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Humans are the major force of change around the globe, transforming land to provide food, shelter, and products for use. Land transformation affects many of the planet’s physical, chemical, and biological systems and directly impacts the ability of the Earth to continue providing the goods and services upon which humans depend.
Unfortunately, potential ecological
consequences are not always considered in making decisions regarding land
use. In this brochure, we identify ecological principles that are critical
to sustaining ecosystems in the face of land-use change. We also offer
guidelines for using these principles in making decisions regarding land-use
A critical challenge for land use and management involves reconciling conflicting goals and uses of the land. The diverse goals for use of the land include:
• infrastructure for human settlement (housing, transportation, and industrial centers);
• recreational activities;
• services provided by ecological systems (e.g, flood control and water supply and filtration);
• support of aesthetic, cultural, and religious values; and
• sustaining the compositional and structural complexity of ecological systems.
To meet the challenge of sustaining ecological systems, an ecological perspective should be incorporated into land-use and land-management decisions. Specifying ecological principles and understanding their implications for land-use and land-management decisions are essential steps on the path toward ecologically based land use.
Key ecological principles deal with
time, species, place, disturbance, and the landscape. While they are presented
as separate entities, the principles interact in many ways.
The time principle has several important implications for land use:
Trophic levels refer to the stages
in food chains such as producers, herbivores, consumers, and decomposers.
Changes in the abundance of a focal species or group of organisms at one
trophic level can cascade across other trophic levels and result in dramatic
changes in biological diversity, community composition, or total productivity.
Changes in species composition and diversity can result from land use through
alterations to such ecosystem properties as stream flow or sediment load,
nutrient cycling, or productivity. The effects of land use on species composition
have implications for the future productivity of ecological systems.
Local climatic, hydrologic, soil, and geomorphologic factors as well as biotic interactions strongly affect ecological processes and the abundance and distribution of species at any one place. Local environmental conditions reflect location along gradients of elevation, longitude, and latitude and the multitude of microscale physical, chemical, and edaphic factors that vary within these gradients. These factors constrain the suitability of various land uses, as well as defining resident species and processes.
Rates of key ecosystem processes, such as primary production and decomposition, are limited by soil nutrients, temperature, water availability, and the temporal pattern of these factors controlled by climate and weather. Thus, only certain ranges of ecological-process rates can persist in a locale without continued management inputs (e.g., irrigation of crops growing in a desert). Chronic human intervention may broaden these ranges but cannot entirely evade the limitations of place without a cost.
Naturally occurring patterns of ecosystem structure and function provide models that can guide sustainable and ecologically sound land use. Only those species adapted to the environmental constraints of an area will thrive there. Precipitation limits which species are appropriate for landscape plantings as well as for managed agricultural, forestry, or grazing systems. Further, some places with unique conditions may be more important than others for conservation of the species and ecosystems they support.
Land uses that cannot be maintained
within the constraints of place will be costly when viewed from long-term
and broad-scale perspectives. For example, establishing croplands and ornamental
lawns in arid areas is possible, but draws down fossil groundwater at a
rate unsustainable by natural recharge. Only certain patterns of land use,
settlement and development, building construction, or landscape design
are compatible with local and regional conditions. In terrestrial systems,
land-use and land-management practices that lead to soil loss or degradation
reduce the longterm potential productivity of a site and can affect
species composition. Land use practices can also influence local climate
(e.g., the urban heat island concept). Sustainable settlement is limited
to suitable places on the landscape. For instance, houses or communities
built on transient lake shore dunes, major flood plains, eroding seashores,
or sites prone to fires are highly vulnerable to loss over the long term.
Ideally, the land should be used for the purpose to which it is best suited.
Land-use changes that alter natural-disturbance regimes or initiate new disturbances are likely to cause changes in species’ abundance and distribution, community composition, and ecosystem function. In addition, the susceptibility of an ecosystem to other disturbances may be altered.
