An economic comparison of control methods of Wyoming big sagebrush in southwestern Montana
Big sagebrush (Artemisia tridentata Nutt.) is a very inefficient user of water and competes strenuously for moisture with more desirable forage plants such as grasses, forbs, and other shrubs. Several control methods have been developed in hopes of increasing range productivity for domestic livestock grazing. Spraying with 2,4- D, burning, plowing and seeding, and rotocutting are the primary means of controlling sagebrush. The objective of this thesis was to conduct an economic comparison among these four Wyoming big sagebrush control methods and determine optimal retreatment intervals. Production of perennial grasses was measured on experimental plots in southwestern Montana 12 years during the period 1963-1986. The data were used to estimate the treatment response function. Sagebrush control is a stochastic dynamic problem and as such the problem was formulated within a stochastic dynamic programming framework. The economic criterion was the expected present value of additional net returns from sagebrush treatment. Decision alternatives included in the DP model were keeping or retreating the sagebrush. The state variables were years since treatment and expected value of forage yield per AUM which was defined as a function of calf price. Based upon a statistically estimated second-order autoregressive difference equation, the calf price transition probability distribution was developed. Given the data available to this study, Wyoming big sagebrush treatment methods of spraying and burning were economically feasible, with spraying the most profitable. Rotocutting was only marginally feasible, and plowing and seeding was not feasible. From the study results it was also concluded that in addition to treatment method., treatment cost and the quantity of sagebrush killed, the expected present value of additional net return and optimal retreatment interval also depend upon previous calf price trend.