Equilibrium and Non-Equilibrium Ecosystems

Equilibrium Systems

"Equilibrium grazing systems are characterized by relatively high levels of climatic stability, resulting in constant levels of primary production." "Conventional range management makes sense in this kind of grazing system... [It] seeks to balance contrary processes by adjusting the destructive power of animals, and hence the number, to match the recuperative power of the plants, thereby sustaining a stable and profitable equilibrium".

Non-Equilibrium Systems

They are found "in areas where rainfall is persistently erratic, both in timing and spatial distribution, mainly in arid and semi arid tropical environment".

"Grazing system is subject to extremely variable rainfall; fluctuation of rainfall may have a much stronger effect on the vegetation than animal number".

"In these environments, it is no longer appropriate to conceive of management as the manipulation of the biological system to achieve maximum output or revenue."

Roy Behnke, Natural resource management in pastoral Africa, paper prepared for UNSO Donor/Agency Consultation Meeting, Paris, December 1993.

Applicability of Equilibrium and Non-equilibrium Concepts to Livestock Production Systems

These definitions are most suited to native grasslands in tropical Africa. The first one fits with the arid tropics, the second corresponds more or less to the semi-arid, the sub-humid and the humid tropics.

They are however poorly adapted to a worldwide study where classifications have to cover a large range of situations.

In pastoral areas of Africa, grazing in "equilibrium" rangeland can have a considerable impact on the vegetation, both in terms of its composition and density, leading to a non-equilibrium situation - a change from an ecological equilibrium system to a non-equilibrium livestock production system. In other continents, grassland is not always native, considerable areas are sown or planted with introduced and genetically improved species, improving productivity and hence introducing an equilibrium livestock productions system, but with major changes to the natural ecological systems.

In the wet tropics where rainforest grows naturally, the vegetation dynamics in woodland introduces another type of imbalance, in which management practices including mechanical maintenance are necessary. This ecosystem could also be called for other reasons a non-equilibrium rangeland system. Additional non-equilibrium systems include the montane and sub-arctic pastoralist systems where extreme snow fall conditions replace rainfall effects as the climatic variability affecting livestock populations.

Reference

Behnke, R. and Kerven C. Redesigning for risk: tracking and buffering environmental variability in Africa's rangelands Natural Resource Perspectives, No.1 (1994) http://www.oneworld.org/odi/nrp/1.html

> > [Livestock & Environment Toolbox Home]