• Characterization of Siberian wheatgrass germplasm from Kazakhstan (Poaceae: Triticeae)

      Jensen, K. B.; Asay, K. H.; Johnson, D. A.; Li, B. J. (Society for Range Management, 2000-05-01)
      Siberian wheatgrass [Agropyron fragile (Roth) Candargy] is known for its establishment and persistence on sandy soils under severe water limitations. Morphology, cytology, and forage and seed characteristics were studied on 59 accessions (JA) of Siberian wheatgrass collected on sandy soils in the desert areas of western Kazakhstan. Plants were grown at Nephi, Ut., from 1993 to 1996 and compared with the check cultivars of Vavilov and P-27 Siberian wheatgrass, and Nordan crested wheatgrass [A .desertorum (Fisch. ex Link) Schultes]. All JA-accessions were autotetraploids, 2n= 4x= 28. The most frequently observed meiotic association was 6 bivalents + 4 quadrivalents. The JA-accessions were morphologically diverse, ranging from short to tall in stature and from dark-green, glaucous to blue-green, strongly pubescent. Mean forage yield, crude protein, and dry matter digestibility were generally lower in the JA-accessions than the check varieties. Entry x year interactions were nonsignificant (P> 0.05) for all measured forage variables. Entries were significantly (P < 0.01) different for dry matter production. Seed weight of Vavilov and mean seed weight of JA-accessions were significantly (P < 0.01) greater than that for the check cultivars P-27 and Nordan. Entries that were highly pubescent had the heaviest seed and greatest capacity to emerge from a 7.6-cm planting depth. Seed yield plant -1 was significantly (P < 0.01) lower in the JA-accessions than cultivars Vavilov, P-27, and Nordan. Sufficient variations exist for seed yield, seed weight, seedling vigor, and forage yield within the JA-accessions to allow for the development of an agronomically suitable, drought tolerant Siberian wheatgrass through selection.
    • Cryptosporidium parvum transport from cattle fecal deposits on California rangelands

      Tate, K. W.; Atwill, E. R.; George, M. R.; McDougald, N. K.; Larsen, R. E. (Society for Range Management, 2000-05-01)
      Cryptosporidium parvumis a fecal borne protozoan parasite that can be carried by and cause gastrointestinal illness in humans, cattle, and wildlife. The illness, cryptosporidiosis, can be fatal to persons with compromised immune systems. At question is the potential for C. parvumin cattle fecal deposits on rangeland watersheds to contaminate surface water. First, C. parvum oocysts must be released from fecal deposits during rainfall, becoming available for transport. In 1996, we examined the transport of C. parvum oocysts in overland flow from fecal deposits under natural rainfall and rangeland conditions at the San Joaquin Experimental Range in Madera County, Calif. Our null hypothesis was that C. parvum oocysts are not released from fecal pats and transported 1 m downslope as overland flow with rainfall. Paired plots were located on 10, 20, and 30% slope sites.Each plot was loaded with four, 200 g fecal pats dosed with 10^5 oocysts g-1. Pats were placed 1.0 m above the base of each plot. Composite runoff samples from each plot were analyzed foroocyst concentration following each of 4 storm events. Oocysts were transported during each storm. Slope was a significant factor in oocyst transport, with oocyst transport increasing with slope. Although not significant, there was an apparent flushing effect of oocysts across storms, with the majority transported in the first 2 storms. A pilot rainfall simulation experiment also revealed a flushing phenomenon from pats during individual rainfall events. C. parvum oocysts in fecal pats on rangeland can be transported from fecal deposits during rainfall events, becoming available for transport to water-bodies. Future studies need to examine surface and subsurface transport of oocysts on rangeland hillslopes for distances greater than 1 m.
    • Economics of grazing weeping lovegrass with stockers in the Southern Great Plains

