With some recent forecasts bringing encouraging news about a potential El Niño, some ranchers have been asking about what they should expect in terms of forage production, if and when the rains come. What they want to know is how soon rangeland productivity will reach the pre-drought levels again. One issue that I always draw their attention to is the levels of residual dry matter (RDM) on the rangelands. Even with the reduction in herd sizes and shorter grazing seasons employed by most producers, more rangelands now have less than recommended RDM levels.
RDM is a measure of the old plant material (without counting summer annuals) that are left standing or on the ground before the fall precipitation comes. It is a great indicator of both forage production and grazing intensity. These leftover plant materials are critical on California rangelands to reduce erosion and nutrient loss, and to create a conducive environment for diverse plant communities to thrive. Optimum RDM levels are site specific, they range from 100-2,100 pounds per acre, and depend on precipitation zone, slope and tree canopy cover. Ideal RDM levels increases with precipitation and slope, and decreases with tree cover. Studies show that too low or too high RDM levels will reduce species composition and forage production, both factors critical to any livestock production system. The good news is that annual rangelands are resilient and will likely return to normal production within two years after bringing RDM level to recommended standards.
Knowing the RDM standards for one's rangeland and continuously monitoring is an important step towards achieving sustainable rangeland management and livestock production.
Details about RDM standards, data collection methods and more can be found in the free UC Agriculture and Natural Resources publication Guidelines for Residual Dry Matter on Coastal and Foothill Rangelands in California.
Author: Fadzayi Mashiri, Ph.D.