Ecological Applications, 17(4), 2007, pp. 974–988
? 2007 by the the Ecological Society of America
ECOLOGICAL MECHANISMS LINKING PROTECTED AREAS
TO SURROUNDING LANDS
ANDREW J. HANSEN1,3AND RUTH DEFRIES2
1Ecology Department, Montana State University, Bozeman, Montana 59717-3460 USA
2Department of Geography and Earth Systems Science Interdisciplinary Center, 2181 Lefrak Hall,
University of Maryland, College Park, Maryland 20742 USA
many of the world’s protected areas. The influence of this land use change on ecological
processes is poorly understood. The goal of this paper is to draw on ecological theory to
provide a synthetic framework for understanding how land use change around protected areas
may alter ecological processes and biodiversity within protected areas and to provide a basis
for identifying scientifically based management alternatives. We first present a conceptual
model of protected areas embedded within larger ecosystems that often include surrounding
human land use. Drawing on case studies in this Invited Feature, we then explore a
comprehensive set of ecological mechanisms by which land use on surrounding lands may
influence ecological processes and biodiversity within reserves. These mechanisms involve
changes in ecosystem size, with implications for minimum dynamic area, species–area effect,
and trophic structure; altered flows of materials and disturbances into and out of reserves;
effects on crucial habitats for seasonal and migration movements and population source/sink
dynamics; and exposure to humans through hunting, poaching, exotics species, and disease.
These ecological mechanisms provide a basis for assessing the vulnerability of protected areas
to land use. They also suggest criteria for designing regional management to sustain protected
areas in the context of surrounding human land use. These design criteria include maximizing
the area of functional habitats, identifying and maintaining ecological process zones,
maintaining key migration and source habitats, and managing human proximity and edge
Land use is expanding and intensifying in the unprotected lands surrounding
protected areas; vulnerability.
ecological processes; ecosystem size; edge effects; habitat; land use change; management;
Human societies have long set aside tracts of land to
conserve nature in the form of hunting reserves, religious
forests, and common grounds (Chandrashekara and
Sankar 1998). The current concept of national parks
evolved in the mid 1800s as European colonists were
converting native landscapes to farms, ranches, and
cities (Schullery 1997). A key goal was the protection of
nature. By minimizing the influence of humans, natural
ecosystems were expected to continue to maintain
ecological processes and native species.
During the 20th century, protected areas became a
cornerstone of the global conservation strategy. New
protected areas continue to be established: the total
number globally has doubled since 1975 (Ervin 2003a).
The term ‘‘protected area’’ refers to any area of land or
sea managed for the persistence of biodiversity and
other natural processes in situ, through constraints on
incompatible land uses (Possingham et al. 2006). The
basic role of protected areas is to separate elements of
biodiversity from processes that threaten their existence
in the wild (Margules and Pressey 2000). Recent
assessments have found that most terrestrial reserves
are adequately protected within their borders (Bruner
et al. 2001, DeFries et al. 2005).
Despite the high level of protection afforded national
parks and other protected areas, many are not
functioning as originally envisioned. Critical ecological
processes such as fire, flooding, and climate regimes have
been altered (Lawton et al. 2001, Pringle 2001). Exotic
species are increasingly invading protected areas
(Stohlgren 1998), and some native species have gone
extinct in protected areas (Newmark 1987, 1995, 1996,
Rivard et al. 2000, Brashares et al. 2001). For example,
11 of 13 national parks in the western United States
have lost large mammal species since park establish-
ment, with 5–21.4% of original species lost (Parks and
Why are many protected areas not functioning well,
despite adequate management within their borders? A
major reason may be that human land use is expanding
Manuscript received 2 August 2005; revised 22 March 2006;
accepted 17 July 2006; final version received 23 September 2006.
Corresponding Editor: M. Friedl. For reprints of this Invited
Feature, see footnote 1, p. 972.
Vol. 17, No. 4
and intensifying on the lands surrounding protected
areas, resulting in changes in ecological function and
biodiversity within protected areas.
Recent satellite-based change analyses are revealing
that human populations and intense land use have
grown rapidly in recent decades around many protected
areas (Hansen et al. 2004). In the tropics, road
construction, conversion for agriculture, and demand
for natural resources are leading to clearing of primary
forest around reserves (Mustard et al. 2004) and
increased hunting of native species (Escamilla et al.
2000). DeFries et al. (2005) found that 66% of 198
reserves in the humid tropics had undergone loss of
forest habitat in the surrounding lands since 1980, with
an average loss rate of 5% per decade within 50 km of
the boundary. In other areas, increases in wealth,
technology, and population density are leading to more
rural settlement in previously wild areas. In the United
States since 1950, for example, rural residential develop-
ment was the fastest growing land use type and now
covers 25% of the lower 48 states (Brown et al. 2005).
Some protected areas are magnets for such rural
development (Chown et al. 2003). The counties around
the Yellowstone National Park, for example, are among
the fastest growing in the United States (Rasker and
Hansen 2000). Even in long-established societies such as
in China, agricultural and urban land uses continue to
push into unprotected wildlands around protected areas
(Vin ˜ a et al. 2007).
In recent decades, ecologists have come to realize that
human impacts on surrounding lands may cross the
boundaries into protected areas (Buechner 1987, Das-
mann 1988, Schonewald-Cox 1988). The creation of
buffer zones around protected areas was recommended
to minimize negative boundary influences (Noss 1983).
Accordingly, UNESCO’s Man and the Biosphere
(MAB) program advocated managing the lands around
protected areas along a gradient of decreasingly intense
land use toward protected area boundaries (UNESCO
1974). More recently, methods have been developed to
evaluate the effectiveness of protected areas, with
consideration of human activities on surrounding lands
(Hockings 2000, TNC 2000, Ervin 2003b). For some
protected areas that are not functioning adequately,
‘‘systematic conservation planning’’ (Margules and
Pressey 2000) has been used to guide management of
the regions around protected areas to better achieve
conservation objectives (e.g., Pressey et al. 2003).
