ECOnnection
Corridors
by Karen Dusek

I sit on a cushion of newly fallen pine needles beside a small pond, lost in the deep muted stillness of the forest. But the longer I sit, the more acutely aware I become of the activity around me. The whole world is on the move - juncos flit from branch to branch; a pair of swans creates a gentle wake on the surface of the water with their paddling feet; clouds collide overhead; leaves rustle in the breeze. The earth and everything on it is in constant motion, sometimes self-willed, sometimes caused by forces beyond their control. Plants grow upward then outward toward the sun and then move further still as their seeds are carried by birds and animals, wind and water, sometimes miles from where they originated. Pollinating insects hover above colorful blossoms in search of nectar. Birds swoop and soar and preen and peck. Amphibians, reptiles, mammals and other creatures dig and run and fight and mate and, when they die, are eaten by bacteria and worms and insects and birds and mammals, their bodies nourishing the soil, which itself moves as it is tunneled through and dug up and washed away.

Movement is a necessary part of life, whether it takes the form of a 1,000-mile semi-annual migration or a nightly flight in search of a meal. But movement can be stopped by obstacles too great to overcome. Mountain ranges, rivers, changes in climate or altitude, beaches, forests, grasslands and other natural phenomena can stop certain species in their tracks, as can roads, fences, clear cuts, shopping malls, housing developments and similar man-made structures.

Impediments to movement can sometimes be beneficial when the thing that is impeded is an alien or invasive species of plant or animal, like purple loosestrife and zebra mussels, that could threaten the future of native species. Naturally occurring obstacles like the Rocky Mountains and the Great Plains have also created distinct eastern and western species in the United States, as Neil Payne and Fred Bryant pointed out in their book, Wildlife Habitat Management of Forestlands, Rangelands and Farmlands. But numerous studies have indicated that barriers to movement that are created by human activity can interfere with wildlife and plant activity such as migration, breeding, seed dispersal, pollination and hunting, creating islands or "patches" of natural habitat that can support only small populations of species with limited ranges. Because the individuals living within the patches don't have much to choose from when it comes to a mate, genetic diversity decreases over time, decreasing their ability to adapt and making them more susceptible to disease, insect infestation and environmental changes. According to the California Center for Wildlife in their book Living with Wildlife (1994) "over the past several decades 42 types of mammals have disappeared from 14 North American parks," including badgers and black bears in Zion National Park and pronghorn, beavers, flying squirrels and red foxes from Bryce National Park. While some species are being reintroduced into the wild, it seems that it will do little good if the reserves where they are released are too small to support them. Recognizing that the fragmentation of ecosystems will eventually lead to the demise of the organism that have become isolated, scientists came up with the idea of creating corridors that would allow populations to safely move from one ecosystem patch to another similar one. A wildlife movement corridor, also known as a "faunal movement corridor" or "landscape linkage," is defined by Payne and Bryant as "a linear, natural, restored or cultural connection between at least two larger similar habitat areas. It maintains gene flow and is used for movement of animals and plants pollinated or dispersed by animals."

There are many considerations when designing wildlife corridors, ranging from length, width and bordering human activities to location and the species that will benefit from their use. Payne and Bryant talk about the two types of animals use wildlife corridors - those that travel through them, including migratory species and young animals that have been told it's time to leave home and make their own way in the world; and those that live within them or that take a substantial amount of time - more than one generation at times - to travel through them, which include plants and many smaller animals such as insects, reptiles, amphibians, birds and small mammals. The first type wants to get through as quickly as possible; the latter type needs adequate food and shelter to sustain them while they are there. Payne and Bryant suggest that long corridors are useful for species that move fast, while shorter ones are appropriate for slower moving species. Width is also important. If corridors are too wide, animals may become confused or intimidated. Whatever width is chosen, the authors recommend that it remain consistent along the entire length of the corridor, which should be as straight as possible, as well, again to avoid confusion.

While the word "corridor" may bring up images of hallways between two walls connecting rooms in buildings, wildlife corridors may be higher than the surrounding landscape, as in the case of strips of trees left in clear-cut forests that allow the passage of forest species. Examples of wildlife corridors that are lower than the adjacent habitat are roads, trails, railroad beds, and rights-of-way for power lines and pipe lines. While the latter type of corridor is generally less desirable because it tends to create patches, Payne and Bryant noted, it can be useful if managed properly. Sometimes, as in the case of the system of abandoned railroad beds being turned into biking and hiking paths through the Rails-to-Trails program, wildlife will take advantage of the same corridors used by humans.

Wildlife biologists have long recognized the importance of riparian corridors to wildlife and plant species. (Riparian zones are ecosystems that occur along streams and rivers and in floodplains.) Payne and Bryant go so far as to say that riparian zones "can provide a system of movement corridors that will mitigate the effect of forest fragmentation by linking all of the old forests in a region into a network." However, they add that, if the larger areas of habitat in a riparian zone are not connected, "they act only as long, narrow pieces of habitat rather than movement corridors."

Neighbors can join together to create wildlife corridors. You can help to create your own by planting tree rows with shrubby undergrowth. According to the Michigan Department of Natural Resources, a row of trees planted in patches can support as many as 38 different species of birds, while a continuous row can support as many as 48 species. (It would be wise to do a little research first to determine the best species to plant in your area.) Encouraging local, state and federal officials to provide safe crossings for wildlife under or over roads and around development is another way you can help.

You may email Karen at karen@lakeshoreguardian.com.