Location: Rangeland Resources & Systems Research
Project Number: 3012-21610-003-31-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Aug 1, 2020
End Date: Dec 31, 2023
Objective 1 – Evaluate the effects of increased precipitation variability (droughts and deluges) and soil texture on grass-shrub competition, plant production, and forage quality. Objective 2 – Evaluate spatial and temporal patterns of livestock foraging influenced by prairie dog abundance and distribution, and impacts to livestock weight gains.
The Cooperator and ARS will collaborate in: A) an experimental design that will test four separate precipitation treatments: 1) increased interannual precipitation variation, 2) increased winter precipitation amount, 3) the combination of 1 and 2, and 4) multi-year summer drought. Increased interannual precipitation will occur through use of partial rainout shelters that reduce growing season precipitation on one plot by 50%, while diverting that same amount to a second plot to increase growing season precipitation. The location of the partial rainout shelter will be switched between experimental plots each year to increase interannual variability in growing season precipitation (+50% in year one, -50% in year two, etc.). Each shelter will be 12 feet wide, 9 feet deep, and 4 feet tall at the center, and will be centered on focal sagebrush plants (<60 cm tall). Second, we will enhance winter precipitation by adding 50% of the historical November-March mean precipitation to plots in this treatment. A third set of plots will receive combined treatments of increased winter precipitation and increased interannual variability. Finally, multi-year drought will be evaluated using partial rainout shelters that reduce incident precipitation by 50% during each growing season (but not winter). The experimental design will be replicated five times at each of two sites with different soil types (clayey and loamy). Experimental infrastructure will be removed from both sites during the winter (November to March) to allow for normal winter grazing by livestock and native grazers, and to avoid snow drifting effects around infrastructure. A weather station at the site will measure precipitation, temperature, wind and other meteorological variables hourly. Additionally, soil moisture will also be continuously measured with two Sentek Enviroscan probes in each soil type to provide high temporal resolution of soil moisture dynamics in response to rain events. On an annual basis we will measure plant species composition and demography, plant production and forage quality. B) novel use of GPS collar tracking to non-invasively quantify the amount of time cattle spend foraging per day on versus off prairie dog colonies. We will use collars that include an activity sensor (3-axis accelerometer) that measures head movements in 3 dimensions plus neck angle, combined with GPS locations recorded 5-min intervals, to track cows over the growing season. We will conduct direct cattle behavioral observations and use these observations to test and further improve site-specific foraging behavior. Maps of animal grazing time within pastures will be developed. To measure variation in the quality of forage that cattle are consuming across the study pastures, we will collect fecal samples from each collared cow twice monthly over the growing season. On the days of collection, cattle will be observed from a distance until a fresh fecal sample can be collected. Samples will be analyzed using a commercial lab for digestible crude protein and digestible organic matter in the diet. Livestock weight gains will be determined by subtracting entry weights from exit weights of cattle.