Such efforts to mitigate boundary influences on
protected areas will be most effective if based on
scientific understanding of the underlying ecological
mechanisms. It can be difficult to ascertain the means by
which human activities outside of protected areas,
sometimes tens to hundreds of kilometers away, can
impact ecological function and biodiversity within
protected areas. Knowledge of these ecological con-
nections could help to answer several management-
oriented questions. How large is the zone of influence
around a protected area? Are all locations within this
zone of influence equally important to protected area
functioning? Which ecological processes or species of
organisms within protected areas are particularly
sensitive to surrounding land use? Which land use types
and intensities are most likely to have negative impacts
within protected areas?
Advances in spatial ecology have allowed an increas-
ing understanding of the ecological mechanisms con-
necting protected areas to surrounding lands. Island
biogeography theory, for example, provides a basis for
predicting extinction rates of species as a function of
habitat fragmentation (Brooks et al. 1999). This theory
can be applied to address the effects of habitat loss
outside of protected areas on species richness within
protected areas (DeFries et al. 2005). Metapopulation
theory provides a basis for determining whether a
subpopulation of a species within a protected area is
dependent upon population source areas located in
surrounding lands (Sinclair 1998, Hansen and Rotella
2002). The purpose of this paper is to draw from diverse
studies of spatial ecology to derive a comprehensive
overview of the ecological mechanisms by which land
use outside of protected areas may influence ecology and
biodiversity with protected areas. This synthesis is meant
to enhance the theoretical underpinning of efforts to
assess the effectiveness of protected areas (e.g., Parrish
et al. 2003) and systematic conservation planning across
regions including protected areas (Margules and Pressey
Our central thesis is that protected areas are often
parts of larger ecosystems and that land use change in
the unprotected portion of the ecosystem may rescale
the ecosystem, leading to changes in the functioning and
biodiversity within the reserve. We first present a
conceptual model of protected areas embedded within
larger ecosystems that often include surrounding human
land use. We then explore the key ecological mecha-
nisms by which this land use on surrounding lands may
influence ecological processes and biodiversity within
reserves. These mechanisms involve ecosystem size,
ecological process zones, crucial habitats, and exposure
to humans. A concluding section suggests how these
ecological mechanisms provide a basis for assessing the
effectiveness of protected areas and systematic conser-
vation planning across protected areas and surrounding
The case studies in the papers that follow provide
more detailed examples of ways in which land use can
influence protected areas. The management implications
of these interactions are developed further in DeFries
et al. (2007).
PROTECTED AREAS AS PARTS OF LARGER ECOSYSTEMS
Protected areas sometimes exclude a portion of the
area that is needed to maintain essential ecological
processes and organisms. This was recognized by scien-
tists studying large mammals with large home ranges that
June 2007975LAND USE CHANGE AROUND PROTECTED AREAS
extended outside national parks (Wright and Thompson
1935, Craighead 1979, Newmark 1985). More recently,
ecologists have established that the spatial domains of
ecological processes such as natural disturbance and
nutrient cycling may extent outside park boundaries
(Grumbine 1990). Because protected areas were often
designated based on factors other than ecological
completeness, such as scenic value (Pressey 1994, Scott
et al. 2001), they sometimes do not include the areas
required to maintain disturbance regimes, nutrient flows,
organism movements, and population processes within
them (Fig. 1a). Following establishment, protected areas
may continue to function as parts of larger ecosystems
because surrounding lands remain undeveloped and
continue to provide functional habitats. If land use
change reduces habitats in the unprotected portion of the
ecosystem, ecosystem function and biodiversity may be
degraded within the protected area. The modern concept
of ecosystem management grew from the goal of
managing regional landscapes to maintain the ecological
integrity of the protected areas that they contain (Agee
and Johnson 1988, Grumbine 1994).
How can the spatial dimensions of the effective
ecosystem encompassing a protected area be quantified?
If the goal of the protected area is to maintain native
species and the ecological processes that they require,
then the spatial extent of the effective ecosystem includes
the area that strongly influences these species and
processes (Grumbine 1990). This area can be mapped
based on the flows of materials, energy, and organisms.
Watershed boundaries are often used to define the extent
of aquatic ecosystems (Pringle 2001). Watersheds
encompass the area of movement of ground and surface
water. Water carries nutrients such as nitrogen and
phosphorous, which are critical to plant and animal
growth. Water also serves as a conduit for the move-
ments of many aquatic and terrestrial organisms. Hence,
strong interactions among many components of an
ecosystem may occur within watersheds. Natural dis-
turbances such as wildfire move across landscapes from
initiation zones to run-out zones and differentially
influence soils, vegetation, and animal habitats within
these zones (Baker 1992). Ecosystem boundaries can be
delineated based on homogeneity of disturbance regimes
(Pickett and Thompson 1978). Similarly, many organ-
larger ecosystem with energy, materials, and/or organisms flowing through the ecosystem. (b) Land use change reduces effective size
of the ecosystem. (c) Land use change alters ecological flows. (d) Land use change eliminates unique habitats and disrupts source–
sink dynamics. (e) Edge effects from land use negatively influence the park.
Conceptual model illustrating the effects of land use change on ecosystem function. (a) Protected areas as part of a
Vol. 17, No. 4
isms move predictably across the landscape, for exam-
ple, to gain access to seasonal resources. Ecosystem
boundaries can be defined based on these movements or
on the area required to maintain particular population
levels of these organisms (Newmark 1985).
In practice, defining the actual boundaries of an
ecosystem is subjective. Although the flows of water,
nutrients, disturbance, and organisms are often interre-
lated, their spatial dimensions are often not identical.
