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5
The Land Acquisition Process
and Biological Preserves:
A Role for Natural Sciences
This chapter examines several ecological issues that pose challenges to
He acquisition of conservation lands and reviews Be current state of
knowledge regarding Lose issues. The dynamic nature of landscapes
and ecological systems is reviewed at multiple scales, as is the impor-
tance of maintaining species and functional ecosystems in lands designat-
ed for conservation and the role of spatial configuration in reserve de-
sign. The effectiveness of the current set of criteria are evaluated for
their effectiveness in addressing Me biological components of the agen-
cies' explicit objectives and the issues noted above. Finally, the com-
mittee's findings are synthesi ed and some modifications to He acquisi-
lion process are suggested that could enhance the ability to meet the
ecological component of acquisition goals.
FUNDAMENTAL ECOLOGICAL CHALLENGES
Geomorphic Processes
Geomorphic processes are the physical and chemical processes that
determine the distribution of energy within a changing landscape. The
distribution of moisture, nutrients, temperature, sediments, and other
resources on ache landscape affect and are integral to He biological re-
sources, productivity, and diversity of ecosystems. Conservation of
~3
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A ROLE FOR NATURAL SCIENCES
115
diversity, a management objective should be to maintain adequate habi-
tats for populations over a wide geographical area. This is particularly
important for adapting to rapid environmental change.
Species Diversity
Technically, species richness refers to the number of species present;
species diversity is a measure of the number of species and their relative
abundance. With habitat fragmentation and disturbance, species become
increasingly rare. Data must be acquired on minimum viable population
sizes and sizes of habitats required to sustain them. For example, Samp-
son (1980) estimates that populations of the greater prairie chicken can
be sustained only on grasslands of 300 hectares or larger and that they
also must be within 20 km of other undisturbed grasslands.
Community Diversity
This concept generally refers to the number of= species inhabiting an
area and encompasses all trophic and nontrophic interactions. Many of
these interactions are highly species-specific. For example, many spe-
cies of herbivorous insects depend on specific plant species. Whitcomb
(1987) reports that assemblages of leaflloppers in grasslands were depen-
dent on the patch size and structure of host stands, and the rarity of
these insects was attributable to the rarity of Weir host plants. Popula-
tions such as these in small, isolated patches are particularly sensitive to
disturbance by physical (e.g., fired and biological forces (e.g., parasites,
predators).
GIobal-&ale Diversity
Conservation of diversity must also be considered at a global scale for
species with migratory habits (e.g., marine mammals and birds). Also,
biogeochemical cycles can be influenced strongly by global phenomena'
such as decreasing ozone.
Decisions to acquire land for conservation should be based upon a
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A ROLE FOR NATURAL SCIENCES 117
The factors controlling species distributions differ with scale. For
example, in He Southwest, He mortality of oak seedlings at local scales
decreases with increasing precipitation, whereas moronity at regional
scales is lowest at the drier latitudes (Neilson and WulIstein, 1983~. In
an area of the Laurentian Great Lakes in Ontario, regional patterns of
fish assemblages appear to be determined by postglacial dispersal and
lake Herman regimes, whereas environmental conditions such as lake
depth and pH assume greater importance in determining species compo-
sitions of individual lakes (Jackson and Harvey, 1989~.
Finally, a dynamic landscape in which the proportions of different
habitat types change through time might exhibit a stable mosaic (Bor-
mann and Likens, 1991) at one spatial or temporal scale but not at an-
o~er. Without a temporally stable patch mosaic at any spatial scale,
fluctuation and change might predominate within areas of any sue (Bak-
er, 1989a).
These examples suggest that the importance of spatial and temporal
scale as they influence conservation objectives must be considered in the
planning for land acquisition. Within a single locality or preserved area,
emphasis may be placed on preventing the local extirpation of a species
or maintaining a representative habitat type. A particular parcel of land
may also be valuM for its aesthetic or recreational value. Therefore,
conservation goals at the local level may emphasize the perpetuation of
a particular ecosystem type. Manipulative management might be re-
quired to preserve populations within a local area, but that might conflict
with attempts to ensure the perpetuation of broad-scale processes (Baker,
1989a).
The landscape level a mixture of natural and human-managed patches
that vary in size, shape, and arrangement (Burgess and Sharpe, 1981;
Forman and Godron, 1986; Urban et al., 1987; Turner, 1989~. Conser-
vation goals may focus on maintaining a particular juxtaposition of
habitat patches. The size and geographic arrangement of patches across
a landscape may influence species success or persistence, and many
wildlife species are wide-ranging and make use of several habitats (For-
man and Godron, 1986~. Management or conservation goals might be
to perpetuate natural fluctuations in landscape structure (e.g., a natural
fire regimes, which implies Hat certain species may fluctuate as well.
