Hilaria Jamesii Research Articles

Spatially explicit management of genetic diversity using ancestry probability surfaces

Abstract Ecological restoration and conservation efforts are increasing worldwide and the management of intraspecific genetic variation in plants and animals, an important component of biodiversity, is increasingly valued. As a result, tailorable, spatially explicit approaches to map genetic variation are needed to support decision‐making and management frameworks related to the recovery of threatened and endangered species and the maintenance of genetic resources in species utilized by humans, such as for restoration or agricultural purposes. Here, we describe and demonstrate a workflow to spatially interpolate patterns of genetic differentiation using novel functions in the r package popmaps (Population Management using Ancestry Probability Surfaces). Our approach uses empirical genetic data to estimate ancestry coefficients across a user‐defined landscape correlated with patterns of differentiation in the focal species. The resulting surface, which we term the ancestry probability surface, includes two components: hard population boundaries and estimations of uncertainty that represent confidence in population assignments (i.e. ancestry probabilities). An ancestry probability surface developed for Hilaria jamesii, an important graminoid utilized in restoration across the western United States, demonstrates the functionality of popmaps. Genetic distances among empirical sites correlated better with least‐cost distances across suitable habitat than with geographical distances, informing the surface over which the interpolation was conducted (i.e. a model indicating habitat suitability). A jackknifing procedure identified parameter values resulting in robust population assignments across the species' range, which were utilized in downstream analyses to estimate ancestry coefficients from empirical data. Ancestry coefficients were translated into ancestry probabilities, which tended to be low for cells that were intermediate in distance between empirical sampling locations representing different populations or when influenced by empirical sampling locations with mixed genetic ancestry. popmaps allows users to tailor parameter values and analytical approaches and thereby incorporate species‐specific biological characteristics and desired levels of uncertainty into maps illustrating patterns of genetic differentiation. Ancestry probability surfaces may be used to guide management or investigate further ecological or evolutionary hypotheses. We discuss how maps produced by popmaps can inform multiple management challenges including species recovery planning and the utilization of commonly used species in restoration.

Leveraging Historic Cattle Exclosures to Detect Evidence of State Change in an Arid Rangeland

Grazing, a defining use of rangelands, can have immediate and legacy impacts in ecosystems with short evolutionary histories of grazing and where climatic conditions are marginal and variable. In arid rangelands of the Colorado Plateau, domesticated ungulates were introduced in the 1800s at high densities and grazing has been maintained in the region at variable stocking rates for approximately the past 150 yr. Historic grazing practices, combined with a marginal climate, may have caused an irreversible shift in the vegetation community leading to limited recovery with cessation of grazing. Using three exclosures ranging from 12 to 50 yr of age, we evaluated vegetation composition, diversity, and cover inside the exclosures and compared them with directly adjacent, actively grazed areas outside of the exclosures in the fall and spring of 2018 and 2019. We then asked 1) How do exclosures and their adjacent unexclosed sites differ in vegetation diversity, composition, and cover? and 2) Are there significant differences in cover of key forage species in exclosed versus unexclosed areas? Overall, there were significant differences in vegetation communities inside and outside of exclosures in both seasons. Composition, alpha, and beta diversity differed between grazed and exclosed sites, with higher alpha and beta diversity in the 50-yr exclosure in the fall. Composition was significantly different between exclosures and unexclosed sites at all sites and in all seasons. Cover of several important forage grasses (Achnatherum hymenoides, Hilaria jamesii, Elymus elymoides) was higher in exclosed areas, while cover of Scleropogon brevifolius and Bouteloua gracilis was higher in unexclosed areas. Taken together, these results indicate limited recovery of vegetation in the absence of grazing, with exclosures exhibiting higher plant diversity, as well as cover of some desirable forage species, suggesting this area has not undergone irreversible state change but recovery may require > 50 yr of grazing cessation.

