OLD FIELD MANAGEMENT FOR WILDLIFE
"Old Field" is a broad term that applies to open, habitats which are transitioning from forbs to grasses to trees, but in general these are areas that are dominated by forbs, grasses, and shrubs. The vegetative make up of these habitats is variable based on the length of time since abandonment, management history, soils, and seed bank. Old field use by wildlife will depend on their size, configuration, vegetation height, percent woody vegetation cover, density, and composition.
Values for wildlife
Many wildlife species depend on a mix of forbs, grasses, and shrubs for habitat. Old fields are used by a variety of wildlife such as golden-winged warbler, quail, grouse, butterflies, bees, cottontail rabbit, deer, snipe, turkey, bobcat, rat snakes, frogs and many others. Shrubland birds which include golden-winged warbler, blue-winged warbler, Bewick's wren, gray catbird, yellow-breasted chat, alder flycatcher, willow flycatcher, field sparrow, and indigo bunting utilize these transitional fields extensively. In order to maintain the mix of forbs, grasses, and shrubs, these early successional species rely on some type of disturbance to keep the field from completely converting to a closed canopy forest.
Small fields, <5 acres, are often less valuable to wildlife than large blocks. Some shrubland birds are considered area sensitive which means they prefer and select large areas of contiguous habitat for breeding. Birds such as the brown thrasher will use smaller fields (<5 acres) but the more uncommon species such as yellow-breasted chat or golden-winged warblers require areas of 25 acres or more. Putting more emphasis on larger blocks will provide quality habitat for a number of species and improve reproduction and survival of many species. Larger blocks will provide a better mix of habitats that can meet the daily needs of a number of wildlife species compared to small fields which may only provide a small amount of the daily needs for a few species.
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Choosing a Field
You may already have good old field habitat with shrubby areas that may only need to be maintained through the removal of larger trees and periodic disturbance. You may have areas that are shallow to bedrock or wet which has made it difficult to maintain the entire field. Trees and shrubs have been invading these areas making it a potential good area for shrubland birds with additional management. Focus your attention on areas that are still primarily open and that are greater than 5 acres in size. Areas 5 acres or less in size will often be less suitable for many wildlife species.
Focus your efforts on large blocky fields. These types of fields have less edge than do long narrow linear fields. Edge is considered the contact zone where two different habitats come together. Edges often concentrate predators as they travel these areas searching for food. Soft edges are generally considered better for wildlife than are hard edges. An example of a soft or "feathered" edge would be an old field habitat that transitions from grass to shrubs to saplings before transitioning into mature forest. More information on edge softening or edge feather can be found HERE. A hard edge would be a crop field that butts up against a mature forest. In order to maximize habitat for early successional wildlife it is best to focus your efforts on blocks of habitat rather than narrow strips.
The actual field size for shrubland birds becomes less important when the field is within a suitable landscape so it is important to consider the landscape when determining your management plan. Managing old fields near other old fields, pasture or hayfields with hedgerows, scrub-shrub wetlands, young forest, power line rights-of-way, or similar habitats is a great way to maintain and enhance conditions for early successional wildlife. Many early successional wildlife species are drawn to suitable landscapes; especially areas with large acreages of open land.
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CREATING AN OLD FIELD
Whether you are creating a new old field by planting, natural revegetation, or enhancing an existing old field there are a number of factors that will be common for all of these. The best old field will contain a mosaic of forbs, grasses, and shrubs. Trees should be kept to a minimum because if they are allowed to mature they will shade out the forbs and grasses reducing the benefit of the field for early successional wildlife. The woody component of the field should be between 10- 30% crown coverage. This includes shrubs and trees. If trees are present they should not be older than 10 years of age. Once saplings get beyond 10 years of age they start crowding out each other and the shading the ground which reduces understory vegetation.
Natural revegetation, also called natural regen, or spray and let grow is the process of idling a field and allowing it to revert back to a more natural state without planting anything, only a temporary cover may be planted in areas that are subject to erosion. Natural regen typically is done on fesuce fields or crop fields, but can also be done with old fields containing a mix of fescue and broomsedge. On fescue dominant fields typically two application of glysophate are used to kill out the fescue. If the fescue is not killed or reduced in the field then native forbs, grasses, and shrubs will be less likely to re-establish in the field. Fescue is able to inhibit the growth of many plants which results in the pure stands we often see in pastures and hay fields. Ideally 2 quarts/acre of glysophate need to be sprayed in the fall (September to November) with a second application in the spring (March to May). Another option is to make 2 spring applications of glysophate at a rate of 2.0 quarts/acre in the Spring. The first spraying should occur in late March/April with the second spraying 4 weeks later.
If native plants like black-eyed Susans, partridge pea, Illinois bundleflower, little bluestem, Indiangrass, big bluestem etc. are growing in your field you may want to consider just using imazapic (Plateau/Impose) to kill the fescue. Glyphosate is a broad spectrum herbicide which kills most plants it comes into contact with. Imazapic is selective and typically kills non-native plants although it will kill native plants that are sensitive to it. However, a number of native plants are resistant or are only stunted by its application. Established plants are less susceptible to imazapic than are new seedlings. Read the imazapic label for species resistance and application rates.
