Stacey A. Gunter

Ecosystem resilience despite large-scale altered hydroclimatic conditions

Climate change is predicted to increase both drought frequency and duration, and when coupled with substantial warming, will establish a new hydroclimatological model for many regions. Large-scale, warm droughts have recently occurred in North America, Africa, Europe, Amazonia and Australia, resulting in major effects on terrestrial ecosystems, carbon balance and food security. Here we compare the functional response of above-ground net primary production to contrasting hydroclimatic periods in the late twentieth century (1975–1998), and drier, warmer conditions in the early twenty-first century (2000–2009) in the Northern and Southern Hemispheres. We find a common ecosystem water-use efficiency (WUEe: above-ground net primary production/evapotranspiration) across biomes ranging from grassland to forest that indicates an intrinsic system sensitivity to water availability across rainfall regimes, regardless of hydroclimatic conditions. We found higher WUEe in drier years that increased significantly with drought to a maximum WUEe across all biomes; and a minimum native state in wetter years that was common across hydroclimatic periods. This indicates biome-scale resilience to the interannual variability associated with the early twenty-first century drought—that is, the capacity to tolerate low, annual precipitation and to respond to subsequent periods of favourable water balance. These findings provide a conceptual model of ecosystem properties at the decadal scale applicable to the widespread altered hydroclimatic conditions that are predicted for later this century. Understanding the hydroclimatic threshold that will break down ecosystem resilience and alter maximum WUEe may allow us to predict land-surface consequences as large regions become more arid, starting with water-limited, low-productivity grasslands.

Functional response of U.S. grasslands to the early 21st-century drought

Grasslands across the United States play a key role in regional livelihood and national food security. Yet, it is still unclear how this important resource will respond to the prolonged warm droughts and more intense rainfall events predicted with climate change. The early 21st-century drought in the southwestern United States resulted in hydroclimatic conditions that are similar to those expected with future climate change. We investigated the impact of the early 21st-century drought on aboveground net primary production (ANPP) of six desert and plains grasslands dominated by C4 (warm season) grasses in terms of significant deviations between observed and expected ANPP. In desert grasslands, drought-induced grass mortality led to shifts in the functional response to annual total precipitation (P(T)), and in some cases, new species assemblages occurred that included invasive species. In contrast, the ANPP in plains grasslands exhibited a strong linear function of the current-year P(T) and the previous-year ANPP, despite prolonged warm drought. We used these results to disentangle the impacts of interannual total precipitation, intra-annual precipitation patterns, and grassland abundance on ANPP, and thus generalize the functional response of C4 grasslands to predicted climate change. This will allow managers to plan for predictable shifts in resources associated with climate change related to fire risk, loss of forage, and ecosystem services.

BEEF SPECIES SYMPOSIUM: Difficulties associated with predicting forage intake by grazing beef cows

The current NRC model to estimate DMI is based on a single equation related to metabolic size and net energy density of the diet; this equation was a significant improvement over previous models. However, observed DMI by grazing animals can be conceptualized by a function that includes animal demand, largely determined by metabolic or linear size, physiological state, genetics, or any combination of these. Even in the database used to generate the current NRC equation, DMI by cows is poorly predicted at the extremes. In fact, across a wide range of actual DMI, predicted DMI is rather flat, indicating an insensitivity of prediction, so the model requires further refinement. A broad-based database was developed that includes pasture and confinement studies with growing, nonlactating, and lactating cattle. New equations are presented for consideration in the new model. It was found that the premise behind earlier NRC equations based on diet digestibility and BW are sound but that for cows, additional drivers based on milk production or calf performance were stronger than BW. Future models should be based on multiple variables, including functions for physiological state, animal suitability to the environment, and activity to modify the predicted DMI. Further, the model could possibly account for imbalances of protein to energy, particularly as they relate to ruminal function. Further, the issue of how reference data were collected (pen vs. pasture) and how the methods or constraints influence DMI must be evaluated. Overall, the new NRC model needs to be more robust in its ability to account for the wide variation in the environment, dietary characteristics, and metabolic demands.

