Roger N. Gates

Using Weather Data to Explain Herbage Yield on Three Great Plains Plant Communities

Abstract Understanding the drivers that account for plant production allows for a better understanding of plant communities and the transitions within ecological sites and can assist managers in making informed decisions about stocking rates and timing of grazing. We compared climatic drivers of herbage production for 3 plant communities of the Clayey ecological site in southwestern South Dakota: the midgrass community dominated by western wheatgrass (Pascopyrum smithii [Rybd.] A. Love); the mixed-grass community codominated by western wheatgrass, blue grama (Bouteloua gracilis [H.B.K.] Lag. Ex Griffiths), and buffalograss (Buchloe dactyloides [Nutt.] Engelm.); and the shortgrass community dominated by blue grama and buffalograss. We used herbage yield and weather data for the period 1945–1960 collected at the South Dakota State University Range and Livestock Research Station near Cottonwood, South Dakota, to develop stepwise regression models for each plant community. Midgrass herbage production was best predicted by current-year spring (April–June) precipitation, number of calendar days until the last spring day with minimum temperature ≤ −1°C, and previous-year spring precipitation (R2 = 0.81). Mixed-grass herbage production was best predicted by current-year spring precipitation and days until the last spring freeze (R2 = 0.69). Shortgrass herbage production was best predicted by current-year spring precipitation (R2 = 0.52). Midgrass plant communities were, overall, 650 kg·ha−1 (SE = 92 kg·ha−1) more productive (P < 0.01) than mixed- or shortgrass plant communities given the same climatic inputs. Our study enables managers to make timely informed decisions regarding stocking rates and timing of grazing on this ecological site in western South Dakota.

Effects of Grazing Pressure on Efficiency of Grazing on North American Great Plains Rangelands

Abstract Comparisons of stocking rates across sites can be facilitated by calculating grazing pressure. We used peak standing crop and stocking rates from six studies in the North American Great Plains (Cheyenne, Wyoming; Cottonwood, South Dakota; Hays, Kansas; Nunn, Colorado; Streeter, North Dakota; and Woodward, Oklahoma) to calculate a grazing pressure index and develop relationships for harvest efficiency, utilization, grazing efficiency, and animal performance and production. Average grazing pressures for heavy, moderate, and light stocking across the study sites were 40, 24, and 14 animal unit days · Mg−1, respectively. These grazing pressures resulted in average harvest efficiency values of 38%, 24%, and 14% and grazing efficiencies of 61%, 49%, and 39% for heavy, moderate, and light stocking rates, respectively. Utilization increased quadratically as grazing pressure index increased, whereas grazing and harvest efficiencies exhibited a linear increase with grazing pressure. The latter indicates that nonlivestock forage losses (e.g., weathering, senescence, wildlife, insects) were disproportional across stocking rates. Average daily gain of livestock decreased linearly as grazing pressure index increased across study sites. Prediction equations reaffirm assumptions of 50% grazing efficiency and 25% harvest efficiency associated with moderate stocking. Novel here, however, is that harvest and grazing efficiencies increased at high grazing pressures and decreased at low grazing pressures. Use of grazing pressure index to “standardize” stocking rates across rangeland ecosystems in the North American Great Plains should improve communication among scientists, resource managers, and the public, and thus better achieve both production and conservation goals on these lands.

Historical Weather Patterns: A Guide for Drought Planning

H ow do we know when drought will occur? In 2002, the Great Plains suffered through a widespread drought that seemed to catch many ranchers off guard. In South Dakota, there was a flurry of extension activity generated to deal with drought issues. Why were so many ranchers caught off guard? One answer may reside in the patterns of past weather data. Being able to anticipate low rainfall and having the flexibility to handle it has been the common advice by extension personnel and ranchers that have successfully weathered the years. To do this, one has to develop the ability to evaluate historical data in regard to making decisions that have long-term implications for successfully navigating through ranching challenges. Our objective is to present historical precipitation data from western South Dakota and derive certain expectations of drought occurrence to show how this can be used in drought planning.

Barriers to Successful Drought Management: Why Do Some Ranchers Fail to Take Action?

Barriers to successful drought management: why do some ranchers fail to take action? DO:10.2458/azu_rangelands_v27i2_dunn

Stand Persistence and Forage Yield of 11 Alfalfa (Medicago sativa) Populations in Semiarid Rangeland