Land managers and planners should be aware of the prevalence of disturbance in nature. Disturbances that are both intense and infrequent, such as hurricanes or 100-yr floods, will continue to produce "surprises." Ecosystems change, with or without disturbance; thus, attempts to maintain landscape conditions in a particular state will be futile over the long term. Attempts to control disturbances are generally ineffectual and suppression of a natural disturbance may have the opposite effect of that intended. For example, suppression of fire in fire-adapted systems results in the buildup of fuels and increases the likelihood of severe, uncontrollable fires. Similarly, flood-control efforts have facilitated development in areas that are still subject to infrequent large events (e.g., the 1993 floods in the upper Midwest), resulting in tremendous economic and ecological impacts. Land-use policy that is based on the understanding that ecosystems are dynamic in both time and space can often deal with changes induced by disturbances.
Understanding natural disturbances
can help guide land-use decisions, but the differences between natural
and human-made disturbances must be recognized. Continued expansion of
human settlement into disturbanceprone landscapes is likely to result
in increased conflicts between human values and the maintenance of natural-disturbance
regimes necessary to sustain such landscapes.
The size, shape, and spatial relationships of land-cover types influence the dynamics of populations, communities, and ecosystems. The spatial arrangement of ecosystems comprises the landscape and all ecological processes respond, at least in part, to this landscape template. The kinds of organisms that can exist are limited by the sizes, shapes, and patterns of habitat across a landscape.
Human-settlement patterns and landuse decisions often fragment the landscape or otherwise alter land-cover patterns. Decreases in the size of habitat patches or increases in the distance between habitat patches of the same type can greatly reduce or eliminate populations of organisms, as well as alter ecosystem processes. However, landscape fragmentation is not always necessarily destructive of ecological function or biodiversity because a patchwork of habitat types often maintains more types of organisms and more diversity of ecosystem process than does a large area of uniform habitat. Making a naturally patchy landscape less patchy may also have adverse affects.
Larger patches of habitat generally contain more species (and often a greater number of individuals) than smaller patches of the same habitat. Larger patches also frequently contain more local environmental variability. This variability provides more opportunities for organisms with different requirements and tolerances to find suitable sites within the patch. In addition, the edges and interiors of patches may have quite different conditions, favoring some species over others. The abundance of edge and interior habitat varies with patch size; large patches are likely to contain both edge and interior species, whereas small patches will contain only edge species.
The extent and pattern of habitat connectivity can affect the distribution of species by making some areas accessible and others inaccessible. The amount of connectivity needed varies among species and depends on two factors: the abundance and spatial arrangement of the habitat and the movement capabilities of the organism.
While gradual reduction in habitat may have gradual effects, once a certain threshold is reached, the effects become dramatic. Land-cover changes are most likely to have substantial effects when habitat is low to intermediate in abundance and small changes may cause large impacts.
The ecological importance of a habitat
patch may be much greater than is suggested by its size and distribution
across the landscape. Some habitats, such as bodies of water or riparian
corridors, are small and discontinuous, but nevertheless have ecological
impacts that greatly exceed their spatial extent. For example, the presence
of riparian vegetation, which may occur as relatively narrow bands along
a stream or as small patches of wetland, generally reduces the amount of
nutrients being transported to the stream. This filtering by the vegetation
is an ecologically important function because excess nutrients that unintentionally
end up in lakes, streams, and coastal waters are a major cause of eutrophication,
acidification, and other water quality problems. Thus, the presence and
location of particular vegetation types can strongly affect the movement
of materials across the landscape and can contribute to the maintenance
of desirable water quality.
Ecologically based guidelines are proposed here as a way to assist land managers and others considering the ecological ramifications of land-use decisions. These guidelines are meant to be flexible and to apply to diverse land-use situations. The guidelines recognize that the same parcel of land can be used to accomplish multiple goals and emphasize that decisions should be made within an appropriate spatial and temporal context. For example, the ecological implications of a decision may last for decades or even centuries.
All aspects of a decision need to
be considered in setting the time frame and spatial scale for impact analysis.
In specific cases, the relevant guidelines can be developed into prescriptions
for action. These guidelines are best seen as a checklist of factors to
be considered in making a land-use decision.
The spatial array of habitats and ecosystems shapes local conditions and responses and local changes can have broad-scale impacts over the landscape. Therefore, it is critical to examine both the limitations placed on a location by the regional conditions and the implications of decisions for the larger area. This guideline suggests two considerations for planning land use:
Some land uses offer more flexibility
in terms of future or adjoining uses than do others. The ecological constraints
of an area determine the flexibility of diverse land uses for that area.
