Carrying capacity as applied to deer can be defined as the number of animals which a given unit of land area can support without deterioration of the forage resource. A population is limited in size by the factor(s) which exerts the greatest resistance to continued growth. Food, cover, water, human interaction, and dogs are some of the more important factors limiting population growth of deer.
In Missouri forests, the carrying capacity for deer is most often limited by the quantity and quality of food. Preferred foods must not only be present in sufficient quantity, but their nutrient content and digestibility (or quality) must be considered when appraising carrying capacity. Protein is deficient in winter and phosphorus is deficient year round in several preferred foods of Ozark deer.
Summer foods are 1.5 times more digestible than winter foods; cellulose is over 4 times more digestible in summer than in winter. Thus, even when ample amounts of browse are available, deer may be poorly nourished. However, in winter, quantity of forage is a more important limiting factor than quality.
Energy may be the most important limiting factor in the forest. Deer are apparently in a negative energy balance and lose weight during most winter. Feeding studies of penned deer show that deer voluntarily decrease food consumption and lose weight during winter. Deer have apparently adapted through evolutionary time to poor quality and quantity of winter foods and depend on fat reserves deposited in late summer and fall to supply much of their winter energy needs.
Good summer and fall nutrition may be critical to winter survival and successful production of healthy fawns the following spring. Acorns are an important energy source during late summer and fall and this probably explains their heavy consumption rate by deer. A late summer drought followed by an acorn failure could be critical for deer in the Missouri Ozarks.
In some cases, deer populations never reach levels that fully utilize the available food. Here, limiting factors other than food cause low deer numbers. Free-running dogs, poaching, and lack of cover or water are examples of such factors.