|
Hosted by AmericanTrails.org
How Greenways Work: A Handbook on Ecology
The role of wildlife corridors,
rivers and greenways, in the landscape.
By Jonathan M. Labaree, October 1997
See Introduction
• Chapter 1 • Chapter
2 • Chapter 3 • Chapter
4 • Chapter 5
Chapter Two: Greenway Functions
Nature is a series of interactions among plants, animals, and even
air, soil, and water. A healthy environment depends upon keeping those
interactions intact. The threats described in the previous chapter result
from alterations we have made in the landscape that hinder natural processes.
The challenge for conservationists is to ensure that we orient future
development in a way which sustains natural processes. Protecting environmental
corridors through establishing and managing greenways represents one
method (to be used in conjunction with other approaches) to safeguard
vital ecological processes.
If we are to understand truly our impact on the landscape, we must
learn to see it not as a bunch of independent pieces a woodlot here,
a river there, and a grassland yonder but as intricately connected parts
of a larger whole. Any given part of a landscape affects other parts.
When designing a greenway, it is important to consider what impact it
will have on natural processes. A greenway like their natural counterparts,
environmental corridors can operate in six basic ways:
- as habitat for plant and animal communities
- as a conduit for plants, animals, water, sediment, and chemicals;
- as a barrier preventing movement;
- as a filter allowing some things to pass while inhibiting others;
- as a source for animals or seeds which move to other parts of the
landscape; and
- as a sink for trapping sediment, toxins, or nutrients.
Since it may not be possible, or desirable, to design a greenway to
fulfill all six functions, planners should identify which ones are most
important to the site. For example, in a heavily developed area, a greenway
can offer scarce habitat. Severely fragmented landscapes would benefit
from a greenway designed to be a conduit allowing animals to reach isolated
protected areas. A greenway which is along a river should be planned
to filter excess nutrients from surrounding lands (in which case it
also acts as a barrier preventing movement of sediments and a sink storing
them). One proposed along an abandoned rail bed in the midwest can act
as a source of native prairie grasses.
|
|
Greenways as habitat
A species' habitat may include many different types of vegetation
and geography, such as wetlands, upland forests, and fields. A
greenway's ability to provide habitat will depend upon its size,
location, and the needs of native species. A greenway that is
200 feet wide will generally contain habitat for fewer species
than one in a similar location that is half a mile wide. A 200-foot-wide
greenway along a river, however, that includes a variety of vegetation,
may provide habitat for as many species as a wider one in a setting
with less natural variation. Some species require more natural
area than others. A 200-foot-wide greenway, therefore, may provide
plenty of habitat for salamanders, beetles, and frogs, but very
little for bears, eagles, and elk.
|
|
|
Greenways as conduit
Conduits are areas in the landscape along which water, animals,
plants, and people move. A river is among the most obvious examples
of a conduit. Water carries sediment, nutrients, leaves, insects,
bacteria, and plankton along with it. Acting as a conduit to connect
otherwise isolated parts of the landscape is an important function
of greenways. Such connections will allow animals to reach necessary
elements of their habitat. As animals or water move along a greenway
conduit, seeds do as well, thus aiding in plant dispersal.
|
|
|
Greenways as barrier
While a greenway may be a conduit to some things, it presents
a barrier to others. Again, a river serves as an example. Small
animals, such as mice, may be unable to cross a river. Or its
moist habitat may be inhospitable to creatures that prefer drier
surroundings. Even very narrow corridors, such as hedgerows, can
present a physical barrier of impassable habitat for some species.
|
|
|
Greenways as filter
A filter prevents the passage of some things but allows the passage
of others. Filtering can occur in a greenway either perpendicular
to its axis or along its length. Large animals, able to traverse
a river, for example, can pass across a riparian greenway, but
small ones may not. Similarly, some animals may be able to move
along the entire length of a greenway, while others may fall victim
to predators or find the habitat inhospitable. The next chapter
deals extensively with a greenway's potential to filter sediments
and nutrients from surface and groundwater.
|
|
|
Greenways as source
A greenway may act as a source, providing surrounding land with
a variety of things. A riparian greenway may be the only source
of water in an otherwise arid landscape. In human-dominated areas,
even narrow strips of relatively undisturbed land, such as hedgerows
or steep slopes, may be a source of seeds of either native or
non-native species.
|
|
|
Greenways as sink
A greenway acts as an ecological sink when something moves into
it but does not travel back out into the surrounding land. Perhaps
the most significant way a greenway can be a sink is by trapping
sediments and nutrients carried in surface and groundwater. This
function is, however, dependent upon a specific time frame because
sediments may eventually wash downstream during a dramatic flood,
or nutrients absorbed by vegetation will re-enter the soil and
atmosphere when the plant decays.
|
|
 |
Related topics:
Adjacent
land use
Benefits
Bike/Ped
facilities
Economic impact
Health & trails
Management
Planning
Rails to Trails
Safe Trails Forum
More resources:
Bibliography
Quotations
Glossary
Acronyms
Tools
Products & services
For more opportunities for
training on trail design, construction, and management see the National
Trails Training Partnership area.
|
Skip
Navigation