      Torell, L. A.; Kirksey, R. E.; Donart, G. B.; Libbin, J. D. (Society for Range Management, 2000-05-01)
      Because of the relatively low cost of seed and ease of establishment, more than 0.4 million ha of weeping lovegrass (Eragrostis curvula (Shrad.) Nees.) were planted on Conservation Reserve Program (CRP) lands in the Southern High Plains. Dryland cropping alternatives including wheat and grain sorghum, give relatively low and variable economic returns. The objective of this study was to evaluate the economics of the lovegrass grazing alternative. Using a tract of weeping lovegrass in Curry County, N.M., animal performance and the economics of 5 grazing management treatments were evaluated, including 12-month and 6-month continuous grazing, seasonal grazing during only the spring and fall, and a 6-pasture rotation system. Fertilization of the pastures was also evaluated for the spring/fall grazing treatment. Average daily gain (ADG) for yearlings grazing weeping lovegrass pastures was found to decline rapidly as the grazing season progressed. The ADG was over 1.36 kg day-1 in early May but gradually declined over the grazing season to less than 0.45kg day-1 by the end of August. To maximize profit, stocker cattl ewould be sold in early September. All of the grazing systems yielded similar net economic returns, but substantially high ereconomic returns could be made by adjusting stocking rates to market conditions. Returning CRP land to dryland cropping or grazing with stocker cattle was estimated to yield nearly identical economic returns. Neither growing traditional crops or grazing lovegrass pastures appear to be economically viable alternatives without government assistance programs in place.
    • Effect of grazing on the population biology of Phalaris aquatica

      Leiva, M. J.; Alés, R. F. (Society for Range Management, 2000-05-01)
      To examine the effect of grazing and potential interactions among grazing and biological traits of plants, we studied patch dynamics, seed production, and seedling survival in a Mediterranean population of the perennial grass Phalaris aquatica L. in grazed and ungrazed plots in southern Spain. Grazing by cattle induced an important (70%) decrease in the abundance of plants over 4 growing seasons. In the ungrazed plots, abundance of plants remained stable. Within these plots there was some (30%) spatial replacement of plants. However, replacement was by tillering and not by genets, genetically different individuals produced from seeds. The lack of genet replacement within the ungrazed plots agrees with results on mortality of young plants that were obtained from an independent field experiment, in which 85–95% of plants in different cohorts died within 1 to 3 growing seasons. This mortality of seedlings and young plants was concentrated in summers, especially when drought was prolonged. In contrast, seed production was apparently not a limit-ing factor for plant recruitment in ungrazed plots as seed output of the perennial grass (25,312 ± 3,255 seeds m-2) was of the same magnitude as seed output in annual grasses that were abundant in the study site. Intensive grazing limited tiller production, patch size, and a summer drought limited recruitment of new adult individuals. These factors resulted in a low tolerance to episodes of high stocking rates from which the perennial grasswas unable to recover.
    • Elk presence inside various-sized cattle exclosures

      Gross, J. A.; Knight, J. E. (Society for Range Management, 2000-05-01)
      Accurate measures of the relative resource impacts from elk (Cervus elaphus) and cattle (Bos taurus and B. indicus) improve land management planning wherever these species cohabitate. Comparisons of utilization inside and outside cattle exclosures are often used for this purpose. The objectives of our study were to determine if (1) elk presence differed inside and adjacent to several different-sized cattle exclosures; (2) there was a relationship between cattle exclosure size and elk presence in exclosures; and (3) a minimum cattle exclosure size is appropriate for assessing elk impacts. Seven different-sized cattle exclosures (4.00, 2.00, 1.00, 0.50, 0.25, 0.10, and 0.05 ha) were compared in western Montana during the spring of 1996 and 1997. Trackplots (1-m2 areas cleared of vegetation) were used to detect elk presence. Chi-square tests indicated elk presence inside all exclosures was less (P < 0.10) than elk presence adjacent to the exclosures. Regression analysis indicated exclosure size and elk presence were correlated (P < 0.03). Elk presence inside exclosures increased with increasing exclosure size. Our results did not support the minimum exclosure size (0.4 ha) recommended in the literature. Cattle exclosures larger than 4 ha appear needed to accurately measure relative resource impacts from elk and cattle; however, this does not ensure that an exclosure > 4.0 ha in size will solve all of the problems associated with this technique.
    • Forage removal and grazing time of cattle on small paddocks

