Carrying capacity defines the number of Animal Units (AU; head of cattle or number of sheep, goats or other animals) that can graze in a rangeland unit without exhausting the vegetation and soil quality – essentially optimally utilising resources. Optimum carrying capacity is where a given unit of rangeland can support healthy populations of animal species, while allowing an ecosystem to regenerate, thus creating a sustainable balance. The stocking rate - defined as the number of animal species grazing a unit of rangeland for a limited period - must be kept fixed on an average year, meeting the carrying capacity to allow regeneration, the fallen seeds to rejuvenate and the soil to recover. However, stocking rates can fluctuate depending on the nature of the vegetation, rainfall variability, herd composition and management system. If the conditions are not favourable for vegetation growth during drought season, the number of livestock or the grazing period must be adjusted to avoid overgrazing. Moreover, the purpose of livestock keeping, i.e. for milk, meat, or wool production, will determine the carrying capacity of a rangeland unit. Factors such as climatic zone, rainfall dependency, class of livestock (steer, dry cow, calves, lactating cow and bull, etc), health of grassland and animal species affect the stocking rate. While relevant in all climatic zones, it is more applicable in arid and semi-arid zones where rainfall is most scarce. This climate smart practice increases production (meat/dairy), increases pasture resilience to extreme climate hazards (drought) and enhances soil fertility.
To effectively implement Carrying capacity improvement:
- Step 1: There is no standard equation to determine the carrying capacity of an area, as many variables apply and factors relevant within each context including size of land unit, amount, frequency and timing of rainfall seasons, type of vegetation, species of animal, etc.
- Step 2: Extension officers should aim to support farmers to continuously monitor rangeland status and realise the impacts of over-grazing and the benefits of finding an equilibrium.
- Step 3: Constant monitoring of the pasture and animals must be carried out throughout the year to check if stocking rate aligns with the carrying capacity of the land unit. If land degradation is identified, adjustments to stocking rates should be considered, in the context of season and landscape regeneration.
- For communal grazing land, it is ideal to use Animal Units (AU) to calculate the relative grazing impact of different kinds and classes of domestic livestock and/or even common grazing wildlife species for one month (AUM = Animal Unit Months). This information should support collective decision-making regarding rangeland resources.
Using a conversion table of, the AUE (Animal Unit Equivalent) and the formula:
1) multiply the number of animals to be grazed on the pasture by AUE to determine total AU, then
2) multiply the total AU by the number of months planned to graze (see formula below or
Worksheet A of the Range Calculator).
Formula: _____________ x _____________ = _____________ x _____________ = _____________
# Animals AUE(table) Animal Units (AU) Months (M) AUM
- Step 4: One option for effectively responding to carrying capacity challenges is shift or changing grazing species if high consumption species are placing pressure on a particular unit of land.
- The Food and Agriculture Organisation (FAO), 1997. Livestock and the environment: Finding a balance. Rome, Italy.
- The Food and Agriculture Organisation (FAO), 2013. Carrying capacity tools for use in the implementation of an ecosystems approach to aquaculture. Rome, Italy.
Benefits
- Identifying, achieving and maintaining optimal carrying capacity helps to avoid rangeland degradation including vegetation depletion and soil erosion, bush encroachment, and optimises resource use.
- Effectively monitoring carrying capacity can allow communities to respond to climate change impacts, resulting from shifting rainfall patterns and temperature regimes.
Drawbacks
- Rainfall dependency, class of livestock and quality of grassland affect stocking rate.
- The stocking rate must be monitored to avoid animal overcrowding, which might cause diseases to spread quickly.
- It is important to monitor the plant species in your pasture and or rangelands to be able to determine its health and trend.
- Reseeding should be considered in areas when land is degrading.
