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II. A PRACTICAL FRAMEWORK FOR MAKING HABITAT PROTECTION DECISIONS |
A. EFFECTS OF DEVELOPMENT ON WILDLIFE HABITAT
The citizens of Colorado have often voiced their intent to preserve environmental values as communities develop and grow. However, these intentions are frequently difficult to realize, in part because achieving environmental protection may pose challenging compromises among needs to preserve the environment, to invigorate the economy, and to protect private property rights. Rising to these challenges requires a scientifically sound, utilitarian approach to protection, an approach that is legally and politically tenable. In this handbook, we will describe practical methods for protecting wildlife habitat. These methods can be applied broadly across a range of landscape types and a variety of political jurisdictions in response to many types of development.
The usefulness of the methods described in this handbook depends on a few key concepts and
assumptions about the ways that people and wildlife share the land. In this chapter, we outline these
assumptions and concepts. In particular, we make three points.
In this chapter, we will assemble these three ideas to provide a framework for making habitat
protection decisions. In the subsequent chapter, we use this framework to offer practical guidance
for what to do, on the ground, to protect wildlife populations and habitats.
Communicating ideas about human impacts on wildlife habitat requires us to think clearly
about ecological concepts, ideas that may not be familiar to all readers. Such thinking requires a clear
vocabulary. Several biological terms will be used frequently in this chapter and the next. These are
defined in Table 1.
| Table 1. Definitions of Ecological Terms. |
| A landscape is a large land area (i.e., multiple square miles) that contains habitat for wildlife. A watershed offers an excellent example of what we mean by a landscape. Within a landscape there are usually different types of vegetation arranged in a mosaic, much like a patchwork quilt. |
| A patch of habitat is what you would think it is -- a spatially separate instance of a given type of habitat. For example, a stand of aspens surrounded by conifers is a habitat patch for some species of cavity nesting birds. |
| A vegetation type is a classification given to plants that are found in the same place on a landscape. For example, stands of trees that are predominantly aspen would be classified as the aspen vegetation type while areas that are covered with grasses and no trees would be classified as the grassland vegetation type. Different wildlife species have different affinities for vegetation types. |
| A population is a group of individuals of the same wildlife species that reside in areas small enough that members of the group are reasonably likely to breed with one another. Thus, a heard of mule deer that uses a creek drainage in the Colorado mountains is, most likely, a single population. However, herds of deer that use drainage separated by peaks are likely to be distinct populations. |
| A community is a group of different wildlife species that are linked by ecological processes (e.g., predation, pollination, competition) at a given location. Often, communities are associated with a particular type of vegetation. Thus, the aspen wildlife community refers to all of the wildlife species (birds, mammals, herptiles) that live in stands of aspen. |
| Biodiversity is the variety of all lifeforms considered at all levels of organization, from the genetic level through the species and higher levels of taxonomic organization, and including the variety of habitats and ecosystems. |
| Fragmentation is the breaking up of continuous areas of habitat into smaller parcels. For example, a forest becomes fragmented when sections are cleared for agriculture or when trees are cleared to build roads. |
| Habitat consists of the physical features (e.g., topography, aspect, stream flow) and biological characteristics (vegetative cover, other animal species) needed to provide food and shelter for wildlife. |
| Species diversity is the number of different species of wildlife, or species richness, and their relative abundance in a given location. As species die out in that location, species diversity declines. |
| Scale is the relative size of an area of interest. If we focus on relatively small areas (say, the area around a house or a single subdivision) our focus is fine scale. If we pay attention to much a larger area (i.e., a county or watershed), we are looking at coarse scales. |
C. SCALE, HUMAN IMPACTS, AND WILDLIFE PROTECTION
Equipped with these definitions, we begin with the idea that residential development influences wildlife at two fundamentally different scales -- the broad "Landscape" scale and the more focussed "Site" scale. At the landscape scale, development influences the distribution, survival, and persistence of wildlife populations and communities. At the site scale, development influences the behavior, survival, and reproduction of individual animals. Effects at the landscape scale can be mitigated by landscape management -- effects of development at the site scale can be mitigated using site management. These two key concepts of scale are illustrated in Figure A and Table 2.
