294
derived from various criteria (e.g., rarity, diversity,
naturalness; see review in Usher, 1986). Sites are
chosen independently of each other on the basis
of the selected scoring criteria (e.g., Master,
1991). In contrast, at each step of the site selection process, RA takes into account the attributes
of both candidate and previously selected sites
(Pressey and Nicholls, 1989a). RA allows for
consideration of other major criteria, such as rarity and diversity during the selection process. A
wide array of selection procedures has been developed recently using RA principles (see Section 20.5).
RA has been reported as being more efficient
than scoring procedures (Pressey and Nicholls,
1989a, 1989b). Efficiency is defined as the ability of a criterion to capture the maximum number
of attributes under consideration in the smallest
number of sites. For example, Pressey and
Nicholls (1989b) calculated that the most efficient
scoring procedure required 45% of the total land
area in New South Wales, Australia, to represent
all the land systems present in the region at least
once. In contrast, an iterative procedure for representativeness included one example of each land
system in 5.7% of the land area (Pressey and
Nicholls, 1989a). However, efficiency of RA
varies with the degree of implementation of the
principles of flexibility and irreplaceability (see
Section 20.5.1) and with the region under consideration (Noss, 1996).
Over the last two decades, a number of largescale assessments have been initiated that emphasize the protection of geographic areas ranking high
in species richness, levels of endemism, number of
rare and threatened species, and intensity of threat.
Three such assessments include GAP (Scott and
Jennings, 1998), The Nature Conservancy's ecoregional planning (The Nature Conservancy, 1996),
and the World Wildlife Fund's ecoregional conservation assessment (Ricketts et aI., 1999a) and
Global 200 (Olson and Dinerstein, 1998) initiatives. Although they differ in specific objectives
and scope, these efforts share an emphasis on representation of conservation targets (see also discussion in Reid, 1998) as the initial step of conservation planning. In contrast, RA aims at
representing processes as well as patterns. The four
strategies have in common some data requirements
and methods.
In practice, conservation scientists have emphasized different aspects of the design of conservation area networks, depending on the objectives. In
some cases, large, well-connected, unmanaged areas are thought to provide the best solution for the
Representativeness Assessments
long-term maintenance of biodiversity (e.g., Noss,
1992,1993; Noss and Cooperrider, 1994; DellaSala
et aI., 1995; Noss et aI., 1999; Soule and Terborgh,
1999a). In other cases, emphasis has been placed
on the importance of embedding conservation areas within a matrix of land managed according to
ecological principles to successfully sustain biodiversity (e.g., Alverson et aI., 1994). The latter emphasis is based on the implementation of the principles of ecosystem management at landscape and
regional levels (Christensen et aI., 1996; Jensen et
aI., 1996). Three conservation approaches use the
concept that well-managed ecosystems will maintain biodiversity: biodiversity management areas
(Davis et aI., 1996), diversity maintenance areas
(Alverson et aI., 1994), and emphasis-use (Everett
and Lehmkuhl, 1997). The general framework presented in this chapter provides the means to evaluate the impact of various aspects of network design on a case by case basis by including
assessment of biotic-environmental relationships
and suitability of land units at multiple scales, in
addition to representation of conservation targets
(Noss and Cooperrider, 1994; Christensen et aI.,
1996).
20.2.4 Is Representativeness Assessment
Relevant to Site Conservation
and Management?
RA is relevant to site conservation and management in two ways. First, it is used to identify networks of sites capable of sustaining all conservation targets. Second, it provides information on
biotic and environmental variation at multiple spatial and ecological scales to guide the design of
each individual conservation area. RA does not produce conservation area designs in the traditional
sense. The land areas selected during RA, as well
as their surroundings, need to be analyzed in a site
conservation planning process such as the framework developed by Poiani et ai. (1998). In contrast
to current practices, RA provides site conservation
planners with information that places the conservation and management activities of individual
conservation areas in the context of the sustainability of conservation targets within the entire
network. For example, landscapes within each conservation area in a regional network may be allowed to fluctuate within the bounds of natural disturbance regimes and other processes, and therefore
conservation targets may be lost locally within
some areas, but maintained or acquired within
others.
derived from various criteria (e.g., rarity, diversity,
naturalness; see review in Usher, 1986). Sites are
chosen independently of each other on the basis
of the selected scoring criteria (e.g., Master,
1991). In contrast, at each step of the site selection process, RA takes into account the attributes
of both candidate and previously selected sites
(Pressey and Nicholls, 1989a). RA allows for
consideration of other major criteria, such as rarity and diversity during the selection process. A
wide array of selection procedures has been developed recently using RA principles (see Section 20.5).
