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Extension Forestry & Natural Resources

Wildlife & Fisheries Biology  -  Environmental & Natural Resources  -  Forest Resources



Managing for Wildlife Diversity in Managed Forests

Greg Yarrow, Professor of Wildlife Ecology, Extension Wildlife Specialist

Fact Sheet 20: Revised May 2009

Managing for a variety of wildlife species usually has involved one or both of the following strategies: (1) managing for habitat diversity, and (2) targeting management for indicator or featured species.

Managing for habitat diversity is based on the theory that communities are mosaics of habitat types, and managing land to maximize the number of habitat types will increase diversity and provide a variety of wildlife. Under this style of management, wildlife that are generalists in their habitat requirements will be favored, while those species with specific habitat requirements will be limited.

Under this type of management, ecotones or edges are increased. Animals that inhabit “edge” such as white-tailed deer, red foxes, rabbits, bobwhite quail, mockingbirds and cowbirds are favored. Species that require large areas of uniform habitat, such as gray squirrels, black bears, yellow-throated warblers and ovenbirds, are not favored.

Managing for indicator species is an attempt to accommodate wildlife species with specific habitat requirements. Under this theory, species that are considered “keystone” species or are strongly associated with a specific habitat type are selected for management. Their presence, relative numbers and health are “indicators” of the relative health of the community at large. Hopefully, the species selected for management can also reflect the needs of other species in the community. An example of this would be selecting the red-eyed vireo as an indictor species to reflect the needs of other migratory songbirds that use bottomland hardwood forests. The problem with this is that you will rarely find a species to serve as an indictor that can reflect the needs of the entire community. So you either select several species or you develop management criteria that are broader than the specific needs of any one species.

In reality, wildlife management requires a balance between managing for maximum diversity and the needs of specific species. It requires management in such a way that all species be accommodated. It has been the struggle for this balance that has led to the development of ecosystem or landscape management as a way to deal with it.

A landowner interested in managing for a wide variety of wildlife is left with the question, “How can I provide all things to all species on my limited amount of land?” The answer is, “You can’t.”  You can look at what land base you have, your resources, interests, goals and objectives. All of these will enter into what you can do to manage nongame wildlife on your land.

Management Practices

The requirements of all wildlife are the basic necessities: (1) cover, (2) food, (3) water and (4) living space. These are the components of habitat. The number of animals a given habitat will support is determined by the amount and arrangement of the components relative to the wildlife species in question. There are a number of things landowners can do to influence habitat for both game and nongame wildlife. Remember, management for specific species will have a positive or negative influence on other species in the community. The key to successful management is a well-thought-out management plan.

Given that, habitat improvements for nongame wildlife are the same as for game species, it’s just a question of how and when to use the various habitat management practices.

The goal of wildlife habitat improvement is to provide the habitat needs of wildlife in a given area. This reduces the land area necessary to support an individual or group and thereby increases the number of individuals the land can carry. Most frequently it is not the quantity of any one habitat component that limits wildlife numbers, but the spatial arrangement to the other requirements in the area. Larger quantities of food, cover or water may be unused by a particular animal because they are spaced too far apart from the other requirements. Wild animals must have food. But they also must have cover to escape from danger and to feel secure. If we provide food and neglect cover needs, animals may never use the food, or if they do, will be eaten themselves.

A clearcut forest can provide abundant food sources for some wildlife, but it may never be used if sufficient forest is not present for escape cover. Forested corridors at least 100 yards wide through clearcuts are needed for security and will be used as travel routes that link disconnected cover blocks. If an animal spends an excessive amount of time traveling to obtain all of its life requirements, its survival is jeopardized. There is increased risk of predation. Properly-arranged habitat components in close proximity enhances survival. Management becomes a task of repeating ideal habitat units across the landscape to increase wildlife numbers. The size of habitat units is relative to a species’ mobility and behavior. A covey of bobwhite quail may range over 40 acres. Some forest-dwelling songbirds may need 500 acres or more of unbroken habitat.