Managing the herbage utilisation and intake by cattle grazing rangelands

Rangelands throughout the world provide clean water, fix solar energy in plants, sequester carbon, and offer recreational opportunities, with other ecosystem goods and services, including food from wild and domestic herbivores. Grazing rangelands with cattle requires constant management to balance the economic sustainability of the farm with other ecological services that rangelands provide. The challenges in management arise from the diversity of the rangeland forage resources at extremely large spatial and temporal scales. To be able to predict the performance of cattle grazing in extensive rangeland environments, estimating herbage intake is paramount because it quantifies energy intake and performance. Nutrient demand is the major driver of herbage intake, and characteristics of the sward and terrain of the landscape dictate how this demand is met. System models that integrate changes in weather patterns and herbage over long periods of time will allow farmers and scientist to monitor changes in herbage mass and utilisation. Dynamic models that include herbage growth components sensitive to weather patterns and animal demands are needed to predict how long-term changes in beef herd management will affect performance and range condition. Vegetation indexes captured across biomes with satellites can accurately quantify the dynamics of aboveground net primary production and changes in nutritional value with confidence. The computer software, PCRANCH, is a program for simulating cow–calf herd dynamics over long periods of time. The models within the PCRANCH software can simulate herbage growth and animal utilisation at large spatial and temporal scales needed for rangeland management and allow ranchers to evaluate the impacts of management on other ecological services. Knowing the long-term impact of management changes on swards enable ranchers to anticipate the ecological and economic benefits of improvements or demonstrate a protection of current ecological services.

Chemical Control of Sand Sagebrush: Implications for Lesser Prairie-Chicken Habitat

Abstract Traditional management of sand sagebrush (Artemisia filifolia) rangelands has emphasized sagebrush control to increase forage for livestock. Since the 1950s shrub removal has been primarily achieved with herbicides. Concerns over declining lesser prairie-chicken (Tympanuchus pallidicinctus; LPC) populations have led to increased scrutiny over the use of herbicides to control shrubs. The objective of our research was to describe changes to LPC habitat qualities following chemical control of sand sagebrush in northwest Oklahoma. Study pastures ranged in size from 10 to 21 ha. Five pastures were sprayed with 2,4-dichlorophenoxyacetic acid (2,4-D) in 2003 (RECENT), five were sprayed with 2,4-D in 1984 (OLD), and four received no treatment (SAGE). We measured habitat structure (sagebrush cover, sagebrush density, visual obstruction [VO], and basal grass cover), and dietary resources (forb density, forb richness, and grasshopper density) in all pastures from 2003 to 2006. OLD and RECENT pastures had less sagebrush (cover and density) and VO than SAGE pastures. OLD pastures produced more annual forbs than either SAGE or RECENT pastures. SAGE pastures had more perennial forbs than RECENT pastures. Herbicide application reduced protective cover while providing no increase in forb abundance in RECENT pastures. Our results indicated that it may take several years to realize increases in annual forbs following application of 2,4-D. However, loss of protective cover may persist for multiple years (20+ yr), and removal of sagebrush did not increase forb richness or grasshopper abundance. Thus, 2,4-D may have limited use as a habitat management tool because it takes numerous years to reap the benefit of increased forb abundance while reducing habitat structure in the long term. Resumen El manejo tradicional de pastizales de artemisa (Artemisia filifolia) ha enfatizado el control de artemisa para aumentar el forraje para el ganado. Desde los 1950s la remoción de arbustivas ha sido lograda principalmente con herbicidas. La preocupación por la disminución de las poblaciones de gallinas de pradera (Tympanuchus pallidicinctus; LPC) ha llevado a aumentar la vigilancia sobre el uso de herbicidas para el control de arbustivas. El objetivo de nuestra investigación fue describir los cambios en la calidad del hábitat de LPC después de controles químicos de Artemisia filifolia en el noroeste de Oklahoma. Los potreros en estudio variaron en tamaño de 10 a 21 ha. Cinco potreros fueron asperjados con 2,4-acido diclorofenoxiacético (2,4-D) en 2003 (RECIENTE), otros cinco fueron asperjados con 2,4-D en 1984 (VIEJO) y cuatro no recibieron tratamiento (ARTEMISA). Medimos la estructura del hábitat (cobertura y densidad de artemisa, obstrucción visual [OV] y cobertura basal de pastos) y fuentes de dieta (densidad y riqueza de hierbas y densidad de chapulines) en todos los potreros de 2003 a 2006. Potreros VIEJO Y RECIENTE tuvieron menos artemisa (cobertura y densidad) y OV que los potreros ARTEMISA. Los porteros VIEJO produjeron más hierbas anuales los porteros ARTEMISA Y RECIENTE. Los potreros ARTEMISA tuvieron más hierbas perennes que los potreros RECIENTE. La aplicación de herbicida reduce la cubierta protectora mientras que no aumenta la abundancia de hierbas en los potreros RECIENTE. Nuestros resultados indican que puede tomar varios años el lograr incrementar las hierbas anuales después de la aplicación de 2,4-D. Sin embargo, la pérdida de cubierta protectora podrá mantenerse por múltiples años (20+ años) y el remover la artemisa no aumenta la riqueza de hierbas y abundancia de chapulines. Entonces, 2,4-D podrá tener uso limitado como herramienta de manejo de hábitat porque toma muchos años obtener el beneficio de aumentar la abundancia de hierbas mientras que se reduce la estructura del hábitat en el largo plazo.

