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Management intensive grazing (MIG) may not maximize plant productivity on rangelands because of morphophysiological traits of grassland vegetation. We examined defoliation and moisture effects on the biomass yield of rhizomatous and caespitose grass pairs that were either phylogenetically similar or of similar agroclimatic adaptation, including two agronomic grasses. From relatively low to high moisture regime adaptation, species pairs included western wheatgrass (Pascopyrum smithii [Rydb.] A. Love) and needle-and-thread (Hesperostipa comata [Trin. & Rupr.] Barkw.), northern wheatgrass (Elymus lanceolatus [Scribn. & J.G. Sm.]) and western porcupine grass (H. curtiseta [Hitchc.] Barkw.), plains and foothills rough fescue (Festuca hallii [Vasey] and F. campestris Rydb.), and smooth and meadow brome (Bromus inermis Leyss. and B. riparius Rehm). Response variables were shoot yield, root-shoot ratio, and water-use efficiency. We hypothesized that caespitose grasses, regardless of their origin or adaptation to agroclimate regime, would respond more determinately in biomass accumulation. Defoliation effects on shoot biomass were more pronounced under high moisture. Low intensity − high frequency defoliation yielded similarly to deferred controls in all grasses, and the same was true for high-intensity − low-frequency (HILF) defoliation in 1 rhizomatous grass. Three of the 4 rhizomatous grasses and 1 caespitose grass yielded greater under HILF defoliation compared with high-intensity − high-frequency defoliation. Caespitose grasses allocated more biomass to roots under low moisture conditions. Water-use efficiency decreased under high moisture conditions and more intense and/or frequent defoliation and peaked in agronomic grasses. Overall, our results suggested that growth patterns corresponded more with phylogenetic similarity as opposed to growth form. A conceptual model from these results showed that across all species, only the introduced bromes generated greater biomass under HILF defoliation, and this may explain why past research consistently concludes that MIG does not enhance plant productivity on rangelands.

The Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis [Beetle & A. Young] S.L. Welsh) alliance is the most extensive of the big sagebrush complex in the Intermountain West. There is a lack of information describing vegetation characteristics, diversity, and heterogeneity of the Wyoming big sagebrush alliance. We annually sampled 48 Wyoming big sagebrush plant communities over 10 yr to delineate major vegetation associations and describe their major vegetation characteristics including canopy cover, density, species richness, and yield. Six associations were identified on the basis of dominant or codominant perennial bunchgrass species, using MRPP analysis, and they included ARTRW8 (Wyoming big sagebrush)/PSSP6 (Pseudoroegneria spicata [Pursh] A. Love, bluebunch wheatgrass), ARTRW8/ACTH7 (Achnatherum thurberianum [Piper] Barkworth, Thurber’s needlegrass), ARTRW8/FEID (Festuca idahoensis Elmer, Idaho fescue), ARTRW8/HECO26 (Hesperostipa comata [Trin. & Rupr.] Barkworth, needle-and-thread), ARTRW8/PSSP6-ACTH7, and ARTRW8/PSSP6-FEID-ACTH7. On average, PSSP6 and FEID associations had the highest total herbaceous cover and annual yields and the HECO26 and ACTH7 associations had the lowest. Perennial forb cover averaged over 5% in PSSP6 and FEID associations and ranged from 0.3% to 3.5% in the other associations. Sagebrush cover was greatest in ACTH7 and PSSP6-ACTH7 and lowest in FEID and HECO26 associations. Habitat suitability criteria for sage-grouse indicated that Wyoming big sagebrush associations at the stand/site level will generally not meet breeding habitat requirements and only attain suitable habitat requirements for other life stages about 50% of the time.

The objective of this study was to evaluate the drought tolerance, compensatory growth, and different plant traits between two native perennial caespitose grasses and two native rhizomatous grasses in response to drought and defoliation. A randomized complete block design at the Swift Current Research and Development Centre (SCRDC) of Agriculture and Agri‐Food Canada (AAFC) examined the effects of water stress and clipping on the plant biomass, plant morphological traits, and relative leaf chlorophyll content (SPAD value) of four native grasses (caespitose grass: Hesperostipa comata and H. curtiseta; rhizomatous grass: Pascopyrum smithii and Elymus lanceolatus). Drought drastically decreased the shoot and root biomass, plant height, number of tillers and leaf growth of P. smithii and E. lanceolatus, as well as the rhizome biomass and R/S ratio of P. smithii. Defoliation had a positive effect on the shoot biomass of P. smithii and E. lanceolatus under well water treatments (100% and 85% of field capacity). However, the compensatory growth of P. smithii and E. lanceolatus significantly declined with increased water stress. In addition, there are no significant changes in plant biomass, plant height, number of tillers and leaves, and SPAD value of H. comata and H. curtiseta under relative dry condition (70% of field capacity). Consequently, these results demonstrated that the rhizomatous grasses possessed a stronger compensation in response to defoliation under wet conditions, but the positive effects of defoliation can be weakened by drought. The caespitose grasses (Hesperostipa species) exhibited a greater drought tolerance than rhizomatous grasses due to the relatively stable plant traits in response to water stress.

Fire plays a central role in influencing ecosystem patterns and processes. However, documentation of fire seasonality and plant community response is limited in semiarid grasslands. We evaluated aboveground biomass, cover, and frequency response to summer, fall, and spring fires and no fire on silty and clayey sites in semiarid, C3-dominated grassland. The magnitude of change in biomass between years was greater than any differences among fire treatments. Still, differences existed among seasons of fire. Summer fire reduced non-native annual forb frequency (3% vs. 10% ± 2%) and Hesperostipa comata, reduced native annual forbs the first year, increased Poa secunda and bare ground, and increased Vulpia octoflora the second year. Fall fire increased grass biomass (1224 vs. 1058 ± 56 kg ∙ ha− 1), but fall fire effects were generally similar to those of summer fire. Spring fire effects tended to be intermediate between no fire and summer and fall fire with the exception that spring fire was most detrimental to H. comata the first growing season and did not increase bare ground. All seasons of fire reduced litter, forb biomass, and frequency of Bromus japonicus and Artemisia spp., and they reduced H. comata, V. octoflora, and native annual forbs the first year, but increased basal cover of C3 perennial grasses (2.2% vs. 0.6% ± 0.4%). Fire during any season increased dominance of native species compared with no fire (6.6% vs. 2.0% ± 1.0% basal cover) and maintained productivity. Seasonal timing of fire manipulated species composition, but increased C3 perennial grass cover and native species dominance with fire during any season indicated that using fire was more important than the season in which it occurred. In addition, fire effects on the vegetation components tended to be counter to previously observed effects of grazing, suggesting fire and grazing may be complementary.