Water and nutrients may be well represented within
watershed boundaries, but organisms may migrate
among watersheds. Hence, it is often difficult to define
a particular ecosystem boundary that is adequate for all
components of the ecosystem. Also, the strength of
interaction must be considered when defining an
ecosystem. Ecological processes and organisms in a
particular location are often strongly linked to some
places, weakly linked to other places, and not linked to
still other places. For example, climate in the Caribbean
is heavily influenced by regional factors and is weakly
linked to Saharan Africa via input of wind-borne loess
(Prospero and Lamb 2003). Thus ecosystem boundaries
are necessarily abstractions that reflect the human choice
of the ecosystem property of focus and the strength of
interactions used in the definition.
In a growing number of examples, protected-area-
centered ecosystems have been defined (see Meffe et al.
2004). For example, the Greater Serengeti Ecosystem
has been defined based on the migratory patterns of the
dominant herbivore, the wildebeest (Sinclair 1995; see
regimes, and organism movements (modified from Hansen et al.  and Gude et al. ). Shown are land allocation,
movement pathways for two migratory species, areas of high predicted bird diversity (biodiversity hotspots), and exurban
development (rural homes). The biodiversity modeling mask refers to locations too high in elevation to be within the domain of the
bird diversity predictions.
Depiction of the Greater Yellowstone Ecosystem as defined based on the biophysical gradients, natural disturbance
June 2007977 LAND USE CHANGE AROUND PROTECTED AREAS
Plate 1). Although Serengeti National Park is insuffi-
cient to maintain the wildebeest and other migratory
mammals within it, the network of wild and semi-wild
public and private lands across the Greater Serengeti
Ecosystem may be nearly large enough to maintain these
populations (Packer et al. 2005; but see Serneels and
Lambin 2001). The Greater Everglades Ecosystem has
been defined to encompass the massive contiguous area
of freshwater slowly flowing seaward in southern
Florida. Everglades National Park includes only a
portion of this large watershed and ecological processes
within it are strongly influenced by unprotected lands
higher in the watershed (NAS 2003). The Greater
Yellowstone Ecosystem, including Yellowstone Nation-
al Park, was defined largely by gradients in topography,
climate, and soils, and the resulting movement of
wildfire and organisms (Keiter and Boyce 1991, Hansen
et al. 2002, Noss et al. 2002). Centered on the Yellow-
stone Plateau and surrounding mountains, natural
disturbance regimes and organisms move across the
elevational gradient from valley bottoms to high
mountains in response to climate and vegetation
productivity (Fig. 2). In these cases, knowledge of the
spatial domain of strong ecological interactions between
protected areas and the surrounding areas has allowed
for specification of the larger effective ecosystem. The
term ‘‘greater ecosystem’’ is often used to describe these
protected-area-centered ecosystems (Keiter and Boyce
Recognizing that protected areas are often parts of
larger ecosystems helps to clarify the effects of land use.
Agriculture, settlement, and other human land uses in
the unprotected part of the ecosystem may alter the
flows of energy, materials, and organisms across the
ecosystem in ways that change ecological functioning
within the reserve (Fig. 1b–e). If, for example, the
portion of the ecosystem where wildfire tends to ignite is
converted agriculture, fire may less frequently spread
into the protected area and alter vegetation succession.
Similarly, if land use decreases the area of suitable
habitats for a wildlife population below some threshold,
the population size may fall to the point where
extinction is likely. Moreover, land use near a protected
area may introduce novel disturbances to which the
ecosystem is not adequately adapted. Human hunting
and intense outdoor recreation are examples. Given that
human land use is rapidly expanding and intensifying in
the unprotected parts of many protected area ecosys-
tems, it is critical that we better understand its effects.
Knowledge of the mechanisms connecting land use to
protected areas can provide an objective basis for
defining the spatial domain of the effective ecosystem
encompassing protected areas and for managing the
unprotected lands to maintain ecological function and
biodiversity within protected areas.
MECHANISMS LINKING LAND USE TO PROTECTED AREAS
Advances in ecological theory have allowed increased
understanding of how the spatial patterning across
landscapes and regions influences local ecosystems
(Turner et al. 2001). Island biogeography, species–area
relationships, metapopulation dynamics, disturbance
ecology, and landscape ecology have increasingly been
applied to questions of conservation biology, including
herd. Many other protected areas include only a portion of area required by migratory species. Wildlife in such protected areas is
especially vulnerable to land use intensification on the surrounding lands. Photo credit: A. Hansen.
Serengeti National Park, Tanzania, was designed to include most of the migratory range of the Serengeti wildebeest
Vol. 17, No. 4
the design of nature reserves (Pressey et al. 1993, Noss
and Cooperrider 1994, Prendergast et al. 1999). These
bodies of theory can also be applied to understanding
how changes in the unprotected parts of greater
ecosystems may influence protected areas. Here we
synthesize across these bodies of theory to develop a
simple conceptual framework for understanding how
changes surrounding protected areas alter the ecological
processes within them. According to our framework,
four general mechanisms link human land uses with
ecological function within protected areas. These mech-
anisms involve effective size of the ecosystem, flows of
ecological process zones, crucial habitats, and exposure
to humans at reserve edges (Table 1). We will describe,
for each of mechanisms, the various forms in which they
may be expressed, the conceptual basis, and illustrative
Effective size of ecosystem
We refer to ‘‘effective size’’ of the ecosystem as the
area that includes ecological processes and organisms
integral to the protected area. This often is correlated
with the area of wild and semi-wild habitats within and
surrounding the protected area. By reducing this
effective size, land use can negatively influence both
ecological processes and community diversity and
structure (Fig. 1b).
Minimum dynamic area.—Island biogeography theory
suggests that the number of species in a nature reserve
results from the balance between colonization and
extinction. If protected areas are increasingly isolated
from external colonization sources, ‘‘extinction will then
become the dominant population process affecting
equilibrium in reserves and species numbers will decline
to a new level,’’ according to Pickett and Thompson
(1978:28). Hence it is critical to maintain recolonization
sources within protected areas. Natural disturbance is a
key force in driving patch dynamics within and among
protected areas and resources available to organisms.