If natural regen is done on a crop field then all that may need to be done is to step back and allow the field to naturally revegetate itself from the local seeds carried on the wind and by birds. If Johnsongrass or other noxious weeds are an issue then it may be necessary to spray the field with glysophate in the fall to kill out the weeds. If over time Johnsongrass becomes an increasing problem then imazapic at a rate of 6 to 8 oz/acre should be sprayed early summer.
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Creating an old field through planting
Some crop and fescue fields may not have a good seed bank or may not have enough of an external seed source to revegetate natural. Also natural regen can take 15-20 years to create a mix of forbs, grasses, and shrubs. If you are not willing to wait or would like to get a jump start on succession you can create the desired mosaic of forbs, grasses, and shrubs by planting them. In an old field situation native grasses should be seeded at a rate of no more than 4 lbs PLS/acre with 3lbs PLS/acre being ideal. This light seeding rate keeps the grasses from dominating the stand. Forbs and legumes should be seeded at a rate of 2 lbs to 4lbs/acre. The ideal situation is a 60:40 mix of forbs to grasses, but a 40:60 mix will also work. When planning your old field planting you should make sure to keep the diversity of plants as high as possible, but you do not have to have the diversity as high as one might use in a prairie restoration. You should have at least 3 native grass species and no fewer than 8 forb/legume species with 10 or 15 being ideal. See Native Grass and Forb Establishment and Management for additional information.
Having shrubs in your old field is a critical structural component. If shrubs do not exist in your field than they can be added through direct seeding or planting of bare root plants. The shrub component should be planted in such a way to create a thicket or group of shrubs. However, you can also plant individual shrubs or small groups of 2 to 30 randomly around the field. These small group or thickets provide additional temporary escape cover, perches for territorial display, thermal cover, and nesting. Larger thickets from 0.1 to 0.5 acres provide dense escape cover and nesting cover for species that need thickets for cover. See Thicket Establishment for additional information.
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Enhancing an existing overgrown field
Often landowners have a field that has just been left go. Maybe it was a hilly pasture that was let go because you no longer graze cattle. Perhaps you have an area that was clearcut, but tree regeneration is minimal or low quality and the area is solid briars and invasive plants. Maybe you just bought this piece of property, and it sat idle for years and the fields have grown beyond old field to a young forest. If you have the time and money you can set these areas back to create a mosaic of forbs, grasses, and shrubs. It can be expensive, but it can be done. The more and bigger the trees and brush more expensive it will be to convert.
If the trees are 10 years or less in age you have several of options to removing them. You can either hire a bulldozer to push the trees into piles and then burn them or you can hire a contractor with a forestry mulcher to grind up the small trees. Trees older than 10 years can still be removed, but the time and expense of removing them with either a dozer or forestry mulcher may not be worth the extra effort. If the trees are older between 6 inches and 18 inches in diameter you may be able to sell them as firewood or possible mulch.
A good dozer operator can clear a field easily and will typically be able to remove the stumps; however, you will have several issues to deal with. A dozer will compact and disturb the soil. This disturbance will result in an increase of noxious weeds and unwanted plant seed germinating and taking over your field. If the soil is not leveled and stabilized after the dozer work, you will have ruts, stump holes, and erosion when it rains. Care should be taken on sites that are beyond a 2% slope as erosion potential will increase with slope and soil type when using a dozer. A dozer should not be used in wet sites because it can alter the hydrology of the site and create large deep mud holes from the equipment and removal of the stumps.
After having the field cleared you will need to deal with large piles of trees to deal with. Whether you have them piled in wind rows or several piles you will either need to burn them or have them hauled off. Leaving the large brushpiles in the past has been recommended because these areas can be used for escape cover. The problem with large brush piles is that they often take years to rot and decompose which can make management of you old field difficult. The other issue is those made of large stumps and logs provide ideal den sites for raccoon, skunks, fox, mink, weasels, and coyotes. You can leave some brush piles, but it is recommended that these are made from the smaller trees and tops of larger trees. Wind rowed trees provide less cover and protection than the smaller branches and tops of trees.
Probably the best method for converting an overgrown old field to the proper mosaic of herbaceous and woody plants is the use of a forestry mulcher. The forestry mulcher comes in a variety of different shapes and sizes. Small units can be fitted to a bobcat or posi-trak, while large units are built around a tracked dozer or wheeled loader. Brush mulching heads are even available to fit on excavators. The smaller skid steer/posi-track units can easily deal with trees and brushless 6 inches or less in diameter while larger units can handle tree greater than a 12 inches in diameter. The excavator models allow the operator to work on steeper hills or around obstacles from a path.