High-grade U ore deposits are in various stages of exploitation across the Grand Canyon watershed, yet the effects of U mining on ecological and cultural resources are largely unknown. We characterized the concentrations of Al, As, Bi, Cd, Co, Cu, Fe, Pb, Hg, Mo, Ni, Se, Ag, Tl, Th, U, and Zn, gross alpha and beta activities, and U and Th radioisotopes in soil, vegetation (Hesperostipa comata, Artemisia tridentata, Tamarix chinensis), and rodents (Peromyscus maniculatus, P. boylii) to waste material at the Kanab North mine, a mine with decades-long surficial contamination, and compared the concentrations (P < 0.01) to those at a premining site (Canyon Mine). Rodent tissues were also analyzed for radium-226 and microscopic lesions. Radioactivities and some elemental concentrations (e.g., Co, Pb, U) were greater in the Kanab North mine biological samples than in Canyon Mine biota, indicating a mining-related elemental signature. Mean rodent Ra-226 (111 Bq/kg dry weight [dry wt]) was 3 times greater than expected, indicating radioactive disequilibrium. Multiple soil sample U concentrations exceeded a screening benchmark, growth inhibition thresholds for sensitive plants, and an EC20 for a soil arthropod. Lesions associated with metals exposure were also observed more frequently in rodents at Kanab North than those at Canyon Mine but could not be definitively attributed to U mining. Our results indicate that Kanab North biota have taken up U mining-related elements owing to chronic exposure to surficial contamination. However, no literature-based effects thresholds for small rodents were exceeded, and only a few soil and vegetation thresholds for sensitive species were exceeded; therefore, adverse effects to biota from U mining-related elements at Kanab North are unlikely despite chronic exposure. Integr Environ Assess Manag 2019;15:112-125. Published 2018. This article is a US Government work and is in the public domain in the USA.

Rotational stocking theoretically enables regrazing of regrowth, but regrowth may be limited in xerophytic vegetation. We tested the hypothesis that regrowth would be slow and fixed in Hesperostipa comata (a caespitose, drought-tolerant grass), while growth would be flexible in Pascopyrum smithii (a rhizomatous, less drought-tolerant grass) under increasing defoliation and moisture, by assessing tiller growth rates, population dynamics and plant yield on marked plants in a Dry Mixed Grass prairie. Plots were clipped in late summer to simulate a deferred control, or intermittently during the growing season (May–August) at high intensity–low frequency (HILF), low intensity–high frequency (LIHF) or high intensity–high frequency and crossed with two water treatments (ambient and addition) in both a xeric upland and a mesic lowland. Growing season defoliation increased tiller growth rates of P. smithii in the upland, whereas HILF and LIHF reduced growth in the lowland. All defoliation regimes increased tiller growth for H. comata. Tiller populations of H. comata increased with frequent defoliation, while tiller populations of P. smithii decreased regardless of defoliation regime. Frequent defoliation, regardless of intensity, reduced yield relative to the deferred control for both grasses. While water addition consistently increased growth rates and reduced differences in tiller number among defoliation treatments, the regrowth of both grasses remained similar under varied defoliation with ambient moisture. High moisture conditions also promoted regrowth more in P. smithii compared to H. comata. In summary, neither grass species displayed an inherently fixed or flexible tiller or plant yield response in response to defoliation or moisture.

Plant community responses to livestock grazing lack conformity across studies, even those conducted within similar ecosystems. Variability in outcomes can often be traced back to short-term or mid-term weather patterns, differences in grazing timing or intensity, or interactive effects of management and weather. Long-term experimental data are needed to determine how grazing intensity affects plant community composition in semiarid ecosystems where precipitation is low and highly variable. However, long-term grazing intensity experiments, particularly experiments with more than two grazing intensity treatment levels, are quite rare. We capitalized on one of the longest-term grazing studies, with 75 yr of sustained stocking rate treatments (none, light, moderate, and heavy), to identify long-term effects of livestock grazing on plant community composition in shortgrass steppe. Plant community composition was similar between moderately and heavily grazed pastures after 75 yr of continuous, season-long (May to October) grazing treatments, and heavy grazing did not extirpate cool-season perennial graminoids. These findings support the long-term sustainability of livestock grazing in the shortgrass steppe, which has high resistance to season-long heavy grazing. Conversely, ungrazed and lightly grazed pastures experienced relatively large shifts in plant community composition, especially in the past 25 yr. Light or no grazing was associated with increased abundance of cool-season perennial graminoids, as well as several weedy and invasive species. Moreover, across most grazing treatments, several aspects of plant community composition have been shifting directionally during the past 25 yr, which recent experiments in this grassland suggest may be a response to increasing atmospheric (CO2). The shortgrass steppe is not only tolerant of fairly high grazing intensities but also likely requires some level of grazing to resist invasion by weedy annuals and to maintain cover of blue grama, a highly drought-tolerant species.

PREMISE OF THE STUDY Vegetative reproduction from belowground bud banks is the primary driver of grassland systems. Despite the importance of bud banks, the timing of recruitment and the crucial link between formation and maintenance is unknown. METHODS We assessed patterns of belowground bud development, dormancy, and mortality associated with three perennial native grasses in the northern Great Plains. Temperature and soil moisture were measured below the soil surface to determine relationships with belowground bud development. KEY RESULTS Blue grama (Bouteloua gracilis) generated more buds over winter that remained dormant; whereas, C3 species needle-and-thread (Hesperostipa comata) and western wheatgrass (Pascopyrum smithii), maintained limited dormant buds throughout winter. Soil temperature was a good predictor for C4 species bud production; whereas, soil moisture was a reliable predictor for C3 buds. Distinct differences existed between C4 species blue grama and C3 species needle-and-thread, whereas C3 species western wheatgrass (Pascopyrum smithii) was intermediate, indicating there is likely a species-specific continuum between the C3 and C4 extremes rather than a stark difference. CONCLUSIONS The ability to predict belowground bud development is a novel insight to native perennial grasses. Native grass species' strategies and adaptability regarding belowground bud bank size and bud phenology are important factors optimizing tiller recruitment given the variable growing conditions. Patterns of bud dormancy and development will provide insight to the underlying mechanisms by which management practices and fluctuations in precipitation amount and growing season length can alter mixed-grass prairie plant community dynamics.

Current federal post-fire land management recommendations in the United States suggest that rangelands be rested from grazing for two growing seasons following fire to allow for proper recovery, despite the lack of empirical literature supporting this recommendation. This project was designed to determine if grazing the first growing season following a spring wildfire alters subsequent productivity and species composition of northern mixed-grass prairie. Following the April 2013 Pautre wildfire in northwestern South Dakota, 100 m 2 exclosures were erected in three burned pastures to simulate two growing seasons of rest. Grazing exclosures were paired with sites grazed both the first and second growing seasons following the fire and replicated across loamy and sandy ecological sites. Prior to grazing the second growing season, five 2 m 2 cages were placed at each grazed site to assess first-year grazing effects. Following the second growing season, productivity and species composition were determined for exclosures and cages. Productivity was greater for loamy than sandy ecological sites (loamy = 2764 kg ha −1 , sandy = 2356 kg ha −1 ; P = 0.0271), but was similar between grazing treatments (rested = 2556 kg ha −1 , grazed = 2564 kg ha −1 ; P = 0.9550). Ecological site strongly determined species composition. Loamy sites consistently contained more Pascopyrum smithii , Bouteloua gracilis and Carex duriuscula than sandy sites (30 v 0%, 18 v 8%, 4 v 1%; P = 0.0004, 0.0457 and 0.0382 respectively). The effects of grazing exclusion were limited to Hesperostipa comata and the non-native Agropyron cristatum composition. H. comata was more prevalent on rested sites (22 v 15%, P = 0.0096). A. cristatum experienced a grazing treatment by ecological site interaction as it was reduced by grazing on sandy sites, but was not affected on loamy sites ( P = 0.0226). Results do not support the notion that a two growing season rest period following fire is required in the northern mixed-grass prairie.

