| Lance T. Vermeire, Amy C. Ganguli, and Robert L. Gillen |
| Authors are Rangeland Scientist, USDA-ARS, Fort Keogh Livestock and Range Research Laboratory, Miles City, Mont. 59301; and former Research Assistant, Department of Range, Wildlife, and Fisheries Management, Texas Tech University, Lubbock, Tex. 79409-2125; and Rangeland Scientist, USDA-ARS, Southern Plains Range Research Station, Woodward, Okia. 73801. |
Abstract |
| Some recent investigations have shown the visual obstruction (VO) measurement method to be an effective means of estimating herbage standing crop non-destructively in tallgrass prairie. Although the method is rapid and inexpensive, visual obstruction models have been limited to tallgrass prairie and sandhills range types. Our primary objective was to evaluate the relationships between visual obstruction and standing crop in shortgrass plains and mixed prairie. Secondly, we wanted to determine whether these models could be integrated with tallgrass prairie models without appreciable losses in prediction capabilities. We conducted 44 trials on non-burned sites with various levels of grazing pressure. Each trial was composed of 20 randomly selected plots and served as 1 experimental unit to represent pasture-level standing crop estimation. Visual obstruction readings were taken from a modified Robel pole placed centrally at the back of 0.1-m2 quadrats and vegetation was clipped to estimate standing crop. Trial standing crop was regressed on visual obstruction and models were compared among range types. Visual obstruction explained 91 and 89% of the variation in shortgrass plains and mixed prairie standing crop, respectively. A single visual obstruction model effectively estimated herbage standing crop across range types and produced a coefficient of determination of 0.93. Although greater precision may be obtained from models developed for specific sites, the ability of a single visual obstruction model to predict standing crop across years, management schemes, and range types indicates visual obstruction models may be successfully employed on a regional basis. |
| Key Words: mixed prairie, non-destructive sampling, Robel pole, shortgrass, tallgrass |