1
An Overview of Ecological Assessment
Principles and Applications
Mark E. Jensen, Norman L. Christensen, Jr., and Patrick S. Bourgeron
1.1 Introduction
Ecological assessments facilitate understanding of
an area's past, present, and future conditions
through comprehensive description of ecosystem
patterns, processes, and functions (Lessard et aI.,
1999). They synthesize our knowledge of ecological systems and commonly describe the biophysical and social limits of a system, the interrelations
of its ecosystem components, and the uncertainties
and assumptions that underlie a given assessment effort. Ecological assessments are not decision documents because they do not resolve issues or provide
direct solutions to specific policy questions. Instead,
they provide the foundation for proposed additions
or changes to existing land management plans or regulatory policies and are a critical component for implementing principles of ecosystem management in
land management planning (Grossarth and Nygren,
1994; Morrison, 1994; Haynes et al., 1996).
Over the years, many different definitions and
approaches have been used in ecological assessment efforts, depending on the discipline, agency,
or audience involved and the associated legislative
or regulatory requirements (Lessard et aI., 1999).
For example, earlier regulatory-based efforts in the
United States commonly followed traditional risk
assessment methodologies (National Research
Council, 1983) and often focused on single resources and stressors over limited geographic
scales. Over the past decade, these have evolved
into ecological risk assessments (Risk Assessment
Forum, 1992; Suter, 1993) that typically include a
wider consideration of the risks to humans and
ecosystem integrity associated with mUltiple stressors. These types of assessment are either predictive, focusing on a particular stressor and estimating possible future effects, or retrospective,
focusing on a particular effect and subsequently
identifying stressors that might have contributed to
the effect (Rapport, 1992; Suter, 1993).
In contrast to regulatory-based ecological assessments, those based on land-use planning have
largely followed traditional methods of land evaluation that hinge on fundamental questions (What
is there? Where is it? When is it present? How does
it function?) in determining optimal land uses and
required management actions for an assessment
area (Klingebiel and Montgomery, 1961; Beek and
Bennema, 1972; Olson, 1974; Food and Agriculture Organization, 1976; Zonneveld, 1988).
Most government agencies collect different information (and at different spatial scales) in their
ecological assessment efforts, largely because a
clearly defined, unifying purpose for such information is lacking. Ecosystem management (Slocombe, 1993; Grumbine, 1994; Jensen and Everett,
1994; Keystone Center, 1996) provides this unifying purpose for ecological assessments: it represents a management philosophy that seeks to
integrate scientific knowledge of ecological relationships within a complex sociopolitical and values framework toward the general goal of protecting native ecosystem integrity over the long term
(Grumbine, 1994). Accordingly, we emphasize the
linkages between ecosystem management philosophies (and related scientific principles) and ecological assessments throughout this chapter.
First, we present a brief overview of the evolution of ecosystem management philosophies within
the United States. Goals and implementation strategies for ecosystem management are discussed and
their relations to ecological assessments are briefly
described. The basic ecological principles that support an ecosystem-based approach to land management are presented next, with particular em13
An Overview of Ecological Assessment
Principles and Applications
Mark E. Jensen, Norman L. Christensen, Jr., and Patrick S. Bourgeron
1.1 Introduction
Ecological assessments facilitate understanding of
an area's past, present, and future conditions
through comprehensive description of ecosystem
patterns, processes, and functions (Lessard et aI.,
1999). They synthesize our knowledge of ecological systems and commonly describe the biophysical and social limits of a system, the interrelations
of its ecosystem components, and the uncertainties
and assumptions that underlie a given assessment effort. Ecological assessments are not decision documents because they do not resolve issues or provide
direct solutions to specific policy questions. Instead,
they provide the foundation for proposed additions
or changes to existing land management plans or regulatory policies and are a critical component for implementing principles of ecosystem management in
land management planning (Grossarth and Nygren,
1994; Morrison, 1994; Haynes et al., 1996).
Over the years, many different definitions and
approaches have been used in ecological assessment efforts, depending on the discipline, agency,
or audience involved and the associated legislative
or regulatory requirements (Lessard et aI., 1999).
For example, earlier regulatory-based efforts in the
United States commonly followed traditional risk
assessment methodologies (National Research
Council, 1983) and often focused on single resources and stressors over limited geographic
scales. Over the past decade, these have evolved
into ecological risk assessments (Risk Assessment
Forum, 1992; Suter, 1993) that typically include a
wider consideration of the risks to humans and
ecosystem integrity associated with mUltiple stressors. These types of assessment are either predictive, focusing on a particular stressor and estimating possible future effects, or retrospective,
focusing on a particular effect and subsequently
identifying stressors that might have contributed to
the effect (Rapport, 1992; Suter, 1993).
In contrast to regulatory-based ecological assessments, those based on land-use planning have
largely followed traditional methods of land evaluation that hinge on fundamental questions (What
is there? Where is it? When is it present? How does
it function?) in determining optimal land uses and
required management actions for an assessment
area (Klingebiel and Montgomery, 1961; Beek and
Bennema, 1972; Olson, 1974; Food and Agriculture Organization, 1976; Zonneveld, 1988).
Most government agencies collect different information (and at different spatial scales) in their
ecological assessment efforts, largely because a
clearly defined, unifying purpose for such information is lacking. Ecosystem management (Slocombe, 1993; Grumbine, 1994; Jensen and Everett,
1994; Keystone Center, 1996) provides this unifying purpose for ecological assessments: it represents a management philosophy that seeks to
integrate scientific knowledge of ecological relationships within a complex sociopolitical and values framework toward the general goal of protecting native ecosystem integrity over the long term
(Grumbine, 1994). Accordingly, we emphasize the
linkages between ecosystem management philosophies (and related scientific principles) and ecological assessments throughout this chapter.
First, we present a brief overview of the evolution of ecosystem management philosophies within
the United States. Goals and implementation strategies for ecosystem management are discussed and
their relations to ecological assessments are briefly
described. The basic ecological principles that support an ecosystem-based approach to land management are presented next, with particular em13