Seeds of many forage species have dormancy, delaying germination in the field. Species from semi-arid environments may have adaptation to fire, therefore, the effects of priming seeds of common forage species in aqueous smoke solutions were studied. Seeds of eight grasses and two legumes were primed in serial dilutions of aqueous smoke solutions and then dried before germination tests. Depending on the species and concentrations of solutions, priming seeds acted independently or in interaction with light and (or) temperature to improve germination in Altai wildrye (Leymus angustus), green needlegrass (Nassella viridula), Kura clover (Trifolium ambiguum), needle-and-thread (Hesperostipa comata), northern wheatgrass (Elymus lanceolatus), orchard grass (Dactylis glomerata), plains rough fescue (Festuca hallii), Russian wildrye (Psathyrostachys juncea), and western wheatgrass (Pascopyrum smithii). Priming seeds of cicer milkvetch (Astragalus cicer) in distilled water or aqueous smoke solutions had no effect o...

Little is known about how defoliation intensity and frequency alter plant community composition and diversity in northern Great Plains mixedgrass communities. We evaluated defoliation effects in combination with watering on vascular plant composition and diversity in two contrasting ecological sites, a drier upland and more mesic lowland, in the Dry Mixedgrass natural subregion of Alberta, Canada. Treatments were applied for three growing seasons (2010 through 2012, inclusive) and included defoliation regimes of high intensity at high frequency, high intensity at low frequency, low intensity at high frequency, and defoliation deferred until the end of the growing season. Moisture regimes were ambient and elevated. Defoliation rather than moisture was the primary determinant of plant composition after 3 yr, particularly in the lowland site. Watering effects on composition were more apparent in the drier upland. All growing season defoliation regimes markedly altered composition relative to the deferred control, with relatively minor differences in composition among growing season defoliation treatments, particularly in the mesic lowland site. We conclude that growing season defoliation alters mixedgrass composition by reducing canopy dominant grasses (Pascopyrum smithii and Hesperostipa comata) and releasing shorter-statured grasses and forbs, which can either increase or decrease diversity depending on site (edaphic) conditions and the relative dominance of midgrasses and shortgrasses (Koeleria macrantha and Bouteloua gracilis). Finally, increased moisture did not ameliorate defoliation effects during the growing season, suggesting compositional responses were predictable and independent of growing season defoliation regime.

Summer climatic moisture balances (precipitation vs. potential evapotranspiration) for topographic slopes favored by present-day xerophytic boreal grasslands (SSW aspects with 61% – 65% gradients) in southwest Yukon were compared to their unglaciated late-Wisconsinan (14 000 – 12 000 cal yr BP) Beringian counterparts. The purpose was to determine whether present-day grasslands are ecologically plausible Beringian relicts or analogues. The Beringian climate was represented by meteorological stations with average July temperatures 4˚C colder than those of present-day grassland areas; all were from Arctic locations. The most commonly occupied grassland slopes received maximum local solar radiation and likely represented the warmest topographic positions in the landscape. Their summer evapotranspiration demands exceeded the 200 mm moisture supply by 189 mm. The same slopes had late-Wisconsinan summer moisture balances of −57 to −101 mm because of colder and shorter growing seasons. Moisture balances for late-Wisconsinan SSW slopes were similar to those of present-day WNW – NW aspects, which do not support grasslands. Differences in moisture deficits indicated present-day xerophytic grasslands were improbable Beringian in situ relicts or analogues. Alternatively, it was hypothesized that present-day Calamagrostis purpurascens communities developed during the Holocene Thermal Maximum (11 000 – 9000 cal yr BP), whereas Hesperostipa comata communities formed less than 3000 years ago after postglacial migration of the species from central North America.

Managers of rangeland ecosystems require methods to track the condition of natural resources over large areas and long periods of time as they confront climate change and land use intensification. We demonstrate how rangeland monitoring results can be synthesized using ecological site concepts to understand how climate, site factors, and management actions affect long-term vegetation dynamics at the landscape-scale. Forty-six years of rangeland monitoring conducted by the Bureau of Land Management (BLM) on the Colorado Plateau reveals variable responses of plant species cover to cool-season precipitation, land type (ecological site groups), and grazing intensity. Dominant C3 perennial grasses (Achnatherum hymenoides, Hesperostipa comata), which are essential to support wildlife and livestock on the Colorado Plateau, had responses to cool-season precipitation that were at least twice as large as the dominant C4 perennial grass (Pleuraphis jamesii) and woody vegetation. However, these C3 perennial grass responses to precipitation were reduced by nearly one-third on grassland ecological sites with fine- rather than coarse-textured soils, and there were no detectable C3 perennial grass responses to precipitation on ecological sites dominated by a dense-growing shrub, Coleogyne ramosissima. Heavy grazing intensity further reduced the responses of C3 perennial grasses to cool-season precipitation on ecological sites with coarse-textured soils and surprisingly reduced the responses of shrubs as well. By using ecological site groups to assess rangeland condition, we were able to improve our understanding of the long-term relationships between vegetation change and climate, land use, and site characteristics, which has important implications for developing landscape-scale monitoring strategies.

Seedling establishment in semiarid prairie sites under reclamation can be facilitated by mulch due to its effects on seedbed conditions. Effects on plant recruitment can also be inhibitory, as mulch can filter out or attenuate environmental signals that break seed dormancy and can negatively affect early seedling performance. A manipulative field experiment was established to determine if straw and hay mulch facilitate seedling emergence and establishment. The reclamation site is an abandoned irrigation area in the mixed grass prairie of southern Alberta, Canada. Soil was tilled and the seedbed prepared through manual harrowing, then plots were broadcast seeded with Elymus trachycaulus, Bouteloua gracilis, Hesperostipa comata, Astragalus canadensis and Linum lewisii. Hay and straw mulch were applied at two rates (300 and 600 g m−2). Seedling emergence and survival were assessed through the first growing season. Both hay mulch rates increased E. trachycaulus and L. lewisii seedling emergence relative to bare ground. A. canadensis seedling emergence was more than ten times higher with low straw and both hay rates than with bare ground. Straw mulch facilitated seedling emergence at a low rate but had a neutral effect at high rates. Effects of low straw and both hay mulch rates on seedling establishment were facilitative for E. trachycaulus and L. lewisii and neutral for B. gracilis. Effects of high straw rates were neutral for E. trachycaulus and L. lewisii and hindered B. gracilis seedling establishment. These results clearly show that low mulch rates can increase native plant establishment during the critical first year of prairie reclamation as they were able to overcome microsite limitations.

