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.
 

Wolves in a Human-Dominated Landscape The status and future of wide-ranging animals in regions increasingly dominated by humans is often a concern to natural-resource managers. Recovery of the gray wolf, listed in 1973 as an endangered species, illustrates this challenge. The wolf was extirpated throughout most of the conterminous U.S. following European settlement, with remnant populations persisting only in northeast Minnesota and on Isle Royale, Michigan.   Natural recolonization in the western Great Lakes region has led to recovery of wolf populations, and the Wisconsin and Michigan populations each number between 80 and 90 animals. Wolf recovery resulted largely from legal protection and changed public attitudes. In addition, large populations of deer, resulting in part from the fragmented forest landscapes typical of the region today, provide a ready source of prey. But how do the current landscape patterns in this human-dominated region influence the wolf habitat and populations?   Wolf habitat use is affected by a number of landscape-scale considerations. Wolves avoided certain landcover classes, such as agriculture and deciduous forests, and favored forests with at least some conifers. Public lands received more use, and private lands were avoided. Wolf packs were also most likely to occur in areas with low road densities; no wolfpack territory was bisected by a major highway. Rapid increases in the wolf population since 1993 have occurred in northern Michigan, where favorable habitat is more abundant and more highly connected than in Wisconsin. In Wisconsin, favorable wolf habitat occurs in relatively small, isolated areas separated by lands with greater road density and human development. Adult mortality in Wisconsin has been high, with dispersing wolves being most vulnerable as they cross lands with more intensive human use. Colonization of the fragmented habitat in Wisconsin may remain dependent on dispersers arriving from larger, saturated populations in Minnesota.

 

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.
 

Ecological Guidelines for Land Use Examine the impacts of local decisions in a regional context.  Plan for long-term change and unexpected events.  Preserve rare landscape elements, critical habitats, and associated species.  Avoid land uses that deplete natural resources over a broad area.  Retain large contiguous or connected areas that contain critical habitats.  Minimize the introduction and spread of nonnative species.  Avoid or compensate for effects of development on ecological processes.  Implement land-use and -management practices that are compatible with the natural potential of the area.

 

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 ecological factors.
 

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 needs.
 

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.
 

Assessing Local Conditions The purpose of land-use planning is to ensure that important societal attributes are sustained. These attributes fall into three groups: infrastructure (e.g., jobs, roads, schools, and firehouses), environmental resources (e.g., open spaces, parks, watersheds, natural areas, and wetlands), and public safety (e.g., avoidance of flood plains, unstable soils, and fire hazards). Land-use planning typically follows several steps in balancing emphasis on these attributes.  First, data on current local conditions are assembled. On the basis of these data, concerns about impacts of development are identified. Then, goals for maintaining values are formulated, and criteria for meeting those goals are specified. Alternative approaches to meeting the goals (e.g., regulations, incentives, or public purchase) are developed, and the best are selected and implemented. The success of the chosen approach is then evaluated relative to the criteria. This evaluation becomes part of the data used in the next iteration of the planning process.  An important step in land-use planning is trying to ascertain how a proposed use will affect current local conditions. A process for identifying the effects of development on wildlife habitat and natural communities in Larimer County, Colorado, provides an example. The process was initiated by assembling a group of stakeholders to work with ecologists to identify areas of the landscape that needed to be protected. This group included developers, landowners, planners, environmental advocates, and decision makers. The participation of stakeholders was important for several reasons. First, no single "ecological standard" can be used to assess the value of one facet of the landscape relative to another. Ultimately, ecological knowledge must be combined with local values to arrive at such assessments. Second, the support of leaders of groups affected by the process must be enlisted.  The stakeholder group identified four landscape features based on importance to biological conservation and availability of spatial data about the features:  areas with one or more imperiled species, habitat for economically important species, areas of high species richness, and  rare plant communites. These features were mapped, and a composite map was created showing all of the county as falling into one or more of the four categories. This map was used to designate areas that required a "Habitat Mitigation Plan." As a requirement for approval of all proposed developments, these plans outline procedures for on-the-ground verification and assessment of the condition of these environmental features. If the features are determined to be at risk with the proposed land use, then steps must be taken to mitigate the effects of development. Such steps include provision of setbacks, enforcement of special regulations and covenants, and transfer of development rights from other areas.  Developers can specify an area in the County and learn if it contains environmentally sensitive areas before preparing a development proposal, increasing the chances that sensitive areas will be avoided by choice rather than by regulation. Alternatively, citizen advocates can learn where development is proposed and can attend review hearings with the support of the best available data on the environmental impacts of the development under review. This mechanism allows the assessment of local conditions to be a dynamic, ongoing process, rather than a static snapshot in time.