Location: Rangeland Resources & Systems Research
Project Number: 3012-21610-002-20-I
Project Type: Interagency Reimbursable Agreement
Start Date: Mar 1, 2015
End Date: Feb 28, 2019
We will examine whether adaptive cattle grazing management (movement of large herds among pastures based on multipe conservation and production objectives) can (1) enhance plant diversity and spatial variability in plant heights, and (2) increase reproductive success of declining grassland birds, thereby contributing to the conservation of grassland biodiversity. One treatment in the study (the adaptive grazing management treatment; AGM) will use short-term, intense grazing at high stock density combined with long-term (> 1 year) rested pastures. We wil compare this treatment with a traditional grazing treatment (TGM) consisting of continuous, season-long cattle grazing at moderate stocking rates. The experiment will be guided by a stakeholder committee with representatives from the ranching community, public land management agencies, and non-governmental conservation organizations, which will work with scientists to determine criteria for livestock movement among pastures based on monthly and annual monitoring. The research team supported by this grant will measure the effect of adaptive grazing management on plant diversity, spatial variability in vegetation heights, and the reproductive performance of native grassland birds species. Within the same experiment, measurements of forage production, livestock production, and soil carbon will be conducted by USDA-ARS scientists. This collective set of measurments will be used to evaluate whether adaptive livestock grazing management can increase ranch productivity and resilience to drought, while also supporting conservation of diverse plant and wildlife communities.
We will use the 6,270 ha USDA Agricultural Research Service Central Plains Experimental Range (CPER), located on the western edge of the Pawnee National Grasslands, about 20 km northeast of Nunn, Colorado, USA (Lat. 40o 50’ N, Long. 104o 42’ W) as the primary study site. The AGM and TGM treatments will both be grazed from May 15 to October15 each year (approximately 150 days), employ the same annual stocking rate (0.6 AUM ha-1, which is the moderate stocking rate recommended by NRCS for upland ecological sites in this region), but will differ in terms of the pulsed grazing timing (start and duration) and rest periods (across years) and stock density. For the TGM treatment, grazing will occur in each pasture the entire grazing season (mid-May to mid-October) with no rest periods, and stocking density will be maintained at 20 yearling steers per 130 ha (0.154 steers ha-1). In contrast, the AGM treatment pastures will be pulse grazed (i.e grazed at high stock density for less than 30 days in a given year) with periodic long-term rest (1 year in 5). Densities of 9 grassland bird species [Horned Lark (Eremophila alpestris), Mountain Plover (Charadrius montanus), McCown’s Longspur (Rhynchophanes mccownii), Killdeer (Charadrius vociferus), Western Meadowlark (Sturnella neglecta), Lark Bunting (Calamospiza melanocorys), Mourning Dove (Zenaida macroura), Brewer’s Sparrow (Spizella breweri), and Grasshopper Sparrow (Ammodramus savannarum) will be measured in a grid of 4 survey points per pasture each year in June. We will locate nests by observing adult behavior and by dragging a rope between two observers 25 m apart to flush birds. Upon finding nests, we will determine age of eggs by floating 1-2 eggs from each nest in water and assigning age based on flotation stage (modified from Westerskov 1950), or estimate age of nestlings by size and physical characteristics. Nests will be monitored and eggs and chicks counted every 2-4 days until nests are empty. We will quantify effects of AGM on nest survival rates of each focal bird species through models that include vegetation structure, grazing treatment, soil texture, topography, rainfall patterns, and time in season as covariates. Our primary objective in these analyses will be to evaluate the degree to which increased grazing-induced heterogeneity in the AGM treatment is linked to increased reproductive performance of species associated with both intensely grazed and ungrazed habitats.