Arrangement of habitat types should consider both horizontal and vertical dimensions. Horizontal arrangement is called interspersion. Interspersion is the intermixing of different habitat types (young forest, mature forest, grassland, row crop land, shrub, etc.) into a mosaic. Consider it as a jigsaw puzzle. All of the pieces of the puzzle must be there in the proper order for the habitat of a particular species to be complete. Wildlife are usually abundant on landscapes with high interspersion. The principle of interspersion says that wherever two required habitat types for an animal meet, the area where the two habitat types meet will be more favorable for wildlife than either type alone. The transition between types is an important consideration. An edge where components from each habitat type intermingle is more beneficial than a sharp change from one into the next.

Bobwhite quail, eastern meadowlarks and grass sparrows are found around cultivated land, and also need open woodland to fly into for escape. Populations of these birds are usually low where agricultural land shifts directly into dense forests. The habitat for these species is vastly improved if cultivated ground transitions to open woodland through successive bands of 1 and 2 year old fallow land, grasses and shrub patches.

Large amounts of edge are not beneficial to all wildlife species. Some need unbroken areas of a certain successional type as a part of their habitat requirements. To attract a diversity of all wildlife, forest and farm owners controlling large sections of land should balance edge with unbroken forest.

Vertical layering refers to how plants grow in different layers within a forest community. Vertical layering or foliage height diversity is an important aspect of habitat arrangement within a forest. Think of it in terms of a high-rise apartment complex. The more canopy levels within a forest, the more habitat or places for wildlife to live. A forest composed of one distinct layer of tall trees provides fewer habitats than a forest with a variety of layers. This is especially true of forest birds. Uniform dense layering throughout the forest, however, is not ideal. Some forest birds, for example, may nest in dense shrub or midstory, but require an open understory for feeding. A patchy pattern of vegetation types within the forest provides a greater variety of food and cover to meet the needs of wildlife. Vertical layering is enhanced in forests with relatively open overstories which provide space and allows sunlight penetration into the stand to promote the growth of saplings, shrubs and herbaceous plants beneath the canopy.

Forest Improvement Practices

Various silvicultural practices can be applied to forest stands to improve their ability to support wildlife. Intermediate-aged forests often lack the structural diversity attractive to many kinds of wildlife. For example, breeding bird densities in regenerating pine-hardwood forests may be as high as those in mature stands. But, densities may be low at mid-succession because of limited sub-canopy growth. Habitat improvement consists of measures to diversify these stands.

An excellent tool for wildlife habitat management is prescribed fire. Forest communities follow a pattern of succession to a climax stage in the absence of disturbances such as fire, windstorm, and other disturbances. However, disturbances are normal events in nature that interrupt succession to create varying stages of plant growth from early pioneer species to climax vegetation. Such a variety is vital to many wild animals, providing food and cover components necessary for their continued existence. Fire disturbance has played a major role in the ecology of many wildlife species and forest communities. As an example, the longleaf forests of the Coastal Plain of South Carolina were climax forests because of the prevalence of fire.

Because it is otherwise controlled in today’s landscape, fire for wildlife and forestry must be prescribed. Usually the fires that are prescribed for timber management in pine stands are not necessarily good burns for wildlife. This is true because most forestry burns are planned and executed to provide a “clean” uniform burn, primarily to reduce hazardous accumulations of fuel. A good prescribed burn for wildlife creates a burned-unburned mosaic that stimulates new vegetation growth for the future while retaining adequate cover for the present. The patchy result of such a burn intersperses a variety of plant species and cover types, meeting the needs of wildlife.

Various firing techniques can be utilized, but backfires which burn into the wind are recommended for most wildlife habitats because they tend to leave unburned patches.

