How Greenways Work: A Handbook on Ecology
Our modifications have created new patterns in the landscape which can threaten ecological functioning.
By Jonathan M. Labaree, October 1997
Chapter One: Impacts of Development
An underlying principle of conservation is that utilizing natural resources does not, in itself, pose a threat to the environment. It is the manner in which we do it that dictates whether our activities are detrimental or benign. Our modifications have created new patterns in the landscape which can threaten ecological functioning. Dramatic shifts in the ratio between natural and developed land has lead to:
Loss of natural space
Developing land for human needs reduces the amount of natural space. As natural space diminishes, so does habitat diversity-- the great variety of forests, prairies, bogs, and deserts which exist in nature. The result is both a decline in the number of species and fewer individuals of those species which do survive.
Converting midwestern short- and tallgrass prairies over to agriculture, for example, has lead to a decline in native grass and wildflower species and in animals adapted to prairie habitat. We have substituted native species with ones which better meet our needs: cattle, corn, wheat, pigs. While this has had advantages for society, it has upset the natural balance of those ecosystems. We are generally able to sustain our agricultural systems only by replenishing fields with fertilizers and groundwater and by protecting them from pests with chemicals.
Fragmentation of natural spaces
Development has an indirect impact on land it leaves untouched. As we convert land, we fragment it into smaller and more isolated patches of natural space (see Figure 1). The new pattern that we have created on the landscape greatly alters the way in which natural systems function. Wildlife and flora populations have evolved, and continue to evolve, in conjunction with their surroundings. They have developed strategies to exploit their environment in order to fulfill basic life needs. Different species utilize different habitats. Any change in their habitat will affect their ability to survive. Two major reasons why fragmentation is destructive are increase in edge habitat and greater isolation between patches.
Edge habitat is an area of transition between two types of land cover. Edges exist throughout nature in many forms and are often areas of high biological diversity because two or more natural communities come together and influence each other. Plants and animals which live in each community utilize the edge as does a distinct set of species specifically adapted to ecological edges. Edge habitat that results from human activity can be disruptive. While some species are adapted to edge habitat, there are many species which require interior spaces, shielded from the influence of surrounding lands. Fragmentation changes the natural balance between edge and interior. Indeed, heavily fragmented landscapes may not have any interior habitat at all.
Isolation of patches In fragmented landscapes, development has left many wildlife populations isolated from needed habitat and other individuals of their species. Some species are not sensitive to humans and survive quite well in our presence. Other species, however, will not come near even a modest development or fly across a cultivated field. Although natural land may still exist in fragmented landscapes, species sensitive to people cannot move freely in order to utilize it. This not only cuts individuals off from habitat, it makes it harder for them to sustain their populations by creating barriers between potential mates.
Degradation of water resources
Wetlands and lands along rivers perform a variety of critical functions related to water resources: controlling floods, trapping sediments, filtering out toxins and excess nutrients, and supporting rich assortments of wildlife and plant species. These same areas are often favored for development because they are flat, arable, or have high residential value. Developing wetlands and riparian zones reduces their capacity to fulfill their functions and threatens the health of the environment.
Decreased ability for nature to respond to change
Species naturally respond to changing conditions both in the climate and in their predators and prey. Development has decreased nature's ability to respond to these changes in two fundamental ways: reducing genetic diversity and hindering wildlife movement. As populations of plant and animal species decline, their genetic diversity also declines, diminishing their ability to adapt to long-term change. In addition to genetic alterations, plants and animals respond to their changing environment through movement. Animals move in response to events such as wildfires or hurricanes. As climate changes, both plants and animals move to stay in environments to which they are adapted. Fragmentation hinders this movement. Pollution may be increasing the rate of change beyond nature's ability to respond
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Updated April 11, 2009