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:-.:J: ~::.... ~D~?~O RESTORATION OF REGULATED RIVERS 393 of populations, species, guilds and other taxonomic and trophic categories across the landscape. It also encompasses the myriad of biophysical processes (functional attributes) that control these phenomena (Hall el ai" 1992; Doppelt el aI., 1993; Noss and Cooperrider, 1994; and many others). However, the sali- ent features of biodiversity, species numbers (alpha diversity) and distribution (beta diversity), are deter- mined by the availability of the resources that are needed by animals and plants in order to reproduce successfully (i.e. complete their life cycle) (Andrewartha and Birch, 1954) and thereby sustain ecosystem integrity (Frissell and Bayles, 1996; Ward, in press), Life history stages are determined by the genome of each species as derived from its legacy of genetic responses to changes in the availability of resources. Hence, the dynamic biophysical components of the landscape are controlled in space and time by envir- onmental changes (e.g, forest fires, spates, drought, disease, earthquakes) that vary in intensity and dura- tion. Similarly, human societies within catchments usually are derived from a mix of cultures (e.g, natives, immigrants) that use or market goods and services to produce wealth or some other measure of the quality of life desired by individuals, Desires and perceptions that individuals have about life-style are dynamic and influenced by heritage, education, earning power, shortages and surpluses of goods such as fossil fuels, laws, taxes and natural resource management policies, among many other social and economic concerns. The point is, that both natural and cultural components of catchments are complex and highly interactive. Humans change catchment landscapes by using or extracting environmental goods and services; whereas, societies change in relation to the quality or ecological integrity of landscapes in which they reside (Blikie and Brookfield, 1987; Schinberg and Gould, 1994; and many others in the rapidly expanding environmental sociology and ecological'economics literature), Within this natural-cultural framework, we recognize that river ecosystems have a certain natural capa~ city to maintain biota and produce biomass (Warren el al., 1979; Frissell el al. 1996; Ebersole el ai" in press) and that biodiversity and bioproduction are dynamic in time and space in relation to availability of resources (Benke el al., 1988), Biotic dynamics derive from natural variation in the environmental setting; equilibrium conditions (e,g, logistic relationship between resources and bioproduction) rarely exist for very long because environmental changes are constantly reconfiguring resource availability. Periodic constraints on species- specific productivity increases opportunities for other species to use resources, inferring that levels of ecosys- tem biodiversity and bioproduction generally are related to the intensity, frequency and duration of distur- . bance events (Huston, 1979; Resh el ai" 1988; Pimm, 1991; Huston, 1994; Reice, 1994). Ecological capacity, therefore, varies from place to place and higher levels of biological richness (specios- ity) and bioproduction are most likely to occur in ecosystems with a long legacy of high spatial and temporal environmental heterogeneity (Connell, 1978; Ward and Stanford, 1983; Salo el ai" 1986; Poff and Ward, 1990; Ward, in press), [n contrast, total unit area biomass (standing crop) of a few species, while also con- strained by inherent ecosystem capacity, may be high under sustained conditions of environmental con- stancy' owing to slow turnover rates. For example, a few species are often extremely abundant and persistent in spring-brooks, lake outlets and reservoir tailwaters, where disturbance events are relatively . benign (e,g. scouring floods, very dynamic diel and annual temperature patterns and rapid changes in trans- port of particulate matter do not occur because of the buffering effect of the lake or reservior) (Ward and Dufford, 1979; Gislason, 1985; Perry and Sheldon, ]986; Valett and Stanford, 1987; Wooton, 1987; Shannon el 01" 1994), Humans tend to dominate ecosystems, thereby superimposing pervasive, continual perturbation on the natural disturbance regimes that sustain habitats and biotic communities, The result is suppression, and in some cases pennanent loss, of environmental heterogeneity and biodiversity, fundamentally reducing the productive capacity of biotic resources (Warren and Liss, 1980; Frissell el al., 1993; Frissell el ai" in press; Ebersole el al., in press), The goal of river restoration should be to minimize human-mediated con- straints, thereby allowing natural re-expression of productive capacity, [n some, ifnot most, intensely regu- lated rivers, human-mediated constraints may have progressed to the point that full re-expression of capacity is neither desired nor possible, Nonetheless, the implication is that basic ecological principles applied to riv- ers in a natural-cultural context can lead to restoration of biodiversity and bioproduction in space and time; but, the constraints must be removed, not mitigated, . ~ . ... .', ':~..:J';:..:'; .~. . 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