The historical context of contemporary climatic adaptation: a case study in the climatically dynamic and environmentally complex southwestern United States

The process of adaptation can be highly dependent upon historical and contemporary factors, especially in environmentally and topographically complex regions affected by Pleistocene glaciations. Here, we investigate Hilaria jamesii (Poaceae), a dryland C4 graminoid, to test how patterns of adaptive genetic variation are linked to its glacial and post‐glacial history. We show that the species persisted in a single, southern refugium during the last glacial period and subsequently migrated throughout its current distribution concurrent with post‐glacial warming. The species’ putative adaptive genetic variation correlates with climatic gradients (e.g. monsoon precipitation and mean diurnal temperature range) that covary with the species’ probable route of demographic expansion. The short timescale and multiple climatic dimensions of adaptation imply that natural selection acted primarily upon standing genetic variation. These findings suggest that restoration and conservation practices should prioritize the maintenance of standing genetic variation to ensure that species have the capacity to respond to future environmental changes.

Root-associated fungal communities colonizing two dominant semiarid grasses: Hilaria sp. and Stipa sp.

AbstractWe conducted a preliminary survey of the fungal communities associated with roots of Stipa hymenoides and Hilaria jamesii, two grasses native to the southwestern United States. Root samples from 10 different plants were collected at a semiarid grassland in Utah. Fungal communities were assessed using microscopic and molecular methods. Roots were cleared with KOH and stained using blue ink to visualize mycorrhizal and endophytic fungi. A total of 100 root segments were surface sterilized and plated on malt extract agar with antibiotics. Fungal endophytes were identified using nrITS primers. Results/Conclusions Microscopic analyses showed that all root samples from both Hillaria and Stipa were colonized by dark septate and arbuscular mycorrhizal fungi. Vesicles and hyaline hyphae also were observed in all the roots. Sclerotia, a characteristic structure of some dark septate fungi were also found. Approximately 75 fungi were isolated representing at least 45 morphotypes. Molecular identification showed that both grasses are colonized by endophytes in the orders Pleosporales, Hypocreales, and Sordariales commonly found in semiarid grasses, liverworts, and mosses.

Soil amendment effects on the exotic annual grass Bromus tectorum L. and facilitation of its growth by the native perennial grass Hilaria jamesii (Torr.) Benth

Greenhouse experiments were undertaken to identify soil factors that curtail growth of the exotic annual grass Bromus tectorum L. (cheatgrass) without significantly inhibiting growth of native perennial grasses (here represented by Hilaria jamesii [Torr.] Benth). We grew B. tectorum and H. jamesii alone (monoculture pots) and together (combination pots) in soil treatments that manipulated levels of soil phosphorus, potassium, and sodium. Hilaria jamesii showed no decline when its aboveground biomass in any of the applied treatments was compared to the control in either the monoculture or combination pots. Monoculture pots of B. tectorum showed a decline in aboveground biomass with the addition of Na2HPO4 and K2HPO4. Interestingly, in pots where H. jamesii was present, the negative effect of these treatments was ameliorated. Whereas the presence of B. tectorum generally decreased the aboveground biomass of H. jamesii (comparing aboveground biomass in monoculture versus combination pots), the presence of H. jamesii resulted in an enhancement of B. tectorum aboveground biomass by up to 900%. We hypothesize that B. tectorum was able to obtain resources from H. jamesii, an action that benefited B. tectorum while generally harming H. jamesii. Possible ways resources may be gained by B. tectorum from native perennial grasses include (1) B. tectorum is protected from salt stress by native plants or associated soil biota; (2) when B. tectorum is grown with H. jamesii, the native soil biota is altered in a way that favors B. tectorum growth, including B. tectorum tapping into the mycorrhizal network of native plants and obtaining resources from them; (3) B. tectorum can take advantage of root exudates from native plants, including water and nutrients released by natives via hydraulic redistribution; and (4) B. tectorum is able to utilize some combination of the above mechanisms. In summary, land managers may find adding soil treatments can temporarily suppress B. tectorum and enhance the establishment of native plants. However, the extirpation of B. tectorum is unlikely, as many native grasses are likely to facilitate its growth.

