Establishment and Trends in Persistence of Selected Perennial Cool-Season Grasses in Western United States

Restoring western US rangelands from a site dominated by invasive annuals, such as cheatgrass and medusahead, to a diverse, healthy, perennial plant ? dominated ecosystem can be difficult with native grasses. This study describes the establishment and trends in persistence (plant/m²) of native grass cultivars and germplasm compared with typically used crested and Siberian wheatgrasses at four locations in Idaho (one), Wyoming (one), and Utah (two) that range in mean average annual precipitation (MAP) from 290 to 415 mm. Sites were cultivated and fallowed 1 yr before planting using two glyphosate applications to control weeds. We monitored seedling establishment of 10 perennial cool-season grass species and plant persistence over 5 yr. Precipitation during the seeding year varied with the Utah sites locations reviving below MAP (4% and 14%), while the Wyoming and Idaho sites received above MAP at 8% and 26%, respectively. Across these four sites, native grass seedling establishment of bottlebrush squirreltail (29 ± 0.08 [standard error] seedling/m²), bluebunch (28 ± 0.05), slender (30 ± 0.05), and Snake River wheatgrasses (28 ± 0.08) was similar to “Vavilov II” Siberian wheatgrass (36 ± 3.20). By yr 5, western, Snake River, and thickspike wheatgrasses were the only native grasses to have plant densities similar to Vavilov II (37 ± 0.29) Siberian and “Hycrest II” (36 ± 0.29) crested wheatgrasses. On sites receiving between 290 and 415 mm MAP, our data suggest that native grasses are able to establish but in general lack the ability to persist except for western, Snake River, and thickspike wheatgrasses, which had plant densities similar to crested and Siberian wheatgrasses after 5 yr.     

Long-Term Persistence of Cool-Season Grasses Planted to Suppress Broom Snakeweed,Downy Brome,and Weedy Forbs

Invasive plants are spreading throughout arid and semiarid rangelands of western North America. Long-lived perennial plants that can persist under harsh environmental conditions are needed to compete with invasive species. The objective of this study was to conduct a long-term evaluation of native and introduced grass species planted to suppress and prevent reinvasion of downy brome (Bromus tectorum L.), snakeweed (Gutierrezia sarothrae [Pursh] Britt. & Rusby), and annual forbs. Seeding treatments comprised three introduced grasses: crested wheatgrass (Agropyron cristatum [L.] Gaertner × A. desertorum [Fisch. Ex Link] Schultes), pubescent wheatgrass (Elytrigia intermedia spp. trichophorum [Host] Beauv.), and Russian wildrye (Psathyrostachys junceus [Fisch.] Nevski); a mix of these introduced grass species, three native grasses: bluebunch wheatgrass (Pseudoroegneria spicata [Pursh]), western wheatgrass (Pascopyrum smithii [Rybd.] A. Löve), and squirreltail (Elymus multisetus [J.G. Sm.] Jones); and a mix of these native grass species, or forage kochia (Bassia prostrata [L.] A.J. Scott). The treatments were seeded in October 2003. Frequency and biomass were measured in 2015 and 2017 in Howell, Utah and in 2015 and 2016 in Nephi, Utah. Crested wheatgrass persisted at both locations (> 62% frequency) along with the rhizomatous grass species, pubescent (> 65%) and western wheatgrasses (> 72%). Russian wildrye was still present at Howell (30%) with little remaining at Nephi (7%). Squirreltail frequency was 13% at Howell and 12% at Nephi. Bluebunch wheatgrass was no longer present at either location (< 1%). Forage kochia remained at Nephi (36%) with little remaining at Howell (4%). Downy brome was present at both locations and was suppressed relative to control plots, at Nephi, by crested wheatgrass and the introduced grass mix (< 9%). Downy brome was > 93% in all plots, at Howell, in 2017. In summary, crested, pubescent, and western wheatgrasses were able to persist over 12 yr at both locations.     

Horse Preference,Forage Yield,and Species Persistence of 12 Perennial Cool-Season Grass Mixtures Under Horse Grazing

