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HABITAT MANAGEMENT OF WHITE-TAILED DEER

D. Lynn Drawe, Rob and Bessie Welder Wildlife Foundation, and J. Alfonso Ortega-S., Instituto Nacional de Investigaciones Forestales y Agropecuarias, and Timothy E. Fulbright, Caesar Kleberg Wildlife Research Institute & Department of Animal & Wildlife Sciences, Texas A&M University-Kingsville

ABSTRACT

Maintaining high quality native habitat is the highest priority in any white-tailed deer management program. Livestock grazing, mechanical and chemical brush management, fire, and planting food plots are some of the tools available to help achieve this objective. These tools must be applied with a clear understanding of the advantages and disadvantages of each. A complete management plan that includes management goals, when and where habitat improvements will be made, plans for maintenance treatments, and costs and expected benefits is essential for maximum effectiveness in improving white-tailed deer habitat.

INTRODUCTION

Habitat management for white-tailed deer (Odocoileus virginianus) involves manipulating the availability or abundance of food, water, space, and cover. The basic habitat management tools available on rangelands of the southwestern United States and northern Mexico include livestock grazing, mechanical and chemical brush management, and fire. Food plots can be planted to supplement native vegetation.

Habitat management tools are like prescription drugs - the right amount can cure many ills, but taking it for the wrong malady or taking it in excess can create many ills. Our objective is to acquaint you with the basic concepts underlying use of the tools of habitat management for white-tailed deer. We cannot prescribe a management plan that will work on all ranches. Ranches differ in vegetation, soils, rainfall, and management practices. With an understanding of the basic concepts, a manager can design a habitat management plan that will be effective under the particular conditions of any ranch or management unit. A habitat management plan must include goals, timing and location of habitat improvements, plans for maintenance treatments, and costs and expected benefits.

HABITAT MANAGEMENT TOOLS

LIVESTOCK GRAZING

Livestock grazing is known to influence white-tailed deer habitat in several ways. Grazing can alter the successional status of a range. Long-term, year-long, continuous grazing can reduce excellent condition range to poor condition, or even to bare ground. This may open up a grassland to the invasion of woody species. For white-tailed deer, some woody cover is a benefit. Woody cover should be in the range of 40-60% to provide good deer habitat. More than a century of heavy livestock grazing in southern Texas and northern Mexico has converted former grasslands to brushlands. Areas formerly marginal habitat for deer are now excellent deer habitat because of overgrazing by cattle; however, now that brush has invaded, it must be carefully managed so as to not surpass the threshold density that becomes detrimental to deer.

The white-tailed deer population of the Welder Wildlife Foundation Refuge (WWFR) has historically varied between 750 and 1,400 deer. Weather, habitat management, and predation appear to be major controlling factors on the WWFR deer herd. Kie et al. (1979) found coyote predation on fawns to be a major controlling factor on the WWFR deer population.

At WWFR deer numbers declined in 1988 and 1989 to the lowest number since counts began, then rebounded in 1990 and 1991. This decline was apparently caused by low fawn survival. Fawn survival in 1987, 1988, and 1989 was extremely low, 6, 9, and 2%, respectively. Fawn crops in 1990 and 1991, 51% and 58%, respectively, were higher than normal following early spring rains which provided dense forb cover during the fawning season. Although we cannot be certain, it appeared that increased ground cover was responsible for lowered fawn predation and thus the rebound in the deer population in 1990 and 1991.

Brush manipulation, specifically the checkerboard roller chopping done in February 1988, may have had a cushioning effect during the decline of the WWFR deer herd. Roller chopping was done in 10-acre blocks, leaving alternating blocks of undisturbed brush. 1988 was at the beginning of a 3-year drought. During summer 1988, deer were seen in roller chopped areas making heavy use of the resprouts of various woody species, particularly granjeno (Celtis pallida) and colima (Zanthoxylum fagara). Roller chopping stimulated resprouting and made the palatable portions of the woody plants more available to deer (Powell and Box 1966). With the lack of herbaceous vegetation during the drought, roller chopped areas appeared to be important as a source of deer food. Naderman (1979) found that openings of various sizes increased the deer population on the P. H. Welder Ranch adjacent to WWFR.