      Broweleit, R. C.; Schacht, W. H.; Anderson, B. E.; Smart, A. J. (Society for Range Management, 2000-05-01)
      Animals used in grazing trials with small paddocks usually have not been exposed to the experimental site and related research procedures. Grazing trials conducted in May and August 1996 on smooth bromegrass (Bromus inermis Leyss.) quantified forage removal and grazing time of heifers adapted or not adapted to small paddocks. Treatments consisted of adapting heifers for 4 days to small paddocks (0.054 ha) and a control treatment of heifers continuously stocked in larger paddocks (>16 ha). On day 5, each group of heifers was moved to similar small paddocks and forage utilization and cattle grazing times were measured after 4 and 24 hours of grazing. In May, when sward structure was comparable in the large and small paddocks, tiller height reduction, leaf length reduction, herbage bio-mass reduction, and grazing time were similar (P > 0.10) for experienced and inexperienced heifers after 4 and 24 hours of exposure to day-5 paddocks. In August, when sward structure differed between the large and small paddocks, leaf length reduction after 4 hours was greater (P < 0.10) by experienced cattle than inexperienced cattle. Herbage reduction in August by experienced cattle was 435 kg ha-1 greater (P < 0.05) than by inexperienced cattle after 24 hours. Cumulative grazing time was 76 minutes (P < 0.10) greater at 4 hours for the experienced cattle than the inexperienced cattle. Grazing animals appear to adapt immediately to small paddocks but other unfamiliar grazing conditions, e.g., sward structure, may require short adaptation periods for experimental animals.
    • Herbivore dunging and endozoochorous seed deposition in a Mediterranean dehesa

      Malo, J. E.; Jiménez, B.; Suarez, F. (Society for Range Management, 2000-05-01)
      Spatial patterns of herbivore defecation within grazing systems are important as they directly affect pasture growth and composition. These effects are partially linked to seed dispersal in dung, a little studied process. This paper focuses on: (i) quantification of dung and seeds deposited by herbivores in a Mediterranean grazing system, and (ii) analysis of the spatial variability of dung and seeds deposited within and among plant communities. We carried out year-long monthly quantifications of the depositions of rabbit (Oryctolagus cuniculus), fallow deer (Dama dama), red deer (Cervus elaphus), and cow (Bos taurus) dung to 32 plots distributed in Quercus rotundifolia Lam. and Fraxinus angustifolia Vahl woodlands, mixed scrub, and Cistus ladanifer L. scrub. We also quantified the germinable seed content of dung. The results revealed differences (p < 0.05) in dung deposition, varying (I) among the 4 species, (ii) within species (except for the red deer) among plant communities, and (iii) within plant communities. An average of 735 seeds/m2 were returned to the soil via dung, with the highest numbers in open woodlands (870–1,888 seeds/m2) and the lowest numbers in scrubs (83–315 seeds/m2). Cows dispersed the most seeds (68%), followed by red deer (20%), rabbits (7%), and fallow deer (5%). Spatial variability in deposition led to accumulations of up to several thousand seeds at points covered by the dung. The effect of seed input to the seed bank and on vegetation may be low at large and medium-sized spatial scales, but it can be very important at small scales and for colonization processes.
    • Late season toxic alkaloid concentrations in tall larkspur (Delphinium spp.)

      Gardner, D. R.; Pfister, J. A. (Society for Range Management, 2000-05-01)
      Tall larkspurs [Delphinium barbeyi (L. Huth), D. occidentale (Wats.), D. glaucescens (Rydb.), D. glaucum (Wats.)] pose a serious poisoning threat to cattle on many summer ranges. Livestock producers often defer grazing until larkspur is mature, but specific information is lacking on toxic alkaloid concentrations in larkspur from pod stage to senescence. Tall larkspur leaves and seed pods were collected about every 2 weeks during the pod stage to senescence from marked plants in locations in Utah (Logan and Salina), Idaho (Ashton, Humphrey, and Oakley), Colorado (Yampa and Montrose), and California (Carson Pass) from 1995 to 1997. Toxic alkaloid concentions in pods (average= 2.9mg/g) exceeded leaf alkaloid concentrations (average= 1.5 mg/g in all species, but the magnitude of the difference varied among the 4 species. Leaves showed a more rapid decrease in toxic alkaloid concentration with plant maturity compared to pods. Seed pods did not begin to lose substantial amounts of toxic alkaloid until larkspur matured and pods began to dessicate. At seed shatter, D. glaucescens pods retained more toxic alkaloid than the other species, and alkaloid concentration was sufficiently high after pods had shattered (3.5 mg/g) to pose a moderate grazing risk. After seed shatter, the toxic alkaloid concentrations in leaves and pods of D. barbeyi, D. occidentale, and D. glaucum were generallyless than 2 mg/g; thus, risk of losing cattle would be low for the remainder of the grazing season
    • Livestock effects on reproduction of the Columbia spotted frog