RA has been reported as being more efficient
than scoring procedures (Pressey and Nicholls,
1989a, 1989b). Efficiency is defined as the ability of a criterion to capture the maximum number
of attributes under consideration in the smallest
number of sites. For example, Pressey and
Nicholls (1989b) calculated that the most efficient
scoring procedure required 45% of the total land
area in New South Wales, Australia, to represent
all the land systems present in the region at least
once. In contrast, an iterative procedure for representativeness included one example of each land
system in 5.7% of the land area (Pressey and
Nicholls, 1989a). However, efficiency of RA
varies with the degree of implementation of the
principles of flexibility and irreplaceability (see
Section 20.5.1) and with the region under consideration (Noss, 1996).
Over the last two decades, a number of largescale assessments have been initiated that emphasize the protection of geographic areas ranking high
in species richness, levels of endemism, number of
rare and threatened species, and intensity of threat.
Three such assessments include GAP (Scott and
Jennings, 1998), The Nature Conservancy's ecoregional planning (The Nature Conservancy, 1996),
and the World Wildlife Fund's ecoregional conservation assessment (Ricketts et aI., 1999a) and
Global 200 (Olson and Dinerstein, 1998) initiatives. Although they differ in specific objectives
and scope, these efforts share an emphasis on representation of conservation targets (see also discussion in Reid, 1998) as the initial step of conservation planning. In contrast, RA aims at
representing processes as well as patterns. The four
strategies have in common some data requirements
and methods.
In practice, conservation scientists have emphasized different aspects of the design of conservation area networks, depending on the objectives. In
some cases, large, well-connected, unmanaged areas are thought to provide the best solution for the
Representativeness Assessments
long-term maintenance of biodiversity (e.g., Noss,
1992,1993; Noss and Cooperrider, 1994; DellaSala
et aI., 1995; Noss et aI., 1999; Soule and Terborgh,
1999a). In other cases, emphasis has been placed
on the importance of embedding conservation areas within a matrix of land managed according to
ecological principles to successfully sustain biodiversity (e.g., Alverson et aI., 1994). The latter emphasis is based on the implementation of the principles of ecosystem management at landscape and
regional levels (Christensen et aI., 1996; Jensen et
aI., 1996). Three conservation approaches use the
concept that well-managed ecosystems will maintain biodiversity: biodiversity management areas
(Davis et aI., 1996), diversity maintenance areas
(Alverson et aI., 1994), and emphasis-use (Everett
and Lehmkuhl, 1997). The general framework presented in this chapter provides the means to evaluate the impact of various aspects of network design on a case by case basis by including
assessment of biotic-environmental relationships
and suitability of land units at multiple scales, in
addition to representation of conservation targets
(Noss and Cooperrider, 1994; Christensen et aI.,
1996).
20.2.4 Is Representativeness Assessment
Relevant to Site Conservation
and Management?
RA is relevant to site conservation and management in two ways. First, it is used to identify networks of sites capable of sustaining all conservation targets. Second, it provides information on
biotic and environmental variation at multiple spatial and ecological scales to guide the design of
each individual conservation area. RA does not produce conservation area designs in the traditional
sense. The land areas selected during RA, as well
as their surroundings, need to be analyzed in a site
conservation planning process such as the framework developed by Poiani et ai. (1998). In contrast
to current practices, RA provides site conservation
planners with information that places the conservation and management activities of individual
conservation areas in the context of the sustainability of conservation targets within the entire
network. For example, landscapes within each conservation area in a regional network may be allowed to fluctuate within the bounds of natural disturbance regimes and other processes, and therefore
conservation targets may be lost locally within
some areas, but maintained or acquired within
others.