Another factor that may have contributed to deer welfare during the 1988-1990 drought was the total removal of cattle from the WWFR. With the paucity of herbaceous vegetation, deer and other wildlife would have been placed under more nutritional stress had the cattle been present to compete for the little forage available.

At the WWFR, Short Duration Grazing (SDG) did not negatively affect range condition. Concentration of cattle and human traffic at SDG cell centers limited water use by white-tailed deer. Home range sizes of deer were similar on SDG and nearby CG pastures. Deer diets were similar in both CG and SDG treatments. Heavy CG provided the best short-term results in terms of deer nutrition compared to SDG (Cohen et al 1989).

MECHANICAL & CHEMICAL HABITAT MANIPULATION

Mechanical brush management methods can be divided into plant removal or top removal. Plant removal methods include grubbing individual plants, root plowing, discing, railing, cabling, chaining, bulldozing, and variations of these basic methods. These brush management techniques only temporarily reduce canopy cover and density of woody plants. Brush re-establishes to the degree that re-treatment is necessary within 10-20 years following root plowing, the most severe treatment. Re-establishment of brush occurs because seeds remain in the soil even if all existing woody plants are killed. Additionall, birds and mammals facilitate dispersal of seeds to treated areas. Less severe treatments, such as discing and herbicide treatments are more temporary than root plowing, with re-treatment necessary approximately each 7-10 years.

Top removal treatments include roller chopping, aerating, and shredding (mowing). These treatments do not kill brush, but only remove the top growth of the plants. Thus, they must be repeated every two or three years to maintain suppression of woody plants. The advantage, especially with aerating and mowing, is that the equipment is reasonably priced and can be purchased by most landowners.

Mechanically clearing large tracts of deer habitat (1,000 acres or more), without leaving portions of the landscape with adequate woody cover, substantially reduces white-tailed deer populations. Root plowing large areas is the most destructive brush control method to white-tailed deer habitat. The initial effects of root plowing include loss of most of the key habitat features for deer. Root-plowed areas may support an abundance of forbs when rainfall is adequate, and these may attract deer; however, during drought deer do not utilize root-plowed areas because browse is not available. Clearing large areas by other methods, such as chaining, also reduces deer densities until brush re-establishes.

Herbicide application is an alternative to mechanical brush management. Several herbicides are available that effectively kill honey mesquite (Prosopis glandulosa) but most commonly applied herbicides will not kill all brush species. Herbicides can be applied from fixed-wing aircraft, from a helicopter, or by hand-held sprayers. Herbicides can be sprayed very accurately from a helicopter and such application is conducive to "patch" patterns of clearing (e.g., spraying 20-acre clearings interspersed in brushland). Strip patterns are usually applied with fixed-wing aircraft. "Backpack" sprayers can be used to treat individual plants.

One advantage of herbicides over mechanical brush control methods is that herbicides do not disturb the soil. Reseeding to restore grasses is not needed after herbicide application. Finally, standing dead brush remains following herbicide application, which may provide screening cover for deer.

A disadvantage of the use of herbicides is that forbs preferred by deer are usually decimated by the herbicide. Two to four years may be required for forbs to grow back in abundance similar to what existed before herbicide application. Deer may make very little use of treated areas until forbs return to their original abundance. Another disadvantage is that herbicide treatments may be more expensive than certain mechanical treatments.

Manipulating canopy cover and density of brush may improve white-tailed deer habitat by (1) reducing competition between woody and herbaceous plants thus increasing yield of herbaceous vegetation, (2) providing openings to serve as focal areas for feeding activity, and (3) increasing nutritional quality, accessibility, and palatability of browse by stimulating growth of immature sprouts from crowns and stem bases. When the goal of brush management is to improve deer habitat, brush management should be designed to foster a landscape containing the optimum structure, spatial arrangement, and dispersion of habitat features required by deer. Optimum habitat for white-tailed deer will include the following habitat features:

• woody plant canopy cover >60% on 40-60% of the landscape; • natural or artificially-created openings 10-40 acres in size comprising ~40% of the landscape and surrounded by brush that provides adequate screening cover; • areas of diverse (>18 brush species), dense brush with tall screening cover and 85% woody plant canopy; • areas where deer can find dense shade in summer or protection from cold in winter (thermal cover); • areas of screening cover behind which deer are concealed; • brush-lined drainage areas that are continuous throughout the landscape and provide loafing and bedding areas, and corridors for movement; and • areas that support browse, prickly-pear cactus, forbs, and mast-producing plant species preferred by white-tailed deer.