If long-term maintenance of biological diversity is a conservation
goal, a management strategy that places regional biogeography and
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118 SETTING PRIORITIES FOR LAND CONSERVATION
landscape patterns above local concerns may be necessary (Noss, 1983).
The acquisition of conservation lands would then require an evaluation
not only of the habitat within a protected area but also the landscape
context in which each preserve exists (Noss and Harris, 1986~. When
assessing the effectiveness of the criteria by which conservation lands
are acquired, the appropriate objectives at multiple scales must be con-
sidered.
Landscape Dynamics
Land conservation is challenging in part because one goal is to pre-
serve areas that are changing (White and Bratton, 1980~. When consid-
ered over long periods, Me species assemblages observed today are
relatively recent (Delcourt and Delcourt, 1991~. Many have formed
only in the past 10,000 years and reflect individual species' responses to
changes in the global environment. Over shorter periods decades to
centuries the patterns of many landscapes are influenced by natural
disturbances (White, 1979; Mooney and Godron, 1983; Pickett and
White, 1985; Turner, 1987; Baker, 1989b). Disturbances may create
openings within forested landscapes, leading to patches of different ages
(Runkle, 1985; Knight, 1987; Baker, 1989a,b). Landscape patterns in
old-growth forests of New England, for example, result from frequent
natural disturbances, such as windstorms, lightning, pathogens, and fire
(Foster, 1988~. A variety of authors have suggested that natural areas
should be sufficiently large to include all normal stages in community
development, and that natural processes of perturbation and recovery
should tee allowed to occur unchecked (Sullivan end Chaffer, 1975;
Pickett and Thompson, 1978~.
Even in the absence of natural disturbances, landscapes are not static.
In the Southeast, for example, forested land has increased during the
past 50-75 years after the wide-scale abandonment of marginal agricul-
tural lands (Odum and Turner, 1990; Turner, 19901. In over areas,
especially the Midwest, forest cover has declined Jverson, 1988; Dunn
et al., 1991~. In addition, many land-management activities (e.g., for-
estry practices, regional planning, and natural-resource development)
involve decisions that alter landscape patterns, with important implica-
tions for conservation (Franldin and Forman, 1987~. Thus, planning for
conservation lands must always assume that the environment is dynamic.
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A ROLE FOR NATURAL SCIENCES
12
components and processes of the area; an expectation of how these
controls may change, either through natural events or human actions;
and an evaluation of the probable effects of these changes on the ecolog-
ical processes and biota of a region (Golley, 1984~.
Disturbance regimes. The frequency, duration, and severity of
abiotic and biotic disturbances are likely to be altered by climate change.
For example, forest-fire frequencies should increase where the climate
becomes warmer and drier (Sandenburgh et al., 1987~. Patterns of
biotic disturbances might be altered. Because their ranges are often
limited by climatic factors, the distributions of pests or pathogens might
change win climate.
Short-term climatic fluctuations provide important insights into the
response times of species and landscape mosaics to rapid environmental
changes in disturbance regimes on the order of decades to centuries.
For example, in northwestern Minnesota, changes in the charcoal influx
to lake sediments demonstrate how alternating periods of cool-and-moist
cycles and warm-and~ry cycles since 1240 A.D. have influenced the
periodicity of fire (Clark, 1988~.
If ecological disturbance regimes are altered, changes are likely in
many landscapes. Habitat types might be eliminated locally from certain
areas. Thus, conservation planning must consider whether the size of an
existing or proposed reserve in a disturbance-prone environment would
be adequate to incorporate an alteration in disturbance frequency or
severity. In addition, if an altered disturbance regime could lead to the
loss of some habitats, the regional context of the reserve and We poten-
tial for Me persistence of He desired habitat in over geographic loca-
tions should be evaluated.
Changes in the lo cation of suitable habitat. A second effect of cli-
mate change might be a gradual movement of potentially suitable condi-
tions for different species. Species would be expected to migrate to
hospitable environments.
However, migration rates are difficult to
predict, because He rates of climate change are not predictable. Fur-
thermore, Here are now new barriers to migration (e.g., cities, agricul-
ture, and roads) and new modes of migration (e.g., cars, trains, trans-
plants for horticulture, forestry, or agriculture.) Range extension In He
future may be less efficient Han in the past, because advance disjunct
colonies have been extirpated by human disturbances, and propagule
sources often have been reduced (Davis, 1989a). The current spatial
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A ROLE FOR NATURAL SCIENCES
123
parks. Current analyses of data on birds, butterflies, and small mam-
mals from the Minimum Critical Sue of Ecosystems project suggest the
importance of large areas ~ovejoy et al., 19861. Nonetheless, large and
small are relative terms. A different approach is to examine the popula-
tion of the lowest density species Frizzy bears or gray wolves in Yel-
lowstone, for examples and determine the area necessary to support what
could be considered a minimum viable population. This suggests that
maximizing resewe size is desirable for maintaining species richness. It
must be recognized, however, Nat even the largest nature reserves, if
left alone, will probably suffer major die-offs of species in a few hun-
dred or a few thousand years (Franke! and Soule, 1981~. For example,
the huge Kruger National Park in Soup Africa about 350 km long and
80 km wide in places- requires significant management to protect many
of its species from major population declines and perhaps even extinc-
tions (Aiken, 1988~.
