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Premise 23 - Properly classifying sites is key
Click below to view some of the premises from Karr and Chu (1999).
From "Restoring Life in Running Waters" by James R. Karr and Ellen W. Chu
(Reprinted with permission from Island Press)
Successful biological monitoring depends on judicious classification of sites. Yet excessive emphasis on classification, or inappropriate classification, can impede development of cost-effective and sensible monitoring programs. Using too few classes fails to recognize important distinctions among places; using too many unnecessarily complicates development of biocriteria. Inappropriate levels of classification also lead to problems. The challenge is to create a system with only as many classes as are needed to represent the range of relevant biological variation in a region and the level appropriate for detecting and defining the biological effects of human activity in that place.
Like a taxonomy of places, classification attempts to distinguish and group distinct environments, communities, or ecosystem types; the proper approach to classification may vary, however, according to specific goals. For aquatic systems, biological (community) classification generally lags far behind classification by physical environment or habitat type (Angermeier and Schlosser 1995).
The characteristics that make streams similar or different biologically--and thus make classification important for biological monitoring--are determined first by the geophysical setting (including climate, elevation, and stream size), and second by the natural biogeographic processes operating in a place (see Premise 6 and Figure 4). Together these are responsible for local and regional biotas. Coastal rainforest headwaters on the Olympic Peninsula, for example, are likely to be biologically comparable, as would be headwater streams in central Illinois.
But even though geophysical context is a fundamental determinant of variation in biological systems, classification based on the geomorphologists' view of stream channel types, or on other landforms occupied by biological systems, is not necessarily the proper level for assessing the biological condition of those systems. In the Pacific Northwest, geomorphologists identify some 50 to 60 channel types based on the interplay of physical and chemical processes that shape stream channels (MacDonald et al. 1991). But recognizing these channel types does not necessarily mean that an equal number of biological classes is needed for biological monitoring. The native biota may not be unique to each of those channel types in terms of species composition, taxa richness, or other important aspects of ecological organization; even if some species replacement occurs, metric norms may not change. Fewer biological categories may therefore work just as well.
Many agency programs rely on geographically delineated ecological regions reflecting prevailing geophysical and climatic regimes (Omernik 1995; Omernik and Bailey 1997). Such ecoregion divisions are valuable, but they are not the be-all and end-all of classification schemes. Indeed, classification at the ecoregion level alone is unlikely to give appropriate weight to every factor important to creating homogeneous sets for comparing the biological condition of streams. Other factors, including topography, geological substrate, and stream size or gradient may be more significant biologically. For example, in the Snake River, Idaho (Maret et al. 1997), and in Kansas streams (Hawkes et al. 1986), neither the distribution of fish species nor that of ecologically defined assemblages coincided with ecoregion boundaries.
In addition to ecoregion, a good classification scheme should consider the defining characteristics of local and regional physical and biological systems. It would make little biological sense, for example, to group large, meandering stream reaches with small, fast-flowing streams even if they are in the same lowland ecoregion; the habitats these stream reaches provide, and therefore the biota that live there, are very different. Likewise, the biological attributes signaling the effects of human activities in two high-elevation first-order streams may not differ just because they are in different ecoregions. In short, ecoregions (or equivalent units) are a useful but not a sufficient basis for a stream classification used in biological monitoring.
Characterizing ecoregions can certainly be useful, but no matter how much such characterization enhances our knowledge of natural landscape variation, it should not get in the way of testing and using metrics diagnostic of human impact. The point of classification is to group places where the biology is similar in the absence of human disturbance and where the responses are similar after human disturbance. In some cases, these groupings may coincide with ecoregion boundaries; in others, they may cross those boundaries. To evaluate sites over time and place, we need groupings that will give reliable metrics and accurate criteria for scoring metrics to represent biological condition (see Premise 15).
| Metric | Predicted Response | Eastern Oregon | SW Oregon | Central Idaho | NW Wyoming |
|---|---|---|---|---|---|
| Taxa richness and composition | |||||
| Total number of Taxa | Decrease | X | X | X | |
| Ephemeroptrea taxa | Decrease | X | X | X | |
| Plecoptera Taxa | Decrease | X | X | X | X |
| Trichoptera Taxa | Decrease | X | X | ||
| Tolerants and intolerants | |||||
| Intolerant taxa | Decrease | X | X | X | |
| Sediment-intolerant taxa | Decrease | X | X | X | |
| % tolerant | Increase | X | X | ||
| % sediment-tolerant | Increase | X | X | ||
| Feeding and Other Habits | |||||
| % predators | Decrease | X | X | X | |
| % scrapers | Variable | X | X | X | |
| % gatherers | Variable | X | X | ||
| Population attributes | |||||
| Dominance | Increase | X |
Table 10: Similar metrics emerge as reliable indicators of human influence across the Pacific Northwest, regardless of ecoregion. Percent sign (%) denotes relative abundance of individuals belonging to the listed taxon or group. Metrics marked with a check are those that responded across a range of intensity for grazing (eastern Oregon and Wyoming) or logging (western Oregon and Idaho)
On the east and west sides of the Cascades, and elsewhere in the Northwest, for example, many of the same metrics respond to the effects of grazing, logging, and urbanization, even though climate, vegetation, terrain, and human land use differ (Table 10). The expected values of these metrics differ--taxa richness, for example, is lower east of the Cascades--which may result from "natural" differences or differences stemming from more widespread human influence on a more fragile eastside landscape. Nevertheless, in both westside and eastside ecoregions, the same metrics respond across a range of human influence, and IBIs composed of these metrics reflect and distinguish among the effects at different sites. Elsewhere, such as across eastern deciduous forests and midwestern prairies, maximum species richness also transcends ecoregion boundaries (Figure 40). Expected species richness seems to be higher for forested landscapes than for prairie or grassland landscapes. Other metrics, such as trophic structure, however, are reliable indicators of human influence across ecoregions for some places and taxa (e.g., North American fishes) but not for others (e.g., benthic invertebrates) (see Premise 13).
Figure 40
Thus, classification based on ecological dogma, on strictly chemical or physical criteria, or even on the logical biogeographical factors used to define ecoregions is not necessarily sufficient for biological monitoring. The good biologist uses the best natural history, biogeographic, and analytical resources available to choose a classification system.
References
Angermeier, P. L., and I. J. Schlosser. 1995. Conserving aquatic biodiversity. Am. Fish. Soc. Symp. 17: 402-414.
Hawkes, C. L., D. L. Miller, and W. G. Layher. 1986. Fish ecoregions of Kansas: Stream fish assemblage patterns and associated environmental correlates. Environ. Biol. Fish 17: 267-279.
MacDonald, L. H., A. Smart, and R. C. Wissmar. 1991. Monitoring guidelines to evaluate effects of forestry activities on streams in the Pacific Northwest and Alaska. EPA/910/9-91-001. US Environmental Protection Agency, Seattle.
Maret, T. R., C. T. Robinson, and G. W. Minshall. 1997. Fish assemblages and environmental correlates in least-disturbed streams in the upper Snake River basin. Trans. Am. Fish. Soc. 126: 200-216.
Omernik, J. M. 1995. Ecoregions: A spatial framework for environmental management. Pages 49-62 in W. S. Davis and T. P. Simon, eds. Biological Assessment and Criteria: Tools for Water Resource Planning and Decision Making. Lewis, Boca Raton, FL.
Omernik, J. M. and R. G. Bailey. 1997. Distinguishing between watersheds and ecoregions. J. Am. Wat. Res. Assoc. 33: 935-949