Wild Ones   Corridors for a Healthier Environment - Part 2  
By Sally Elmiger

This is the second article in a series that discusses how corridors connecting natural areas can help sustain our environment, native plants, and local wildlife, and how Wild Ones members can start creating them in their own communities.

So, after reading the first article on corridors, did you rush out to see if your community’s natural spaces were “fragmented”? Did you see a bit of woodland down the street, or a wetland at the back of your neighbor’s yard? Or did you see open spaces linked by stream channels, naturalized utility routes, and rail-to-trail bikeways? If you saw the latter, you needn’t read any further. However, for those who didn’t, this article describes the types of potential corridor opportunities for your community – the many elements in our everyday landscapes that can be used by plants and animals (and people too!) to move from one green place to another, and live life in between.

A Review

Definition of a corridor: “…avenues along which wide-ranging animals can travel, plants can propagate, genetic interchange can occur, populations can move in response to environmental changes and natural disasters, and threatened species can be replenished from other areas.”

Before looking at different types of corridors, let’s briefly review why these links are important. The natural world functions on an “ecosystem” level, or combinations of landscape elements that all work together. When one landscape element is disconnected from another, it forms a “patch” or relatively small area with limited habitat variety. Many patches are formed by human development, which isolates landscape elements from each other. Small, isolated patches of plants and animals don’t have the genetic diversity to adapt to changes in their environment, or a new threat or disease.

This is an example of “fragmentation.” Fragmentation not only changes the way our landscapes look, it changes the way our landscapes function. And the more fragmented our natural areas become, the more difficult it is for plants and animals to survive. If we have fragmented landscapes, we need to create links between them. These links expand the available habitat by providing a relatively safe travel route, increased opportunity for genetic interchange, and a place to go if a species’ current living quarters no longer meets its needs.

Natural Corridors

In many developed and developing communities, there are two types of naturally occurring corridors – a river or stream corridor, and a tree line or hedgerow corridor. While both corridor systems are complex in structure and function, we’ll describe them here in general terms just to understand their basic characteristics.

The “riparian” corridor is a water route dominated by a river, stream, or other linear water feature. The river or stream is also usually vegetated on both banks by flood plain and then upland vegetation. Riparian corridors are often left undeveloped, and therefore provide an opportunity to act as a link between natural areas. Because water, rich floodplains, and uplands are all part of riparian corridors, they provide a great diversity of habitats. Diverse growing conditions support a large variety of plant species. Plant diversity also promotes animal diversity through varied food sources and nesting sites. In addition, the availability of water and upland areas allows many wildlife species to carry out their full life cycle within the riparian corridor.

The vegetation along streams and rivers also provides significant benefits to the fish, animals, and organisms that live in the streams. A major threat to water quality is sediments and pollutants that are washed off surfaces such as parking lots and lawns (fertilizers/pesticides) and into streams. But if the storm water must first cross a vegetated “buffer,” then the stems and detritus from the plants help to slow the water down, allowing the water to infiltrate the soil and be taken up by the plants. The slowing of the water also allows sediments to settle out before reaching the stream. Trees and shrubs along a stream also contribute organic material to the water, such as leaves and logs or branches. The leaves tend to biodegrade in the water, providing food for aquatic organisms. The logs and branches provide habitat structure for spawning fish, and loafing turtles and ducks to name a few. The streamside vegetation also shades the water and keeps it cool for fish and other aquatic inhabitants. Lastly, the roots of the plants keep the banks of the stream in place, providing erosion protection and minimizing sediment in the streambed. So the riparian corridor not only provides a link for moving wildlife safely from one green space to another, it also protects the water quality within the stream itself.

Tree rows, sometimes known as hedgerows, also provide an opportunity for wildlife and plant migration. These landscape elements are often narrow rows of trees, shrubs, and herbaceous plants that are in place to separate properties or farm fields in agricultural areas. Tree rows can be made up of native or non-native plant species, depending on the amount of past disturbance. If native vegetation exists, the tree row can be an important source of seed in a highly disturbed landscape. Tree rows can be continuous, or can provide “stepping stones” from one large habitat area to another. The Michigan Department of Natural Resources reports that a patchy tree row with trees and shrubs can attract up to 38 different bird species, and a similar but continuous tree row can attract up to 48 different bird species. Many communities strive to retain tree rows as important landscape elements when farm properties are developed.