This guideline calls for examining local decisions within the regional
context of ecological concerns as well as in relation to the social, economic,
and political perspectives that are typically considered.
Impacts of land-use decisions can, and often do, vary over time. Long-term changes that occur as a response to land-use decisions can be classified into two categories:
Planning for the long term requires consideration of the potential for unexpected events, such as variations in temperature or precipitation patterns or disturbances. Estimating the occurrence and implications of these unanticipated events is difficult, but land-use plans should attempt to include them and estimate likely changes.
Long-term planning should also recognize
that one cannot simply extrapolate historical land-use impacts forward
to predict future consequences of land use. Transitions of land from one
use or cover type to another often are not predictable because of changes
in demographics, public policy, market economies, and technological and
Rare landscape elements provide critical
habitats or ecological processes. For example, in the Southern Appalachian
Mountains, 84% of the federally-listed terrestrial plant and animal species
occur in rare communities. While these communities occupy a small area
of land, they contain features important for the region’s biological diversity.
Therefore, rare landscape elements need to be identified, usually via an
inventory and analysis of vegetation types, physical features, hydrology,
soils, and associated species. Once the inventory is complete, effects
of land-use decisions on these landscape elements and species can be routinely
estimated. These effects can then be considered in view of the overall
goal for the project, the distribution of elements and species across the
landscape, and their susceptibility, given likely future land changes in
the vicinity and region. Strategies to avoid or mitigate serious impacts
can then be developed and implemented.
Depletion of natural resources disrupts
natural processes in ways that often are irreversible over long periods
of time. The loss of soil via erosion that occurs during agriculture and
the loss of wetlands and their associated ecological processes and species
are two examples. To prevent diminishment, those resources at risk must
first be determined. For example, in the southwestern United States, water
might be the most important resource. Evaluation of whether a resource
is at risk is an ongoing process as the abundance and distribution of resources
change. Ways to avoid actions that would jeopardize natural resources should
be identified and considered. Some land actions are inappropriate in a
particular setting or time, and they should be avoided. Examples are farming
on steep slopes, which might produce soil loss; logging, grazing, or farming
too close to streambanks, which may jeopardize water quality and aquatic
habitats; and growing plants with high water demands in arid areas.
Large areas are often important to maintaining key organisms and ecosystem processes. Habitat patch size is critical to the survival of a species or population when it is rare or disconnected. In most parts of the nation, large areas of natural habitats are becoming less common as they are fragmented into smaller habitat patches suitable for fewer species. A useful management approach generally favors protecting large areas and smaller areas that are well-connected to other habitats.
Habitat connectivity is not always a positive attribute for species and ecosystems. Land uses that serve as connectors to species’ movement can have long-term positive effects on populations; but, at the same time, corridors can facilitate the spread of nonnative species or diseases.
The importance of spatial connections
depends on the priorities and elements of a situation. A first step in
implementing this guideline is to examine the spatial connectivity of key
habitats in an area, determining which patches are connected and whether
the connectivity varies with time. Second, opportunities for connectivity
must be promoted. Sometimes, those opportunities can complement other planning
Nonnative organisms often have negative effects on native species and the structure and functioning of ecological systems. Land-use decisions must consider the potential for the introduction and spread of nonnative species. For example, kudzu, first used for erosion control, is now overwhelming and killing native trees. Land planning should consider vehicle movement along transportation routes, the planting of native species, and control of pets. For example, the spread of the gypsy moth is correlated with overseas transportation of eggs, larvae, and adults in the cargo holds of ships or along roads when egg sacs are attached to vehicles or outdoor furniture. The introduction of aquatic organisms (e.g., the zebra mussel) transported incidentally with shipping traffic is a comparable example for aquatic ecosystems. Many of these introductions have had devastating effects.
Growing native species can reduce
the need for planting nonnative species, particularly in urban, suburban,
or other developed areas. The planted native species can then reseed themselves.
Native species are also adapted to long-term variations in climate or disturbance
regimes to which nonnative species often succumb. Environmental conditions
associated with native vegetation may also deter the spread of nonnatives.