Scale, in turn, determines the usefulness of actions chosen to modify the impacts of
development. To illustrate this idea, it might be useful to think of a rural landscape, a large area that
is predominantly undeveloped, but that contains a few spatially separate subdivisions. The impacts
of people within those subdivisions occur at fine scales. At these scales, we will refer to human
impacts on wildlife as "site effects" (Table 2). Such effects include the influences of dwellings, roads,
and people's behavior on the behavior, reproduction, and survival of individual animals. Examples
of site effects include avoidance of structures and roads by wildlife, changes in mortality rates (such
as cats preying on songbirds, or highway deaths), and increases in human/wildlife conflict (such as
bears in trash cans). Taken together, these site effects produce what we will call a "disturbance zone"
around a house or a subdivision (Figure A).
| Table 2. The Landscape Scale and the Site Scale. | |||
| SCALE OF EFFECTS OF DEVELOPMENT | EXAMPLES OF EFFECTS OF DEVELOPMENT | TYPE OF PROTECTION | EXAMPLES OF PROTECTION TOOLS |
| Landscape Scale | Conversion of habitat
patches to residential
development.
Fragmentation of habitat patches by roads. |
Landscape Management | Zoning
Clustering
Transportation planning
Transfer of development rights
Conservation easements |
| Site Scale | Increased predation by
domestic pets.
Increased disturbance
from human activity.
Reduced cover of native vegetation. |
Site Management | Control of pets
Buffer requirements
Maintenance of native plants in
landscaping
Sensitive lands overlays |
We define a "disturbance zone" as the area surrounding a house, road, or a subdivision in which the value of habitat for wildlife is meaningfully reduced by human activity and/or structures. A meaningful reduction in value occurs whenever an area is avoided by native wildlife or when the ability of individual animals to survive and/or reproduce declines in the area.
Although site effects of a given development are important at that location, such effects are not the only way that development influences wildlife. At larger scales, such as a valley containing several subdivisions, site effects accumulate and disturbance zones add together to cause what we will call "landscape effects". Landscape effects cause changes in the behavior, reproduction, and survival of populations, which, in turn, influence the composition and persistence of communities of wildlife. Landscape effects include reductions in habitat area (which results in diminished animal numbers) and increases in habitat isolation (which constrains the movement of animals among patches of habitat or seasonal ranges).
Differentiating between the scales of human effects is important because scale determines the
kinds of approaches we can use to manage the ways that development influences wildlife.
At the scale of a specific subdivision, site effects can be mitigated by "site management", which includes all of the actions that can be taken by people to moderate their effects on the behavior and survival of individual wildlife. Examples of such management include buffering of roads and structures, avoiding critical habitat by site design, management of vegetation, and control of pets. The primary goal of site management is to reduce the size of the zone of disturbance.
In contrast to site management, the goal of landscape management is to reduce harmful effects
of increases in the density and distribution of the human population on populations and communities
of wildlife, as opposed to individual animals. In general, this means managing the type and intensity
of development and its spatial location in a broader area -- such as a county or a basin as opposed to
a subdivision. In so doing it is possible to maintain the variety and extent of valuable habitats and to
preserve opportunities for animal movement among those habitats by using techniques that steer
development away from areas that have high value for wildlife and towards areas that have low
value.
The opportunity to use site level and landscape management depends on the history of
development in a given area. We can think of the extent of development as a continuum extending
from relatively undeveloped, rural areas to areas that are predominantly urban (Figure B). The
emphasis in a plan for wildlife protection depends on the position of an area of interest along this
continuum. Landscape management may be most effective in rural areas, whereas site management
is likely to be most effective in urban areas.
At the rural end of the development gradient, there is large opportunity for landscape level management, simply because there is abundant wildlife habitat. As a result, it is possible to plan for development by identifying the areas of high wildlife value and encouraging development elsewhere. Because undeveloped areas predominate the landscape, the fragmentation of the landscape by new development still leaves large undisturbed areas. This means that there is ample opportunity for movement of wildlife among habitat patches. County governments and private landowners will have primary responsibility for protection programs in rural areas.
In contrast, municipal governments play a much more important role in habitat protection in urban areas. Because much of the landscape has been fragmented by development, opportunities for effective landscape management are not as great as in rural areas. Thus, site level management becomes much more important at the urban end of the gradient.
This rural-urban continuum is useful for organizing our thinking about protecting habitat, but it should not be used as a fixed recipe for management. All areas contain some blend of the attributes described above, and as a result, all habitat protection programs should contain elements of landscape level and site level management. In the next chapter, we offer some general guidelines for managing people and development to achieve habitat protection.
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