Achieving optimum dispersion (even distribution of habitat features across the landscape) and juxtaposition (close proximity of required habitat features) of should be a goal of brush management. Decisions to make before using brush control to improve deer habitat include:

• Is brush management really necessary? Many landscapes in their natural state possess an optimum combination of these habitat features and brush manipulation will degrade habitat quality for wildlife. Too often, the decision to control brush is based on a desire to "do something" or a perceived need rather than a biological need for habitat improvement. Unfortunately, on much rangeland in Texas and Mexico, overgrazing and previous efforts at brush control have resulted in landscapes of dense brush in which habitat improvement is needed. • How can I apply brush management in a manner that provides optimum habitat for deer? Brush management is often applied in a manner convenient to the equipment operator. A well-thought-out and well designed plan to create a landscape that possesses well interspersed and juxtaposed habitat features needed by deer is a critical first step that should be taken before any brush management operation. Brush management reduces the quality of habitat for white-tailed deer when applied without proper planning and without regard to the habitat features required by deer. • Can I afford periodic maintenance of the areas that I have treated? All brush management methods are only temporarily effective. Follow-up treatments are critical. Brush management planning must include allocating funds to periodically retreat areas where brush has been manipulated. Long-term effects of brush management should be given equal consideration to short-term effects in management plans. • Are soils and rainfall suitable for brush management? Certain ranches may have soils that are unsuitable for manipulation or rainfall may be too low. For example, root plowing saline soils may bring salts to the surface and inhibit plant growth. Certain soils are more prone to invasion of undesirable plants such as goldenweed (Isocoma sp.) following disturbance.

The objective of brush management for white-tailed deer habitat improvement should be to create a habitat mosaic that maximizes the value of the landscape as deer habitat. Soils, plant community composition, past management history, and objectives of the landowner vary greatly from one ranch to the next. Consequently, the best approach to tailoring brushy rangelands to enhance white-tailed deer habitat may vary from ranch to ranch. Management plans for improving habitat for white-tailed deer should therefore be based on the following general concepts that can be modified and adapted to fit the specific circumstances:

• clear small (~20 acres) irregularly-shaped patches scattered throughout the landscape. These clearings should total 40% of the landscape. Leave relatively wide corridors of brush separating the patches that total 60% of the landscape; • areas of tall, dense, diverse brush with canopy cover 85% should be interspersed throughout the landscape to provide cover for mature bucks; • avoid disturbing brush in and along natural drainage areas; • use the brush control method best suited to the habitat. Root plowing is not recommended.

FIRE

Fire has a varied impact on wildlife depending on fire characteristics, size and shape of the area burned, and cover available to animals during the fire. The primary impact of fire on wild animal populations is the effect on the habitat. If the fire-altered habitat is enhanced for a particular species, then that species can be expected to increase after the fire, and vice versa. Therefore, changes in animal species diversity and population density can be expected following fire. Better knowledge of these changes would allow the manager to attain predetermined objectives.

Prescribed burning can easily be designed to have the least initial or direct impact on wildlife populations and create the greatest benefit for those populations following the fire. Conducted during the dormant season, i.e., winter in south Texas and northern Mexico, fire has little direct impact on animal populations. Detriments will be outweighed by benefits derived from the increased post-burn productivity of the ecosystem. Although animal species composition may change for a short time, the area will return to normal pre-burn species composition and density within 2-3 years following the fire. A cool fire which allows some unburned areas within the major burn will create more edge and further enhance animal populations. A patchwork of relatively small burned and unburned areas can be used to create more edge.

Although more studies of the effects of fire on wildlife populations in south Texas and northern Mexico are needed, some general impressions about the effect of fire on animals can be made: Burning during winter lessens mortality since most animals are less active at this time. Rarely are animals, other than an occasional snake, directly killed by the fire, especially if burning is done on a cold day. On a cold day any animal that is out often is more curious about than afraid of the fire. At the WWFRwe have observed white-tailed deer (Odocoileus virginianus texanus) travel back and forth through the flames of a cool fire and in the smoke immediately in the flame front. The direct impact of fire on animals during the dormant season is minimal.