Negative impacts of development might
be avoided or mitigated by some forethought. To do so, potential impacts
need to be examined at the appropriate scale. At a fine scale, the design
of a structure may interrupt ecoregional processes, while at a broad scale,
patterns of watershed processes may be altered, for example, by changing
drainage patterns as a result of development. How proposed actions might
affect other systems (or lands) should be examined. Human uses of the land
should avoid structures and uses that might have a negative impact on other
systems; at the very least, ways to compensate for those anticipated effects
should be determined. It is useful to look for opportunities to design
land use to benefit or enhance the ecological attributes of a region. For
example, parts of golf courses can be designed to serve as wildlife habitat,
or traffic in rural areas can be concentrated on fewer and more strategically
placed roads, resulting in decreased traffic volumes and flows within the
region as a whole and less impact on wildlife.
Because local physical and biotic
conditions affect ecological processes, the natural potential for productivity
and for nutrient and water cycling partially determine the appropriate
land-use and -management practices for a site. Land-use practices that
fall within these place limits are usually cost-effective in terms of human
resources and future costs caused by unwarranted changes on the land. Implementing
land-use and -management practices that are compatible with the natural
potential of the area requires that land managers have an understanding
of the site potential.
These guidelines do not address the environmental, social, economic, and political tradeoffs that often occur in setting land policy. Tradeoffs are often based on subjective value judgments reflecting economic, social, cultural, and aesthetic preferences accorded by a society to different objectives and variation in local circumstances. For example, consideration of such tradeoffs are central components of land-use agreements in the restoration of the Everglades and in developing options for fisheries and ancient forests in the Pacific Northwest.
However, society and the ecological community have not yet converged on a consistently applicable mechanism for incorporating science into land-use policy. Positive steps in integrating scientific ideas and land-use management are being taken at both the international and national scales. At the local scale, an unprecedented increase in numbers of watershed alliances and other types of nongovernmental organizations has occured in response to the perception that government agencies are not doing enough to manage the land sustainably. In each case, science is only a part of the solution, although an essential part.
The ESA Land Use Committee would like to acknowledge those who contributed to the production of this brochure. We would like to thank Doug Norton, Bill Painter, and Jessica Cogan, U.S. Environmental Protection Agency, for reviewing and providing comments on the brochure as it developed. We acknowledge and appreciate the skills of Lori Hidinger in developing this brochure. We would also like to acknowledge the following for the photographs used in the brochure: V. Dale (ORNL), J. Franklin (UWash), K. Hammond (USDA), J. Hanula and K. Franzreb (USGS), R. Mieremet (NOAA), S. Smith (UNLV), W. Tarpenning (USDA), and K. Weller (USDA). Finally, we would like to gratefully thank the U.S. Environmental Protection Agency for funding the production of this brochure.
This brochure is based on an Ecological Society of America White Paper, "Ecological Principles and Guidelines for Managing the Use of Land," published in Ecological Applications, Volume 10, Number 3 (June 2000). The White Paper is also available on the ESA website Click here.
The authors of the White Paper upon which this brochure is based served as members of the ESA Committee on Land Use:
Sandra Brown1, University of Illinois, Champaign, Illinois;
Richard A. Haeuber2, Sustainable Biosphere Initiative, Ecological Society of America, Washington, DC 20036;
N. Thompson Hobbs, Colorado Division of Wildlife and Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO 80523;
Nancy J. Huntly, Department of Biological Sciences, Idaho State University, Pocatello, ID 83209-8007;
Robert J. Naiman, College of Ocean and Fishery Sciences, University of Washington, Seattle, WA 98195-2100;
William E. Riebsame, Department of Geography, University of Colorado, Boulder, CO 80309;
Monica G. Turner, Department of Zoology, University of Wisconsin, Madison, WI 53706;
Tom J. Valone3, Department
of Biology, California State University, Northridge, CA 91330-8303.
1 current address: Winrock International, 1611 North Kent Street, Suite 600, Arlington, VA 22209
2 current addres: 1712 Johnson Avenue, NW, Washington, DC 20009
3 current address: Department of Biology, St. Louis University, St. Louis, MO 63103
1707 H Street, NW Suite 700
Washington, DC 20036