Savory brittleness scale
The Savory brittleness scale is used to describe the annual distribution of humidity in a particular environment. It was developed by Allan Savory, a Zimbabwean biologist. The scale is used in land management because the distribution of humidity affects the way that land, particularly when degraded, responds to being rested. The scale is designed to be used to guide the management of cattle or livestock in the maintenance and restoration of land that is brittle or subject to desertification.
The scale ranges from 1 to 10 with 1 being non-brittle and 10 being very brittle. The scale is subjective; there is no formula for its calculation. A tropical rainforest is considered a 1 on the scale, and an arid desert such as the Sahara is considered a 10.
The scale includes the distribution of humidity throughout the year, but not the total amount of rainfall. For this reason, it differs from an aridity index. Thus, some high rainfall environments, e.g., Zambia, with 2,000 mm annual rainfall and distinct wet and dry seasons, is higher on the brittleness scale because of the long portions of the year without rainfall. An environment with lower total rainfall distributed fairly evenly throughout the year, such as parts of England with 600 mm annually, are lower on the brittleness scale.
Effect of Brittleness
While total rainfall is important for understanding the ability of an area to be productive during the growing season, brittleness is proposed to give an indication of the ability of insects and bacteria to degrade dead plant material throughout the year. A brittle environment may be characterized by grasses which grew during the rainy season and which died during periods of extended dryness and are still standing at the time the rains return. This lack of decay means the dead grasses shade new plant growth, reducing the productivity of the area during the rainy season.
Non-brittle lands, such as rain forests, recover quickly after they are cleared, whether or not they are rested from grazing. Continuous availability of moisture promotes a continuous cycle of the growth, death and decomposition of new plants, so space is made for following generations.
At the other end of the scale are brittle and very brittle lands. If left rested after being cleared these lands often recover only very slowly.
- Edge, Aspen (Autumn 2007), "Lessons from a Brittle Landscape", Permaculture Magazine (53): 47–50
- Keppel, Wilma, Landscape brittleness: how "good" management can harm land, retrieved August 5, 2007
- Savory, Allan Holistic Management: A New Decision Making Framework Second edition 1998 Island Press.