLlrbation. In contrast, nonresistant riparian
<br />zones or communities will change to a ne~v system state
<br />or equilibrium typified by a different composition (e.g.,
<br />dominance by exotics), different structure (e.g., losses of
<br />the ~-wody component), altered productivity (e.g., shifts
<br />in above- and below-ground biomass), or a change in
<br />ecosystem functions (e.g., influences on water quality).
<br />After cessation of perturbations, resilient riparian ecosys-
<br />tems usually sho;v signs of recovery through measurable
<br />changes in composition, stnlctLlre, or function (Figure ? ~.
<br />In these situations, cessation of those human perturbations
<br />that harm the riparian ecosystem may be all that is neces-
<br />sary to achieve restoration. Because some ecosystems re-
<br />cover more quickly than others, it is important to monitor
<br />changes before implementing other, often more costly,
<br />measures. Failure to wait minimally may result in wasting
<br />limited funds; at worst, it may exacerbate the extent of
<br />degradation.
<br />When losses in ecosystem structure, composition, or
<br />function reach a sufficient magnitude, the simple cessation
<br />of perturbations may not be sufficient for ecosystem recov-
<br />ery (Figure 2). Factors that may diminish resilience and,
<br />1lence, prevent recovery include species extinctions, intro-
<br />ductions of exotics, excessive soil erosion, pollution, and
<br />severe changes in geomorphology or hydrology. In these
<br />Rather-than referring to a 'handbook,
<br />land managers should obtain .'
<br />the "blueprints" for the ultimate
<br />outcomes of planned~restoration~~
<br />`activities from intact streams.
<br />situations, the ecos-ystem may remain degraded indefinite-
<br />ly even after the cessation of activities that caused degra-
<br />dation. In this scenario a concerted and active effort will
<br />be needed to accomplish restoration.
<br />Conceptual Approaches to Restoration
<br />The basic goal of riparian restoration is to facilitate a
<br />self-sustaining occurrence of natural processes and link-
<br />ages among the terrestrial, riparian, and aquatic ecosys-
<br />tems. An important initial component of any restoration
<br />plan should be an evaluation of the ecological status of
<br />existing riparia] and aquatic systeuZS. Ideally, this assess-
<br />ment should be conducted at the ~~-atershed scale, while
<br />still bein sufficiently detailed to depict specific reaches or
<br />channel units ~rhere particular restoration activities might
<br />ultimateI~~ Deco:. Tile objecti~-e~ o~ tine initial resource analy-
<br />sis shoLlid L~~ to identi`~~ il) th.ose re:~dles that are relati~~e-
<br />ai, t"r t~ n,i i
<br />I:- intact i~~v~. <<_o,_o'~e. c alp ~ct~ e~:ident) and ~cortily
<br />c~` p-ot_~:_n;,. ~~_ _ .,_ ~r,. a._... ;n~....:__--._.._ strate,ies;
<br />(_~ tilos~ rea~,iles ~`.aere restor~ti,~,: i~ feasible with changes
<br />Cl CLlire:'.: laIi_"; Lime ~ Cti~'iClt~ l`:' l\-iiPi~Lii i;i:.~e expenditures
<br />of mone~~; (~) tho=e areas that could he restored but only at
<br />high costs and ~~-ith a high probability of failure, and
<br />(~) those reaches that are in a condition where restoration
<br />is not technically feasible due to extreme conditions of
<br />alteration, degradation, or sociopolitical limitations.
<br />~~"hen planning for ecosystem restoration, it may be
<br />useful from a strategic perspective to partition riparian
<br />zones into those capable of rapid recovery, those with a
<br />slo«' rite o; natural recoyer~; and those with little or no
<br />resilience ca'pacit~~ (i.e., loss of ecosystem integrity, Figure Z).
<br />The greatzst efforts should be initially focused on the for-
<br />mer because of a greater potential f~_~r successfLil restora-
<br />tion ~~~it':-. lo'~~~erE':~~riss or e~.~:~nd~`_~.;~•s. ~~~~nly after areas
<br />Special issue S~ 4',a'er~~:?C r~c,.~-~•;c~ Fish?ries ~ -
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