River Ecology and Restoration - River Dynamics and Integrated River Management - page 680

(1) Geographic domain. The range of sites being classified varies from rivers of the world to local
differences in the composition and characteristics of patches within one reach of a single river.
(2) Variables considered. Some classifications are restricted to hydrology, geomorphology, and aquatic
chemistry. Other community classifications are restricted to biotic variables of species composition and
abundance of a limited number of taxa. Many classifications include both abiotic and biotic variables.
Even purely abiotic classification systems are relevant to biological evaluations because of the important
correlations (e.g., the whole concept of physical habitat) between abiotic structure and community
composition.
(3) Incorporation of temporal relations. Some classifications focus on describing correlations and
similarities across sites at one, perhaps idealized, point in time. Other classifications identify explicit
temporal transitions among classes, for example, succession of biotic communities or evolution of
geomorphic landforms.
(4) Focus on structural variation or functional behavior. Some classifications emphasize a parsimonious
description of observed variation in the classification variables. Others use classification variables to
identify types with different behaviors. For example, a vegetation classification can be based primarily
on patterns of species co-occurrence, or it can be based on similarities in functional effect of vegetation
on habitat value.
(5) The extent to which management alternatives or human actions are explicitly considered as
classification variables. To the extent that these variables are part of the classification itself, the
classification system can directly predict the result of a management action. For example, a vegetation
classification based on grazing intensity would predict a change from one class of vegetation to another
class based on a change in grazing management.
Comparison of the degraded system to an actual unimpacted reference site, to the ideal type in a
classification system, or to a range of similar systems can provide a framework for articulating the desired
state of the degraded system. However, the desired state of the system is a management objective that
ultimately comes from outside the classification of system variability.
10.3.3.4 Analyses of Species Requirements
Analyses of species requirements involve explicit statements of how variables interact to determine
habitat or how well a system provides for the life requisites of fish and wildlife species. Complete
specification of relations between all relevant variables and all species in a river system is not possible.
Thus, analyses based on species requirements focus on one or more target species or groups of species.
In a simple case, this type of analysis may be based on an explicit statement of the physical factors that
distinguish good habitat for a species (places where it is most likely to be found or where it best
reproduces) from poor habitat (places where it is unlikely to be found or reproduces poorly). In more
complicated cases, such approaches incorporate variables beyond those of purely physical habitat,
including other species that provide food or biotic structure, other species as competitors or predators, or
spatial or temporal patterns of resource availability.
Analyses based on species requirements differ from synthetic measures of system condition in that
they explicitly incorporate relations between “causal” variables and desired biological attributes. Such
analyses can be used directly to decide what restoration actions will achieve a desired result and to
evaluate the likely consequences of a proposed restoration action. For example, an analysis using the
habitat evaluation procedures might identify mast production (the accumulation of nuts from a productive
fruiting season which serves as a food source for animals) as a factor limiting squirrel populations. If
squirrels are a species of concern, at least some parts of the stream restoration effort should be directed
toward increasing mast production. In practice, this logical power is often compromised by incomplete
knowledge of the species habitat requirements.