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FOR-76
Landscape Ecology and
Ecosystems Management
Thomas G. Barnes, Extension Wildlife Specialist
his publication introduces the concepts and Principles of Landscape Ecology
Tprinciples of landscape ecology for managing To understand landscape ecology, we have to
wildlife and other natural resources. It is intended focus on some of its important principles: land-
to raise public awareness and give an overview of scape composition, structure, function, and
a new philosophy and method for managing natu- change.
ral resources at the landscape level. • Composition involves the genetic makeup of
A landscape is a heterogenous area composed populations, identity and abundance of species
of a cluster of interacting ecosystems that are re- in the ecosystem, and the different types of
peated in various sizes, shapes, and spatial rela- communities present.
tionships throughout the landscape. Landscapes • Structure involves the variety of habitat patches
have different land forms, vegetation types, and or ecosystems and their patterns—the size and
land uses. Another way of looking at a landscape arrangement of patches, stands, or ecosystems—
is as a mosaic of habitat patches across which or- including the sequence of pools in a stream,
ganisms move, settle, reproduce, and eventually snags and downed logs in a forest, and vertical
die and return to the soil. The best way to envi- layering of vegetation.
sion a landscape is to look at the land from an • Function involves climatic, geological, hydro-
aerial perspective or to examine aerial photographs logical, ecological, and evolutionary processes
to see how a particular piece of land fits into the such as seed dispersion or gene flow.
larger picture. • Change involves the continual state of flux
Landscape ecology is the study of structure, present in ecosystems.
function, and change in a heterogenous land area
Figure 1. Landscapes composed of interacting ecosystems. It is an in- A landscape consists of three main compo-
consist of the matrix terdisciplinary science dealing with the interrela- nents: a matrix, patches, and corridors (Figure 1).
(the dominant feature), tionship between human society and our living If we understand these components and their in-
patches, and corridors that space. Landscape ecology is a relatively new sci- terrelationships, we can make better management
connect the patches. ence, although Europeans decisions at the landscape level.
have been using its prin-
Matrix ciples much longer than Matrix
Patch B Americans. We can learn
corridor a great deal from examin- The matrix, the dominant component in the
Patch A ing how the Europeans landscape, is the most extensive and connected
have taken an almost landscape type, and it plays the dominant role in
corridor completely human-domi- landscape functioning. If we try to manage a habi-
nated landscape and at- tat without considering the matrix, we will likely
tempted to restore fail to provide what wildlife need in that area.
Patch C ecological functions to its For instance, if your goal is to enhance the
systems. number of different species in a 40-acre forest
patch surrounded by soybean fields, you will not
create wildlife openings in the forest. That is, you
will not want to create more edge (the outer zone
of a patch that differs from its interior) because in
an agricultural matrix, any type of opening will
This publication is intended to be a companion to FOR-75, “An Ecosystems Approach create more and smaller forested patches in that
to Natural Resources Management.”
area, further reducing the amount of interior habi- It is well documented that adjacent habitats
tat available to the wildlife that need it. affect each other through changes in microcli-
The characteristics of matrix structure are the mates and the transfer of nutrients, materials, or
density of the patches (porosity), boundary shape, seeds, etc. between communities. These changes
networks, and heterogeneity. If an area has been ultimately affect ecological processes such as gene
broken up but the patches are fairly close together, flow and species composition in each community.
the patches are still dense enough to be useful for For example, breaking up the forest or creating
animal movement. However, if you open up a large openings in the forest matrix creates smaller for-
forested area by creating small openings, the est patches, with the matrix becoming open land
patches may not be dense enough to sustain cer- (Figure 3). Thus, fragmentation of forest patches
tain kinds of animals, and you could have a prob- results in drier microclimates, which:
lem with predation on other wildlife by raccoons, • alter species composition and favor exotic, in-
opossums, black rat snakes, or blue jays. A reduc- vasive species
tion in density might also increase nest parasitism • increase the susceptibility of windthrow of ex-
by brown-headed cowbirds on neotropical migrant isting trees
songbirds. We can illustrate how lack of density • exacerbate a loss of forest interior wildlife spe-
can create problems with brown-headed cowbirds. cies (like neotropical migrant songbirds)
Some parts of eastern Kentucky do not have a large • reduce the genetic diversity of the remaining
problem with brown-headed cowbirds because the populations, and
matrix there is forested land. However, these birds • allow for the invasion of exotic, weedy species.