      Bull, E. L.; Hayes, M. P. (Society for Range Management, 2000-05-01)
      We evaluated reproduction and recruitment of the Columbia spotted frog (Rana luteiventris Thompson) in 70 ponds used by beef cattle and in 57 ponds not used by beef cattle in northeastern Oregon. No significant differences were detected in the number of egg masses or recently metamorphosed frogs in grazed and ungrazed sites. No pond characteristic measured could predict egg mass numbers, but percent aquatic vegetation and dissolved oxygen had some ability to predict recently metamorphosed frog numbers. Both variables explained 65% of the variability in recently metamorphosed frog numbers in grazed ponds. At ungrazed ponds, 4 additional variables (presence of fish, elevation, percent of rock, and conductivity) were required to achieve the same level of variability in predicting recently transformed frog abundance. The egg mass volume was larger at grazed than at ungrazed ponds suggesting that grazed ponds may have a greater food abundance or larger (older) individuals.
    • Livestock guard dogs reduce predation on domestic sheep in Colorado

      Andelt, W. F.; Hopper, S. N. (Society for Range Management, 2000-05-01)
      We surveyed the effectiveness of livestock guard dogs for reduc-ing predation on domestic sheep in Colorado during 1993. The number of producers using dogs increased from about 25 in 1986 to >159 in 1993. The proportion of sheep with dogs increased from about 7% in 1986 to about 68% in 1993. Producers with dogs, compared to producers without dogs, lost smaller proportions of their lambs to predators, especially coyotes (Canis latrans Say), and smaller proportions of ewes and lambs to black bears (Ursus americanus Pallas) and mountain lions (Felis concolor L.). Overall, producers who did not have guard dogs lost 5.9 and 2.1 times greater proportions of lambs to predators than producers who had dogs in 1986 and 1993, respectively. Proportions of sheep killed by predators decreased with the number of years that producers used guard dogs. Mortalities of ewes to predators regardless of type of operation and lamb mortality on open range decreased more from 1986 to 1993 for producers who obtained dogs between these years compared to producers who did not have dogs. Of 160 producers using dogs, 84% rated their dogs overall predator control performance as excellent or good, 13% as fair, and 3% as poor. More producers (n = 105) indicated effectiveness of their dogs did not change with time, compared to producers (n = 54) indicating effectiveness changed. More producers (n = 35) also indicated their dogs became more effective over time compared to producers (n =19) indicating their dogs became less effective. Estimates provided by 125 producers indicate that their 392 dogs saved 891,440 of sheep from predation during 1993. A total of 154 of 161 (96%) producers recommend use of guard dogs to other producers.
    • Observations of predator activity at wildlife water developments in southern Arizona

      DeStefano, S.; Schmidt, S. L.; DeVos, J. C. (Society for Range Management, 2000-05-01)
      Wildlife water developments have been constructed and maintained throughout the arid western United States to benefit big game and upland gamebird populations. There is debate, however, over possible detriments to wildlife from artificial water sources in deserts and other arid environments. One concern is that water developments attract predators, which then impact the prey populations that these developments are intended to benefit. To examine the extent of predator activity around water developments, we examined 15 paired water and non-water (random) sites for sign (scats, tracks, visual observations, animal parts such as feathers and bones, and carcasses) of predators and prey. Predator sign was 7x greater around water sites than non-water sites (P = 0.002). Coyote (Canis latrans Say) sign accounted for 79% of all predator sign and was 7x greater near water than away from water (P = 0.006). Amount of sign for all prey species combined was not different between paired sites (P = 0.6), but results for individual species and groups of species was variable; passerine and gallinaceous bird sign was greater around water sites (P = 0.008), ungulate sign was not different between water and non-water sites (P greater than or equal to 0.20), and lagomorph sign was almost 2x greater away from water than near water (P = 0.05). Predators were probably attracted to wildlife water developments to drink rather than hunt; without water developments, predators may be even more concentrated around the fewer natural water sites.
    • Picloram, fertilizer, and defoliation interactions on spotted knapweed reinvasion

