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Rangeland Carrying Capacity Evaluated Through Science-Based Methodology

The Issue

The California Land Conservation Act of 1965, popularly known as the Williamson Act, applies to all forms of agriculture including the extensively managed rangelands which cover 40 percent of California. It is one of the major public policies that conserves rangeland open space values, which are provided mostly by private livestock producers. In establishing values, the Williamson Act considers actual use of the land instead of potential use.

Livestock carrying capacity estimates for Williamson Act parcels in Tulare and Fresno Counties historically had been developed though landowner surveys. County assessors identified a need to determine livestock carrying capacity through science-based methodology in order to more accurately assess the lands in accordance with the requirements of the Act.

What Has ANR Done?

Carrying capacity estimates are one part of determining present-use land values, and remotely sensed image analysis and geographic information systems (GIS) provide a second part--a science-based, defensible, repeatable and widespread method for modeling carrying capacity.

A system was developed for Tulare and Fresno counties which utilizes grazing capacity score cards based to accurately determine the carrying capacity of individual parcels and ranches. This system developed by James Bartolome, Professor of Range Ecology - UC Berkeley, William Frost, Natural Resource Advisor, Neil McDougald, Natural Resource and Livestock Advisor and Richard Standiford, Forest Management Specialist, is based upon rangeland science principles. The score cards take into consideration (1) rainfall, (2) influence of woody species canopy cover on herbaceous production, (3) effect of slope on animal use and (4) residual dry matter standards.

Nina Maggi Kelly established validation and verification parcels for AUM capacity by using elevation, precipitation, slope and canopy cover data in a GIS system. These layers were used with the scorecards to estimate grazing carrying capacity per parcel, and the AUMs per acre were then calculated.

The Payoff

System benefits livestock industry and open space

This Cooperative Extension project provided a science-based method for determining carrying capacity and appraising 977,617 acres of rural land under Williamson Act contract in Tulare and Fresno Counties. This process ensured sustainability of the Williamson Act program and preservation of the livestock industry and open space in the two counties.


Supporting Unit: Madera County

Neil McDougald
Livestock and Natural Resources Farm Advisor
Fresno and Madera Counties
328 Madera Ave.
Madera, CA 93637
559-675-0639 FAX