Rural System's

Modern Wild Faunal Resource System Management

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An Alternative Definition of Carrying Capacity

Many definitions of carrying capacity have been given and used. Edwards and Fowle reviewed some as of 1955 and Barber listed others in 1974. It is complex and the phrase should be used only in a superficial way with the public. Because of multiple definitions, it is unlikely that it will clarify discussions among professionals. In some groups a common definition might be agreed upon to expedite work. It might be:

Life-group-specific carrying capacity is the mean quality biomass of animals of a life group (under the influence of social and behavioral constraints) for which a particular area, having objectives (e.g., quality, units, etc.) specified by users of the population, will supply all energetic and physiological requirements over a long but specified period.

Debate continues about the proper meaning: whether single or multiple species, year-around or seasonal, annual or planning period, current or historical, and the size of the population (micro-site, regional, national, etc.)

There are two types, species or life-group specific and composite species.

Composite species work requires only minor changes in the definition.

The concept is one of land expressed in animal units or animal unit months AUMs. Animals of different size consuming different amounts of food can influence the number on an area. Time must be specified. Actual carrying capacity changes among years. There are social limits to the animals on an area; foraging capacity may not be reached. Capacity can be changed by managers; it is not innate, but has an upper limit that few have considered or explored, and never in the wild with public funding.

As in ranching, in a year with abundant forage (due to water, nutrients, etc.) it is unwise to have too few animals to consume the available forage. When a poor forage year occurs and the rancher has many animals in preparation for a "good" year, the range may be damaged. The manager is in a strategic battle: how many animals should be present now to produce the population that will consume the forage that will occur in the next growing season producing an unknown amount of forage. Suitable herd size on a tract in one year can be wasteful if the forage is abundant and cannot be consumed. Similarly, suitable herd size in one year may produce very undesirable conditions in the following year if there is drought or low forage productivity. Excessive cows on a range (or deer) is very bad if there is no demand for the (prices or hunters), even if forage looks good.

Feedforward is needed as the manager predicts the range of future forage. (Predicting the amount is a silly exercise.) Interest rates cannot be predicted well either. The manager works within the decision space of the bounds of Forage , F, and the Market, M.

Note that animals can exceed the capacity, a problem with the term when viewed as analogous to a pail or bucket but not to a load on a truck.

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Last revision January 14, 2004.