Initial Invasion of Cheatgrass (Bromus tectorum) into Burned Piñon-Juniper Woodlands in Western Colorado

We studied initial invasion of cheatgrass (Bromus tectorum) into burned pinon-juniper woodlands to determine: (1) if particular features enhance invasion and (2) if particular grasses promote or retard invasion. We compared cheatgrass cover among roads, burn edges, seeded interiors, unseeded interiors and unburned woodlands and quantified grasses present or absent near cheatgrass. Invasion was favored by burn edges, roads and seeded interiors, but not unseeded interiors. Odds of finding cheatgrass were seven times higher near prairie junegrass (Koeleria macrantha), but six times lower near James' galleta (Hilaria jamesii) and two times lower near intermediate wheatgrass (Agropyron intermedium). Invasion may be favored: (1) in burn edges because of higher seed-bank survival, (2) along roads because of moisture, disturbance and dispersal and (3) in seeded interiors because of seed-mix contamination or seeded species that enhance invasion.

Arbuscular Mycorrhizal Assemblages in Native Plant Roots Change in the Presence of Invasive Exotic Grasses

Plant invasions have the potential to significantly alter soil microbial communities, given their often considerable aboveground effects. We examined how plant invasions altered the arbuscular mycorrhizal fungi of native plant roots in a grassland site in California and one in Utah. In the California site, we used experimentally created plant communities composed of exotic (Avena barbata, Bromus hordeaceus) and native (Nassella pulchra, Lupinus bicolor) monocultures and mixtures. In the Utah semi-arid grassland, we took advantage of invasion by Bromus tectorum into long-term plots dominated by either of two native grasses, Hilaria jamesii or Stipa hymenoides. Arbuscular mycorrhizal fungi colonizing roots were characterized with PCR amplification of the ITS region, cloning, and sequencing. We saw a significant effect of the presence of exotic grasses on the diversity of mycorrhizal fungi colonizing native plant roots. In the three native grasses, richness of mycorrhizal fungi decreased; in the native forb at the California site, the number of fungal RFLP patterns increased in the presence of exotics. The exotic grasses also caused the composition of the mycorrhizal community in native roots to shift dramatically both in California, with turnover of Glomus spp., and Utah, with replacement of Glomus spp. by apparently non-mycorrhizal fungi. Invading plants may be able to influence the network of mycorrhizal fungi in soil that is available to natives through either earlier root activity or differential carbon provision compared to natives. Alteration of the soil microbial community by plant invasion can provide a mechanism for both successful invasion and the resulting effects of invaders on the ecosystem.

Direct Effects of Soil Amendments on Field Emergence and Growth of the Invasive Annual Grass Bromus tectorum L. and the Native Perennial Grass Hilaria jamesii (Torr.) Benth

Bromus tectorum L. is a non-native, annual grass that has invaded western North America. In SE Utah, B. tectorum generally occurs in grasslands dominated by the native perennial grass, Hilaria jamesii (Torr.) Benth. and rarely where the natives Stipa hymenoides Roem. and Schult. and S. comata Trin. & Rupr. are dominant. This patchy invasion is likely due to differences in soil chemistry. Previous laboratory experiments investigated using soil amendments that would allow B. tectorum to germinate but would reduce B. tectorum emergence without affecting H. jamesii. For this study we selected the most successful treatments (CaCl2, MgCl2, NaCl and zeolite) from a previous laboratory study and applied them in the field in two different years at B. tectorum-dominated field sites. All amendments except the lowest level of CaCl2 and zeolite negatively affected B. tectorum emergence and/or biomass. No amendments negatively affected the biomass of H. jamesii but NaCl reduced emergence. Amendment effectiveness depended on year of application and the length of time since application. The medium concentration of zeolite had the strongest negative effect on B. tectorum with little effect on H. jamesii. We conducted a laboratory experiment to determine why zeolite was effective and found it released large amounts of Na+, adsorbed Ca2+, and increased Zn2+, Fe2+, Mn2+, Cu2+, exchangeable Mg2+, exchangeable K, and NH4+ in the soil. Our results suggest several possible amendments to control B. tectorum. However, variability in effectiveness due to abiotic factors such as precipitation and soil type must be accounted for when establishing management plans.

