| A unit of Lasting Forests
evolving since March 30, 1999 |
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A Total Forest Management Plan
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See Edges
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| Edge treatment for a forest wildlife management clearing |
| Stand Number |
Area (Acres) |
Edge Length (Feet) |
Edge Length (Meters) |
Edge Length (Miles) |
Edge / Area Ratio |
| 126 37 12 |
23.60 6.30 46.66 |
4,241 2,191 5,964 |
1,293 668 1,818 |
0.80 0.42 1.13 |
180 348 128 |
The edge-to-area ratio is an expression of the average number of feet in the edge to every acre in the stand. For many animal species, the more edge the better. For some bird species, nesting at the edge can be wasteful because cowbirds parasitize their nests and predators (birds and mammals such as the opossum) seem to "work" the edges, eating eggs and nestlings.
How far into a forest stand pests and predators penetrate is still being investigated. If the distance is 300 feet as some people report, than a stand must be at least 6.5 acres if any portion is to be "safe" from such losses. Smaller areas do have more edge per unit area and these edge zones are excellent foraging areas and are used in many ways other than nesting. Forest edges next to fields are good for some wild animals, bad for others. Similarly, edges can have drying winds that reduce the quality of the forest growth and other conditions for trees and plants at the edges. To solve the problem or to gain more knowledge to improve decisions will require that we gain more knowledge about the value or relative importance of individual species and the net effect of the edge volume on each species. The phenomena at the forest edge are very complex!
A border established along the edge of a forest will create diverse habitat for wildlife. Many wildlife species thrive in the edge, or zone, where two different habitat types join. A forest border has width on both sides, one toward one, one toward the other type. Borders exist between fields and forests but also between forest types (pines and hardwoods) and between ponds and forests.
Naturally-occurring forest edges near openings contain a variety of small trees, shrubs and herbaceous vegetation that require full sun-light to grow. This diversity of plants offers wildlife many sources of food and shelter. A human-created edge can be as effective as a naturally occurring edge in creating environments for select animals. If the edge vegetation is thick, it can protect the trees in the forest. There are two methods which can be used to create an edge.
The planted border (it really should be considered to be a managed volume with length, height, and width), in a field next to a forest, should be at least 25 feet wide and should provide a gradual change in plant height from the open area to the forest. Small trees should be planted (or encouraged by thinning and pruning, for example an old dogwood) adjacent to the forest. Then, shrubs should be planted or encouraged next to the small trees. Finally, herbaceous vegetation (for example, lespedeza) should be planted next to the shrubs. This border will soften the forest edge and make it attractive to wildlife. Many species of trees, shrubs and vines can be used. Flowering dogwood, crabapple, serviceberry, American holly, and apple trees are some small trees well-adapted for use in borders. Shrubs should be planted 10 to 12 feet away from the forest edge. Blackberry, viburnums, blueberry, sumac, elderberry, and bayberry are some of the shrub species that can be planted. Vines of grape, Virginia creeper, trumpet vine, and morning glory grow well and are used by wildlife. Herbaceous vegetation may include grasses, legumes, and wildflowers. Vines and herbaceous vegetation should be planted, encouraged by fertilizer, or competitors discouraged by mowing or spot killing in the zone between the shrubs and the open area.
Selective cutting can thin the forest and open the tree canopy to allow sunlight to reach the forest floor. This will allow a diverse layer of vegetation to grow in the forest edge. As a general rule, trees which produce nuts or berries, such as oak, hickory, cherry, dogwood, holly, or walnut, should be retained. The trees within 30 feet of the edge may be thinned.
Vines and shrubs growing naturally in the forest should be left untouched. The branches from trees that are cut can be piled (teepee-like) to create nesting and cover areas for the wildlife. As the piles decay, other vegetation will grow and provide the necessary shelter. The best time to cut selectively in order to create the border is in the late fall or winter when the trees are dormant.
The border will require periodic maintenance. In planted borders, the shrub and herbaceous vegetation must be cut or mowed every 2 to 4 years in mid-July to reduce density and prevent larger trees from taking over. In selectively cut areas, thinnings may be required every 10 years to maintain an open canopy.
On development sites where some of the forests are being cleared and some retained, borders can become a valuable asset to the landowner and human community because of flowering and fruiting plants and, of course, to many wildlife species. Creating borders can count toward the "afforestation mitigation". In Maryland, a forest management plan will be required if selective cutting is the chosen method. Planted borders would require a landscaping plan.
or C = d where r is the radius and d is the diameter.
I once developed tables, anticipating graphs of the relations of edges of forest or other openings when developed as hexagons. Almost circular, and thus the smallest edge length per unit area, the manager can study the changes that result from decisions about the size of openings, the edge lengths needed, and the distances between edges and corners. A sample of the 3-page table once included in plans:
| Changes that Occur in Characteristics of Hexagons with Change in Area | |||||||
| Area | Edge Length | Distance between Edges | Distance between Corners | ||||
| Acres | Ha | Feet | Meters | Feet | Meters | Feet | Meters |
| 0.5 | 0.20 | 549.4 | 167.4 | 158.3 | 48.2 | 183.1 | 55.8 |
| 5.0 | 2.02 | 1737.2 | 529.5 | 500.5 | 152.6 | 579.1 | 176.5 |
| 20.0 | 8.09 | 3474.4 | 1059.0 | 1001.0 | 305.1 | 1158.1 | 353.0 |
The following automatically-made computations can aid you in understanding the relations of areas, their shapes, sizes, and their edge lengths.
| Simulate with your entry ... ask "What if ... then what?" |
Under development
Which information do you have...radius (1), diameter (2), or area in acres (3)?
The edge length (in feet) of your circle of interest is
Which information do you have... area in acres (1) or area in hectares(2)?
What is the approximate length (in feet) of the long axis of the ellipse?
What is the approximate length (in feet of the short axis of the ellipse?
The edge length (in feet) of the ellipse is
What is the area of the square (in square feet)?
What is the length (in feet) of one side of the square?
The length of the edge (in feet) of the square is
The length of the square is xxx times greater than the edge of a circle of the same area.
What is the area of the rectangle?
What is the length of the smallest side?
What is the length of the longest side?
The length of the perimeter is xxx feet, zzz times greater than a circle of the same area.
What is the meaning of the shape index (in butterfly habitat analyses) if edge/ (area0.5)?
Lateral Edge
Edge phenomena may occur between layers within a forest. Some of the same phenomena that exist between forests and field (the vertical edge or edge volume) must operate at the horizontal also.
The edge-area G is
G = (g-1) x Area
where g is the number of layers in the forest, pond, etc.
Enter the area of interest (e.g., a forest stand)__
Enter the number of conspicuous layers in the forest (g=layers , typically 2-4))g
Edge and its effects on animals exists for only a few species of relatively low mobility.
See the Supplement (some duplications)
See edges in Modern Wild Faunal System Management
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This Web site is maintained by R. H.
Giles, Jr.
Last revision July 1, 2004.