Landslides, floods, wildfires, and hurricanes initiate
succession and maintain resources for species associated
with each seral stage. Bormann and Likens (1979) used
TABLE 1. General mechanisms by which land use surrounding protected areas alters ecological processes within reserves.
and type DescriptionExamples
Change in effective size of
Minimum dynamic areaTemporal stability of seral stages is a function of the
area of the reserve relative to the size of natural
As wild habitats in surrounding lands are destroyed, the
functional size of the reserve is decreased and risk of
extinction in the reserve is increased.
Hurricanes in Puerto Rico
Fragmented forests in Kenya
(Brooks et al. 1999); harvest
of primary forest outside
Calakmul Biosphere Reserve,
Mexico (Vester et al. 2007).
Loss of predators on Barro
Colorado Island (Terborgh
et al. 2001).
Trophic structure Characteristic spatial scales of organisms differ with
trophic level such that organisms in higher levels are
lost as ecosystems shrink.
Change in ecological flows
into and out of reserve
Initiation and run-out
Key ecological processes move across landscapes.
Initiation and run-out zones for disturbance may lie
Land use in upper watersheds or airsheds may alter flows
into reserves lower in the watershed or airshed.
Fire in Yellowstone National
Park (Hansen and Rotella
Rainfall in Monte Verde cloud
forest (Lawton et al. 2001).
Location in watershed or
Loss of crucial habitat
outside of reserve
Seasonal and migration
Lands outside of reserves may contain unique habitats
that are required by organisms within reserves.
Organisms require corridors to disperse among
reserves or to migrate from reserves to ephemeral
Large mammals in the Greater
Serengeti (Serneels and
Lambin 2001); antelope in
Greater Yellowstone (Berger
Increased exposure to
humans at park edge
Unique habitats outside of reserves are population source
areas required to maintain sink populations in
Negative human influences from the reserve periphery
extend some distance into protected areas.
Birds around Yellowstone
National Park (Hansen and
Eurasian badgers in Donana
Park (Revilla et al. 2001);
spread of disease from pets
to lions in Serengeti National
Park (Packer et al. 1999).
June 2007979LAND USE CHANGE AROUND PROTECTED AREAS
the term ‘‘shifting steady-state equilibrium’’ to define
landscapes where disturbance was adequate to maintain
each seral stage in relatively constant proportion over
time. The location of disturbance shifts across the
landscape over time, but the representation of early-
and late-seral patches across the landscape remains
within a steady state. Such landscapes can support
relatively high numbers of organisms because recoloni-
zation sources are continuously maintained for species
requiring either early- or late-seral conditions.
Pickett and Thompson (1978:27) defined ‘‘minimum
dynamic area’’ as ‘‘the smallest area with a natural
disturbance regime, which maintains internal recoloni-
zation sources, and hence minimizes extinction.’’ In
other words, minimum dynamic area is the smallest area
within which the natural disturbance regime maintains a
shifting steady-state equilibrium.
As land use change reduces the effective size of the
ecosystem containing a protected area, the ecosystem is
increasingly likely to fall below the minimum dynamic
area (Baker 1989). In this case, the protected area itself
will be too small to maintain a dynamic steady-state
equilibrium under the influence of natural disturbance.
At this point, recolonization sources for species are lost
and extinction rates will rise. How big does an ecosystem
need be to maintain a dynamic steady-state equilibrium?
Shugart (1984) and Baker (1992) suggested that a
landscape needs to be at least 50 times larger than the
area of the largest disturbance to maintain this
We are not aware of any studies that have docu-
mented a change in effective ecosystem size resulting in
loss of minimum dynamic area and loss of species within
a protected area. Baker (1989) found that the Boundary
Waters Canoe Area in northern Minnesota was not
large enough to maintain a fire-induced steady-state
equilibrium. Wimberly et al. (2000) found that the
minimum dynamic area induced by fire in the Oregon
Coast Range in pre-European settlement times was
larger than the old-growth forest reserves maintained
today. McCarthy and Lindenmayer (1999, 2000) used
spatially explicit population viability models to estimate
the minimum size of protected areas needed to maintain
viable populations of forest marsupials in Australia
under various disturbance regimes.
Species–area effects.—A well-known tenet of island
biogography theory is that the number of species that
are found on an oceanic island or in a habitat fragment
is a function of its area. A large body of empirical
evidence indicates that the number of species (termed
species richness), S, increases with area A, according to
the equation S¼cAz, where c and z are constants (e.g.,
Rosenzweig 1995). Hence, species richness increases with
island or habitat area, at a decelerating rate for larger
areas. The primary explanation is that a given species is
less likely to go extinct if the area of suitable habitat is
large enough to provide the resources to allow for a
population size larger than a minimum viable popula-
tion below which risk of extinction is elevated (Pimm
et al. 1988).
The species–area relationship has been used to predict
the consequences of reducing the size of a habitat
through conversion to intensive land uses (for a review,
see Cowlishaw 1999). A contraction in habitat from its
original area to its new area is predicted to lead to a
decline from the original number of species to a new
total based on the size of the fragment. This number is
expected to be further reduced through time as the
effects of isolation lead to local extinctions within the
fragment, due to small population sizes. In a test of this
approach, Brooks et al. (1999) surveyed birds in upland
forest fragments in Kenya. They compared current
species richness for forest birds with that from the time
prior to habitat fragmentation, using museum records.
They found that each of the five habitat fragments had
undergone extinctions of forest birds and that the
number of extinctions was close to that predicted, based
on the change in area.
Following habitat fragmentation, the relaxation to the
new reduced species richness may take decades to
centuries or more (Burkey 1995, Brooks et al. 1999).
The term ‘‘extinction debt’’ is used to denote the number
of species that are expected to become extinct as the
community adjusts to a new, smaller, area of habitat. In
the New World tropics, deforestation is sufficiently
recent that few extinctions have yet occurred. In
confirmation of the species–area approach, however,
Brooks and Balmford (1996) and Brooks et al. (1997)
found that the predicted number of extinctions for
Atlantic forests of South America and insular Southeast
Asia closely matched the numbers of species currently
listed as threatened with extinction. In tropical forests of
Africa, Cowlishaw (1999) predicted that current defor-
estation will eventually result in the extinction of .30%
of the forest primate fauna in each of several countries.