Effects of Nitrogen Deposition on an Arid Grassland in the Colorado Plateau Cold Desert

Historically, ecosystems in the southwestern United States derived much of their nitrogen (N) from N-fixation in biological soil crusts. Today, these regions have highly reduced crust cover, and atmospheric deposition may be the dominant source of N. This study investigates the effects of increased nitrogen deposition on nitrogen uptake, photosynthesis, and growth of the two main forage grasses on the Colorado Plateau, galleta (Hilaria jamesii [Torr.] Benth.) and Indian ricegrass (Oryzopsis hymenoides, [Roemer J.S. Schultes] Ricker ex Piper). Plots were fertilized for 2 years with 0, 10, 20, and 40 kg nitrogen ha-1 annually, up to 43 the estimated current annual deposition rate, in 2 applications per year (spring and summer). Half-plots were fertilized with either (NH4)2SO4 in KCl solution or with KNO3 solution to determine possible differences in the effects of NH4+ and NO3 in this system. Neither grass increased leaf photosynthesis or tiller size due to supplemental N. Galleta also did not increase tiller density, while estimated live tiller density in Indian ricegrass increased up to 50% in the second year. Nitrogen applications accelerated the onset of water stress in both species presumably through stimulating ecosystem transpiration. Nitrogen form did not significantly affect any aspect of grass physiological performance or growth. However, leaf nitrogen in NH4+/-fertilized plants was significantly more isotopically enriched than in NO3-fertilized plants, suggesting that both species incorporated NH4-N only after it had been enriched by soil turnover. Seedlings of Russian Thistle (Salsola iberica, Sennen Pau), a noxious annual invasive weed on western rangelands, grew rapidly in the first summer on plots with 40 kg nitrogen ha-1 per annum, and more so on plots fertilized with NO3 than with NH4+. The study suggests that changes in the timing and amount of nitrogen input may alter community composition through facilitating the invasions of summer-active noxious weeds.

Effects of Nitrogen Deposition on an Arid Grassland in the Colorado Plateau Cold Desert

Abstract Historically, ecosystems in the southwestern United States derived much of their nitrogen (N) from N-fixation in biological soil crusts. Today, these regions have highly reduced crust cover, and atmospheric deposition may be the dominant source of N. This study investigates the effects of increased nitrogen deposition on nitrogen uptake, photosynthesis, and growth of the two main forage grasses on the Colorado Plateau, galleta ( Hilaria jamesii [Torr.] Benth.) and Indian ricegrass ( Oryzopsis hymenoides , [Roemer & J.S. Schultes] Ricker ex Piper). Plots were fertilized for 2 years with 0, 10, 20, and 40 kg nitrogen ha −1 annually, up to 4× the estimated current annual deposition rate, in 2 applications per year (spring and summer). Half-plots were fertilized with either (NH 4 ) 2 SO 4 in KCl solution or with KNO 3 solution to determine possible differences in the effects of NH 4 + and NO 3 − in this system. Neither grass increased leaf photosynthesis or tiller size due to supplemental N. Galleta also did not increase tiller density, while estimated live tiller density in Indian ricegrass increased up to 50% in the second year. Nitrogen applications accelerated the onset of water stress in both species presumably through stimulating ecosystem transpiration. Nitrogen form did not significantly affect any aspect of grass physiological performance or growth. However, leaf nitrogen in NH 4 + -fertilized plants was significantly more isotopically enriched than in NO 3 − -fertilized plants, suggesting that both species incorporated NH 4 -N only after it had been enriched by soil turnover. Seedlings of Russian Thistle ( Salsola iberica , Sennen & Pau), a noxious annual invasive weed on western rangelands, grew rapidly in the first summer on plots with 40 kg nitrogen ha −1 per annum, and more so on plots fertilized with NO 3 − than with NH 4 + . The study suggests that changes in the timing and amount of nitrogen input may alter community composition through facilitating the invasions of summer-active noxious weeds.