pose a potential problem in other areas of eastern Ultimately, small preserves that are set aside
Kentucky where the matrix has been highly frag- for their content may fail unless people intervene
mented by coal mining, agriculture, and urban de- with intensive management, which is expensive
velopment (Figure 2). and time consuming. To refer again to the example
Boundary shape also has implications for of the glade, opening the surrounding forest habi-
neotropical migrant birds and edge species of wild- tat increases the kinds and numbers of exotic plant
life. The more uneven the boundary, the more species that overcome the rare plants unless in-
edge. Within matrix areas, networks connect habi- tensive, site-specific management like herbicide
tats of different size and shape, creating what is treatment, hand pulling, etc. is implemented.
called heterogeneity within the landscape. These Similarly, fragmenting the forest surrounding a
different habitat patches usually are replicated cave could alter the cave’s microclimate; certainly,
throughout the matrix. nonpoint source pollution would alter its climate
For example, the forests of eastern Kentucky vary and make the cave unsuitable for bats or other
by slope, landscape position, and soil type. Ridgetop unique organisms like blind cavefish.
forests are dominated by pine and oaks, cove sites
are mixed hardwood stands, south- and west-fac-
ing slopes are oak-hickory forest, etc. If a chance Patches
event like a tornado were to occur, it might tear up Patches are nonlinear surface areas that differ
one or two areas, but it would not wipe out all habi- in vegetation and landscape from their surround-
tat for a species because the same habitat type is ings. They are units of land or habitat that are
replicated several times in an area. The overall dam- heterogeneous when compared to the whole. They
age to wildlife would not be as great because that include four different types: disturbance, remnant,
type of habitat would still be close by. environmental resource, and introduced.
• Disturbance patches are either natural or artifi-
Context vs. Content cial. They result from various activities, includ-
When natural resources are managed at the land- ing agriculture, forestry, urbanization, and
scape level, context—where the biological element weather (i.e., tornados, hurricanes, ice storms,
is placed in the landscape—is just as important as etc.). If left alone, a disturbance patch will even-
content. In other words, you must consider the sur- tually change until it combines with the matrix.
rounding matrix when attempting to conserve an • Remnant patches result when humans alter the
area for its unique ecological attributes. Thus, if the landscape in an area and then leave parcels of
land is being set aside to preserve rare plants (such the old habitat behind. Remnant patches are
as wildflowers in a glade) or animals (such as bats generally more ecologically stable and persist
in a cave), the content—or community—we are longer than disturbance patches.
interested in is affected by the context of the envi- • Environmental resource patches occur because
ronment if the surrounding landscape is altered. of an environmental condition such as a wet-
land or cliff line.
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Figure 2. Eastern Kentucky forest matrix has been fragmented by Figure 3. Notice how the forested matrix has begun to be converted to an
mining, agriculture, and human habitation. “open lands” matrix.
• Introduced patches are ones in which people est. Thus, from a habitat standpoint, the first im-
have brought in nonnative plants or animals or portant concept is patch size, which determines
rearranged native species. Animals moving from how much energy can be stored in that patch as
one area to another can also bring in these well as the number of species that can reside there.
nonnative elements. A larger patch can normally support a larger num-
ber of species and a greater variety of habitat types
Patches as Islands (Figure 4).
Several aspects of patches are important from
an ecological perspective and affect landscape-level Worse Better
management decisions. The approach used most
often in analyzing patch habitats is to think of them Better
as islands. Much of the current thinking about land- Size
scape patch management has its roots in the theory
of island biogeography. This theory was developed
in 1967 by MacArthur and Wilson to explain the
patterns of species diversity on oceanic islands. It Shape
has also proven useful and applicable to a variety
of ecological situations because an island is simply
defined as a patch or parcel of favorable habitat
surrounded by unfavorable habitat. Just as wildlife Configuration
disperse to oceanic islands, terrestrial wildlife and
plants move between habitat islands. MacArthur
and Wilson’s theory suggests that various dispersal
events could therefore be predicted.
A key concept in MacArthur and Wilson’s Number
theory is that an equilibrium point exists in a popu- orse
W
lation between the rate that new species come in Figure 4. The size, shape,
and the rate that previously existing species become configuration, and number
extinct. Once this point is reached, the island’s of patches all affect the
populations of species are then maintained at this Patch Size and Edge Effect amount of interior habitat
equilibrium diversity. Island populations, then, have A concept getting closer consideration these in the patch. Small, single,
a tendency to “seek out” this equilibrium. days is the relationship between habitat patch size rectangular patches provide
Island size and relative isolation (distance to and the edge effect. In 1933, in Game Management, the last amount of interior
the mainland) affect both these rates and their Aldo Leopold wrote that creating edge and maxi- habitat, and large circular
equilibrium point. Relatively isolated and small mizing the amount of interspersion, or the juxta- patches provide the most
fragments offer the lowest equilibrium species di- position, of habitats was beneficial for wildlife. Held interior habitat.