Even if a habitat fragment is suitable to support a population of inter-
est, there is no assurance Nat We population will remain viable if it is
isolated from over populations, because genetic variability may be lost
through inbreeding. The shape of a reserve and "edge effects" influenc-
es the relative amount of edge to interior, which in turn influences bio-
logical diversity and susceptibility to disturbance (Burgess and Sharpe,
1981; Ranney et al., 1981; Harris, 1984, Lovejoy et al., 1986~. A
circular area, for example, has the lowest edge to area ratio, whereas a
long, thin rectangle has a much larger edge to area ratio in fact, it may
be all edge.
For decades, the interspersion of habitat types, the creation of edge
effects, and the juxtaposition of different kinds of plant communities
were believed to enhance wildlife habitat values (Harris and Scheck,
1991~. It is now recognized that tile creation of distinct edges (e.g.,
clear-cuts next to old grouchy may reduce He biological value of an area
by increasing susceptibility of undesirable disturbances (Franklin and
Forman, 1987~.
The effects of habitat fragmentation and connectivity have been stud-
ied extensively through empirical studies and models. Miine et al.
(1989) found Hat wintering white-tailed deer did not use sites containing
suitable habitat Hat were isolated from other suitable sites. In northern
Florida, approximately half of He breeding bird species characteristic of
hardwood forests do not reproduce in small forest fragments occurring
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128 SEl-llNG PRIORIES FOR LAND CONSERVATION
simple question if it is a fairly distinct, cleancut feature, such as a bog.
The delimitation of bog vegetation is easily dete~ined. If, however,
the objective is to protect a representative sample of biological commu-
nity that is widespread, the question of size immediately arises.
Wherever possible, habitat chosen for acquisition should not be frag-
mented. Rather, habitat should be continuous but appropriately should
include natural disturbance regimes. When it is not possible to find an
area of continuous habitat Hat is large enough, two solutions are evi-
dent: acquire the necessary area and encourage the return of natural
vegetation between the fragments, or ensure the core area is surrounded
by a matrix of habitat fragments and corridors that provide for species
populations larger Can the actual protected area can.
The best-chosen and best~esigned area for biological diversity con-
servation is nonetheless vulnerable to outside factors. Total watersheds
and their management need to be taken into account in design and man-
agement. Otherwise problems may result, such as Be toxic agricultural
runoff Hat poisoned waterfowl in the Kesterson Wildlife Refuge. Acid
rain emanating from anthropogenic sources far from a resews can alter
lake acidity and even growing patterns or survival of trees.
While He extent, rate, and details of climate change introduced by
artificial release of greenhouse gases might be a matter of disagreement,
it could have a major negative effect on biological diversity (Peters and
Lovejoy, 1992~. Few measures can be taken to avert such adverse
effects. When possible, the best measure is to conserve attitudinal gradi-
ents that will allow species to move upsIope in the event of temperature
increase. If attitudinal gradients are not available, latitudinal gradients
can be considered, but this involves much more extensive expanses of
natural habitat. This assumes of course that the only climatic change
will involve temperature as opposed to rainfall, snowmelt, directions of
currents, etc.
ENHANCING THE ECOLOGICAL EFFECTIVENESS
OF THE ACQUISITION PROCESS
Gap Analysis
Past land-acquisition strategies have focused on saving critically en
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A ROLE FOR NATURAL SCIENCES 131
\ ~ ~
~~ Hualalai
Kona \ Mauna Loa
at' ~
\ n ~ A .
Arch
it -f ~
V''-1 /
~ / Naalehu
FIGURE 5-3 Gap analysis of Hawaii. Source: Scott, 1991.
Mauna Kea;\~ 1 Species
2 species
O 3 species
G 4 species
id] Preserves
years to complete. It is not clear whether gap analysis could be applied
to aquatic systems.
Geographic Information Systems
The geographic information system (GIS) is a powerful tool to plan
for and acquire lands. The power of GIS lies in the ability to manipu-
late and analyze spatially distributed data (Figure 5~. A GIS consists
of the computer hardware and software for entering, storing, transform-
ing, measuring, combining, retrieving, and displaying digitized thematic
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!