Effects of soil amendments on germination and emergence of downy brome (Bromus tectorum) and Hilaria jamesii

Downy brome is an introduced Mediterranean annual grass that now dominates millions of hectares of western U.S. rangelands. The presence of this grass has eliminated many native species and accelerated wildfire cycles. The objective of this study was to identify soil additives that allowed germination but inhibited emergence of downy brome, while not affecting germination or emergence of the native perennial grass Hilaria jamesii. On the basis of data from previous studies, we focused on additives that altered the availability of soil nitrogen (N), phosphorus (P), and potassium (K). Most water-soluble treatments inhibited downy brome germination and emergence. We attribute the inhibitory effects of these treatments to excessive salinity and ion-specific effects of the additives themselves. An exception to this was oxalic acid, which showed no effect. Most water-insoluble treatments had no effect in soils with high P but did have an effect in soils with low P. Zeolite was effective regardless of P level, probably due to the high amounts of Na+ it added to the soil solution. Most treatments at higher concentrations resulted in lower downy brome emergence rates in soils currently dominated by downy brome than in uninvaded (but theoretically invadable) Hilaria soils. This difference is possibly attributable to inherent differences in labile soil P. In Stipa soils, where Stipa spp. grow, but which are generally considered to be uninvadable by downy brome, additions of high amounts of N resulted in lower emergence. This may have been an effect of NH4+ interference with uptake of K or other cations or toxicity of high N. We also saw a positive relationship between downy brome emergence and pH in Stipa soils. Hilaria development parameters were not as susceptible to the treatments, regardless of concentration, as downy brome. Our results suggest that there are additions that may be effective management tools for inhibiting downy brome in calcareous soils, including (1) high salt applications, (2) K-reducing additions (e.g., Mg), and (3) P-reducing additions.

Dominant cold desert plants do not partition warm season precipitation by event size.

We conducted experiments to examine the quantitative relationships between rainfall event size and rainwater uptake and use by four common native plant species of the Colorado Plateau, including two perennial grasses, Hilaria jamesii (C(4)) and Oryzopsis hymenoides (C(3)), and two shrubs, Ceratoides lanata (C(3)), and Gutierrezia sarothrae (C(3)). Specifically, we tested the hypothesis that grasses use small rainfall events more efficiently than shrubs and lose this advantage when events are large. Rainfall events between 2 and 20 mm were simulated in spring and summer by applying pulses of deuterium-labeled irrigation water. Afterwards, pulse water fractions in stems and the rates of leaf gas exchange were monitored for 9 days. Cumulative pulse water uptake over this interval (estimated by integrating the product of pulse fraction in stem water and daytime transpiration rate over time) was approximately linearly related to the amount of pulse water added to the ground in all four species. Across species, consistently more pulse water was taken up in summer than in spring. Relative to their leaf areas, the two grass species took up more pulse water than the two shrub species, across all event sizes and in both seasons, thus refuting the initial hypothesis. In spring, pulse water uptake did not significantly increase photosynthetic rates and in summer, pulse water uptake had similar, but relatively small effects on the photosynthetic rates of the three C(3) plants, and a larger effect on the C(4) plant H. jamesii. Based on these data, we introduce an alternative hypothesis for the responses of plant functional types to rainfall events of different sizes, building on cost-benefit considerations for active physiological responses to sudden, unpredictable changes in water availability.