Reestablishing cool-season (C3) grass communities on low elevation rangelands of the Colorado Plateau is notoriously difficult, raising questions about the viability of restoring native species and continuing to actively graze these landscapes. We conducted a seeding experiment on an arid (15.4 cm rain/year), historically heavily-grazed rangeland in Northern Arizona to test the effects of seeding technique and simulated seasonal climate scenarios on germination and recruitment of four species of native, cool-season bunchgrasses: Achnatherum hymenoides, Hesperostipa comata, Poa secunda, and Elymus elymoides. Initial results indicated that C3 grasses germinated significantly more in drill-seeded treatments under simulated high precipitation years than in other treatment types. Five years post-treatment, P. secunda and E. elymoides were not observed but simulated drill-seeded treatments, had significantly higher densities of A. hymenoides and H. comata recruits relative to most other treatment types. Simulated drill seeding also increased soil disturbance which increased the establishment of the invasive weed Salsola tragus in year 1, but not thereafter. Although it appears critical to coordinate effective seeding techniques with high winter–spring precipitation, predicting such events may not be possible at some sites, suggesting that seeding low elevation, arid rangelands of the Colorado Plateau may not always be realistic under a future climate that is drier and less predictable.

Plains rough fescue ( Festuca hallii (Vasey) Piper [Poaceae]), once dominant in rough fescue grasslands of central Canada and the northern US, recovers poorly if disturbed by cattle grazing or oil and gas production soil handling techniques. This long-lived bunchgrass requires 3 to 5 y to become established, during which time it may be exposed to competition from faster-growing species. Our first research objective was to assess the recovery of F. hallii by comparing a monoculture seeding to a mixed seeding of native grass (Poaceae) species including F. hallii, Koeleria macrantha (Ledeb.) Schult., Elymus trachycaulus (Link) Gould ex Shinners ssp. subsecundus (Link) A. Love & D. Love, Pascopyrum smithii (Rydb.) A. Love, Nassella viridula (Trin.) Barkworth, Hesperostipa comata (Trin. & Rupr.) Barkworth, and Bouteloua gracilis (Willd. ex Kunth) Lag. ex Griffiths. Our second objective was to evaluate plant community development of both seeding mixes. We established seeding experiments on 3 field sites in central Alberta, Canada. When seeded as a monoculture, the F. hallii plant community that resulted included native species re-established from the seedbank or seed rain, such as Helictotrichon hookeri (Scribn.) Henr. (Poaceae). In the native species seed mix, wheatgrasses ( E. trachycaulus ssp. subsecundus and P. smithii ) dominated in the first 3 y with low F. hallii cover. We recommend seeding F. hallii with few or no aggressive species, such as wheatgrasses, in the seed mix.

Native plant communities invaded by cheatgrass ( Bromus tectorum L.) are at risk of unnatural high intensity fires and conversion to cheatgrass monocultures. Management strategies that reduce cheatgrass abundance may potentially allow native species to expand and minimize further cheatgrass invasion. We tested whether the selective herbicide imazapic is effective in reducing cheatgrass and “releasing” native species in a semiarid grassland and shrub steppe in north-central Oregon. The experiment consisted of a completely randomized design with two treatments (sprayed with 70 g ai · ha −1 of imazapic and unsprayed) and three replicates of each treatment applied to either 2.5 or 4 ha plots. We repeated this experiment in three different sites dominated by the following native species: 1) bluebunch wheatgrass ( Pseudoroegneria spicata [Pursh] A. Love ssp. spicata ) and needle and thread ( Hesperostipa comata [Trin. & Rupr.] Barkworth), 2) needle and thread and Sandberg bluegrass ( Poa secunda J. Presl), and 3) big sagebrush ( Artemisia tridentata Nutt.). Nested frequency of all plant species in 1-m 2 quadrats was collected for 1 yr pretreatment and 4 yr posttreatment. In all three sites, cheatgrass frequencies were significantly lower in sprayed plots than unsprayed plots for 3–4 yr posttreatment ( P Machaeranthera canescens [Pursh] Gray) and big sagebrush, increased in sprayed plots, and increases occurred only at two sites. These results suggest that a short-term reduction in cheatgrass alone is not an effective strategy for increasing the abundance of most native perennial plant species.

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.

Summary 1. It has been suggested that much of the elevated CO2 effect on plant productivity and N cycling in semi-arid grasslands is related to a CO2-induced increase in soil moisture, but the relative importance of moisture-mediated and direct effects of CO2 remain unclear. 2. We grew five grassland species common to the semi-arid grasslands of northern Colorado, USA, as monocultures and as mixtures of all five species in pots. We examined the effects of atmospheric CO2 concentration (ambient vs. 780 p.p.m.) and soil moisture (15 vs. 20% m ⁄ m) on plant biomass and plant N uptake. Our objective was to separate CO2 effects not related to water from water-mediated CO2 effects by frequently watering the pots, thereby eliminating most of the elevated CO2 effects on soil moisture, and including a water treatment similar in magnitude to the water-savings effect of CO2. 3. Biomass of the C3 grasses Hesperostipa comata and Pascopyrum smithii increased under elevated CO2, biomass of the C4 grass Bouteloua gracilis increased with increased soil moisture, while biomass of the forbs Artemisia frigida and Linaria dalmatica had no or mixed responses. Increased plant N uptake contributed to the increase in plant biomass with increased soil moisture while the increase in plant biomass with CO2 enrichment was mostly a result of increased N use efficiency (NUE). Species-specific responses to elevated CO2 and increased soil moisture differed between monocultures and mixtures. Both under elevated CO2 and with increased soil moisture, certain species gained N in mixtures at the expense of species that lost N, but elevated CO2 led to a different set of winners and losers than did increased water. 4. Elevated CO2 can directly increase plant productivity of semi-arid grasslands through increased NUE, while a CO2-induced increase in soil moisture stimulating net N mineralization could further enhance plant productivity through increased N uptake. Our results further indicate that the largest positive and negative effects of elevated CO2 and increased soil moisture on plant productivity occur with interspecific competition. Responses of this grassland community to elevated CO2 and water may be both contingent upon and accentuated by competition.