Cool-season grass mixtures are rarely evaluated for preference, yield, and persistence under horse grazing. The objectives of this research were to evaluate horse preference, forage yield, and persistence of cool-season grass mixtures under horse grazing. Eight commercially marketed and four experimental perennial cool-season grass mixtures were planted in 2009 in a randomized complete block with five replicates and grazed by four adult horses during 2010, 2011, and 2012. All mixtures contained four to six cool-season perennial grass species. Specie density measurements were taken in each spring and fall, and yield was mechanically measured before each grazing period. After grazing, preference was determined by visually assessing percentage of forage removal on a scale of 0 (no grazing) to 100 (100% of vegetation removed). Data were analyzed using a mixed-model analysis of variance and liner regression. Horses preferred mixtures containing tall fescue, perennial ryegrass, Kentucky bluegrass, and timothy (P < .001). Horses had less preference for mixtures containing ≥30% orchardgrass (P < .001). Mixtures had similar (P = .11) forage yields that ranged from 6,100 to 7,082 kg ha⁻¹. After 2 years of grazing, orchardgrass and tall fescue increased; Kentucky bluegrass remained stable; and festulolium, meadow fescue, and perennial ryegrass had the greatest rate of decline in mixtures. Orchardgrass became the dominate species, regardless of initial percentage in the mixture. Mixtures containing tall fescue, perennial ryegrass, Kentucky bluegrass, and timothy should be planted in midwestern US horse pastures; however, mixtures will likely transition to tall fescue and Kentucky bluegrass–dominated pastures.     

Grazing Preferences and Vegetation Feedbacks of the Fire-Grazing Interaction in the Northern Great Plains

The fire-grazing interaction is well studied in mesic grasslands worldwide, but research is limited in semiarid systems. We examined the principal drivers and feedbacks of the fire-grazing interaction on the strength of cattle grazing selection, herbaceous biomass, crude protein, and vegetation structure and composition in two pastures in the Northern Great Plains. Cattle showed significant preference, use, and grazing utilization in recently burned patches that declined as time since fire increased. Cattle selection was driven by significantly increased crude protein in recent burns. Grazing utilization of 70% in patches with < 1 yr after fire established low herbaceous biomass, but the extent to which it was maintained varied with precipitation. Herbaceous biomass increased to nonburned levels 2 yr after fire, and crude protein decreased to nonburned levels 120 d after fire. Species composition was influenced primarily by site and year, though bare ground and litter were influenced by the fire-grazing interaction. Our data indicate that mixed-grass prairies of the Northern Great Plains are resilient to the fire-grazing interaction and that rest from grazing following fire is likely ecologically unnecessary. The use of the fire-grazing interaction is an alternative management strategy suitable for the Northern Great Plains, effectively increasing heterogeneity of grassland habitat.     

Seasonal Losses of Surface Litter in Northern Great Plains Mixed-Grass Prairies

Surface litter protects rangeland soils against wind and water erosion and provides food and nesting materials for wildlife and insects. However, the ability of grassland systems to provide these services depends on the little studied topic of seasonal surface litter decomposition. Seasonal and annual surface litter decomposition rates were determined between 2014 and 2015 in central and western South Dakota at three mixed-grass prairie locations. Residue bags containing surface litter were placed in the field in late fall (1 November) of 2014 and removed after the winter (1 April), spring (1 July), and summer + fall seasons (1 November) of 2015. The litter was analyzed for total C, total N, acid detergent fiber (ADF), and acid detergent lignin (ADL). Average winter temperatures ranged from −5^oC to −15^oC, while summer temperatures ranged from 10^oC to 35^oC. Litter decomposition was lowest during the winter (0.57−0.86 g [kg × day]⁻¹) and greatest during the summer + fall (2.12−2.69 g [kg × day]⁻¹). Over the entire season, 40.8−62% of the surface litter decomposed. Winter litter decomposition was positively correlated with air temperature (r = 0.62, P < 0.01) and snow depth (r = 0.61, P < 0.01), and negatively correlated with C/N ratio (r = −0.65, P < 0.01), ADF (r = −0.35, P < 0.05), and ADL (r = −0.25, P < 0.05) concentrations. These findings indicate that winter decomposition cannot be ignored and that winter surface litter decomposition increases with snow depth.     

Climate-Driven Interannual Variability in Net Ecosystem Exchange in the Northern Great Plains Grasslands

The Northern Great Plains grasslands respond differently under various climatic conditions; however, there have been no detailed studies investigating the interannual variability in carbon exchange across the entire Northern Great Plains grassland ecosystem. We developed a piecewise regression model to integrate flux tower data with remotely sensed data and mapped the 8-d and 500-m net ecosystem exchange (NEE) for the years from 2000 to 2006. We studied the interannual variability of NEE, characterized the interannual NEE difference in climatically different years, and identified the drought impact on NEE. The results showed that NEE was highly variable in space and time across the 7 yr. Specifically, NEE was consistently low (?35 to 322 g C·m^?2·yr^?1) with an average annual NEE of ?2 ± 242 g C·m^?2·yr^?1 and a cumulative flux of ?152 g C·m^?2. The Northern Great Plains grassland was a weak source for carbon during 2000–2006 because of frequent droughts, which strongly affected the carbon balance, especially in the Western High Plains and Northwestern Great Plains. Comparison of the NEE map with a drought monitor map confirmed a substantial correlation between drought and carbon dynamics. If drought severity or frequency increases in the future, the Northern Great Plains grasslands may become an even greater carbon source.     