Phosphorus Pools in Tree and Intercanopy Microsites of a Juniper–Grass Ecosystem

Gradients of soil‐nutrient distribution between trees and intercanopy areas are common in many semiarid woodland ecosystems. To test if microsites under and between canopies influenced P pool distribution in a semiarid woodland dominated by one‐seed juniper [Juniperus monosperma (Engelm.) Sarg.] and galleta grass [Hilaria jamesii (Torr.) Benth.], we compared inorganic, organic, and microbial P pools under trees and intercanopy areas of two Aridisols. Soils collected (5–15 cm depth) under eight tree canopies and in eight intercanopy areas from a Calciorthid and a Camborthid were subjected to a sequential P fractionation scheme. Soils and microsites were significant independent factors determining total soil P, which ranged from to 1123 μg P g−1 soil Resin P was significantly influenced by the interaction of soils with microsite. Organic hydroxide P was the largest organic P fraction and exceeded or equaled the amount of resin P. It differed significantly between the Calciorthid at 10.1 μg P g−1 soil and the Camborthid at 22.1 μg P g−1 soil (SE = 1.6). Microsite and soil did not significantly affect microbial P, which ranged from 12.9 μg P g−1 soil to 17.0 μg P g−1 soil Nutrients and microbial activity are usually concentrated under canopies in semiarid and arid ecosystems. This research shows that P pools distribution in the studied ecosystem did not follow this general pattern, and that soils may be more important in determining P pool distribution than microsites.

Sewage Sludge Effects on Soil and Plant Quality in a Degraded, Semiarid Grassland

AbstractA major problem affecting grassland productivity in the semiarid southwestern USA is the low quantity of soil organic matter and plant‐available N. In this study, dried, anaerobically digested sewage sludge was applied at three rates (22.5, 45, and 90 Mg ha−1) to a degraded semiarid grassland site to determine the effects of sludge on soil chemical and heavy metal properties, and vegetative yields and quality over two growing seasons. Most nutrients, including soil N, P, and K, increased linearly as a result of sludge amendment. Soil pH decreased linearly from 7.8 to 7.4 with the application of sludge after the second growing season, but did not significantly increase the solubility of soil heavy metals (Pb and Cd). On the other hand, the levels of DTPA‐extractable soil micronutrients (i.e., Cu, Mn, Zn) increased linearly with sludge rates to levels recommended for adequate plant growth. Total herbaceous plant yields increased significantly with sludge amendment, particularly at the 45 Mg ha−1 sludge rate, as compared with the control treatment. Blue grama [Bouteloua gracilis (H.B.K.) Lag. ex Steud.] yields increased two‐ to threefold in amended plots over the unamended control after two growing seasons. The forage quality of blue grama, galleta [Hilaria jamesii (Torr.) Benth.], and bottlebrush squirreltail [Sitanion hystrix (Nutt.) J.G. Sm.], improved significantly as the levels of tissue N, P, and K, and crude protein increased linearly with sludge application. As expected, levels of Cd and Pb in all plant tissues did not increased significantly as a result of sludge amendment. All micronutrients increased to acceptable levels in deficient plant tissues. Sewage sludge applied at the rate of 45 Mg ha−1 gave the most favorable soil and vegetation results.

Microbial community in the rhizosphere of native plant species growing on reclaimed coal mine soils varying in age

Abstract Soil microorganisms in the rhizosphere are important in the revegetation and stabilization of drastically disturbed areas in the semiarid Southwest, as the microbial community is often responsible for the modification of many adverse soil properties. In this study, the soil microbial community was evaluated in the rhizosphere and the nonrhizosphere of two grass species, galleta (Hilaria jamesii,) and alkali sac‐aton (Sporobolus airoides,), and a shrub, fourwing saltbush (Atriplex canescens), growing on a reclaimed coal mine spoil 3 months to 2.25 years after topsoiling and revegetation. Many soil chemical properties and most microbial populations decreased in both soil zones with reclamation age. However, the rhizosphere of galleta and alkali sacaton still had significantly higher levels of soil N, P, organic matter (OM), and microbial populations than did the nonrhizosphere after 2.25 years of plant growth. The rhizosphere of fourwing saltbush had significantly higher EC and SAR values and funga...

