2.3 Landscape Ecology
considered landscape ecology because, while it
considered temporal dynamics, their important
work did not consider space.
Moreover, the spatial scale at which landscape
ecologists work is often considerably broader than
traditional ecology. Traditional plant ecology, for
example, has focused inordinately on scales of 1
square meter and one growing season. However,
the distribution, abundance, and processes affecting species at the community level are partly a
function of the landscape in which they live. By
acknowledging this interaction, a landscape study
adds spatial heterogeneity to a population, community, or ecosystem study. Expanding the spatial
scale can reveal how the distribution and abundance of species within a local community are influenced by the larger regional context in which it
is embedded. As larger areas are considered,
longer-term temporal processes become important
determinants of ecological dynamics.
Understanding phenomena within their spatial
context can provide important insight for management. The original efforts to save the Northern
Spotted Owl (Strix occidentalis caurina) in the
northwestern United States focused primarily on
the total amount of reserved habitat without COnsidering the ability of juveniles to disperse to suitable habitat within the landscape. Spatial models
led researchers to conclude that the original patchy
preserves were especially vulnerable to extinction
and showed that the arrangement and size of habitat patches on the landscape were as important as
the overall amount of habitat (Harrison et aI.,
1993). Thus, patch-level diversity at a larger scale
can influence species diversity and species distributions at local and regional scales.
The consequences of adding broad-scale spatial
heterogeneity and long-term temporal dynamics are
profound. The spatial dimension allows for integration across studies from studies of small organisms to regional analysis. It allows for the analysis
of impacts at scales different from those normally
incorporated into the system. Expanding the time
frame for temporal dynamics allows us to integrate
history, both abiotic and biotic, and the activities
and cultures of human beings into our analysis.
2.3.2 Landscape Structure, Function,
and Change
Three properties of landscapes are important for assessment. First, landscapes have structure. That is,
there are spatial relationships between elements.
The relationship may be between trees and gaps in
a forest. At a broader scale, there is a relationship
33
between forest and agricultural patches in a landscape mosaic. Landscapes have spatial continuity
between these elements, but they are not homogeneous. Landscapes exhibit spatial pattern and internal heterogeneity. It is this heterogeneity that is
of interest. The continuity of the landscape suggests
that it also has boundaries where landscape elements come together. Boundaries and barriers may
prevent particular species from responding to
changes by shifting between habitat types or sites,
and this in tum may result in decreased diversity
(Wiens et aI., 1985; Forman and Moore, 1992; Vos
and Opdam, 1993; Forman, 1995). Boundaries, natural and anthropogenic, are very important in designing research and monitoring for ecological
assessment.
Second, landscapes also have function. That is,
there are interactions among spatial elements.
These may be flows of energy, materials, species,
or genes among component elements of the landscape (Forman and Godron, 1986; Forman, 1995).
These ecological functions are often important in a
societal context. For instance, woodland corridors
have been shown to act as conduits for many
wildlife species. This may increase gene flow between interbreeding populations of important
species and so help to maintain species diversity.
A wetland or riparian zone may function as a filter for pollutants and maintain or increase water purity within the system (Forman, 1995).
Patterning and patchiness of both structure and
function can be recognized at virtually every scale
of investigation. Thus, landscapes may be of any
size. In fact, we suggest that the notion of landscape is scale independent in the same sense as
ecosystem is scale independent. This is a widely
held view (Allen and Hoekstra, 1992); however,
some researchers, among them Forman (1995),
hold that a landscape "is a mosaic where the mix
of local ecosystems or land uses is repeated in similar form over a kilometers-wide area" (Forman,
1995, p. 13). In this view, landscapes occupy a limited portion of the spectrum of ecological scales.
We find that the scale-independent definition of
landscapes is preferable because it can then be easily applied to any ecological property important for
assessment (Turner, 1995). The questions and purpose of the assessment will determine the relevant
scales.
Third, landscapes change. There is an alteration
of structure and function of the ecological mosaic
(the elements arrayed in space) over time. Clearly,
change is a natural process, and natural changes in
dynamical ecological systems are integrated from
the smallest organisms to the watershed and re-
considered landscape ecology because, while it
considered temporal dynamics, their important
work did not consider space.
