Every hunter knows the edge. It is where the field meets the woods, where the clearcut meets the standing timber, where the creek bottom meets the ridge. It is where the deer come out to feed at dusk, where the turkeys strut in the spring, where the sign is heaviest and the shots are closest. The edge is the most productive place in the woods, and every hunter learns it early, because the edge is where the animals are.
But the edge is also a symptom. It is what happens when a forest is cut into pieces, by roads and fields and subdivisions and pipelines, until what was once a single unbroken expanse of habitat becomes a mosaic of fragments, each one surrounded by edge. Ecologists call this habitat fragmentation, and they have a name for what it does to the creatures that live in the fragments. They call it the edge effect.
The United States is crossed by a dense web of roads, and the ecological consequences are measurable.
- 4 million miles of public roads in the United States
- 1 to 2 million large animals are struck by vehicles each year, including an estimated 1.5 million deer
- Roads and development have fragmented forest cover across the eastern US, reducing interior habitat for species that avoid edges
Source: Federal Highway Administration and State Farm deer collision data.
What the Edge Does
The edge is not just a line. It is a zone, a band of altered conditions that extends into the forest from the boundary. Light reaches the ground differently at the edge. Wind moves differently. Temperature and humidity shift. The understory grows thicker, and with it come the species that like thick understory: the deer, the turkeys, the rabbits, the generalists that thrive on disturbance.
But the edge also brings the species that prey on the generalists. The cowbird, which lays its eggs in the nests of other birds, follows the edge. The raccoon and the skunk and the opossum, which raid nests, follow the edge. The house cat, which kills billions of birds a year, follows the edge. And the interior species, the warblers and thrushes that need deep, unbroken forest, retreat from the edge, pushed back into the shrinking core of the fragment, until there is no core left and they are gone.
This is the paradox of the edge. It is the most productive place in the woods, and it is also the place where the woods are dying. The deer love it. The hunter loves it. And the forest, the deep, old, unbroken forest, is being eaten away from the outside in, one edge at a time.
The Hunter on the Edge
There is a reason the hunter and the deer both gravitate to the edge, and it is the same reason. The edge is where the food is. The edge is where the cover meets the open, where the browse is thick and the escape is close. The deer come to the edge to feed, and the hunter comes to the edge to wait for the deer. It is a relationship as old as hunting itself, and it is not, in itself, a problem.
The problem is that we have made too many edges. A forest with a few natural edges, a field here, a creek there, is a healthy, diverse place. A forest that has been cut into a hundred small fragments by roads and subdivisions is not. The difference is a matter of degree, and the degree has been rising for a century. The eastern United States, once a nearly unbroken forest, is now a patchwork, and the patches are getting smaller and the edges are getting longer and the interior is disappearing.
Annual Deer-Vehicle Collisions, Selected States
Approximate annual figures from State Farm and state transportation data.
The Shape of the Forest
There is a way to measure fragmentation, and it is called the edge-to-area ratio. A large, round forest has a low ratio: a lot of interior, a little edge. A small, irregular forest has a high ratio: a little interior, a lot of edge. As forests are cut into smaller and more irregular pieces, the ratio climbs, and the interior habitat, the deep forest that the warblers and thrushes need, shrinks faster than the total area. You can lose half the interior of a forest while losing only a fraction of its total acreage, simply by cutting it into pieces.
This is what the roads do. A road is not just a strip of pavement. It is a line of edge, running through the forest, fragmenting it on both sides. A single road through a large forest can double the amount of edge, and the interior species feel it. The deer, of course, do not mind. The deer thrive on edge. And so the hunter, following the deer, finds himself in a landscape that is increasingly edge and decreasingly forest, and it is easy to mistake the abundance of deer for the health of the woods.
But the deer are not the whole story. The deer are the part of the story that the hunter sees, because the deer are the part that comes to the edge. The warblers are the part the hunter does not see, because the warblers are retreating, and the retreat is silent, and it is happening in the deep forest that the hunter, following the deer, has stopped visiting.
Still hunt. Move slowly. And when you sit on the edge at dusk, waiting for the deer, remember that the edge is a symptom as well as a place. It is where the forest is being cut into pieces, and it is where the pieces are being lost. The deer will be there. The deer are always there. But the forest, the deep, old, unbroken forest, is somewhere behind you, shrinking, and the edge is the line where it is happening.
The hunter who hunts the edge should know what the edge means. It means the forest is being divided. It means the interior is being lost. It means the abundance of the edge is, in a real sense, the abundance of a wound. And the hunter, of all people, should be the one who notices.
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Data source: Federal Highway Administration and State Farm deer collision data.