The effect of three osmotic agents on free proline and amino acid pools in Atriplex canescens and Hilaria jamesii

Three commonly used osmotic agents, mannitol, sucrose, and polyethylene glycol 4000, were used to simulate water stress in two arid region plant species, Hilaria jamesii (Torr.) Benth. and Atriplex canescens (Pursh) Nutt. Large amounts of mannitol (300–1400 μmol/g dry wt.) and sucrose (450–660 μmol/g dry wt.) were absorbed by both plant species, while insignificant amounts of polyethylene glycol 4000 were absorbed. During osmotic stress, Hilaria jamesii accumulated large quantities of proline, while A. canescens accumulated only a small amount. Shoot proline content of both species varied significantly with the osmotic agents used to simulate water stress. These results indicate that use of absorbable osmotic agents to simulate water stress may have important metabolic effects on the concentration of free proline and other metabolites.

The role of endomycorrhizal fungi in iron uptake by Hilaria jamesii

Abstract The semiarid warm season grass galleta [Hilaria jamesii (Torr.)] was used in a series of mycorrhizal experiments to determine the mechanism of enhanced iron (Fe) absorption under conditions of Fe deficiency. Galleta was grown from seed in sterilized soil which had either been infested with mycorrhizal fungi or left uninfested. The four fungal species used to infest the soil were Glomus albidum, Glomus fasciculatum, Glomus macrocarpum, and Glomus mosseae. After 85 days of growth, the nonmycorrhizal and mycorrhizal plants were removed from the soil and placed in complete Hoagland's hydroponic nutrient solutions with phosphorus (P) at 1/5 the normal concentration. Galleta, grown hydroponically from seed, was used as a second nonmycorrhizal control. At the end of ten days of growth, the plants were transferred to Hoagland's nutrient solution at 1/5 the phosphorus concentration and without Fe. The plants were grown for twenty days in this solution; at the end of the growth period, all of the treatment...

Control of Big Sagebrush (Artemisia tridentata) with Pelleted Tebuthiuron

Ground applications of pelleted tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} at 0.6 kg ai/ha (20% formulation) reduced big sagebrush (Artemisia tridentataNutt. # ARTTR) density by an average of 84 and 92% after 28 months, whereas 1.1 kg/ha killed 94 and 97% of the plants when applied in January or May, respectively. Total standing crop of grasses was unaffected 4 months after tebuthiuron applications. Significant increases in grass production occurred during the second and third growing seasons following tebuthiuron treatment. Desirable forage grasses such as galleta [Hilaria jamesii(Torr.) Benth.], blue grama [Bouteloua gracilis(Wild. ex H.B.K.) Lag. ex Griffiths], and crested wheatgrass [Agropyron cristatum(L.) Gaertn.] generally increased in tebuthiuron-treated plots, whereas sand dropseed [Sporobolus cryptandrus(Torr.) Gray # SPECR] and ring muhly [Mulenbergia torreyii(Kunth.) Hitchc. & Chase] production remained unchanged in comparison with untreated areas.