Simulation of Sandsage-Bluestem Forage Growth Under Varying Stocking Rates

Abstract The effect of stocking rate on forage growth has attracted much research attention in forage science. Findings show that forage growth may be affected by stocking rate, and there is a consensus that high stocking rates lead to soil compaction, which could also in turn affect forage growth because of the changing soil hydrology and increased soil impedance to forage root penetration. In this study we used a modeling approach to investigate the effect of stocking rates on the growth of sand-bluestem forage at Fort Supply, Oklahoma. The GPFARM-Range model, which was originally developed and validated for Cheyenne, Wyoming, was recalibrated and enhanced to simulate soil compaction effects on forage growth at Fort Supply. Simulations without the consideration of soil compaction effects overestimated the forage growth under high stocking rate conditions (mean bias [MBE]  =  −591 kg · ha−1), and the agreement between the simulated and observed forage growth was poor (Willmotts d  =  0.47). The implementation in the model of soil compaction effects associated with high stocking rates reduced the bias (MBE  =  −222 kg · ha−1) and improved the overall agreement between the observed and the simulated forage growth (d  =  0.68). It was concluded that forage growth under increasing soil compaction could be predicted provided such sensitivities are included in forage growth models.

Forage choice in pasturelands: Influence on cattle foraging behavior and performance

We determined if combinations of adjacent pastures of 3 forage species led to complementary relationships that influenced animal behavior and performance over monocultures. Grazing bouts, behavioral levels of activity, blood urea N (BUN), chemical composition of feces, BW, and herbage biomass before and after grazing were monitored when beef calves strip-grazed 3 replications of 4 treatments from June 14 through August 23, 2013 (9 animals/treatment). Animals grazed monocultures of: 1) tall fescue (TF), 2) alfalfa (ALF), 3) sainfoin (SAN), or 4) a choice of strips of forages TF, ALF, and SAN (CHOICE). The lowest and greatest incidence of foraging bouts occurred for cattle in CHOICE and SAN, respectively (P < 0.01). Animals in CHOICE grazed SAN > ALF > TF (P < 0.01). Animals on TF and CHOICE took greater number of steps than animals grazing a monocultures of either legume (P = 0.01). Calves in TF had lower BUN (P < 0.01) and fecal CP concentration (P < 0.01) than calves grazing the remaining treatments, whereas animals in SAN showed the greatest concentrations of fecal CP (P < 0.01). Fecal NDF concentration was the greatest for animals grazing TF and the lowest for animals grazing SAN (P < 0.01), whereas fecal ADF concentration was greater for animals grazing TF and SAN than for animals grazing CHOICE and ALF (P = 0.02). Calcium, Mg, and Zn concentrations were the lowest in feces from calves grazing TF and the greatest for calves grazing a monoculture of either legume (P < 0.05). When averaging both periods, animals grazing SAN, ALF, or CHOICE gained more BW than animals grazing TF (P < 0.01). Thus, calves in CHOICE incorporated tall fescue into their diets, were more active, and displayed a lower number of grazing bouts than calves grazing monoculture of either legume. Herbage diversity may lead to levels of ADG comparable to legume monocultures with the potential benefit of maintaining plant species diversity in pasturelands.