Moreover, the spatial scale at which landscape
ecologists work is often considerably broader than
traditional ecology. Traditional plant ecology, for
example, has focused inordinately on scales of 1
square meter and one growing season. However,
the distribution, abundance, and processes affecting species at the community level are partly a
function of the landscape in which they live. By
acknowledging this interaction, a landscape study
adds spatial heterogeneity to a population, community, or ecosystem study. Expanding the spatial
scale can reveal how the distribution and abundance of species within a local community are influenced by the larger regional context in which it
is embedded. As larger areas are considered,
longer-term temporal processes become important
determinants of ecological dynamics.
Understanding phenomena within their spatial
context can provide important insight for management. The original efforts to save the Northern
Spotted Owl (Strix occidentalis caurina) in the
northwestern United States focused primarily on
the total amount of reserved habitat without COnsidering the ability of juveniles to disperse to suitable habitat within the landscape. Spatial models
led researchers to conclude that the original patchy
preserves were especially vulnerable to extinction
and showed that the arrangement and size of habitat patches on the landscape were as important as
the overall amount of habitat (Harrison et aI.,
1993). Thus, patch-level diversity at a larger scale
can influence species diversity and species distributions at local and regional scales.
The consequences of adding broad-scale spatial
heterogeneity and long-term temporal dynamics are
profound. The spatial dimension allows for integration across studies from studies of small organisms to regional analysis. It allows for the analysis
of impacts at scales different from those normally
incorporated into the system. Expanding the time
frame for temporal dynamics allows us to integrate
history, both abiotic and biotic, and the activities
and cultures of human beings into our analysis.
2.3.2 Landscape Structure, Function,
and Change
Three properties of landscapes are important for assessment. First, landscapes have structure. That is,
there are spatial relationships between elements.
The relationship may be between trees and gaps in
a forest. At a broader scale, there is a relationship
33
between forest and agricultural patches in a landscape mosaic. Landscapes have spatial continuity
between these elements, but they are not homogeneous. Landscapes exhibit spatial pattern and internal heterogeneity. It is this heterogeneity that is
of interest. The continuity of the landscape suggests
that it also has boundaries where landscape elements come together. Boundaries and barriers may
prevent particular species from responding to
changes by shifting between habitat types or sites,
and this in tum may result in decreased diversity
(Wiens et aI., 1985; Forman and Moore, 1992; Vos
and Opdam, 1993; Forman, 1995). Boundaries, natural and anthropogenic, are very important in designing research and monitoring for ecological
assessment.
Second, landscapes also have function. That is,
there are interactions among spatial elements.
These may be flows of energy, materials, species,
or genes among component elements of the landscape (Forman and Godron, 1986; Forman, 1995).
These ecological functions are often important in a
societal context. For instance, woodland corridors
have been shown to act as conduits for many
wildlife species. This may increase gene flow between interbreeding populations of important
species and so help to maintain species diversity.
A wetland or riparian zone may function as a filter for pollutants and maintain or increase water purity within the system (Forman, 1995).
Patterning and patchiness of both structure and
function can be recognized at virtually every scale
of investigation. Thus, landscapes may be of any
size. In fact, we suggest that the notion of landscape is scale independent in the same sense as
ecosystem is scale independent. This is a widely
held view (Allen and Hoekstra, 1992); however,
some researchers, among them Forman (1995),
hold that a landscape "is a mosaic where the mix
of local ecosystems or land uses is repeated in similar form over a kilometers-wide area" (Forman,
1995, p. 13). In this view, landscapes occupy a limited portion of the spectrum of ecological scales.
We find that the scale-independent definition of
landscapes is preferable because it can then be easily applied to any ecological property important for
assessment (Turner, 1995). The questions and purpose of the assessment will determine the relevant
scales.
Third, landscapes change. There is an alteration
of structure and function of the ecological mosaic
(the elements arrayed in space) over time. Clearly,
change is a natural process, and natural changes in
dynamical ecological systems are integrated from
the smallest organisms to the watershed and re-