Grass Species Adaptability in the Southern High Plains: A 36-Year Assessment

A 36-yr old species adaptation test was evaluated and the relative quality of some persisting native and introduced grass species was determined. The site was Conlen loam on the Rita Blanca National Crasshntd in Dallam County, Texas. Of the 25 species planted, only yellow bluestem (Bothriochloa ischaemum),l Caucasian bluestem (Bothriochloa caucasica), and galleta (Hilaria jamesii) tended to dominate the plots on which they were originally planted. Yellow and Caucasian bluestem had spread into plots phmted to other grasses but galleta had spread very little. Yellow bluestem was as high or higher in protein, mineral content, and digestibility (IVDMD) than the other grasses analyzed [Caucasian bluestem, galleta, sideoats grama (Bouteloua curtipendula), blue grama (Bouteloua grads), and western wheatgrass (Agropyron smithii)]. The contents of Caucasian bluestem and galleta were not signlflcantly different from those of yellow bluestem, except that galleta was lower in IVDMD, especially when mature. These 3 grasses merit consideration in range seeding programs on Conlen and similar soils in the Southern High Plains. For many years, there has been a continuing search for grasses that will increase the productivity of rangelands. Both introduced species and improved selections of native species have been investigated. On the Southern High Plains, there have been some successes with introduced species but when prolonged droughts occur, the introduced species are often replaced by annual weeds, native grasses, or persistant introduced grasses from adjacent or nearby plots. Sites of adaptation studies are often destroyed after the selections are rated and little attention is given to plants that may have invaded the test species. Although comparatively short-term adaptation studies are valuable for cursory evaluation of species, they do not evaluate long-term persistance, indicate aggressiveness of species in invading other species, nor indicate species which may become prevalent where a test species has failed. Authors are soil scientist, USDA-ARS, Conservation and Production Research Laboratory, Bushland, Texas 79012; range scientist, USDA-ARS, Southern Plains Range Research Station, Woodward, Okla. 73801. This article is a contribution from USDA, Agricultural Research Service, P.O. Drawer 10, Bushland, Texas 79012.

Successional Trends in an Ungrazed, Arid Grassland over a Decade

A study has been made of the vegetational condition of a formerly grazed area, Chesler Park, in Canyonlands National Park. A comparison was made with the same area 10 years earlier. The lo-year successional changes are also compared to baseline data of 10 years earlier from Virginia Park, an adjacent ungrazed area. Because of inaccessibility and long isolation from disturbances, Virginia Park is presumed to be in climax condition and is the control for this study. Chesler Park shows a successional trend after 10 years toward the vegetational condition of Virginia Park. This is exemplified, with only one major exception (Hilaria jamesii), by responses of the perennial grasses (Stipa comata, Orysopsis hymenoides, Sporobolur cryptandrus, Bouteloua gracilis) and the cryptogamic community, particularly the moss, Torta other areas of Canyonlands had been variously grazed in prior years. The initial study compared the vegetation and soils of Chesler Park with those of an adjacent, but smaller (97ha) ungrazed area, Virginia “Park.” The access to Virginia Park is impassable for cattle or horses due to high rock walls and therefore the area remains relatively undisturbed. For this reason results of this initial study provided an invaluable source of baseline data against which future vegetational changes in grazed areas can be compared. Gross environmental characteristics vary little between the two parks. The climate of the area is semiarid to arid. It is a country of extremes with an annual temperature range of as much as 55’ C. Annual precipitation is generally from 20 to 25 cm, of which warm season rainfall constitutes from 55$&-75% of the total. Although overall park attendance has increased significantly during the decade (Wylie 1981) the study areas have remained relatively isolated-Chesler Park was closed to vehicular traffic in 1971, and Virginia Park, because of its inaccessibility, has never been subjected to such traffic. Both areas are now accessible only The author is with the Department of Biology, University of Nevada-Rena,, Reno 89557. Appreciation is extended to the Research Advisory Board, University of NevadaReno, for financial support of a portion of this study; also, to the ranger staff of Canyonlands National Park for the hospitality provided. Manuscript received March 27, 198 I. 114 by foot and, because of their remoteness, this usage is considered to be moderate. The purpose of this study was to investigate vegetational and fioristic changes over a decade in an area which had been formerly grazed and to compare the decadeend condition with that of a similar, adjacent area which had not been formerly grazed. Data were collected in 1977 from 20 sites in Chesler Park for comparison with those from 20 Chesler sites in 1967. The 1977 composition is also compared with the undisturbed and presumably climax condition of Virginia Park in 1967.