A ROLE FOR NATURAL SCIENCES
133
data that have been registered to a common coordinate system. Because
the data can be accessed, transformed, and manipulated interactively,
they can serve as a testing ground for studying environmental processes,
analyzing the results of trends, or anticipating the possible results of
planning decisions 03urrough, 1986~. Planners and decision makers can
use GIS to explore a range of possible scenarios (e.g., alternative ar-
rangements of conservation areas) and evaluate potential consequences
of a course of action before changes are made in the landscape. Impor-
tantly, quantitative assessments can be conducted over a broad range of
spatial and temporal scales.
GIS is used widely in urban and regional planning, natural resource
planning and management, and landscape architecture (Iohnston, 1987;
Ripple, 1987; Johnson, 1990~. Forest managers routinely use Me inven-
tory capabilities of GIS at the federal level (Chambers, 1986), state level
(losta and Davis, 1987), and local level (Wakely, 19871. GIS also is
being used to explore the implications of land-management alternatives.
Application of GIS to aquatic conservation efforts is more difficult,
although it has been used, for example, to establish buffer zones around
rivers to determine how land use would change water quality Johnston
et al., 1988; Osborne and Wiley, 1988~. GIS systems are easily linked
with remote sensing imagery, and linkages with simulation models are
being developed rapidly (CouIson et al., 1991~.
A recent review of GIS applications in natural resources and ecology
(Johnson, 1990) highlights several important operations that are relevant
to conservation planning. First, GIS can be used to determine the spa-
tial coincidence of different types of spatially distributed data. Coinci-
dence analyses result in digital maps showing the areas of overlap be-
tween two or more data layers (e.g., soils and vegetation). For exam-
ple, GIS and remote sensing imagery have been linked successfully to
predict the occurrence of species populations based on the coincidence
of required habitat and environmental factors (Scepan et al., 1987; Sten-
back et al., 1987; Hodgson et al., 1987) and to identify potentially
suitable sites (Palmeirim, 1988; MiIne et al., 1989~. By selectively
weighting habitat characteristics and describing spatial variables such as
patch size, shape, and arrangement, die quality and quantity of habitat
can be estimated Johnson, 1990~. Second, temporal changes in land-
scape patterns can be quantified using GIS Person, 1988; Turner,
1990~. Although temporal analyses have emphasized the detection of
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136 SEWING PRIORITIES FOR LAND CONSERVATION
management agencies) accomplish their objectives In a variety of ways,
ranging from day-to~ay management decisions at individual sites to
agencywide decisions, such as assigning priorities for acquiring lands for
conservation purposes. Each agency has a unique combination of mis-
sions, traditions, policies, and explicit priorities Hat drive its land-acqui-
sition policies. In principle, that diversity facilitates a variety of conser-
vation strategies ranging from total protection of pristine lands to the
acquisition of lands for intensive management and manipulation for
specific objectives. But a critical question is whether this system gives
adequate consideration to conservation issues that transcend the jurisdic-
tiona] boundaries of the federal land-management agencies.
Many additional important conservation issues are becoming apparent
to the scientific community. A few examples are climatic change, de-
clines in populations for entire groups of species, and fragmentation and
~nsular~zation of biotic communities. Natural ecosystems are spatially
and temporally dynamic; furthermore, the importance of a single site to
regional biological diversity is variable. The tendency, however, has
been to establish geographically fixed wildlife refuges with immovable
borders that inhibit species survival.
Rivers are the products of their drainage basins, and We biological
integrity of stream and river systems is dependent to a large extent on
land uses and management practices in the entire watershed. Such land
uses, as well as outside factors, such as demographics, must be consid-
ered to identify and protect critical areas. Long-term planning is needed
to develop a land-acquisition strategy that considers acquisition projects
in the context of Be landscape on a scale appropriate to the needs of
affected plant and animal species. A recent Naitonal Research Council
report on restoration of aquatic ecosystems also addresses landscape
considerations and suggests Rat {ong-term planning be done by regional
planning programs organized by watershed basin (NRC, 1992b).
The ultimate goal of conservation activities should be sustainability of
renewable resources, Including cultural and biological dimensions.
Addressing the problem of sustainability requires an interdisciplinary,
complementary approach among natural and social scientists, as well as
cooperation among agency programs with diverse and often conflicting
mandates. Land-acquisition programs can play a significant role in
achieving Be goal of sustainability Trough the acquisition of critical
areas.
Achieving sustainability requires a recognition of practices that are
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138 SElTING PRIORITIES FOR LAND CONSERVA17ON
dinate federal land acquisition, promote and facilitate collection and
transfer of information, and develop a long-term plan aIld strategy for
land acquisition. Such cooperation is a challenge that will require ~nsti-
tutional innovation.
Representative terms from entire chapter:
land conservation