versity, while nearby large islands offer the high- as dogma by wildlife biologists until recently, this
philosophy is unfortunately the most overused con-
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cept Leopold discussed. He stated that increasing migrants, the minimum patch size should be
the edge increases the number of wildlife species in 10,000 acres.
an area. However, if we look at things from a land- Patch shape is also important. A circular patch
scape perspective, edge is the one habitat not in minimizes the amount of edge compared to a thin,
short supply. Although edge is good for certain spe- rectangular strip patch, which has only a narrow
cies, particularly generalist or game species, it fa- band of interior habitat. If the strip is narrow
vors those species over interior species, or species enough, there is no interior habitat for interior
that require specific habitat types. species, and ultimately the diversity in the strip
Unfortunately, fragmented habitats with a large would be low.
percentage of edge can become an ecological trap. There are also functional ramifications related
These islands of habitat may look good for some to edges and patch size. In general, the higher the
species of birds to build their nests in, but they interior-to-edge ratio, the less patch border you
also attract a wide host of nest predators, includ- have, which decreases the amount of interaction
ing raccoons, skunks, opossums, blue jays, and rat with the surrounding matrix. A higher interior-
snakes. These animals decrease the nesting suc- to-edge ratio also:
cess of any birds in that area. For instance, in a • decreases the probability of barriers that could
recent study, scientists compared nesting success limit the movement of organisms
of loggerhead shrikes in fencerow habitat versus • decreases the probability of habitat diversity
those in more contiguous forested habitat. In within the patch, which would not necessarily
fencerow habitats, the bird’s nesting success be harmful because it would be natural, not
dropped almost to the point that they could not artificial, diversity
replace themselves due to nest predation. • decreases the importance of corridors for spe-
Additionally, patch size has implications for cies movement, as they are able to move more
neotropical migrant songbirds if the surrounding freely throughout the matrix
matrix is good habitat for brown-headed cowbirds. • increases species diversity and the total number
If present in the matrix (and they will be present of animals within the patch.
in an agricultural matrix), cowbirds will lay their A low interior-to-edge ratio would do exactly
eggs in the nests of neotropical migrant birds. The the opposite.
neotropicals cannot recognize the cowbirds’ eggs,
and they end up raising cowbirds rather than their
own species. Habitat Fragmentation
It is important to keep patches in the landscape One of the issues related to patch size is habi-
as large as possible because the habitat in shortest tat fragmentation. Fragmentation is a process that
supply in the landscape is contiguous forest or occurs along a continuum (Figure 5) in which a
grassland. An important consideration from a particular area is initially all one habitat type (a
landscape perspective is how to maximize patch forest, for example) and is eventually decreased
size and minimize the edge effect because nest until only isolated patches remain. It results in
parasitism begins to drop off significantly at 50 habitat loss and discontinuity and eventually leads
yards from a forest edge. Therefore, anything more to habitat isolation. Fragmentation ranges from
than 50 yards into a patch could be considered creation of small disturbance patches to wide-
interior habitat. spread habitat loss and insularization.
So, in a patch 100 yards across, how much would There are two components to fragmentation: 1)
be interior habitat? None would be interior habitat a decrease in the amount of interior habitat and 2)
because if you go 50 yards in on each side, there is a decrease in the connectivity between those habi-
nothing left. In general, as patches get larger, there tat patches. As an example, suppose we started out
is more interior habitat. And if a patch is large with all forestland; then, three farmers move in and
enough, there is significantly more interior habi- farm their small areas. As time passes, development
tat. But how big should habitat patches be to mini- creeps in, and the farms expand their agricultural
mize the influence of exotic or edge species? This base, resulting in larger gaps between habitat
requirement varies by species; nest parasitism by patches. At this point, the landscape is moving from
cowbirds, for example, may extend up to 900 yards a forest matrix to an agricultural matrix. In the be-
into the forest interior. There are no definitive ginning, there is still connectivity between forest
guidelines except “the bigger, the better.” patches even though it is narrow. At the endpoint
Furthermore, patch shape and configuration of the continuum, there is a totally different type
also influence how large the patches need to be. of habitat. From the wildlife standpoint, many of
Scientists estimate that if we are to maintain mini- the original species would have two options: move
mum viable populations for many neotropical to another area, or perish.
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