Native plant individuals often persist within communities dominated by exotics but the influence of this exposure on native populations is poorly understood. Selection for traits contributing to competitive ability may lead to native plant populations that are more tolerant of the presence of exotic invaders. In this way, long-term coexistence with an exotic may confer competitive advantages to remnant (experienced) native populations and be potentially beneficial to restoration. In past studies we have documented genetic differentiation within native grass populations exposed to the exotic invader Russian knapweed (Acroptilon repens). Here, we examine populations of a cool-season grass, needle-and-thread (Hesperostipa comata [Trin. & Rupr.]) and a warm season, alkali sacaton (Sporobolus airoides [Torr.]) collected from Russian knapweed-invaded sites and adjacent noninvaded sites to assess their relative competitive ability against a novel exotic neighbor, Canada thistle (Cirsium arvense). Experienced S. airoides (from within A. repens invasions) appear to better tolerate (accumulate biomass, leaf nitrogen content, and to initiate new tillers) the presence of a novel competitor (C. arvense). Experienced and inexperienced H. comata genets differ in their response to the presence of C. arvense. Relative neighbor effects of native grasses on C. arvense were generally greater from experienced grasses. The ability to compete with novel neighbors may be driven by general competitive traits rather than species-specific coevolutionary trajectories. Irrespective of competitive mechanisms, the conservation of native species populations within weed invasions may provide an important restoration tool by retaining unique components of native gene pools selected by competitive interactions with exotics.

Elevated CO2 affects plant productivity, but also water availability and plant species composition in semi-arid grasslands, thereby potentially causing complex effects on CH4 consumption and N2O emission. We studied the effects of atmospheric CO2 concentration (400 vs 780 μL L−1), water content (15 vs 20% gravimetric soil moisture), and composition of semi-arid grassland species (perennial grasses Bouteloua gracilis, Hesperostipa comata, and Pascopyrum smithii; sub-shrub Artemisia frigida; invasive forb Linaria dalmatica grown in monoculture and all five species together) on CH4 consumption and N2O emission in a full factorial greenhouse experiment. We used a unique method where we measured microbial effects on CH4 consumption and N2O emission in isolation from effects of gas diffusivity. Microbially mediated CH4 consumption was significantly higher under elevated CO2 (by 20%), but was not affected by soil water content or plant species composition. Microbially mediated N2O emission was not significantly affected by elevated CO2, but was significantly higher with high water content (by 67%) and differed significantly among species. Treatment effects on CH4 consumption and N2O emission often could not be explained simply by differences in soil moisture, suggesting that treatment-induced changes in other soil and microbial properties played a role in causing these effects.

Rhizosheaths are structures composed of mucilage secreted from plants and adherent soil particles that form a cylinder around the root. Using scanning electron microscopy (SEM), we observed bacteria associated with rhizosheaths of the grasses Achnatherum hymenoides, Calamovilfa longifolia, Hesperostipa comata, and Pascopyrum smithii from a sand dune area in Harding County in northwestern South Dakota. The greatest numbers of bacteria, observed with SEM (529 mm-2), and the greatest number of culturable bacteria (9.9 × 107 CFU · g-1 or 5178 CFU · mm-2) were on rhizosheaths of C. longifolia. Rhizosheaths of all the grasses examined contained a higher density of bacteria than the surrounding soil. Nitrogen fixation, as assayed by reduction of acetylene to ethylene, was present in some rhizosheaths. Bacterial nifH gene sequences amplified from bacteria associated with rhizosheaths were most similar to those from Alcaligenes latus and Mesorhizobium loti.

Invading exotics typically face new competitors and an absence of specialized herbivores in their new ranges. Biological control attempts to reunite invasive weeds with coevolved herbivores and restoration can reduce the return of invaders by maximizing competition from native species. The integration of both approaches is seldom examined in detail, although the two should complement each other. We investigated the potential to suppress an important invasive plant, Canada thistle (Cirsium arvense [L.] Scop.), by integrating biological control and competition from two native grasses frequently used in rangeland restoration. We evaluated the impacts of Ceutorhynchus litura F. (Coleoptera: Curculionidae), a weevil used for Canada thistle biological control, alone and in combination with either needle and thread grass (Hesperostipa comata [Trin. & Rupr.] Barkworth) or alkali sacaton (Sporobolus airoides [Torr.] Torr.) in greenhouse competitive plantings. Weevil herbivory reduced root, but not shoot, biomass of Canada thistle. Competition from H. comata did not reduce biomass of thistles, but combinations of the weevil and H. comata greatly reduced thistle root biomass. S. airoides suppressed Canada thistle root biomass independent of weevils. Weevils had a positive indirect effect on the cool-season grass H. comata, presumably by reducing the competitive ability of thistles, but had no effect on biomass of the warm-season grass, S. airoides. Benefits of weevil presence as an augmentation of grass competition appear to depend on appropriate timing, and weevils provided the most benefit to the cool-season competitor. Our results suggest that restoration efforts can be complemented with insect biocontrol agents, although the timing of impact will depend on the particular weed species, grass competitors, and biocontrol insect agents involved.

Shrubsteppe ecosystems in the Intermountain West have suffered extreme alteration from a variety of factors. Using a retrospective approach, I studied the effects of horse and cattle grazing at the northern edge of the range in southern British Columbia, Canada, where the shrubsteppe is not as heavily altered and ungrazed sites remain in areas dominated by antelope bitterbrush (Purshia tridentata). I measured shrub and understory cover at 10 sites that were either ungrazed, lightly grazed, or heavily grazed. Cover of antelope bitterbrush decreased with grazing, and cover of big sagebrush (Artemisia tridentata) increased with grazing intensity. I sampled 72 species of vascular plants in the understory. Livestock grazing resulted in more bare soil, especially at sandy rather than rocky sites, and in quadrats located in the interspaces between shrubs. More bare soil was associated with less spikemoss (Selaginella spp.) and less microbiotic crust cover. Of the 3 most common bunchgrasses, sand dropsee...

Contemporary evolution may explain the success of some exotic plant invasions. However, the evolutionary response of recipient native plant populations to exotic invasion has received relatively little attention. Because plant populations are genetically variable, contemporary evolution may also occur in native populations following entry of invasive species. Previously, we documented molecular differences in native populations; here we extend these studies to evaluate growth of native species in a common garden experiment. We seek to determine if three populations of two native grass species (Hesperostipa comata and Sporobolus airoides ) demonstrate evidence of contemporary evolution in response to invasion by Acroptilon repens . We obtained 50 genets of the two native grass species from communities long-invaded (25 � 80 years) by A. repens and from adjacent, noninvaded areas, and planted five transplants of each genet into two A. repens infestations (Laramie and Fort Steele, Wyoming, USA) to document their growth and survival. Cumulative differences between collections from invaded and noninvaded communities were species-specific. S. airoides displayed a consistent positive response to long-term coexistence with A. repens , whereas the performance of H. comata originating from invaded communities was not different from H. comata collected from noninvaded communities. In general, genets from invaded communities had fewer tillers than genets from noninvaded communities, but their relative tiller production (percent increase) was greater for genets from invaded communities at both field transplant sites for both grass species. Basal area increase and overall performance of collections from invaded and noninvaded communities of origin depended on transplant site and grass species. The results suggest that native species have the potential for adaptation to coexist with exotic invasives, although that potential may differ among species.

