20.4 Suitability of Land Areas
important for two reasons: (1) a representative
network should incorporate all relevant aspects of
biotic and environmental variability, and (2) a conservation target may respond differently to conservation or management practices depending on location-specific biotic-environmental interactions.
Two types of surrogate data are used to delineate or attribute land units if biotic data are limited. An environmental stratification may serve as
a surrogate for biotic data when they are not available regionally (Mackey et aI., 1988, 1989; Belbin,
1993; Kirkpatrick and Brown, 1994; Bourgeron et
aI., 1995a; White et aI., 1999), or the distribution
of one or more group of indicator taxa may be used
as a surrogate for total biodiversity (Pressey et aI.,
1993; Margules et aI., 1994; Scott and Jennings,
1998). Ideally, any surrogate data should be tested
for their actual surrogacy value (e.g., Bedward et
aI., 1992; Kirkpatrick and Brown, 1994), but it is
often not possible to do so before conservation decisions are required (Faith and Walker, 1996).
Therefore, regardless of the type of surrogate, any
surrogacy methods used to make conservation decisions should be robust (Ricketts et aI., 1999b) and
should not make unwarranted assumptions (Faith
and Walker, 1996).
20A Suitability of Land Areas
Once land units have been delineated and their ecological properties determined, their suitability for
conservation must be assessed. The presence or absence of key targets, defensibility, viability, landuse practices, road density, and management status
are common criteria used to determine conservation suitability value (McHarg, 1969; McKendry
and Machlis, 1993; Davis et aI., 1996) in light of
the specific objectives of a conservation assessment. In this section, we discuss some of the factors that constrain the suitability of sites for the
long-term protection of regional diversity by affecting ecological conditions and persistence of
patterns and processes.
20.4.1 Assessment of
Ecological Conditions
The effects of management practices and natural
processes on biotic patterns should be assessed at
multiple scales by contrasting the current condition
of an area with other managed or unmanaged areas that occur in the same biophysical environment.
It is often useful to conduct an analysis of the historic range of variability (HRV) (see Chapter 19)
297
to characterize past fluctuations in pattern and
process, resulting in determination of the upper and
lower limits or range of variability within which an
ecosystem historically operated. Knowledge of
how far an ecosystem departs from its historical
range is gained by comparison of its current state
with HRV (Morgan et aI., 1994; Landres et aI.,
1999; Swetnam et aI., 1999). Analyses can focus
on the processes or disturbance regimes operating
on an ecosystem, such as the frequency and severity of disturbance, or they can focus on the states
of the system resulting from processes, such as descriptions of the size, shape, and other characteristics of patches (Swanson et aI., 1994; Cissel et aI.,
1998; Kaufmann et aI., 1998). There are known
limitations to the power of HRV analyses, but careful application of the method can provide important information (see Chapter 19; also see Landres
et aI., 1999).
20.4.2 Maintenance of Patterns
and Processes
Estimates of the persistence of patterns and
processes are required for each land unit as well as
at larger scales. Assessment of persistence should
take into consideration information about biotic
patterns, biophysical environments, processes, and
existing conditions at different hierarchical levels
(Levin, 1992; Bourgeron and Jensen, 1994). For
example, both coarse-scale and site-level conditions are important for assessing the population viability of many species (Glenn and Collins, 1994).
Across the landscape, reproducing populations in
high-quality habitats may be sources for populations in other areas (sinks; see Pulliam, 1988). In
areas with less suitable habitats, where mortality
exceeds reproduction, populations are dependent
on immigration from source populations to maintain existing numbers (Ritchie, 1997).
Within a landscape, the quality of the local habitat depends on many factors, including ecosystem
complexity, biodiversity, vegetation composition
and structure, land-use patterns, road density, and
fragmentation (see Chapters 17 and 27 through 29
for discussions of economic and sociopolitical factors). The potential for manipulating ecosystem
components (e.g., vegetation) to improve habitat
should also be included in the determination of suitability. Analyses should be developed that integrate
relevant factors into a single index or a suite of indices of suitability (e.g., Davis et aI., 1996) that
meet the specific objectives of an assessment. For
example, Bourgeron et al. (1 999b ) determined the
important for two reasons: (1) a representative
network should incorporate all relevant aspects of
biotic and environmental variability, and (2) a conservation target may respond differently to conservation or management practices depending on location-specific biotic-environmental interactions.