The implication of the species–area relationship for
protected areas is that the number of species in a
protected area will decline as the effective size of the
reserve is reduced through destruction of the unpro-
tected habitats surrounding the reserve. This point was
illustrated by Pimm and Raven (2000). They focused on
biodiversity hotspots around the world identified by
Myers et al. (2000). These hotspots have already suffered
disproportionate loss of primary vegetation, meaning
that the many species they contain are under particular
threat of extinction. Using the species–area relationship,
Pimm and Raven (2000) predicted that more species
would be lost if only hotspots now in a protected status
were saved than if all hotspot habitats (both inside and
outside protected areas) were saved.
The species–area approach was applied to three of the
case study locations reviewed in this Invited Feature:
Maasai East Africa, Southern Yucata ´ n, and Greater
Yellowstone (H. L. Rustigian et al., unpublished manu-
script). Habitats that had been deforested and converted
to agriculture, settlements, or rural dispersed homes
Vol. 17, No. 4
since pre-European settlement times were considered not
suitable for native bird and mammal species. Based on
loss of habitats from pre-European settlement times, the
ecosystem around each park, they predicted a loss of 5–
14% of species among the sites (Table 2). If all
unprotected habitats were converted to human land
uses, 9–35% of species were predicted to be lost.
A limitation of the species–area approach to estimat-
ing fragmentation effects is that species differ in their
tolerance to the type and intensity of human land use.
Many native species find suitable habitat in human-
altered landscapes and some of these species become
more abundant under certain land uses (McKinney
2002). The approach will be most effective if it is applied
to species that are unable to tolerate the human-induced
changes to the unprotected portion of the ecosystem.
The approach will also be more accurate if the quality of
lost habitats is considered. Vester et al. (2007) found that
tall primary forest has been disproportionately de-
stroyed in the southern Yucata ´ n region. Several species
of trees and butterflies are uniquely associated with this
forest type and may have been disproportionately
affected by its loss in area.
Trophic structure.—A third consequence of reducing
the effective size of nature reserves is an altered
representation of organisms at various levels of the
food chain. Perhaps the most typical case is the loss of
high-level predators and the release of meso-level
predators or herbivores. Home range size and density
are associated with level in the food chain. Top
predators tend to have relatively large home range
requirements and low densities. Consequently, they are
particularly sensitive to extinction as effective reserve
size decreases (Schonewald-Cox 1988, Woodroffe and
Perhaps the most direct evidence that trophic
structure in protected areas varies with effective size of
ecosystem comes from correlational studies of species
extinction in protected areas of differing size. Rivard
et al. (2000) found that extinction rates of mammals in
Canadian national parks were associated both with park
area and with the extent of intense land use outside of
parks. Moreover, they found that species with large
home ranges, typical of species at higher trophic levels,
were more likely to suffer extinction. Evidence for
similar patterns in aquatic systems comes from Post
et al. (2000), who studied trophic structure in 25 north-
temperate lakes. They found that the length of food
chains was positively related to ecosystem size (size of
the lake). Specifically, higher trophic levels were more
commonly found in larger lakes.
In some systems, these top predators influence the
abundance of organisms lower in the food chain with
cascading effects throughout the ecosystem. Hence, loss
of the top predators may allow meso predators or
herbivores to become increasingly abundant. This effect
on trophic structure was documented in a study of island
habitat fragments created by a water impoundment
project in Venezuela (Terborgh et al. 2001). Vertebrate
predators went extinct on small- and medium-sized
islands but remained on larger islands. Densities of seed
predators and herbivores were 10–100 times higher than
those on the mainland, probably due to the release from
predation. These changes cascaded through the food
chain, resulting in severe reductions in densities of
canopy tree seedlings and saplings.
Trophic cascades associated with top predators are
also suggested in the Greater Yellowstone Ecosystem.
The recent reintroduction of the wolf (Canus lupis), a top
predator that had been extinct for 60 years, appears to
be expanding the scavenger community, reducing
mesocarnivores and ungulate population sizes, releasing
the riparian plant community that was overbrowsed by
ungulates, and allowing for expansion of riparian-
dependent bird communities (Ripple and Beschta 2004).
Thus, reduction in the effective size of a protected
area is predicted to result in losses in species due to
change in landscape dynamics, species–area effects, and
loss of top carnivores. As the unprotected lands around
nature reserves are increasingly converted to intense
human land uses, effective ecosystem size is reduced. For
relatively few protected areas do we know the effective
size of the ecosystem and the rate of loss to human land
use. Rustigan et al. (unpublished data) found that, for
three case study landscapes, the loss rate since presettle-
ment times was substantial: 11%, 30%, and 45% for
Greater Yellowstone, Mayan Forest, and Greater
Serengeti ecosystems have been converted to intense
Ecological process zones
Justas organismsmove acrosslandscapes atcharacter-
istic scales, ecological processes result in flows of energy
and materials along predictable pathways. These flows
remaining habitat and habitat remaining if all unprotected lands are converted to human land uses.
Loss of habitat since pre-European settlement times and predicted extinctions of birds and mammals under current
No. (and %) species predicted extinct
Maasailand, East Africa
Greater Yellowstone, USA
Mayan Forest, southern Yucata ´ n Peninsula
Notes: Data are from H. L. Rustigian et al. (unpublished manuscript). Richness is the number of species.
June 2007 981 LAND USE CHANGE AROUND PROTECTED AREAS
may be important to ecological function in influencing
localecological processessuchasprimary productivity or
habitat suitability. To the extent that land use conversion
and intensification alters ecological flows across the
landscape, it may impact the ecological functioning and
biodiversity within protected areas (Fig. 1c).