Question What is the impact of prescribed fires on the cover and composition of vegetation in Artemisia tridentata ssp. vaseyana steppe?Location: United States Department of Agriculture, Agricultural Research Service, United States Sheep Experiment Station, eastern Idaho (44°14′44″ N, 112°12′47″ W).Methods: Multiple prescribed fires were lit in 2002 and 2003 in an Artemisia tridentata ssp. vaseyana (mountain big sagebrush) steppe ecosystem that was relatively free of exotic plants. Measurements of cover components and plant species frequencies were taken pre- and for 2 to 3 years post-fire.Results: Cover of forbs and grasses returned to pre-fire levels after two years. Shrub cover declined from 36 to 6% in the first year post-fire. Fire reduced the frequencies of three species, A. tridentata ssp. vaseyana, Festuca idahoensis, and Cordylanthus ramosus, of rangeland plants. Frequencies of four plant species, Hesperostipa comata, Polygonum douglasii, Chenopodium fremontii and Chenopodium leptophyllum increased, but only P. douglasii increased for more than a year.Conclusion: This study demonstrates that in an Artemisia tridentata ssp. vaseyana steppe ecosystem without significant non-native species or anthropogenic disturbances vegetative cover and species composition of the herbaceous community are only minimally altered by fire. The herbaceous component returned to pre-fire conditions within three years of a fire.Nomenclature: USDA Natural Resources Conservation Service, Plants database http//plants.usda.gov/

In areas where land is disturbed to extract energy resources such as coalbed methane, improper soil management may result in soils impaired by elevated salinity. The objectives of this study were to evaluate the emergence and growth of three native grass species (Pseudorogeneria spicata, Hesperostipa comata, and Pascopyrum smithii) as a function of soil salt content and matric potential. The study consisted of nine treatments, combining three soil salinity levels (0.80, 5.0 and 11.0 dS/m) and three matric potential ranges (-0.1 to -1.0, -1.0 to -7.0, and less than -7.0 bars). Seedling emergence, plant height, aboveground biomass, and belowground biomass were significantly decreased by increasing soil salinity and decreasing soil moisture. This resulted in large reductions in growth when soil moisture was decreased within a salinity treatment. Emergence for plants grown in elevated salinity increased as much as 26.7 % when moisture was high. At low soil moisture, elevated salinity resulted in emergence losses as high as 88.3 %. Losses in aboveground biomass ranged from 23.0 to 97.9 % at moderate salinity and 27.3 to 98.5% at high salinity. Results indicate that the impacts of elevated soil salinity are highly influenced by soil moisture. Additional

Invasive alien plants frequently possess greater seed banks than native species in disturbed areas, but native disturbance-adapted species may also possess large seed banks. We analyzed seed banks of ten sites with varying grazing histories in a shrub-steppe ecosystem dominated by antelope bitterbrush (Purshia tridentata) in the Okanagan valley in British Columbia, Canada. Overall effects of grazing on seed banks were overshadowed by site-specific differences, but canonical correspondence analysis (CCA) showed that the composition of the seed bank was significantly affected by bare soil which was positively correlated with grazing. Other factors affecting seed bank composition included litter, cover of spikemosses (Selaginella), shrub cover and microbiotic crust cover. The seed bank of the invasive herb diffuse knapweed (Centaurea diffusa) was largest at two of the three most heavily grazed sites. Cheatgrass (Bromus tectorum), another invasive species, exhibited large seed banks at all sites regardless of grazing history. Native species such as sand dropseed (Sporobolus cryptandrus) and Douglas’ knotweed (Polygonum douglasii) had substantial seed banks (> 1500 seeds m-2). Planting sand dropseed, Douglas’ knotweed, needle-and-thread grass (Hesperostipa comata) or their ecological equivalents could aid in the restoration of arid ecosystems because of their adaptation to disturbance and persistence of seeds in the soil.

Ecological impacts of invasive plant species are well documented, but the genetic response of native species to invasive dominance has been often overlooked. Invasive plants can drastically alter site conditions where they reach dominance, potentially exerting novel selective pressures on persistent native plant populations. Do native plant populations in old exotic invasions show evidence of selection when compared to conspecific populations in adjacent, noninvaded areas? We employ amplified fragment length polymorphism (AFLP) analysis to screen a large number of loci from two native grass species (Hesperostipa comata (Trin. & Rupr.) Barkworth and Sporobolus airoides Torr.) that occur in old infestations of the invasive forb Acroptilon repens. We then compare observed locus by locus F(ST) values with distributions of F(ST) estimated from simulation models under expectation of neutrality. We also compare the proportion of loci possibly linked to selection and those not linked to selection which exhibit parallel trends in divergence between two community types (invaded, noninvaded). Few loci (H. comata, 2.6%; S. airoides, 8.7%) in the two native grasses may be linked to genes under the influence of selection. Also, loci linked to selection showed a greater portion of parallel trends in divergence than neutral loci. Genetic similarities between community types were less than genetic similarity within community types suggesting differentiation in response to community alteration. These results indicate that a small portion of scored AFLP loci may be linked to genes undergoing selection tied to community dominance by an invasive species. We propose that native plants in communities dominated by exotic invasives may be undergoing natural selection.

Emergence is examined in populations of Hesperostipa comata, and this grass is compared to individuals, populations, and three additional species of Achnatherum. The Achnatherum species are closely related and more distantly related to H. comata. Emergent properties are assessed through measurements of grass spikelets and the divergence from vectors of isometry as expressed in individuals, populations, species, and species groups. Our results demonstrate that the strongest degrees of emergence are expressed at the levels of individuals, species, and groups of species, with the strongest of all being seen when H. comata is compared with the trio of Achnatherum species; populations express the least emergence. This reflects evolutionary differentiation as expressed through the ontogenetic events that led to the formation of spikelets. It can be related to concepts of local and global time; the flow of energy, matter, and information; and the driving force of the expression of novelty (entropy) in organized ...

This work examined the response of native grass populations to long-term presence of non-indigenous invasive plant species (NIPS). Two native grass species common to arid and semi-arid rangelands were identified (alkalai sacaton [Sporobolus airoides] and needle and thread grass [Hesperostipa comata]) as remnants of native communities subjected to NIPS Russian knapweed [Rhaponticum repens]). Maternal grass individuals were collected to examine the influence of the invasions on population genetics and phenology of the two grass species. In controlled greenhouse settings and field plantings, this work examined the growth, seed production, and germination of seedlings of the two grasses in competition with Russian knapweed and NIPS Canada thistle [Cirsium arvense]; and genetic variability of the two grasses via amplified fragment length polymorphism and Inter-Simple Sequence Repeat analyses. Results showed that maternal lines of the grasses demonstrate evidence of natural selection via the presence of the invaders. Continued work was recommended to obtain superior seed sources for native species to target the tradeoffs between phenotypic plasticity and increased vegetative growth, to develop wild seed collection protocols and production techniques so that native plants may be used to restore degraded areas and to reduce the chances of future exotic invasion.