The advantages of the forestry mulchers are that they can easily deal with small brush and trees without disturbing the soil. This can reduce noxious weeds and unwanted seeds from germinating and reduce soil erosion. There are no large piles of tree stumps to deal with and burn. You will not have large stump holes to fill in or level off. Depending on the size and type of unit used the operator can have much better control and will be able to leave some areas uncut to help create the mosaic. They can also leave preferred trees or shrubs much easier than a dozer operator can.
However, there are disadvantages to the forestry mulcher. Depending on the size of the brush and trees and the type of head used there may be large amounts of mulch ranging from a few inches to a foot in length laying on the ground. In some instances mulch can be a foot or more thick. This heavy mulch will smoother out new plants for several years as it rots. If thick mulch is a problem you can either use a small skid steer or loader to move the mulch into piles or allow the mulch to rot and cure for a year before burning your field. The forestry mulcher does leave the stump and root systems in tact this means that you will need to treat resprouting stumps with a herbicide such as glyphosate or triclopyr. After the mulch and sprouting has been taken care of you can either broadcast additional native grasses and forbs over the area or allow the area to naturally regenerate.
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Maintaining an old field
If you have an existing old field or created one through natural regen or planting you need to maintain that field in the optimum mosaic of forbs, grasses, and shrubs. Existing old field often need management to bring them back to that optimum arrangement. Over several years' native grasses, shrubs, and forbs will take over the field. After 3 to 7 years it may be necessary to burn (fall/early winter) or strip disk (fall/early winter) to help keep the field in the early successional stage that includes forbs, grasses, and shrubs. Mowing has been recommended in the past for maintaining an old field; however, mowing only does not help to properly maintain an old field.
Mowing only does not work adequately for maintaining areas of native grasses. The mowing creates thatch which smoothers desirable plants. It also does not disturb the soil to allow desirable forb seeds to germinate. Mowing can be used to temporarily set back succession of woody plants and areas dominated by forbs. However, mowing over shrub thickets will only result in the reduction in height of the shrubs. The canopy will still be closed after one good growing season. If mowing only is used it will not control woody invaders like sweetgum, red maples, ash, osage orange. As areas get overgrown with shrubs mowing is not enough to reset succession on those areas to keep the small tree and shrubs from maturing and becoming a closed canopy. Overtime the slow invasion of woody plants into the herbaceous areas will reduce those areas until the whole field is now shrubs and trees.
If you can use fire, burning in April to early May can be done to help favor native grasses like broomsedge while decreasing exotic cool season grasses like fescue. Dormant season burns November through March can be used to favor forbs. Many of the desirable shrub species found in an old field are resistant to fire. These species once established can be top killed by fire, but will quickly resprout. If your shrubs are less than 10 years old you may want to consider protecting them from fire by disking or mowing around the thickets. Depending on the time of the burn, frequency, fuel loads, and moisture levels, fire can kill even resistant shrubs. For instance shrubs along the edge of established native grasses are more likely to be killed then those deeper in the thicket. Herbaceous areas should be burned every 1 to 3 years and shrub areas if they will burn should be done every 7 to 10 years. Annual burning should not be used for extended periods of time. It should only be used to control woody plants in areas where invasion is becoming a problem. Annual burning reduces the value of the area for wildlife by removing cover and thus reducing the value of your old field. See Prescribed Fire for additional information.
If you are unable to use fire and have a light to medium disk available you can always disk strips in the herbaceous portion of your old field. If you have a heavy bog or offset disk you may also be able to disturb the shrub areas after mowing them. Disking helps break up thatch and disturb the soil to allow forb seeds to germinate. Disking along thickets will break rhizomes and young seedlings that maybe trying to invade the herbaceous areas. Strip disking of herbaceous areas should be done on a 2 to 3 year rotation with strips disked and other not disked each year. Woody areas should only be disked every 7 to 10 years if you are able to. Disking should be done from November through May. See Strip Disking for additional information.
When managing your old field you will almost certainly have invasive plants like honeysuckle, kudzu, sericea lespedeza, privet, and fescue invade your field. These invasives will throw your old field system out of balance, making the habitat unusable for many species of wildlife. You may also have native invaders like tulip popular, sweetgum, green ash, and red maple which although if left unmanaged will eventually take over the field and result in a closed canopy forest, their presence will have less of a detrimental effect on wildlife.
The best method for dealing with non-native invasive plants and native invaders is to use fire or herbicides. Spot spraying the field is much easier and cost effective than whole field applications, so learning to identify invasive plants and yearly inspections is key to keeping these species at bay and helping maintain the quality of your old field. In an old field situation that contains some fescue spraying imazapic will eliminate the fescue while having limited effect on the natives. Triclopyr can be used when woody plants are an issue without affecting grasses, but it will kill many forbs. Always read and follow the labels of any herbicides you use.
The key in creating and maintaining an old field is disturbance which keeps the tree canopy from closing up and shading out the forbs and grasses and preventing shrubs from taking over the herbaceous portion of the field. Not all trees will need to be killed, but suppression of trees will help maintain the field in a stage of grass, forbs, and shrubs. Using a combination of mowing, fire, disking, and herbicides will better enable you to maintain the quality of your old field for wildlife.
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