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Defining Restoration Goals *at the ecosystem -level framework encourages res- torationists to both pay attention to landscape -level dy- namics and to attempt to integrate an understanding of these large -scale processes with the small-scale processes of soil ecology and species biology. He also points out that the "management" part of the phrase encourages thinking about the widest possible range of interventions that affect both large- and small-scale processes. The use of ecosystem -level goals for restoration and conservation has been strongly criticized, in large part be- cause key concepts and terms are poorly defined (Gold- stein 1999) (Table 1). For example, the idea of ecosystem management suffers from vagueness in the definition of ecosystem, as well as in the definitions of other terms used to define the goals of ecosystem management (i.e., ecosys- tem integrity or ecological health) (Wilcove & Blair 1995). Allen (1996) has pointed out, however, that many of the concepts used in species -based conservation and restora- tion are similarly vague. "Minimum viable population size" can be given a mathematical definition, but is hard to apply to real -life situations. Levels of anthropogenic dis- turbance and pollution that affect the health of popula- tions are vigorously debated (for example, the controver- sies over organochlorine pollutants in the Great Lakes and iiieffects on organisms [Carpenter 1995; and related ar- ]). The goal of conservation biology that "compo- nents of the ecosystem should [not] be perturbed beyond natural boundaries of variation" (Mangel et al. 1996, p. 338) leaves open the definitions of what are the "compo- nents of the ecosystem" (never mind the definition of eco- system) as well as what are the natural boundaries of vari- ation. Many other examples could be cited. Lack of precision in the definition of ecological terms has been a controversial issue for decades in ecology as a science, but has not prevented its effective application in both conser- vation and restoration. Thus, although criticisms of the vagueness of terms used to develop ecosystem based goals may be legitimate (Goldstein 1999), the same criti- cisms apply to other foci for restoration. To deny the im- portance of ecosystem -level processes because of prob- lems of definition ignores both the importance of these processes and the long history of using poorly defined terms to good purpose in many specific cases of restora- tion and conservation. However, even if we accept the fuzziness of the gen- eral concepts invoked in ecosystem management and restoration, there are additional problems of definition that hamper the use of ecosystem functions as a basis for restoration goals (Table 1). The fundamental premise of this approach is the recognition of ecosystem processes, 11111ctions, that create and drive the system, and that D1Oth a result of structure (e.g., species composition) and a causative factor in creating structure. However, the concept of ecosystem function is equally vague. Every discussion of this idea lists a somewhat different set of items. Table 2 lists an amalgam of items culled from a va- riety of sources; it is as idiosyncratic and individualistic as (and has no greater validity than) any other list. The point is that the processes that make up ecosystem func- tion are as variable as the definition of ecosystem itself. Just within this list, there is tremendous heterogeneity. Some processes, such as nutrient cycling or .energy flow integrate the activities of numerous organisms (e.g., the extraordinary, if poorly recognized, diversity of soil or- ganisms; Wall & Moore 1999). Others, such as succession or mutualisms, reflect the biology of particular species and are population -level phenomena, rather than ecosys- tem processes as usually defined. Some processes (e.g., diversity) reflect purely biological phenomena, whereas others reflect purely physical phenomena (disturbance regimes caused by storms) and still others reflect com- plex mixtures of biological and physical forces (soil for- mation and water quality). The items in Table 2 are also heterogeneous in terms of the scales of space and time over which they apply and over which they are mea= sured. Some items (e.g., succession and mutualisms) are variously included or excluded from lists of ecosystem functions, depending on the viewpoint of the list - maker. Measurable components of each of the processes listed in Table 2 have the same problems of heterogene- ity, although they are more readily definable. Table 3 lists, as examples, the quantifiable components of three of the most commonly cited ecosystem functions. Again, the measurable components of each process are heterogeneous with respect to the time and spatial scales of the phenomena they index, and heterogeneous Table 2. Processes included under the rubric "ecosystem functions." Category Process Material flow Physical elements Biological structure Energy flow Nutrient cycling Nutrient retention /loss Carbon storage Productivity Water flow Water turnover rates, flow rates (aquatic) Transfers to /from other ecosystems Disturbance regimes (fire, disease, storms) Water quality Landscape structure Soil formation Trophic structure Predation /herbivory rates Succession Resilience /resistance Diversity Mutualisms Passive vs. active dispersal MARCH 2000 Restoration Ecology 5