The ideal approach to prescribed burning for wildlife habitat improvement is to divide the pine forest into burn units and burn a certain amount each year, using fire at different seasons primarily between late winter and mid-summer. Also, adjoining units should not be burned in the same year, creating different stages of plant growth. Within burn units, key cover such as plum thickets, abandoned orchards or old homesites should be protected from fire.

A 2-year burning rotation is recommended for wildlife habitats favoring quail, rabbits and open-woodland-loving songbirds such as bluebirds, towhees and chats. A 3-year burn rotation is better for deer, wild turkey, and species that require less open conditions. Using fire at different times during the season and using different burn rotations on adjacent units can provide a wide array of habitat types for the widest variety of wildlife. Exclusion of fire from pine types for 5 or more years greatly reduces habitat quality for many wildlife species.

As useful as prescribed burning is for wildlife, it has its limitations. Burning is not usually appropriate in hardwood forests. Also, fire alone will do little to improve habitat quality in dense pine stands with a closed canopy.

A forest composed mostly of a single layer of trees, whether it is a mature hardwood forest or a pine plantation, offers limited wildlife habitats. Thinning timber can be extremely beneficial to some wildlife in these forests, because the removal of some trees in the stand makes space available for other kinds of vegetation, and sunlight penetration through the opened canopy allows new plants to grow. Thinning can be used to promote vertical layering within a forest, influence composition and improve forest tree health.

Artificially-regenerated pine forests can be of low value to wildlife during mid-succession because of canopy closure and reduction of the understory. Thinning can improve habitat quality of these stands. Ideally, pine plantations should be thinned as soon as its economically practical, at least before age 15, and should be prescribed burned as soon as the pines can tolerate fire. Stocking rates of trees should be reduced to around 60 square feet of basal area per acre.

Careful thinning can enhance mast production in hardwood forests. In most forest stands, a few high-quality oaks produce a disproportionate share of the mast. During the fall when mast is present, good mast-bearing oaks and other hardwood species can be marked and observed over a 2- or 3-year period. Non-producing and otherwise inferior trees can then be removed. Thinning around the mast-bearing trees will allow them to develop crowns and produce a larger crop. Thinning will also allow understory soft mast trees and shrubs such as dogwood to bear more fruit.

Thinning activities should be dispersed through the forest and vary in intensity. The result is a patchy pattern from open understory to dense, shrubby growth. Removing trees at varying intensity along a forest edge is a useful technique to create a transition zone that minimizes contrast between cover types. Such a gradual edge is ideal for many types of wildlife. As an example, by removing 75 percent of tree cover from the first 50 feet of forest edge, 50 percent of tree cover from the next 50 feet, and 25 percent from the next 50 feet creates a cover condition that ranges from open land to weed to shrub to forest.

When thinning or harvesting a stand, retain at least 4 to 5 den trees (trees with cavities) and at least that many snags (dead and dying trees) per acre. These should be at least 5 inches in diameter – the larger the better. These trees are used by a variety of birds, mammals and reptiles. Forestry thinnings tend to remove these important trees, so efforts should be made to retain them.

Timber Harvesting Practices

Timber harvesting creates either even-aged or uneven-aged stands. Even-aged management utilizes clearcutting, seedtree and shelterwood harvests. Uneven-aged management relies on single-tree or group-selection harvests. Each method will favor some species of wildlife and adversely impact others.

With even-aged management, the mosaic created by cutover stands interspersed through stands of older trees creates a diverse environment that provides habitat for an array of wildlife. Clearcutting, seed-tree and shelterwood cutting encourages virgorous growth of early succession herbaceous plants and new woody growth that provide abundant food, brood cover and escape cover for many kinds of wildlife. They can result in new forests with a high component of soft and hard mast-producing trees.

Even-aged forest management minimizes vertical layering in a stand, but allows for development of maximum horizontal diversity. In even-aged management, diversity is enhanced by manipulating the size, shape and age differential of each stand. This is called “all-aged management in even-aged units” and is one of the simplest ways to manage forests for wildlife.