Cool-season annual pastures with clovers to supplement wintering beef cows nursing calves

In December of 3 years, 87 beef cows with nursing calves (594 ± 9.8 kg; calving season, September to November) at side were stratified by body condition score, body weight, cow age, and calf gender and divided randomly into 6 groups assigned to 1 of 6 cool-season annual pastures (0.45 ha/cow) that had been interseeded into a dormant common bermudagrass (Cynodon dactylon [L.] Pers.)/bahiagrass (Paspalum notatum Flugge) sod. Pastures contained 1 of the following 3 seeding mixtures (2 pastures/mixture): 1) wheat (Triticum aestivum L.) and ryegrass (Lolium multiflorum Lam., WRG), 2) wheat and ryegrass plus red clover (Trifolium pretense L., WRR), or 3) wheat and ryegrass plus white (Trifolium repens L.) and crimson clovers (Trifolium incarnatum L., WRW). All groups had ad libitum access to grass hay (12% crude protein; 58% total digestible nutrients). The second week in December, cow estrous cycles were synchronized and artificially inseminated. In late December, a bull was placed with each group for 60-d. Data were analyzed with an analysis of variance using a mixed model containing treatment as the fixed effect and year as the random effect. Body weight and condition scores did not differ (P ≥ 0.27) among cows between February and June. Calf birth weights or average daily gain did not differ (P ≥ 0.17) among treatments; however, calves grazing pastures with clovers did tend (P = 0.06) to weigh more than calves grazing grass only. Weaning weight per cow exposed to a bull was greater (P = 0.02) for WRR and WRW than WRG. Cows grazing winter-annual pastures containing clovers tended to wean more calf body weight per cow exposed to a bull than cows grazing the grass only pastures.

Effects of sand sagebrush control in southern mixed-grass prairie rangeland on cattle performance and economic return1

ABSTRACT To evaluate the effects of sand sagebrush (Artemisia filifolia Torr.) control in native rangelands on cattle performance, 15 pastures (10 to 21 ha each) were selected in northwest Oklahoma. Eleven pastures had been sprayed with 2,4-dichlorophenoxyacetic acid in 1984 or 2003 to establish differences in sagebrush cover. The pastures were categorized into 3 sagebrush cover levels: 1) high (27 ± 2.7% cover, n = 4), 2) medium (10 ± 2.7% cover, n = 6), and 3) low (5 ± 2.7% cover, n = 5). From 2003 to 2008, steers (BW = 202 ± 6.1 kg) were stocked annually in late January and grazed until mid-August. The high, medium, and low pastures were stocked at 47, 69, and 69 animal-unit-d/ha, respectively. Cattle were supplemented with oilseed-based cubes (41% CP) from January through April at a rate of 0.68 kg/ steer daily. From January to April, ADG did not differ (P = 0.96) among treatments, but from April to August steers grazing the high pastures gained BW faster (P

Effects of mass airflow rate through an open-circuit gas quantification system when measuring carbon emissions1

Methane (CH) and carbon dioxide (CO) represent 11 and 81%, respectively, of all anthropogenic greenhouse gas emissions. Agricultural CH emissions account for approximately 43% of all anthropogenic CH emissions. Most agricultural CH emissions are attributed to enteric fermentation within ruminant livestock; hence, the heightened interest in quantifying and mitigating this source. The automated, open-circuit gas quantification system (GQS; GreenFeed, C-Lock, Inc., Rapid City, SD) evaluated here can be placed in a pasture with grazing cattle and can measure their CH and CO emissions with spot sampling. However, improper management of the GQS can have an erroneous effect on emission estimates. One factor affecting the quality of emission estimates is the airflow rates through the GQS to ensure a complete capture of the breath cloud emitted by the animal. It is hypothesized that at lower airflow rates this cloud will be incompletely captured. To evaluate the effect of airflow rate through the GQS on emission estimates, a data set was evaluated with 758 CO and CH emission estimates with a range in airflows of 10.7 to 36.6 L/s. When airflow through the GQS was between 26.0 and 36.6 L/s, CO and CH emission estimates were not affected ( = 0.14 and 0.05, respectively). When airflow rates were less than 26.0 L/s, CO and CH emission estimates were lower and decreased as airflow rate decreased ( < 0.0001). We hypothesize that when airflow through the GQS decreases below 26 L/s, breath capture was incomplete and CO and CH emissions are underestimated. Maintaining mass airflow through a GQS at rates greater than 26 L/s is important for producing high quality CO and CH emission estimates.