Two types of surrogate data are used to delineate or attribute land units if biotic data are limited. An environmental stratification may serve as
a surrogate for biotic data when they are not available regionally (Mackey et aI., 1988, 1989; Belbin,
1993; Kirkpatrick and Brown, 1994; Bourgeron et
aI., 1995a; White et aI., 1999), or the distribution
of one or more group of indicator taxa may be used
as a surrogate for total biodiversity (Pressey et aI.,
1993; Margules et aI., 1994; Scott and Jennings,
1998). Ideally, any surrogate data should be tested
for their actual surrogacy value (e.g., Bedward et
aI., 1992; Kirkpatrick and Brown, 1994), but it is
often not possible to do so before conservation decisions are required (Faith and Walker, 1996).
Therefore, regardless of the type of surrogate, any
surrogacy methods used to make conservation decisions should be robust (Ricketts et aI., 1999b) and
should not make unwarranted assumptions (Faith
and Walker, 1996).
20A Suitability of Land Areas
Once land units have been delineated and their ecological properties determined, their suitability for
conservation must be assessed. The presence or absence of key targets, defensibility, viability, landuse practices, road density, and management status
are common criteria used to determine conservation suitability value (McHarg, 1969; McKendry
and Machlis, 1993; Davis et aI., 1996) in light of
the specific objectives of a conservation assessment. In this section, we discuss some of the factors that constrain the suitability of sites for the
long-term protection of regional diversity by affecting ecological conditions and persistence of
patterns and processes.
20.4.1 Assessment of
Ecological Conditions
The effects of management practices and natural
processes on biotic patterns should be assessed at
multiple scales by contrasting the current condition
of an area with other managed or unmanaged areas that occur in the same biophysical environment.
It is often useful to conduct an analysis of the historic range of variability (HRV) (see Chapter 19)
297
to characterize past fluctuations in pattern and
process, resulting in determination of the upper and
lower limits or range of variability within which an
ecosystem historically operated. Knowledge of
how far an ecosystem departs from its historical
range is gained by comparison of its current state
with HRV (Morgan et aI., 1994; Landres et aI.,
1999; Swetnam et aI., 1999). Analyses can focus
on the processes or disturbance regimes operating
on an ecosystem, such as the frequency and severity of disturbance, or they can focus on the states
of the system resulting from processes, such as descriptions of the size, shape, and other characteristics of patches (Swanson et aI., 1994; Cissel et aI.,
1998; Kaufmann et aI., 1998). There are known
limitations to the power of HRV analyses, but careful application of the method can provide important information (see Chapter 19; also see Landres
et aI., 1999).
20.4.2 Maintenance of Patterns
and Processes
Estimates of the persistence of patterns and
processes are required for each land unit as well as
at larger scales. Assessment of persistence should
take into consideration information about biotic
patterns, biophysical environments, processes, and
existing conditions at different hierarchical levels
(Levin, 1992; Bourgeron and Jensen, 1994). For
example, both coarse-scale and site-level conditions are important for assessing the population viability of many species (Glenn and Collins, 1994).
Across the landscape, reproducing populations in
high-quality habitats may be sources for populations in other areas (sinks; see Pulliam, 1988). In
areas with less suitable habitats, where mortality
exceeds reproduction, populations are dependent
on immigration from source populations to maintain existing numbers (Ritchie, 1997).
Within a landscape, the quality of the local habitat depends on many factors, including ecosystem
complexity, biodiversity, vegetation composition
and structure, land-use patterns, road density, and
fragmentation (see Chapters 17 and 27 through 29
for discussions of economic and sociopolitical factors). The potential for manipulating ecosystem
components (e.g., vegetation) to improve habitat
should also be included in the determination of suitability. Analyses should be developed that integrate
relevant factors into a single index or a suite of indices of suitability (e.g., Davis et aI., 1996) that
meet the specific objectives of an assessment. For
example, Bourgeron et al. (1 999b ) determined the