Many wild animals will not abandon an established home range to move into better habitat. If their habitat begins to decline, they will remain in the declining habitat until they eventually die out. Only a few individuals will usually move out to occupy new habitat. For this reason, when even-aged management is practiced on a large scale, local abundance of a given wildlife species will be a temporary occurrence. The population will fluctuate with succession because the habitat changes. To maintain stable populations of early to mid-successional stage wildlife favored by even-aged forest management, harvesting should be done in relatively small units. If the goal is to favor late-successional wildlife in even-aged forests, cutting units can be large if managed on a long rotation.

Size, shape and distribution of clearcuts have major effects on wildlife because of the radical change in cover types. For this reason, clearcutting should be well planned when wildlife is a major factor. For many kinds of wildlife, 20-acre or smaller cutting units are large enough. Cutting boundaries should be irregular, with fingers or projections to increase edge effect. Relatively long, narrow cuts that follow natural contours also create more edge. Forested corridors of 100 yards or more in width should be left between cuts and linked to existing forest. Thinning can be done in these corridors to commercially utilize part of the trees, and they can eventually be harvested completely as the adjacent clearcuts get older. Forest corridors should be maintained along perennial streams, with extensions up the stream drainages. These corridors should at least be wide enough that you can’t see through them. They will serve to separate cutover uplands and form a natural tie into a continuous forest network.

Some wildlife species require large tracts of continuous forest. This can be achieved by several means, and generally requires long rotations of 60-100 years or more. Even-aged forest management for these species can involve the use of large cutting units from 80 acres to several hundred acres in size. Even-aged, sustained-yield harvesting with small cutting units can provide the same results. Either way, a large amount of continuous forest is present.

Uneven-aged forest management also favors wildlife needing a continuous forest environment. Edge wildlife species are generally not favored. Vertical layering is enhanced and horizontal diversity declines. With single tree selection, shade intolerant trees such as oaks will sprout but are suppressed in the forest. Group-selection harvesting can improve forest habitat diversity because it removes the tree canopy from small areas across the forest and allows pockets of new vegetation to grow. The herbaceous, shrub and sprout growth provide browse, nesting cover and escape cover in an otherwise uniform forest. Group-selection also encourages regeneration of shade-intolerant trees such as oaks that are needed for mast production. Single or group-tree selection readily facilitates the retention of den, snag and mast trees for wildlife.

Forest Regeneration Practices

Many animals need several stages of plant succession available to them in order to live, reproduce and flourish. That is why wildlife are abundant in areas that have a balance of older forest and regenerating forest. Several things can be done to enhance wildlife habitat when a forest is regenerated. During site preparation, efforts should be made to save living trees as well as snags, because snags are temporary. Living trees continue to provide dens and mast. Soft mast trees such as dogwood, sassafras and black cherry should not be destroyed. Retain some groups or clumps of mature trees in clearcut areas. These islands should be about one-third acre in size and contain mast-bearing trees such as oaks or beech.

If pine stands are being artificially regenerated, tree planting rates should be reduced to 400 to 600 trees per acre. This will delay canopy closure. On appropriate sites, longleaf pine should be considered for planting. An open canopy is more easily maintained with longleaf than with lobolly or slash pine because longleaf has a smaller, more narrow crown. For the same reason, longleaf stocking can be higher than for loblolly or slash and still permit an open canopy.

Mixed forest stands of hardwood and pine beneficial to wildlife can be created by reducing pine planting rates to around 200 trees per acre and selectively controlling competition with herbicides.

Habitat diversity can be improved by regenerating pine stands in areas of mostly hardwood forests. These stands provide escape cover and other benefits. They should be no larger than 20 acres and randomly spaced. Similarly, hardwood stands can be retained or allowed to develop in areas managed for pine. Forested corridors between clearcut and regenerated pine stands and along streams are logical places to manage for hardwoods.

 

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This article is a publication of Clemson University Cooperative Extension's Forestry & Natural Resources team.
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