      Jacobs, J. S.; Sheley, R. L.; Carter, J. R. (Society for Range Management, 2000-05-01)
      Spotted knapweed (Centaurea maculosa Lam.) management may be enhanced by integrating strategies that stimulate and maintain competitive grasses. The objective of this study was to determine if picloram, fertilizer, and timing and frequency of grass defoliation could be integrated to minimize spotted knapweed reinvasion. Sixteen chemical treatments [4 picloram rates (0.00, 0.14, 0.28, and 0.42 kg a.i. ha- 1) and 4 fertilizer rates (source: 16-20-0, N-P-K; material: 0.0, 66, 132, 198 kg ha-1)] were applied in the spring of 1994 to 4 by 4 m plots and factorially arranged in a randomized-complete-block design. Within each plot, 6 grass defoliation treatments were randomly applied to 1 by 1 m sub-plots. From 1994 through 1997, 60% of the aboveground grass biomass was hand clipped and removed from the plots during the spring, summer, fall, alternating spring/fall, all 3 seasons. A control received no grass defoliation. The experiment was replicated 4 times at 2 sites dominated by spotted knapweed. At peak standing crop in 1997 spotted knapweed density, grass and spotted knapweed biomass; and percent cover of spotted knapweed, grass, litter, and bare ground were measured. Data were analyzed as a split-plot using analysis of variance. Four years after treatment all rates of picloram reduced spotted knapweed density, biomass, and cover, and increased grass yield. Nitrogen and P fertilizer tended to increase spotted knapweed density and biomass. Nitrogen and P fertilizer plus defoliation in all 3 seasons caused a greater increase in spotted knapweed reinvasion at the site with Kentucky bluegrass (Poa pratensis L.) than the site with timothy (Phleum pratense L.) and smooth brome (Bromus inermis Leys.). Fall-only defoliation and no defoliation appear to deter spotted knapweed reinvasion better than defoliation in all 3 seasons and alternately in the spring and fall.
    • Postburning legume seeding in the Flooding Pampas, Argentina

      Juan, V. F.; Monterroso, L.; Sacido, M. B.; Cauhépé, M. A. (Society for Range Management, 2000-05-01)
      In Argentina, Paspalum quadrifarium Lam. (paja colorada) forms tall dense grassland communities in the flooding pampas. Referred to locally as “pajonales”, these grasslands generally have very low nutritional value for cattle, except at the post-burn regrowth stage. To improve forage quality and consumption by breeding cattle, Lotus tenuis Walst et Kit. is over seeded immediately after burning of paja colorada pajonales. The objectives of this experiment were to follow the after seeding cover of lotus, evaluate weed control, and assess disease incidence and severity.The experiment was carried out in Azul, Buenos Aires provinceof Argentina, between September 1993 to September 1996. The postburn seedbed was very favorable for lotus germination and establishment. The most effective chemical weed control was obtained with 2,4-DB used alone or in combination with dicamba. Lotus increased markedly the quality of the pasture forage due to its high crude protein content. Four fungus diseases were found: Botrytis cinerea Pers., Stem phylium sp. Wallroth, Uromyces loti Blytt. and Fusarium spp. Link ex Fr. However, these caused only light foliar damage and did not impair lotus germination or establishment. The overseeding of lotus after burning of P. quadrifarium pajonales, is a very effective technique to improve carrying capacity and animal performance.
    • Quantifying spatial heterogeneity in herbage mass and consumption in pastures

