Economic Optimum Big Sagebrush Control for Increasing Crested Wheatgrass Production

Abstract

AbStnCt An approach was developed for estimating the economic optimum rate of initial overstory kill for increasing seasonal forage availability. The model was formulated using: (1) a biological production function relating understory production to initial kill percentage, (2) a derived demand function for seasonal forage value, and (3) a cost of overstory kill function for each control method. The specific optimum solution will vary irith the situation; however, the general model may be applied to any ranching situation where understory forage production is constrained by undesirable overstory vegetation. The model was iilustrated using the big sagebrush-crested wheatgrass vegetation type on a Utah cow-calf-yearling operation with prescribed burning, 2,4-D spray ing, and tebuthiuron application as control methods. For the ranch analyzed, a big sagebrush kill rate between 92 and 100% is optimal depending on the derived demand and cost-of-kill functions used. Kill rates that differ from the optimum caused significant opportunity costs to be incurred. Investments in control of undesirable vegetation to increase forage production have the potential to increase red meat production, ranch profits, and other benefits to society such as reduced soil erosion. To achieve such benefits requires careful planning, implementation, and monitoring of vegetation control projects. The purpose of this study was to investigate and develop usable mathematical and tabular approaches for estimating the optimum (profit maximizing) rate of initial overstory kill for increasing seasonal forage availability on a given ranch. The focus is how the ranch should approach biological and economic decisions for the alleviation of an identified seasonal forage bottleneck in a yearlong ranch operation. The biological relationship between overstory dominance and understory production has been documented for many vegetation types (Ffolliott and Clary 1982, Bartlett and Betters 1983). The analytical approach examined in this study was illustrated using big sagebrush (Artemisia tridentata Nutt.)-crested wheatgrass (Agropyron deserrorum (Fisch. ex Link) Schult., A. crisratum (L.) Gaertn.) vegetation relationships in a Utah cow-calf-yearling operation. The rate of big sagebrush reestablishment on a specific site depends on the percentage initial kill, subsequent grazing management, ecological adaptation of sagebrush to the site, and reinvasion of sagebrush from outside the treatment area (Pechanec et al. 1965, Hull and Klomp 1966, Johnson and Payne 1968, Winward 1983). Benefits from brush reduction include improved range condition, increased forage and livestock production, ease of working cattle, increased feed for wildlife, and improved watershed conditions (McDaniel 1980). Multiple use management may dictate that not all big sagebrush be removed. However, Evans et al. (1979) examined the biological relationships and recommended