|
WATERSHED RESTORATION
<br />Various other land management approaches seek to
<br />alter and improve riparian conditions or specific habitat
<br />features, yet they may not represent ecological restoration.
<br />Activities often confused with ecological restoration in-
<br />clude creation, rehabilitation, reclamation, mitigation, re-
<br />placement, and enhancement. These activities typically
<br />emphasize altering ecosystem components for a particular
<br />human purpose (National Research Council 1992, 1996).
<br />Creation
<br />Rehabilitation
<br />Rehabilitation implies making the land useful again after
<br />natural or anthropogenic disturbances. Restoration to
<br />predisturbance conditions and functions is not implied in
<br />the definition of relenbilitntion. The creation of a crested
<br />wheatgrass (Agrop~rorr cristnturn) stand where sagebrush
<br />steppe (Arterrrisin triderrtntn) once existed or the planting of
<br />exotic grass species after a forest fire could be construed as
<br />rehabilitation bttt is not ecological restoration.
<br />Creation is defined as establishing a new ecosystem that
<br />previously did not exist on a particular site. For example,
<br />developing a sustainable wetland in an area formerly occu-
<br />pied by upland plant communities would represent creation.
<br />Creation also includes attempts to create specific riparian fea-
<br />tures that previously did not exist on the treated site. Exam-
<br />ples include the planting of willows or alders (Alrurs spp.) on
<br />riparian wetland sites naturally occupied by sedges or rushes,
<br />placement of boulders in streams with floodplains comprised
<br />of fine sediment, and constriction of secondary channels
<br />where none existed previously (Quammen 1986) .
<br />Reclarnatiorz
<br />Reclamation is traditionally defined as the process of
<br />adapting wild or natural resources to serve a utilitarian
<br />human purpose (National Research Council 1992). Histori-
<br />cally; this often included the conversion of riparian or wet-
<br />land ecosystems to agricultural, industrial, or urban uses.
<br />More recently, however, reclnrnntion has been defined as
<br />the process resulting in a stable, self-sustaining ecosystem
<br />that may or may not include some exotic species. Reclaimed
<br />sites may have similar, although not identical, structure
<br />and function of the original land (Jackson et al. 1990.
<br />C
<br />L;
<br />Replacement
<br />Replncernerrt is the substitution of a native species or
<br />ecosystem feature with an exotic species or foreign object;
<br />often, it is considered another form of rehabilitation. Ex-
<br />amples of replacement would include the planting of tton-
<br />native trees or the placement of boulders, gabions, or
<br />weirs to substitute for natural features. The introduction of
<br />brook trout (Salveliruu fontinnlis) or smallmouth bass
<br />(Micropteris dolornieui) in streams historically occupied by
<br />native salmonids is an example of ecological replacement.
<br />Mitigation
<br />Mitigation is an attempt to alleviate any or all of the
<br />detrimental effects or environmental damage that arise
<br />from anthropogenic actions. The construction of fish
<br />hatcheries or the modification of headwater fish habitats
<br />to compensate for losses caused by dams is a mitigation
<br />approach. Wetland creation is often suggested as mitiga-
<br />tion for the destruction of natural wetlands from construc-
<br />tion, fill, or other human activities. However, these con-
<br />structed wetlands seldom display the structural or
<br />functional attributes of the native wetlands they replaced
<br />(Quammen 1986; M. Kentula, U.S. Environmental Protec-
<br />tion Agency, personal communication).
<br />Pervrbed Sable Srat_
<br />Enhnncernent
<br />Na;'.;: u~ C/nanic Sta:a
<br />
<br />~ i~~r,~
<br />Figure 2 represents the conceptual responses of individual riparian plant communities
<br />to human perturbations and response pathways after cessation of perturbations. Resis-
<br />tant plant communities exhibit few deviations from natural equilibria-when exposed to
<br />a perturbation. In contrast, nonresistant communities shift to a perturbed state unlike
<br />that of the natural dynamic state (i.e, changes in composition, structure, or productivi-
<br />ty). After activities that caused ecosystem degradation (perturbations) stop, resilient
<br />communities will recover to natural system states. Nonresilient communities are those
<br />lacking potential for natural recovery and are characterized as having lost ecosystem
<br />integrity. In the absence of active restoration activities, they may remain indefinitely in
<br />an altered ecosystem state.
<br />Enhancement is any improvement of a
<br />structural or functional attribute fora sp~-
<br />cies or habitat. However, when enhance-
<br />ment activities are focused only on a sinle
<br />species or specific component of an eco~~ s-
<br />tem, they may create conditions oucia~ t»~
<br />context of a natural riparian and sire::-•~
<br />system. For example, in-stream struct:;rzs
<br />(e.g., rock jetties, gabions, pool exce.~~ations'~
<br />are often used with the objective of fish
<br />habitat enhancement. However, these struc-
<br />tures can severely alter streambank struc-
<br />ture, sediment transport dynamics, and
<br />hydrologic connectivity with riparian vege-
<br />tation, resulting in disruptions or losses of
<br />riparian-stream linkages. When in-stream
<br />spoils, rocks, or boulders are piled on a
<br />streambank, conditions may no longer be
<br />suitable for nahtral establishment of ripariar.
<br />vegetation nor for adjustments in channel
<br />morphology to natural variations in sedimer`
<br />transport and stream floe-. Such p'?: ~ _~l'.
<br />FlShar~~, ~~5'.i~~ !~SJE ~, 4~,,dtPr~r~a~ R~St O'd`.: ~!'
<br />rertureaCOn Cessaicn of Perturbations
<br />
|