Fire can benefit wildlife by increasing food supplies. Powell and Box (1966) reported increased white-tailed deer and cattle use of brush resprouts after mechanical treatment. They attributed the increased use to greater palatibiliity and higher nutrition in the more succulent resprouts. In current research, we also are finding increased deer use of brush resprouts after a fire. Not only does top removal create resprouts which are more palatable, but also the new growth is more available. Top removal reduces the overall height of brush plants and removes the restriction to browsing caused by sharp thorns and stiff, old growth.

The white-tailed deer prefers mid-successional stages of vegetation. Chamrad (1968) and Drawe (1968) found that deer in the Coastal Prairie prefer forbs. With advanced succession and heavy mulch accumulations, forb production appears to be suppressed. Scifres and Kelly (1979) found increased forb production with prescribed burning. We also hoped that fire would remove excessive mulch accumulations and promote forb growth. The answer to this question is not completely clear at this point, and probably lies more in timing of burning than in any other factor. For example, in the study of two consecutive late winter (Jan-Feb) burns, forbs, particularly perennial forbs such as bundleflower (Desmanthus virgatus), frogfruit (Phyla incisa and P. nodiflora), and wild petunia (Ruellia nudiflora), were suppressed; whereas, an early winter (Dec.) burn promoted growth of sagewort (Senicio imparipinnatus) (Hansmire et al. 1988). A fire in early winter or in the dead of winter when all plants are dormant did not suppress forb growth, but a fire after growth initiation of cool season plants killed any growing herbaceous plant. In particular we have noticed varying responses from, but generally a reduction in, the amount of Texas wintergrass (Stipa leucotricha) after a late burn.

FOOD PLOTS

The use of food plots for white-tailed deer should be considered as one more tool in an overall management program in which the highest priority is maintaining high quality native habitat. Avoiding overgrazing by livestock, keeping an equilibrium between deer densities and carrying capacity of the habitat, and application of habitat improvement practices are keys to achieving proper management. Under no situation should food plots be used as a tool for increasing deer densities beyond the carrying capacity of the habitat.

Several objectives may be accomplished by planting food plots:

• to increase the nutritional value and the quantity of forage available for deer. Seasonal variation in rainfall and temperature are major factors determining quantity and quality of forage available for deer. If rainfall is adequate, availability of forbs and browse may be good for supplying protein and energy requirements for body and antler growth during a part of the year. If native habitats are unable to provide a uniform high quality diet year round year, food plots may help to overcome this deficiency; • to use food plots as a marketing strategy. Food plots may indicate to hunters the commitment of the landowner to deer management for producing better quality hunting; • to increase visibility of deer during the hunting season or for photography purposes. The presence of food plots may work as an attractant, making deer more visible during the hunting season and allowing the manager to monitor body and antler growth during the year.

Food plots must be planted in the best quality soils of the ranch. If the ranch does not have soils suitable for growing crops, trying to plant food plots may be a mistake. Best farming practices are essential, especially if no irregation is available. Deep tillage and weed control are the keys to maximizing production of food plots. Timing in soil preparation is a very important issue - soil should be prepared in advance in order to store and conserve moisture. In south Texas and northern Mexico, i.e., areas with less than 20 inches of annual rainfall, soil preparation for planting warm season food plots should be done in late summer to store moisture during September and October for planting the next year in March. The use of herbicides and light cultivation during winter are recommended to maintain a good seedbed (i.e., good soil tilth) and to avoid loss of stored moisture to weed growth.

In order to supply high quality supplemental forage throughout the year, cool and warm season food plots may be planted. Cool season food plots planted with mixtures of grasses such as oats, wheat, triticale, and/or legumes such as hairy vetch, Austrian winter peas, alfalfa, and hubam clover can provide good quality forage form November to May. Warm season food plots that include lablab, cowpeas, soybeans and milo may provide forage from early spring to late fall. Lablab can produce around 6,000 pounds of forage per acre per year on dry matter basis. Perennial food plots provide permanent cover and do not require annual planting; however, they usually are less productive than annuals. Some species that may be used include Maximilian sunflower, Engelmann daisy, bush sunflower, and Illinois bundleflower. Forage production in perennial food plots generally ranges from 2,000 to 3,000 pounds per acre.