Disturbance initiation and run-out zones.—Disturb-
ances tend to be initiated in particular landscape settings
and move to other locations in the landscape. Inter-
actions between the location where disturbance gets
started (initiation zones) and locations where disturb-
ances move to (run-out zones) influence the nature of the
disturbance regime in an area (Baker 1992). In south-
western Montana, for example, lightning strikes occur
across the landscape, but more frequently ignite fires in
dry valley-bottom grasslands than in moist conifer
forests in the uplands (Arno and Gruell 1983). These
fires then spread upslope to the conifer forests. Thus, the
juxtaposing of grasslands and conifer forests strongly
influences the regional fire regime. Local disturbance
regimes can best be maintained in protected areas that
include the disturbance initiation zones within their
boundaries (Baker 1992). In the case of the Montana
example, a protected area placed only in the upland
conifers may suffer more or less frequent fire, depending
on the management of the valley-bottom grasslands
outside of the protected area.
It is also important to include disturbance run-out
zones within the boundaries of protected areas. Run-out
zones may contain unique abiotic conditions and habitat
patterns important to ecological processes and organ-
isms. For example, flood severity often increases from
headwaters to large floodplains. The large scours and
bare gravel bars and the mosaic of seral stages that form
on floodplains support high levels of biodiversity (Saab
1999). A protected area that does not contain this
disturbance run-out zone will not include these unique
riparian vegetation communities. In protected areas that
omit either the initiation or run-out zones, human
manipulation of disturbance may be required to main-
tain landscape patterns and organisms (Baker 1992,
Arcese and Sinclair 1997).
Location in watershed or airshed.—Protected areas
may be heavily influenced by hydrologic flows and
weather systems. For example, protected areas through-
out the world are threatened by cumulative alterations
in hydrologic connectivity within the larger landscape
(Pringle 2001). Humans are altering hydrologic flows
directly by dams, water diversions, groundwater extrac-
tion, and irrigation, and indirectly by altering land
cover, which may change rates of transpiration, runoff,
and soil storage. These flows of water transport energy,
nutrients, sediments, and organisms.
The location of a given protected area within a
watershed, relative to regional aquifers and wind and
precipitation patterns, can play a key role in its response
to human disturbance transmitted through the hydro-
logic cycle. Protected areas located in middle and lower
watersheds often experience altered flow regimes and
inputs of exotic organisms and pollution from upstream.
The Colorado River within Grand Canyon National
Park, for example, has undergone a dramatic trans-
formation due to dams and intense land use in the
headwaters of the watershed (Cohn 2001). Altered water
temperatures and loss of flood deposition of sediments
have changed habitats, leading to a substantial reduc-
tion of native fishes. Waterborne seeds of exotic plants
such as saltcedar (Tamarix spp.) have led to entirely new
riparian communities and loss of native riparian species
such as the Willow Flycatcher (Empidonax traillii).
Protected areas in upper watersheds, in contrast, are
vulnerable to land use lower in the watershed. These
human activities may provide vectors for exotic species
and disease to penetrate the upper watershed. They may
also result in genetic isolation of populations in head-
waters. In the northern Rocky Mountains, USA, native
west-slope cutthroat trout (Oncorhynchus clarki lewisi)
historically occupied entire watersheds. Subpopulations
in headwaters may have been dependent on source
populations in lowlands. Mainstream populations were
forced to extinction by the introduction of exotic trout
species and possibly by habitat changes associated with
irrigation and other intense land uses. Consequently,
populations surviving in headwater streams in national
parks are subject to a high probability of extinction,
probably because they no longer receive immigrants
from source populations in lowland streams (Shepard
et al. 1997).
This discussion of watershed effects also applies to
airsheds. Change in regional land use may alter climate
and nutrient deposition within downwind protected
areas considerable distances away (Lawton et al.
2001). Tropical montane cloud forests in Central
America depend upon prolonged immersion in clouds.
Clearing of forests in Costa Rica’s Caribbean lowlands
appears to have reduced cloud cover and increased
cloud height in cloud forests, such as in Monte Verde
National Park, altering ecosystem function and possibly
contributing to the decline of 20–50 species of frogs and
toads in Monte Verde National Park (Nair et al. 2003).
Such changes in ecosystem processes are especially
difficult for managers of protected areas to perceive
because they may result from changes in the air or
watershed at long distances from the protected area.
Protected areas may not contain the full suite of
habitats required by organisms to meet their annual life
history requirements. Seasonally important habitats
may lie outside the boundaries of protected areas. Land
use in the unprotected portion of ecosystems may alter
or destroy these seasonal habitats, as well as movement
corridors connecting these habitats to protected areas
This situation is common because of the nonrandom
location of protected areas relative to biophysical
Vol. 17, No. 4
conditions and habitats. Protected areas are often
located in relatively harsh biophysical settings and
represent the colder or hotter, drier, more topograph-
ically complex, and/or less productive portions of the
broader ecosystems in which they lie (Scott et al. 2001).
Intense human land use, in contrast, is often centered on
more equitable and productive landscape settings
(Seabloom et al. 2002, Huston 2005). Consequently,
the unprotected portions of ecosystems often contain
habitats crucial for organisms that reside within the
protected areas for portions of the year. Intense land use
may be disproportionately centered on these unpro-
tected crucial habitats (Hansen and Rotella 2002).
Seasonal and migration habitats.—Animals often
move across the landscape seasonally to obtain required
resources. For protected areas at higher elevations, key
winter ranges are often outside the boundaries of
protected areas. Similarly, protected areas in more arid
regions often do not contain wet-season habitats. Land
use may alter these unprotected seasonal habitats or the
movement pathways between seasonal habitats.