ABSTRACT Livestock producers in the Northern Great Plains value alfalfa (Medicago sativa L.) for increasing forage production and quality in grazing lands. However, alfalfa persistence can be poor, especially under grazing. Demand exists for alfalfa that can establish and persist in semiarid grazing lands. A naturalized population of predominantly yellow-flowered alfalfa (Medicago sativa L. subsp. falcata [L.] Arcang.) was found growing and reseeding on private and public rangeland in northwestern South Dakota. This naturalized alfalfa population demonstrates persistence in this semiarid environment. A study, initiated in May 2006 at the Antelope Range and Livestock Research Station near Buffalo, South Dakota, evaluated stand persistence and forage yield of 11 alfalfa populations transplanted into mixed-grass prairie. Populations were pure falcata, predominantly falcata, hay-type sativa, or pasture-type sativa populations. Transplants were space planted on 1-m centers within three exclosures (35 × 35 m) divided into two sections, which were either mob grazed by cattle or protected from mob grazing. Mob grazing began in August 2007 and continued periodically through 2008 and 2009. Survival, plant height, plant canopy diameters, and biomass data were collected. Grazing, dry spells, and ice sheets subjected alfalfa plants to substantial stress. High mortality of grazed plants occurred during the 2008–2009 winter. Hay-type sativa and pasture-type sativa populations exposed to mob grazing had poor final survival (<19%) and forage yield in July 2010. However, pure falcata and most predominantly falcata populations had higher survival (>38%) and forage yield. Low mortality and high yield of protected plants indicated that accumulated stress from mob grazing weakened grazed plants, increasing environment-related mortality (e.g., winterkilling). Falcata-based populations persistent under mob grazing and adapted to the regional environment have potential for use in the Northern Great Plains.

A systems approach to forecast agricultural land transformation and soil environmental risk from economic, policy, and cultural scenarios in the north central United States (2012–2062)

ABSTRACT Grassland conversion to row-crop production in the north central United States has been a growing threat to socio-economic and environmental sustainability for producers, conservationists, and policy-makers alike. We used a system dynamics model of the region to forecast agriculturally driven land transformation through mid-twenty-first century. The base-case scenario projection showed that farmland area continued to increase, from under 200,000 km2 to over 230,000 km2. Unmitigated, the soil environmental risk (SER) of such changes reached conservative estimates of Dust Bowl-era externalities. Systems analyses show that reducing livestock production costs, doubling conservation compliance requirements, and livestock–cropping integration had the largest impact on grassland conservation and mitigating SER. The largest SER effects came from eliminating conservation incentives or raising cultivation incentives, despite improvements in reduced tillage and enhanced agronomy. Several system archetypes were identified within the policy scenarios: ‘fixes that backfire’ and ‘success-to-the-successful’. For scenarios creating favourable impacts, time delays caused some behaviours to worsen before positive gains were realized. If implemented, patience and persistence to ensure that these scenarios reach their full potential will be necessary. Our scenarios provide quantitative forecasts around measures for sustainable intensification. These projections can aid regional stakeholders in enhancing discussions currently taking place about sustainable agriculture in the region.

Diffusion limitations and metabolic factors associated with inhibition and recovery of photosynthesis following cold stress in Elymus nutans Griseb.

We studied the effects of cold stress (5°C) and re-warming (25°C) on gas exchange, photosystem II, key photosynthetic enzyme activities, gene expression, and carbohydrate metabolite concentrations in two Elymus nutans genotypes differing in cold resistance (DX, cold-tolerant and ZD, cold-sensitive). Cold stress led to irreversible reductions in photosynthetic rate. This reduction was accompanied by declining stomatal and mesophyll conductance (gs and gm), transpiration rate (Tr) and photochemical efficiency in both genotypes, however there were smaller decreases in DX than in ZD. Cold-tolerant DX maintained higher photosynthetic enzyme activities and transcript levels, as well as higher reducing sugar concentrations and sucrose accumulation. The relationship between Pn and internal leaf CO2 concentration (Pn/Ci curve) during cold and re-warming was analyzed to estimate the relative influence of stomatal and non-stomatal components on photosynthesis. Stomatal limitation, non-stomatal limitation, and CO2 compensation point (CP) increased in both genotypes under cold stress, but to a lesser extent in DX. Maximum CO2 assimilation rate (Pmax), and carboxylation efficiency (CE) declined, but DX had significantly higher levels of Pmax and CE than ZD. Following cold-stress recovery, the maximum quantum yield of PSII (Fv/Fm), apparent electron transport rate (ETR), Rubisco activity, Rubisco activation state and CE in DX resumed to the control levels. In contrast, Pn, Pmax, gs, gm, and Tr recovered only partially for DX, suggesting that incomplete recovery of photosynthesis in DX may be mainly related to diffusion limitations. Higher Rubisco large subunit (RbcL) and Rubisco activase (RCA) transcript levels, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) activity, and carbohydrate accumulation contributed to higher photosynthetic recovery in DX. These results indicate that the maintenance of higher Pn and Pmax under cold stress and recovery in cold-tolerant DX could be attributed to reduced diffusion limitations and rapid recuperation of metabolic factors.

Effects of Short-Term Cattle Exclusion on Plant Community Composition: Prairie Dog and Ecological Site Influences

On the Ground Maintaining cattle and prairie dogs on rangelands is important ecologically, economically, and culturally. However, competition between these species, both actual and perceived, has led to conflict. We explored the effects of short-term (2-year) cattle exclusion on plant communities both on and off prairie dog towns and among three common ecological sites. Plant communities were different between on-town and off-town plots and among ecological sites but were similar between cattle-excluded and nonexcluded plots. Plant community composition did not differ between rangeland targeted for moderate forage utilization and that in which cattle had been excluded for 2 years.