RE: How to determine carrying capacity of land?
CARRYING CAPACITY OF DEER HABITAT
For the purposes of this discussion, carrying capacity (CC) is defined as the number of animals a given unit of habitat can sustain in good physical condition without causing damage to the habitat. The term CC, as used in this section, should not be confused with the terms absolute CC or CC K. These later definitions of CC are used by population biologists to describe the maximum number of animals a unit of habitat can support (the theoretical point in a population growth model in which births equal deaths and the population stops growing).
Determining CC for deer habitat can be useful when attempting to formulate management strategies. Developing a CC estimate gives the deer manager a ceiling with respect to the maximum population
size that should be carried on a given unit of habitat. As with population estimates, the exact number of animals in a CC estimate is not precise. For example, if an estimated population of 500 animals
occupy a given unit of habitat and these animals are in excellent condition, then it may be assumed the given unit of habitat has a CC of at least 500 animals.
Deer managers often assume the maximum CC can be determined by noting the number of the total estimated population at the point when physical indices begin to deteriorate. At this point, deer
managers may infer the herd is at or slightly above the CC. The danger of this assumption is often a deer herd can exist at and periodically exceed CC for several years before physical indices show signs of severe
overpopulation. The actual CC may, in fact, be substantially lower than the point at which a decline in physical condition is first observed.
When a deer herd has been allowed to exceed CC for any period of time, habitat quality is adversely affected. The most nutritious forage species in the habitat are the first to be depleted. A deer herd can eliminate some of these species from the habitat entirely. If no seed source or rootstock is left, some of these species may never be re-established naturally. The long-term effects of such overpopulation on habitat quality, deer quality, and CC are severe. The CC may actually be reduced to a point much lower than it had originally been. Once the quality of habitat has been significantly reduced and measures are then taken to reduce the population to within the CC, the total number of animals that can be supported in good condition may be much lower than before overpopulation occurred.
Natural mortality remains too low in many of these cases to return these herds to CC. As these populations are allowed to exceed CC, habitat quality is further diminished and actual CC is lowered. Deer managers in many areas are faced with this dilemma, particularly on sites with poor to marginal habitats. Deer populations have not been kept at levels low enough to allow for habitat quality to recover. This may be due to either pressures from user groups or the sheer inability to implement an adequate harvest.
In some cases, habitat quality may never recover regardless of how low population levels are reduced. Exceeding CC can lead to a repetitive The relationship between carrying capacity and deer density is relatively simple—when deer density exceeds carrying capacity (CC) for a significant
period of time, both CC and deer density often are reduced. Exceeding CC can lead to a repetitive cycle of poor deer herd and habitat conditions. This cycle is not easily interrupted and often cannot be stopped.
FACTORS INFLUENCING CARRYING CAPACITY
Carrying capacity fluctuates throughout the year depending on habitat conditions, rainfall, and various habitat changes, such as timber and farming operations. Supplemental feeding and planting
often are employed in an attempt to increase CC for a particular unit of deer habitat. These activities are seldom of sufficient scale to affect CC significantly. Such practices may only serve to compound problems
associated with gross overpopulation. In these instances, attempts to reduce herd density are more desirable than attempts to increase carrying capacity.
Actual biological CC for deer may not coincide with a social or ecologically based carrying capacity. An area where deer/human interactions are a primary concern may have a much lower CC based on
factors such as deer/vehicle collisions or deer damage to crops and ornamental plants. This may be referred to as social carrying capacity. A case involving endangered or fragile plant communities may have an
acceptable CC for deer much lower than is biologically practical. In many cases, social CC is greater than biological CC as people often desire to have more deer than the habitat can support.
Rainfall usually is the only climatic factor affecting CC in the Deep South. Habitat quality may be improved in the form of abundant mast crops and increased amounts of native browse in years with abundant rainfall. Physical indices may show corresponding improvements resulting from increased rainfall in herds maintained below CC. In 44cases where population levels are at CC, increases in habitat quality are generally negated because coinciding reproductive increases may add additional deer to the herd, further compounding the problem of too many deer.