Declining forage availability effects on utilization and community selection by cattle

Land managers of salt desert shrub and sagebrush steppe vegetation have concerns regarding appropriate stocking rates in summer for ephemeral stream riparian zones because of elevated levels of use on woody vegetation. We determined utilization levels of forage species over time as a fixed animal density decreased available forage as a means of approximating the stocking rate suitable for an area and identifying plant species for monitoring. Trend in abundance of important plant species will ultimately determine appropriate stocking rate in a particular management situation. Forage utilization by cattle during mid-summer for 2 successive years was measured weekly for 3 weeks in streamside (channel and floodplain) and adjacent upland (terrace and saline upland) vegetation communities along the ephemeral stream. Measures were also made of crude protein and dry matter content of plant species. Plant communities used by cattle were also recorded. Utilization of streamside and terrace vegetation declined markedly over the 3 weeks, while utilization of forage in saline uplands was lower than in other areas and did not decline over weeks of study. More cattle selected streamside and terrace areas with the most succulent forages than saline uplands with less succulent forages. Woody plants in channel areas, cottonwood (Populus deltoides Bartr. ex Marsh.) particularly, were higher in protein, more succulent, and more severely grazed than other species. Management of cottonwood probably limits the stocking rate used in these communities. Declines in weekly utilization of forages after the first week indicated intake may have been declining. If so, lower levels of utilization may be needed to maintain animal performance. Maintenance of cottonwoods and animal performance considerations may dictate a lower stocking rate than achieved in this midsummer study.