Populations of several large-mammal species within
the Maasai Mara Reserve and Amboseli National Park
in Kenya have declined in abundance during the past 30
years in the face of rapid intensification of land use in
the surrounding regions (A. J. Hansen et al., unpublished
report). Of the 15 species analyzed, eight species in the
Massai Mara Reserve and one species in Amboseli
declined significantly during this time. The declines were
severe for several species and ranged from 0.7% to 2.5%
of the population size per annum. These population
changes were statistically associated with human use
factors in the wet-season habitats outside of the
protected area boundaries. In tropical forests of Borneo,
Indonesia, long-distance migrations of bearded pigs
have been disrupted by the logging of the dipterocarp
trees whose fruits are prime food sources for the pigs
(Curran et al. 1999). Berger (2004) documented that the
225-km movement corridor for pronghorn antelope
(Antilocapra americana) between summer and winter
range in Greater Yellowstone passes through a 1 km
wide bottleneck that is now threatened with natural gas
Population source–sink habitats.—The crucial habitats
outside of protected areas may be especially rich in
resources and may act as population ‘‘source’’ areas.
These habitats may allow subpopulations to produce
surplus offspring that disperse to less productive
habitats in protected areas and allow persistence of the
subpopulations in the reserves. For example, Hansen
and Rotella (2002) found that bird populations in the
Greater Yellowstone Ecosystem were concentrated in
small hotspots in productive, lowland settings outside
protected areas. These source habitats have been
disproportionately used for agriculture and rural home
sites (Gude et al. 2007). This intense land use has
converted these low-elevation source areas for the
populations to sink areas and reduced the viability
of subpopulations in the more marginal habitats in
protected areas. Similarly, Arcese and Sinclair (1997)
suggested that most of Serengeti National Park is a sink
for the lion population and that the species is maintained
there because of connectivity with the Ngorongoro
Conservation Area, which is a population source area
The migratory movements of many organisms across
greater ecosystems are often quite obvious to park
managers and local people. Hence, the problem of
unprotected seasonal habitats has received considerable
attention in many regions. Designation and protection
of migration corridors is increasingly widely used to
minimize or mitigate conflicts between human land use
and migrating wildlife (e.g., Miller et al. 2001).
Proximity to humans
Human presence on the periphery of protected areas
may cause changes in ecosystem processes and biodiver-
sity that extend varying distances into the protected area
(Fig. 1e). Some of these edge effects result in habitat
change. For example, clearing of forests to the edge of
the protected area boundary may lead to elevated
disturbance rates and high levels of forest mortality
within the forest reserve (Laurance et al. 2000).
Other types of edge effects do not cause visible
changes in habitat, but have strong influences on
organisms in protected areas nonetheless. Hunting and
poaching often extend the footprint of human settle-
ments into adjacent protected areas (Escamilla et al.
2000, Revilla et al. 2001). For example, on the western
border of Serengeti National Park, poaching was
estimated to extend up to 25 km into the park (Campbell
and Hofer 1995). Exotic organisms and disease also may
spread from border communities into protected areas.
Bison (Bison bison) in Yellowstone National Park
contracted brucellosis while commingling with livestock
in winter range outside of the park (Yellowstone
National Park 1997). This has led to a substantial
management challenge now that the disease has been
largely eradicated from livestock herds in the United
States. Similarly, lions in Serengeti National Park
underwent dramatic population declines from the canine
distemper that they contracted from domestic dogs
living outside the park (Packer et al. 1999). Human
recreation is sometimes elevated near borders of
protected areas and may displace wildlife (Hansen
et al. 2005).
Many of these edge effects are proportional to the
density of the adjacent human population (Woodroffe
and Ginsberg 1998, Brashares et al. 2001). Hence, these
effects may be increased under human population
growth around protected areas.
IMPLICATIONS FOR CONSERVATION AND MANAGEMENT
This framework of mechanisms linking land use with
protected areas can enhance the various ongoing
conservation and management approaches. The frame-
June 2007983LAND USE CHANGE AROUND PROTECTED AREAS
work provides a conceptual basis for: (1) mapping the
boundaries of the effective ecosystem encompassing a
protected area; (2) monitoring and assessing manage-
ment effectiveness; (3) systematic conservation planning
and management of the effective ecosystem; and (4)
assessing vulnerability of protected areas to land use
change. We will discuss each of these applications.
Managers need to be able to quantify the boundaries
of the effective ecosystem encompassing a protected area
in order to know where to monitor land use change,
assess management effectiveness, and implement region-
al conservation strategies to maintain the protected area.
The ecosystem boundaries should include the areas that
are strongly connected to the protected area in
ecological processes or organism movements and
population processes. The mechanisms framework
provides a conceptual basis for mapping these con-
nections and identifying the boundaries of the effective
ecosystem. The area of seminatural habitats contribut-
ing to effective ecosystem size can be mapped using
remote-sensing techniques (Rogan and Chen 2004). The
spatial and temporal dynamics of natural disturbance
regimes can be mapped from historic records or
projected with computer simulation models (e.g., Baker
1989). Movements of organisms can be quantified
through use of telemetry and other methods (e.g., Berger
2004). Mapping of population processes and source–
sink dynamics requires both field studies and simulation
modeling (e.g., Hansen and Rotella 2002). Quantifica-
tion of human edge effects can be done with human
surveys and other assessment methods (Campbell and
Hoffer 1995). In addition to these quantitative methods,
expert opinion often will be needed to delineate
ecologically meaningful boundaries.
Management effectiveness and monitoring
After a period of focus on the creation of new
protected areas, many managers and conservationists
are attending to the assessment of how well existing
protected areas are working. For example, the World
Commission on Protected Areas (WCPA) has developed
a six-step process for assessing management effective-
ness. ‘‘The process begins with establishing the context
of existing values and threats, progresses through
planning and allocation of resources (inputs), and, as a
result of management actions (process), eventually
produces goods and services (outputs) that result in
impacts or outcomes’’ (Hockings 2003:826). This ap-
proach may be based on results of questionnaires of
managers and other stakeholders or on quantitative data
from ecological measurement. Our framework of
mechanisms provides a conceptual basis for portions
of the process. ‘‘Context’’ can be evaluated by assessing
threats from land use relative to the places and processes
identified in our ecological mechanisms. ‘‘Planning’’ and
management ‘‘process’’ can be aimed at maintaining the
connections and functions identified by our mechanisms.
