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4. Estimating Carrying Capacity

Timothy E. Fulbright Texas A&M University Press ePub

4

Estimating Carrying Capacity

KEY CONCEPTS

▼ Carrying capacity is the number of animals per unit area that a habitat can support without degrading forage and other resources.

▼ The number of animals the habitat can support changes continually in time and space depending on availability of food, water, cover, and usable space.

▼ Nutritional-based estimates of carrying capacity should incorporate nutrient needs of free-ranging animals and production needs such as lactation, account for effects of antinutrition factors such as tannins, and include adjustments for habitat preferences.

▼ Forage- or nutritional-based models to estimate carrying capacity may provide values useful as a guideline for management, but values should be regarded as ballpark estimates and may be inaccurate. Management decisions regarding whether deer numbers exceed carrying capacity of the habitat are best made by monitoring level of utilization of important, or key, deer forages.

Carrying Capacity Defined

White-tailed deer population densities vary geographically. The Edwards Plateau region of Texas supports higher densities of white-tailed deer than any other rangeland area in the United States, with greater than 45 deer/km2 (see fig. 1.2; Quality Deer Management Association 2008). In contrast, much of the Great Plains region from Canada south to the Texas Rolling Plains supports fewer than 15 deer/km2. Deer densities in the Great Plains may be locally greater along riparian corridors and other wooded areas such as shelterbelts. Much of the Cross Timbers and Prairies and South Texas Plains supports 15 to 30 deer/km2. Although white-tailed deer were almost extinct by the 1970s because of poaching, habitat destruction, and screwworm infestation, an estimated white-tailed deer population density of 10 to 20 deer/km2 exists in northeastern Mexico (Villarreal G. 1999). These regional differences in deer densities result in part from regional differences in hunting pressure, geographic variation in human population densities, and numerous other factors, many of which may be beyond the control of wildlife managers. Carrying capacity can be enhanced and maintained by habitat management. Proper wildlife habitat management is based on the concept of carrying capacity and an understanding of the limitations of the concept. One of the limitations is that carrying capacity is conceptual rather than an absolute value.

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6. The Plow: Food Plots

Timothy E. Fulbright Texas A&M University Press ePub

6

The Plow: Food Plots

KEY CONCEPTS

▼ White-tailed deer are attracted to and may derive nutritional benefits from food plots, particularly in habitats relatively low in forage nutritional value.

▼ Converting good-quality white-tailed deer habitat to cultivated food plots should be avoided.

▼ Planting food plots is not a substitute for proper habitat and population management.

▼ Food plots do not increase carrying capacity of the habitat—they are a supplement to natural vegetation.

▼ The use of food plots in rangelands is restricted by low rainfall and by soils that are unsuited for cultivation.

Role of Food Plots in Deer Management

Planting food plots for white-tailed deer is a popular form of supplemental feeding (fig. 6.1; Koerth and Kroll 1994; Donalty, Henke, and Kerr 2003). In a recent survey of hunting lessees and landowners in South Texas, 56 percent of respondents said they plant some form of food plots (Bryant, Ortega-S., and Synatzske, n.d.), and 41 percent said they planted them in both summer and winter. Twenty-three percent of landowners in Texas who lease hunting rights plant food plots (Adams, Thomas, and Ramsey 1992).

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5. The Cow: Livestock and White-Tailed Deer Habitat

Timothy E. Fulbright Texas A&M University Press ePub

5

The Cow: Livestock and White-Tailed Deer Habitat

KEY CONCEPTS

▼ Cattle grazing can reduce grass cover and increase forbs in productive plant communities dominated by mid- to tall grasses, but whether or not the increase in forbs may result in improved deer nutritional status or productivity is unclear.

▼ Cattle grazing during winter may reduce forage available to deer, even at moderate stocking rates.

▼ As a general rule, rangelands dominated by native vegetation and grazed by domestic livestock should be managed so that livestock consume 25 percent or less of annual production of herbaceous vegetation to avoid degradation of white-tailed deer habitat and to minimize diet overlap between livestock and deer.

▼ Introduction of exotic deer species is a threat to white-tailed deer populations because exotics are highly competitive with white-tailed deer and can potentially displace them.

Livestock Grazing and Deer

Most rangelands are grazed by domestic animals, although in recent years livestock have been removed on some private ranches in Texas. About 20 percent of respondents in a recent survey of landowners and hunting lessees in South Texas said livestock have not grazed their lease or ranch in the past three years (Bryant, Ortega-S., and Synatzske, n.d.). Contrasting viewpoints exist among natural resources managers in regard to cattle grazing and white-tailed deer. Aldo Leopold (1933) espoused the view that cattle can be used as a tool to improve deer habitat, although he cautioned that livestock grazing can also destroy habitat. Another, similar view is that cattle grazing and deer are complementary and grazing the two together is more efficient use of rangeland. A third view is that livestock grazing is simply destructive to wildlife habitat. An overall goal of this chapter is to present what is known from the scientific literature regarding livestock grazing and white-tailed deer and allow readers to follow the chain of evidence to develop, change, or reinforce their own view on the topic. Our interpretation of the relevant literature is that production of livestock and of white-tailed deer are compatible land uses only when numbers of each are properly adjusted based on available forage. We focus on seven aspects of livestock grazing in this chapter: (1) diet overlap between deer and livestock; (2) effects of livestock grazing on plant communities; (3) social interactions between deer and livestock; (4) grazing systems and deer; (5) calculation of correct cattle stocking rates to benefit deer habitat; (6) livestock water developments, such as earthen stock ponds, and fencing; and (7) effects of grazing on predation on deer. The effect of exotic ungulates on white-tailed deer is a topic related to livestock grazing. Continued introduction and increase of exotic deer and other ungulates may negatively impact white-tailed deer populations.

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7. The Ax, Plow, and Fire: Brush Management for White-Tailed Deer

Timothy E. Fulbright Texas A&M University Press ePub

7

The Ax, Plow, and Fire: Brush Management for White-Tailed Deer

KEY CONCEPTS

▼ Brush management may benefit or harm white-tailed deer habitat; thus, careful planning and understanding of plant and plant community responses to brush control are critical.

▼ Landscapes that have not been mechanically or chemically treated to control brush should remain untreated if quality white-tailed deer habitat is the management goal.

▼ Brush management may improve white-tailed deer habitat by increasing yield of herbaceous vegetation; creating openings for feeding activity; and increasing quality, accessibility, and palatability of browse.

▼ Created openings for feeding areas should be about 8.1 ha in size and should be interspersed within a matrix of woodland or shrubland to provide wooded travel corridors and daytime bedding sites for white-tailed deer.

▼ Stands of tall, dense, diverse brush are important for thermal and hiding cover and should not be subjected to brush management.

Deciding to Apply Brush Management

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Appendix 1. Common and Scientific Names of Selected Animals and Plants

Timothy E. Fulbright Texas A&M University Press ePub

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