Knowledge of the many mechanisms of vesicular stomatitis virus (VSV) transmission is critical for understanding of the epidemiology of sporadic disease outbreaks in the western United States. Migratory grasshoppers [ Melanoplus sanguinipes (Fabricius)] have been implicated as reservoirs and mechanical vectors of VSV. The grasshopper-cattle-grasshopper transmission cycle is based on the assumptions that (i) virus shed from clinically infected animals would contaminate pasture plants and remain infectious on plant surfaces and (ii) grasshoppers would become infected by eating the virus-contaminated plants. Our objectives were to determine the stability of VSV on common plant species of U.S. Northern Plains rangelands and to assess the potential of these plant species as a source of virus for grasshoppers. Fourteen plant species were exposed to VSV and assayed for infectious virus over time (0 to 24 h). The frequency of viable virus recovery at 24 h postexposure was as high as 73%. The two most common plant species in Northern Plains rangelands (western wheatgrass [ Pascopyrum smithii ] and needle and thread [ Hesperostipa comata ]) were fed to groups of grasshoppers. At 3 weeks postfeeding, the grasshopper infection rate was 44 to 50%. Exposure of VSV to a commonly used grasshopper pesticide resulted in complete viral inactivation. This is the first report demonstrating the stability of VSV on rangeland plant surfaces, and it suggests that a significant window of opportunity exists for grasshoppers to ingest VSV from contaminated plants. The use of grasshopper pesticides on pastures would decrease the incidence of a virus-amplifying mechanical vector and might also decontaminate pastures, thereby decreasing the inter- and intraherd spread of VSV.

High-latitude (61.9˚ – 62.8˚ N) graminoid plant communities located near the northern limit of boreal forest occurrence in the Carmacks – Pelly Crossing area of Yukon were sampled and classified, and four sociations were recognized: Calamagrostis purpurascens (purple reedgrass), Hesperostipa comata (needle-and-thread grass), Poa glauca – Artemisia frigida (glaucous bluegrass – pasture sagewort), and Pseudoroegneria spicata – Artemisia frigida (bluebunch wheatgrass – pasture sagewort). These plant communities occurred primarily on south – southwest slopes (180˚ – 230˚) with 45% – 75% gradients. Relative to southern Canada mixedgrass prairie, Yukon grasslands were likely species poor, had less total canopy cover, and produced less than half as much aboveground herb biomass (typically 200 – 300 kg/ha). The distribution of the sociations appeared limited to ~60˚ – 65˚ N latitude in the Yukon-Alaska region. Calamagrostis was the most abundant and widespread grassland sociation in the study area. The four sociations occupied less than 4% of the Carmacks – Pelly Crossing landscape, although they represented the most extensive high-latitude boreal grassland vegetation in Canada (≥ 2600 ha) and they were among the most northerly in North America.

The competitiveness of plants within a community is dictated to some extent by their association with microorganisms in the soil. That association is affected by root exudates and possibly by their quality. The competitiveness of species under various grazing regimes has been defined by their response to grazing as decreaser, increaser, or invader. To test the hypothesis that there are recognisable differences in the chemical fingerprints of the root exudates of decreasers, increasers and invaders, seeds of 8 grasses, representing these 3 designations, were germinated and grown for 2 weeks in a root exudate trapping system in the laboratory. Tentative identification of the suite of compounds recovered from the root exudates by a solvent extraction technique was done with the help of gas chromatography/mass spectrometry and authentic samples. Eleven identified compounds, present in all exudates as major peaks, but absent in the blanks, were selected for semi-quantitatively comparing the 3 grazing response groups. For all 11 compounds, there was always at least 1 of the grazing response groups that had the highest percentages. That is to say, they were qualitatively, based on the 11 compounds selected, but not quantitatively similar. DOI:10.2458/azu_jrm_v55i4_dormaar

In August 1994, wildfire burned 6,500 ha of native Dry Mixed Prairie in southeastern Alberta. The following year, a study was initiated to monitor the recovery of major plant communities. Burning was followed by 3 successive years of drought, reducing total vegetative cover by 10%. Exposed soil increased to a high of 23%, three years after the fire. Litter and grass production were reduced through 1997, with the greatest decline in 1995 when grass production on burned and unburned areas averaged 890 and 1,468 kg ha(-1), respectively. Of the major forage species, Stipa spp. and Koeleria macrantha (Ledeb. J.A. Schultes f.) were affected for a single year and Agropyron spp. 2 years by burning. Both Agropyron and Stipa abundance displayed interactions with topographic position in response to fire. In 1995, Agropyron increased on uplands with burning from 90 to 143 kg ha(-1), but decreased on lowlands from 383 to 238 kg ha(-1), a pattern repeated in 1996. In contrast, Stipa declined at both positions, but only for a single year. Where livestock grazing occurred after the fire, forage removal was greater on burned areas. Drought conditions, in combination with summer wildfire, reduced Dry Mixed Prairie range productivity and ground cover for several years and intensified livestock grazing, highlighting the need for changes in rangeland management under these conditions. DOI:10.2458/azu_jrm_v55i2_erichsen-arychuk

The influence of cattle grazing on carbon cycling in the mixed grass prairie was investigated by measuring the CO(2) exchange rate in pastures with a 13 year history of heavy or light grazing and an ungrazed exclosure at the High Plains Grasslands Research Station near Cheyenne, Wyo. In 1995, 1996 and 1997 a closed system chamber, which covered 1 m(2) of ground, was used every 3 weeks from April to October to measure midday CO(2) exchange rate. Green vegetation index (similar to leaf area index), soil respiration rate, species composition, soil water content, soil temperature, and air temperature were also measured to relate to CO(2) exchange rates of the 3 grazing treatments. Treatment differences varied among years, but overall early season (mid April to mid June) CO(2) exchange rates in the grazed pastures were higher (up to 2.5 X) than in the exclosure. Higher early season CO(2) exchange rates were associated with earlier spring green-up in grazed pastures, measured as higher green vegetation index. As the growing season progressed, green vegetation index increased in all pastures, but more so in the ungrazed exclosure, resulting in occasionally higher (up to 2 X) CO(2) exchange rate compared with grazed pastures late in the season. Seasonal treatment differences were not associated with soil temperature, soil respiration rate, or air temperature, nor was there a substantial change in species composition due to grazing. We hypothesize that early spring green-up and higher early season CO(2) exchange rate in grazed pastures may be due to better light penetration and a warmer microclimate near the soil surface because of less litter and standing dead compared to the ungrazed pastures. When all the measurements were averaged over the entire season, there was no difference in CO(2) exchange rate between heavily grazed, lightly grazed and ungrazed pastures in this ecosystem. DOI:10.2458/azu_jrm_v53i2_lecain