Human Corridors

As you can imagine, there are many types of corridors that are the result of human development and technology – roadways, railroads, utility linecorridors, canals, and trails to name a few. Unlike natural corridors, the main purpose of human corridors is to move people from place to place. However, conservation of the natural landscape on both sides of these corridors can also provide significant – and in some places the only – connections between patches of nature. In this article, we’ll focus on two of these corridors: the abandoned railroad right-of-way, and the utility line corridors.

At the height of railroad transportation, there were almost 300,000 miles of rail lines. Today, this form of transport is gradually being replaced with the automobile and truck. When the trend in transportation shifted, and rail lines became obsolete, people started transforming the lines into “rail-trails.” As of 2002, more than 11,600 miles of rail line are being used as bikeways, hiking and horse trails, and in-line skating routes.

But rail-trails have more to offer than just places for human transportation and recreation. In the Midwest, many railroad lines traversed fire-dependent plant communities, such as prairies and oak openings. The sparks from the rail cars often started fires next to the tracks, which, in turn, sustained the plants within the railway corridor. Remnants of these communities exist today next to abandoned rail lines, providing native food sources and habitat for wildlife, as well as native seed for dispersal.

Utility line right-of-ways are another opportunity to enhance or create wildlife corridors. In most cases, utility companies trim trees and mow the ground layer of a utility easement so that the lines are easily accessible for repair and not affected by vegetation. This maintenance can be expensive. Creative partnerships have been made between concerned organizations to assist the utility companies in maintaining their easements, but in a much more wildlife-friendly manner.

For instance, an alliance between the National Wild Turkey Foundation, the U.S. Forest Service, Outward Bound, and the East Coast energy company of Haywood EMC was formed to enhance habitat for wild turkey in utility easements on U.S. Forest Service parklands. This project was centered in North and South Carolina, and Georgia. The group worked together to identify six sites where permanent grass and forb wildlife openings were established and are now being managed to benefit wild turkeys, as well as other wildlife species.

What’s Next

Now that you know which landscape features constitute a corridor, check out your community to see how your natural areas are linked. If your town or city has some work to do, the next article in this series will talk about several successful corridor projects that extend habitat areas, promote non-motorized transportation and offer recreation, all through the same linear routes. These popular amenities are called “greenways,” and are growing in popularity and miles.

NOTE:
How do Corridors Help Native Plants?
This article sounds like it’s more about wild “life” than wild “plants”! Well, the lesson here is – if we help wildlife to move from natural area to natural area, we will also help the wild plants do the same. A study undertaken by researchers at the University of Florida showed that more birds were flying between natural areas that had a connection, than between natural areas that weren’t connected. Birds eat berries, and are important dispersal agents for the seeds in the berries. In a similar study by the same group, it was shown that plants were more consistently pollinated between connected natural areas than unconnected ones. This means that the butterflies and bee pollinators could make it safely from one area to the other through the connecting corridor.

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Sally Elmiger has a graduate degree in Landscape Architecture from the School of Natural Resource at the University of Michigan, and works as a community and environmental planner for Carlisle/Wortman Associates, Inc. in Ann Arbor, Michigan. She is a member of the Ann Arbor (MI) Chapter of Wild Ones.

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References

Ecology of Greenways. Design and Function of Linear Conservation Areas; Smith, Daniel S., Hellmund, Paul Cawood, eds.; University of Minnesota Press; Minneapolis, Minnesota; 1993.

American Wild Lands web site: www.wildlands.org.

Power Lines; Haywood Electric Membership Corp.; Waynesville, North Carolina; December, 2003.
Rail-Trails and Safe Communities; Tracy, Tammy and Morris, Hugh; Rails-to-Trails Conservancy; Washington D.C.; 1998.

Michigan Department of Natural Resources website: www.michigandnr.com. University of Florida News and Public Affairs web site: www.napa.ufl.edu.

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