Plant Community and Soil Environment Response to Summer Fire in the Northern Great Plains

Fire is an important process in many ecosystems, especially grasslands. However, documentation of plant community and soil environment responses to fire is limited for semiarid grasslands relative to that for mesic grasslands. Replicated summer fire research is lacking but necessary because summer is the natural fire season and the period of most wildfires in the western United States. We evaluated summer fire effects on soil temperature, soil moisture, aboveground biomass, root biomass, and functional group composition for 2 yr in semiarid C₃-dominated northern Great Plains. Following pre-treatment measures, four 0.75-ha sites were burned during August for comparison with nonburned sites, and the experiment was repeated the next year on adjacent sites to assess weather effects. Soils were about 0.5°C cooler on burned sites in the first experiment and similar in the second. Burned sites were consistently 1% drier than nonburned sites. Litter was reduced by fire but did not account for changes in soil moisture because differences occurred before the growing season. Current-year aboveground biomass and root biomass were similar between treatments, indicating productivity was resistant to summer fire. Perennial C₃ grasses increased in dominance because of positive biomass responses to fire for all but the bunchgrass, Hesperostipa comata, and a reduction of annual grasses. Perennial C₄ grasses were unaffected by summer fire. H. comata was resilient, with biomass on burned sites equaling nonburned sites the second growing season. Biomass was more responsive to precipitation than fire, and the fire-induced changes in species composition suggest exclusion of fire may be a greater disturbance than summer fire.     

多年生禾草物候特征与分蘖动态的研究

本文根据河南省的气候特点,研究了三种主要当家禾草(苇状羊茅,多年生黑麦草、无芒雀麦)在一年内的物候期特征以及分蘖动态.结果表明禾草在生长期内都在进行不同程度地分蘖,在一年内有三个分蘖高峰期、一个平缓期和一个负增长期,且分蘖期的分蘖速度最快,物候期内单株分蘖数和全年分蘖总数在果后营养期中达到最大.另外,与直根系的豆科牧草混播有利于禾草秋季的分蘖.     

多年生禾草物候特征与分蘖动态的研究

本文根据河南省的气候特点，研究了三种主要当家禾草（苇状羊茅，多年生黑麦草、无芒雀麦）在一年内的物候期待征以及分蘖动态。结果表明：禾草在生长期内都在进行不同程度地分蘖，在一年内有三个分蘖高峰期、一个平缓期和一个负增长期，且分蘖期的分蘖速度最快，物候期内单株分蘖数和全年分蘖总数在果后营养期中达到最大。另外，与直根系的豆科牧草混播有利于禾草秋季的分蘖。     

四川低山丘陵地区多年生冷季型优良牧草引种试验

2001～2003年在四川省洪雅县对从国内外引进的15个多年生冷季型牧草品种的生育状况、产量、营养品质等指标进行了试验研究.结果表明:由于气候原因紫花苜蓿和百脉根不能结实;白三叶品种Ladino和紫花苜蓿品种Amerigraze702的产草量最高,而单位面积粗蛋白质产量最高的是红三叶品种Cherokee;所引进的禾本科牧草中只有鸭茅品种Pennlate可以越夏.     

Patch-Burning Buffers Forage Resources and Livestock Performance to Mitigate Drought in the Northern Great Plains

Summer droughts in North America's northern Great Plains are expected to increase in frequency and duration as precipitation shifts toward spring and fall. Two rangeland experimental stations in North Dakota experienced drought in 2017 relative to 25-year averages. The southwest location had a 170-mm deficit from the 360-mm normal rainfall and was grazed by cattle (Bos taurus L.) and sheep (Ovis aries L.); the south-central location had 109 mm below the 403-mm normal rainfall and was grazed by cattle. We evaluated patch-burn grazing as a drought resilient land management strategy in the northern Great Plains by comparing average daily gains, fecal density, available forage biomass, and forage crude protein content. At the southwest location, livestock performed better during the drought season compared with animals on the same pastures in the previous year, which had near-normal rainfall but no fire. At the central location, cows on patch-burned pastures performed better than cows on continuously-grazed, unburned pastures in the same year under drought conditions; all cows were nursing calves and calf gains did not vary between treatments. In both locations, the burned patches had higher fecal density and lower available forage biomass than patches not yet burned throughout the grazing season, indicating grazer attraction to burned areas. Despite drought, burned patches maintained grazer attraction and animal performance was maintained or even improved, which contrasts with the expected relationship between animal performance and precipitation. This study indicated that prescribed patch-burning might mitigate drought by buffering forage resources (crude protein content and availability) and maintaining animal performance (average daily gains).