Combustion products of burning vegetation can increase seed germination of many species of fire-prone plant communities. We tested the influence of heating sagebrush (Artemisia tridentata Nutt.) subcanopy soil, aqueous extracts of artificially burned soil, and sagebrush smoke on the emergence of several range plant species of the sagebrush-steppe. In addition, test seeds were exposed to sagebrush smoke and aqueous slurries of artificially burned sagebrush subcanopy soil to determine their effect on plant growth. As compared to the control, substrates previously heated from 250 to 750 degrees C significantly (P less than or equal to 0.05) increased the emergence of Thurber's needlegrass [Achnatherum thurberianum (Piper) Barkworth] and needle-and-thread [Hesperostipa comata (Trin. &Rupr.) Barkworth]. Sagebrush smoke and aqueous slurries of artificially burned soil significantly increased the emergence of Sierra Nevada needlegrass [Achnatherum occidentalis (Thurber) Barkworth], Indian ricegrass [Achnatherum hymenoides (Roemer &Schultes)Barkworth], and antelope bitterbrush [Purshia tridentata (Pursh) DC.]. Rates of new leaf production and leaf elongation following treatment of seeds with the smoke of burning sagebrush were significantly greater for cheatgrass (Bromus tectorum L.), basin wildrye [Leymus cinereus (Sribner &Merr.) A. Love], Idaho fescue (Festuca idahoensis Elmer ), Sierra Nevada needlegrass, and needle-and-thread as compared to the control. After 83 days of growth, smoke-treated seeds of basin wildrye and needle-and-thread produced significantly greater plant mass than their controls. Smoke treatment of certain seeds before sowing is potentially useful for range plant seedings.

Diffuse knapweed (Centaurea diffusa Lam.), an invasive weed, has reduced forage production and biodiversity, and increased soil erosion on over a million hectares of rangeland in the western United States. This study evaluated the effects of a single grass defoliation on establishment of diffuse knapweed seeded at 2 rates into a bluebunch wheatgrass (Pseudoroegneria spicata [Pursh.] Scribn and Smith)/needle-and-thread (Stipa comata Trin. &Rupr.) community and a crested wheatgrass (Agropyron cristatum (L.) Gaertn.) community. Six defoliation levels (0, 20, 40, 60, 80, 100%) and 2 seeding rates (3,000, 6,000 diffuse knapweed seeds) were applied to 1 m2 plots in a randomized-complete-block design (n=4). Diffuse knapweed was seeded in the fall of 1992, and grasses were defoliated on 28 April 1993. The number of flowering culms and weed seedlings were counted in September 1993. Densities of diffuse knapweed seedlings, juveniles, and adults, as well as plant standing crop, were determined in May 1994. Seed rate had minimal effect on diffuse knapweed density. By May 1994, densities of diffuse knapweed were about 20 and 30 plants m-2 on undefoliated bluebunch wheatgrass and crested wheatgrass plots, respectively, indicating that defoliation is not required for this noxious weed to become established. Higher levels of grass defoliation (>60%), especially of bluebunch wheatgrass, enhanced diffuse knapweed establishment, indicating that moderate (

A Stipa-bouteloua community, cultivated in the autumn of 1928 and abandoned in the spring of 1932, reverted to a community dominated by needle-and-thread (Stipa comata Trin. and Rupr.). An exclosure to prevent grazing was constructed in 1978 to include equal portions of previously cultivated and adjacent native range, while the remainder of the area continued to be subjected to moderate to heavy grazing pressure. This permitted a study to determine the effects of the brief period of cultivation on forage production, species recovery, and soil physical and chemical characteristics compared to those of native prairie. After 14 years of protection from grazing, needle-and-thread accounted for 79% of foliar cover of the abandoned cultivation and 18% of the untreated range while blue grama [Bouteloua gracilis (HBK.) Lag. ex Steud] occupied 1 and 51% on the same treatments, respectively. After 60 years, the soil on the abandoned cultivated area showed reduced carbon, total nitrogen, available phosphorus, and hydraulic conductivity but increased N03-N. Grazing reduced hydraulic conductivity, NH4-N, available mineralizable nitrogen (chemical index), available phosphorus, and total carbohydrates but increased carbon, total nitrogen, and N03-N. Cultivation and grazing resulted in reduced root mass. To facilitate a rapid transition from blue gramb to needle-and-thread stable communities, input of energy, such as cultivation, may well be required.

During 1987 and 1988, a study was conducted in northern Nevada to examine root growth of cheatgrass (Bromus tectorum L.) and 2 native species, needle-and-thread grass (Stipa comata Trin. & Rupr.) and rabbitbrush (Chrysothamnus viscidiflorus (Hook.) NW.), after fire. Profile wall maps were used to determine the distribution of roots in the soil profile for the 2 native species. Root morphology differed between the 2 species: needle-and-thread grass had a flabelliform root system, whereas rabbitbrush had a main tap root with 2-4 major lateral roots. Although total root biomass differed between the species, more than half the root biomass was in the top 0.2 m of soil for both needle-and-thread grass and rabbitbrush. Measurements of root length density were used to evahmte the interaction between root systems of cheatgrass and the native species. Root production of plots with only the native species was not significantly different from that of plots with both the native species and cheatgrass for the first 2 years after fire. Furthermore, root production of plots in a recently burned area was also not significantly different from that in an area burned 12 years prior to our study. Thus, root systems of these species rapidly occupied the belowground space and competed for soil resources

Components of the organic matter were studied in soil under 3 Mixed Prairietypes: grasslnd dominated by needle-and-thread/blue grama (Stipa comata Trin. and Rupr./Bouteloua gracilis (HBK.) Lag. ex Steud.) in good range condition; grassland significantly modified by grazing, dominated by blue grama and in poor range condition; and grassland, dominated by needle-and-thread/blue grama in good range condition, but converted to cropland and under continuous wheat for 4 years. The soils were sampled on 13 April 1988. Concentrations of total organic carbon in the upper 2 cm were 1.39, 2.70, and 1.87%, respectively. The higher organic carbon under blue grama was caused by an active, ramified, fine rootmass which gave rise to most of the monosaccharides being of microbial origin. The monosaccharides in the lower Ap horizon in the cropland were generally of plant origin from incorporated

In perennial grassland dominated systems, belowground bud banks regulate plant community dynamics. Plant community responses to disturbance are largely driven by the ability to generate future aboveground growth originating from belowground axillary buds. This study examined bud bank dynamics for Bouteloua gracilis, Hesperostipa comata, and Pascopyrum smithii following fire in northwestern mixed-grass prairie in eastern Montana, USA. Belowground axillary buds were counted and classified for three growing seasons to determine immediate and short-term effects of summer, fall, and spring prescribed burns on patterns of bud bank activity, dormancy, and mortality. Prescribed burns did not result in immediate mortality of B. gracilis, H. comata, or P. smithii buds. Surprisingly, spring prescribed burns immediately increased the number of active B. gracilis buds. Summer fire, however, reduced B. gracilis active bud numbers. Fall burns immediately activated P. smithii buds, whereas fire did not influence any immediate bud dynamics for H. comata. Reduced bud numbers of H. comata may limit the ability to respond to fire. Season of fire directly manipulated bud activity, dormancy, and mortality for these species throughout the growing and dormant seasons following fire. Using season of fire to manipulate bud bank dynamics illustrates potential to improve post-fire management strategies based on known bud development trajectories and bud dynamics following fire.