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Silhouette of a wild red-legged Partridge

Proper habitat management is the backbone of wildlife management. When creating wildlife habitat, it is critical to provide all necessary resources in an accessible fashion. Many wildlife species depend upon several different habitats to meet daily and seasonal needs. For example, bobwhite quail require access to 3 to 4 cover components throughout much of the year (e.g., early succession grasses and forbs for brood rearing, perennial native grasses for nesting and roosting, and shrubby or brushy areas for escape and loafing cover) in a relatively small amount of space (<40 acres). White-tailed deer, on the other hand, are quite mobile and traverse great distances to seek out specific types of cover to meet daily and seasonal needs. Whether it’s the addition of foraging, brood rearing, or nesting cover for bobwhite quail, the “usability” of these cover types will be dictated by their interspersion (i.e., intermixing) within the property boundaries.

The Edge

Where land management seeks to provide all the needs of wildlife in relatively close proximity, or better stated as striving to maximize interspersion of different cover types, we invariably arrive at the topic of edge. Edge is defined as the juncture of two or more different cover types. The easiest visual example is where forest and open land meet; producing an easily identifiable edge. This type of edge is often called a “hard edge” due to the extreme dissimilarity of the two adjoining cover types (forest and field). Edge may also occur where two similar cover types (e.g., two loblolly pine stands) abut one another but are of different ages. However, edges are not always discernable and oftentimes combine elements of both forests and openlands (i.e., shrubs and small trees interspersed between the two cover types). Determining just where the forest ends and the field begins may be somewhat difficult. In this case, edge may be termed an ecotone, or transitional edge.

Importance of Edge

So why is edge important? It has long been known that edges support the greatest diversity and abundance of wildlife, particularly game species. Aldo Leopold, in his landmark book on wildlife management (Game Management, 1933, page 132), summed it up best in that “The potential density of game of low mobility requiring two or more types is, within ordinary limits, proportional to the sum of the type peripheries.

In the above, the “type peripheries” is what we call edge. So why is game more abundant along edges? The greater abundance (and diversity) of wildlife along edges is due to habitat diversity produced by creating simultaneous access to two cover types. Not only does wildlife have access to two different cover types along an edge, but also, in some cases, access to the edge itself. Consider for a moment, the edge between a closed canopy hardwood forest and a grass field. Along the edges of the forest, sunlight penetrates down along the side of the stand and for some distance into the stand. As such, the vegetation composition (numbers of different plant species) and structure (the physical dimensions of these plant species) along the outer edges of the forest often consist of shrubby plants and vines, creating greater vegetation diversity from which wildlife such as birds may find cover favorable for foraging, nesting, roosting, or escaping predators. For the most part, wherever you have a diversity of both vegetation composition and structure, you have a greater potential for providing specific cover requirements to meet the needs of a wider array of wildlife species.

Levels of Edge

It is important to keep in mind that edge is relative to the animal, not the landowner creating it. Furthermore, edge can be viewed from different “levels” or spatial scales by wildlife. It is relatively easy for us (humans) to identify the edge between a forest and open land or between perennial and annual stands of grass. And for most land management purposes, this will be sufficient. However, these edges may or may not be perceptible, or even important, to some wildlife. As an example, consider a migratory Cooper’s hawk. A Cooper’s hawk may “see” edges of major physiographic regions (Lower Coastal Plain of Alabama all the way up to the Boreal Hardwood Transition area of the Great Lakes states) as it migrates from wintering to breeding grounds. This same Cooper’s hawk may also “see” edges of woodlots interspersed among pastures and row crop fields. Within one of these woodlots, a Cooper’s hawk may “see” even more edges; that of a 63-year old white oak tree within a 34-year-old mixed pine-hardwood stand. So, in essence, we do in fact live in a world full of edges!

How much edge?

How much edge should I create on my property? Well, that depends on your management goals. If your property consists solely of 1 or 2 cover types, then creation of additional edge will undoubtedly increase habitat diversity and subsequently wildlife diversity. However, this will only work up to a certain point; the property will eventually become “maxed out” on edge. Leopold’s key phrase “within ordinary limits” has far reaching connotations. Once “maxed out” on edge, any additional edge becomes redundant and likely will not add any significant wildlife diversity to the property, and in fact may become a hindrance for some wildlife.

Creating too much edge may negatively impact some wildlife. For example, many forest-dwelling songbirds require rather large blocks of contiguous forest for successful breeding. Additionally, where forest edges may attract a diversity of wildlife, they also attract a diversity of predators (avian, mammalian, and reptilian) and nest parasites (birds which lay their eggs in other birds’ nests). Avian, mammalian, and reptilian predators also key in on these edge habitats because, due to the increased diversity of potential prey items, securing food resources is often easier. As such, birds nesting along forest edges may experience lower nest success that those nesting further within the forest. The same applies for ground nesting birds such as bobwhite quail, turkeys, meadowlarks, and a multitude of grassland sparrows. Those birds having to nest close to an edge of a grassland may be more susceptible to nest predation. In deed, having too much edge can be a double-edged sword!

Depending the land and wildlife management objectives of a property, edge habitat may be created by various means. Within forested lands, edge habitats may be created through intentional (harvest of entire stands, group selection cuts, or by the removal of individual trees) or unintentional (tornado, wildfire, disease and insect infestation) means. Within open lands, disking and prescribed fire may be used alternately (1/3 of the field at a time) to produce a diversity of distinct plant communities within a single field. In some larger fields, shrubs and trees may be planted to increase vegetation diversity. Whether dealing with forest or open land, creation of edge will likely add greatly to overall habitat diversity, and subsequently wildlife diversity of a property.

Additional Information

Along with, and related to edge, are two additional things to consider; habitat interspersion and habitat juxtaposition. Interspersion is the intermixing of different habitat types. Juxtaposition is proximity of different habitat components to one another.

Poor Interspersion, Good Interspersion, Poor Juxtaposition, and Good Juxtaposition

Good Interspersion - Poor Juxtaposition and Good Interspersion - Good Juxtaposition

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