The U.S. National Park Service and the Canadian
Park Service (Parks Canada Agency 2005) have each
established inventory and monitoring (I&M) programs
aimed at assessing the condition of parks and determin-
ing management effectiveness. Within the U.S. National
Park Service I&M Program, our mechanisms framework
has been used to guide selection of monitoring
indicators, delimitate the effective ecosystem, and guide
analysis of trends in threats and ecological response
(D. A. Jones et al., unpublished manuscript).
It is apparent that many protected areas may become
degraded by land use and other factors occurring in the
unprotected parts of the surrounding ecosystem. Thus,
maintaining protected areas often will require some level
of conservation-oriented management in the unpro-
tected portion of the ecosystem. ‘‘Systematic conserva-
tion planning’’ (Margules and Pressey 2000) provides a
coordinated approach for assessment and management
across regional landscapes. Our mechanisms framework
provides design criteria for regional management
(Table 3). Knowledge of land use patterns, the spatial
dynamics of these ecological mechanisms, and the
responses of ecological processes provide a context to
identify places in the unprotected parts of the ecosystem
that are most critical for maintaining ecological function
within protected areas. Management should focus on
maintaining effective ecosystem size, ecological process
zones, crucial habitats for organisms, and on minimizing
negative human edge effects. Coupled with understand-
ecological processes and biodiversity within reserves.
Criteria for managing regional landscapes to reduce the impacts of land use change outside of protected areas on
MechanismType Design criteria
Change in effective size of reservespecies–area effect; minimum dynamic area; trophic
disturbance initiation and run-out zones; placement
in watershed or airshed
ephemeral habitats; dispersal or migration habitats;
population source sink habitats
poaching; displacement; exotics/disease
maximize area of functional
identify and maintain ecological
maintain key migration and
manage human proximity and
Changes in ecological flows into
and out of reserve
Loss of crucial habitat outside of
Increased exposure to human
activity at reserve edge
INVITED FEATURE 984
Vol. 17, No. 4
ing of the socioeconomic dynamics in the region
(DeFries et al. 2007), the mechanisms offer a compre-
hensive approach for understanding and managing these
vitally important regions to maintain ecological function
while minimizing negative impacts on surrounding
Vulnerability of protected areas to surrounding land use
With limited resources for conservation, it is necessary
to identify which protected areas are most vulnerable to
land use change so that mitigation strategies can be
focused on these areas (Wilson et al. 2005). Three classes
of factors that may influence the vulnerability of a
protected area to land use intensification are: the
ecological properties of the protected area and sur-
rounding ecosystem; the type and rates of land use
conversion and intensification; and the properties of the
surrounding human communities. We suggest that the
most vulnerable protected areas will be those with the
1) The protected area is small or poorly placed
relative to minimum dynamic area of disturbance; shape
of species–area curves; biophysical gradients and the
resulting areas of organism movements; and watershed
2) The protected area is in close proximity to dense
human populations, intense land use in critical portions
of the ecosystem, or is likely to come in close proximity
under future land use change.
3) The surrounding human community lacks incen-
tives or resources for forwarding ecological goals of
The first point follows from the fact that the spatial
extent of ecosystem processes may differ from place to
place. For example, spatial patterns of precipitation may
determine whether organisms migrate over small or
large areas. Thus, the key to assessing vulnerability of
protected areas is to evaluate not the absolute size of the
area, but its size relative to the effective ecosystem it
exists within. Quantitative assessment of the spatial
extent of biophysical factors, hydrologic flows, distur-
bance, and organism movements relative to size and
location of the protected area provides a context for
assessing the vulnerability of the protected area to land
use change in the unprotected portion of the ecosystem.
The intensity and type of land use in surrounding
lands also differs among protected areas. Parks
surrounded by intense land uses, such as urban and
suburban, are more vulnerable than those set in a
wilderness context. Also, land use types differ in their
likely influence on protected areas. Land uses such as
commercial farming may elicit all four of the mecha-
nisms previously described, whereas others such as
tourism or poaching may involve a single mechanism
The socioeconomic fabric of surrounding human
communities probably also influences the vulnerability
of protected areas. Protected areas located in areas
where surrounding communities rely on bushmeat or
forest products are likely to be more vulnerable.
Protected areas also vary in the enforcement of policies
to protect reserves (Bruner et al. 2001). For example,
elephant populations fared better in African countries
that were able to control poaching prior to the ivory ban
in the 1980s (Leakey and Morell 2001). Protected areas
surrounded by human communities that benefit from
them may be less vulnerable due to a higher likelihood
TABLE 4. Varying effects of different land use types on ecological mechanisms altering reserves.
Type of land use change
Large-scale commercial farming
Note: An ‘‘x’’ indicates that a land use type is likely to invoke the specified ecological mechanism
and to influence ecosystem function and biodiversity within protected areas.
June 2007 985LAND USE CHANGE AROUND PROTECTED AREAS
of regional-scale management to forward the goals of
the protected area (Rasker and Hansen 2000).
Finally, we suggest that the confluence of these factors
has a larger effect on the protected area than the
additive effect of the individual factors. With further
refinement and testing, such criteria could provide a
basis for evaluating the global network of protected
areas and for identifying those that are the highest
priority of conservation attention, based on vulnerabil-
ity to land use change. Within a regional context, the
principles also can be applied to strategic land use
management to conserve elements of the landscape most
crucial to reserve function, while allowing land use to
fulfill human needs on those portions of the landscape
less crucial to the functioning of reserves.
The case studies in this Invited Feature provide
examples of regional assessments and management
implications around several protected areas in varying
ecological and socioeconomic settings. The concluding
paper by DeFries et al. (2007) explores in detail the
interactions between protected areas and local people
and opportunities for achieving regional-scale manage-
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