Several selections of Creeping bundleflower (Desmanthus virgatus) have been tested in northern Mexico and south Texas. Dry matter production ranges from xxxx to xxxx for the accessions 90906, xxxxx, mmmm, and yyyyy. An interesting characteristic of these accessions is that they were able to produce over xxxx seed per acre in Mexico, a valuable characteristic for birds or for selfreseeding. Other plants with potential to be used in warm season food plots are Centrocema scottii, Centocema brazilianum, and mucuna, which may produce over 6000 pounds per acre of forage and good seed crops.

Skip-row planting is recommended for south Texas in areas with 18 inches of annual rainfall. This practice increases moisture availability and plant survival. It also reduces seed costs. Inoculation of legume seed is recommended to take advantage of capacity of these plants to fix atmospheric nitrogen. Fertilizers low in nitrogen and high in phosphorus should be used when planting inoculated legumes.

The size of the food plot is dependent on deer density. For example, for a deer density of 35 adult deer per square mile, the size of a warm-season food plot should be at least 14 acres. The shape of the food plot should be a square to avoid competition with the vegetation on the edges.

Finally, are the major advantages of food plots? (1) Increased value of hunting lease; (2) greater visibility of deer; and (3) a source of high quality forage when the native habitat is unable to provide it.

SUMMARY

The highest priority in a management program for white-tailed deer is to maintain high quality native habitat. Livestock grazing, mechanical and chemical habitat manipulation, fire, and the use of introduced plants for improving quality of the deer diet are some of the tools that may be used to accomplish the overall objective. Best results can be expected when all these tools are used in combination and in the proper proportions according to the situation found on each ranch. A comprehensive management plan that includes management goals, timing and location of habitat improvements, plans for maintenance treatments, and costs and expected benefits is essential for maximum effectiveness in improving white-tailed deer habitat.

Livestock grazing is known to influence white-tailed deer habitat in several ways. Grazing can alter the successional status of range. More than a century of heaviy livestock grazing in southern Texas and northern Mexico has converted former grasslands to brushlands. Areas formerly marginal habitat for deer are now ecellent deer habitat because cattle overgrazing; however, brush must be carefully managed so as to not surpass the threshold density that becomes detrimental to deer. Long term, year-long, continuous grazing can reduce excellent condition range to poor condition, or even to bare ground. This may open up the grassland to the invasion of woody species. Woody cover is a benefit to white-tailed deer habitat and it should be kept in the range of 40 to 60%.

Mechanical brush management can be divided into plant removal or top removal. Plant removal methods include grubbing individual plants, root plowing, discing, railing, cabling, chaining, bulldozing, and variation oft these basic methods. Top removal includes roller chopping, aerating, and shredding. All brush management methods are only temporarily effective and follow-up treatments are critical. Manipulating canopy cover and density of brush may improve white-tailed deer habitat by reducing the competition between woody and herbaceous plants, providing openings to serve as focal areas for feeding activity, and increasing nutritional quality, accessibility, and palatability of browse by stimulating growth of immature sprouts from crowns and stem bases. Decisions to make before using brush control to improve deer habitat include: Is brush management necessary? How can I apply brush management in a manner that provides optimum habitat for deer? Can I afford maintenance for the treated areas? Are soils and rainfall suitable for brush management?.

Prescribed burning can be designed to have the least initial or direct impact on wildlife populations and create the greatest benefit for those populations following the fire. If the habitat is altered by the fire and is enhanced for some species, then that species can be expected to increase after the fire. Fire can benefit wildlife by increasing food supplies. The use of brush resprouts by deer can increase because of increased palatability and higher nutritional quality. Timing is a critical factor when burning, because different effects can be obtained in botanical composition of the vegetation after burning.

The use of food plots for white-tailed deer should be considered as one more tool in an overall management program in which the highest priority is maintaining high quality native habitat. Food plots may increase the nutritional value of forage available for deer, and they may also show the hunters commitment of the rancher to deer management by increasing visibility of the animals during the hunting season. Care should be taken to select the correct plant species, use the best farming practices, select the correct number and shape of plots, and use adequate fencing.