      Hirata, M. (Society for Range Management, 2000-05-01)
      A sward-based technique for quantifying the spatial heterogeneity in herbage mass and consumption was developed and tested in a bahia grass (Paspalum notatum Flügge) pasture grazed by cattle. For five, 2-day grazing periods from May to October, pre- and post-grazing herbage masses were nondestructively estimated with an electronic capacitance probe at 182, 50x50 cm locations along 2 permanent line transects. At the same time, undisturbed herbage accumulation during grazing was measured inside exclosures and the results used to estimate accumulation under grazing at each location. Estimation of herbage mass was relatively good; R2= 0.88 to 0.98. Spatial heterogeneity in herbage mass and the stability of the spatial pattern were well quantified. The pattern of spatial heterogeneity observed early in the grazing season remained quite stable for 5 months until the late grazing season. Spatial heterogeneity in the rate of defoliation was also well quantified in spite of some negative values. The technique is of potential value for quantifying the spatial hetero-geneity in herbage mass and consumption by animals in grazed pastures, though further studies are necessary for testing the applicability of the technique to pastures of other plant species or of multiple species.
    • Soil properties and species diversity of grazed crested wheatgrass and native rangelands

      Krzic, M.; Broersma, K.; Thompson, D. J.; Bomke, A. A. (Society for Range Management, 2000-05-01)
      Crested wheatgrass (Agropyron cristatum (L.) Gaertn.) is an introduced grass used extensively for rangeland revegetation in the semiarid and arid regions of western North America. The long-term effects of crested wheatgrass on soil properties and plant community were evaluated on 5 grazed sites in the southern interior of British Columbia, Canada. Each site included plant communities of native bluebunch wheatgrass (Pseudoroegneria spicata (Pursh) Scribn. & Smith) and 14- to 60-year-old stands of crested wheatgrass. Soil samples and plant data were collected in June 1997. Species numbers were similar for native and crested wheatgrass rangelands, while the diversity index of crested wheatgrass rangeland was lower due to lower evenness. Crested wheatgrass and native grasses were observed to produce similar amounts of root biomass. Most soil properties were similar under the 2 rangelands. One of the exceptions was soil carbon at 0–7.5 and 7.5–15 cm depths, which was higher on crested wheatgrass than native rangeland. Soil nitrogen at 15–30 cm depth was also higher on crested wheatgrass rangeland. Greater soil penetration resistance was observed at 7.5 and 9 cm depths on crested wheatgrass than native rangeland. Higher soil compaction was caused by grazing of crested wheatgrass earlier in the season when soils are wetter relative to the native rangeland. The results of this study indicate that seeding of crested wheatgrass combined with the long-term grazing by cattle did not result in the degradation of soil properties, but plant diversity was reduced relative to grazed native, bluebunch wheatgrass rangeland.
    • Viewpoint: Selecting the 5 most important papers in the first 50 years of the Journal of Range Management

      McClaran, M. P. (Society for Range Management, 2000-05-01)
      A graduate seminar to select the 5 most important papers published in the first 50 years of the Journal of Range Management (JRM), 1948–1997, cultivated an appreciation for the development of the discipline of rangeland science and management, and provided some historical perspective to judge the JRM. A review of textbooks, and papers describing early milestones and the use of citation counting were helpful in developing criteria to discriminate the importance of papers. The greatest disagreement among the 9 participants focused on the use of citation counts as a criterion: 2 students used only counts and 3 students refused to use counts. Eighteen papers received at least 1 vote as a top 5 paper, and 2 plant succession-vegetation monitoring papers were clearly the most popular. The exercise revealed that discontent with the JRM is not new. Although the JRM now covers a wider variety of topics, including both reductionist and synthetic works, some students felt that it was less encompassing of multiple values of rangelands and the breadth of rangeland science than recent texts. The students found that the selection of important papers expanded their understanding of the discipline and their resolve to publish in the JRM. Ideally, others will be challenged to perform this review for the benefit of students, the discipline, and the JRM.
    • Western ragweed effects on herbaceous standing crop in Great Plains grasslands

      Vermeire, L. T.; Gillen, R. L. (Society for Range Management, 2000-05-01)
      Western ragweed [Ambrosia psilostachya DC. ], a major forb species in mixed and tallgrass prairies, is considered to have little value for cattle grazing but is an important food item for bobwhite quail [Colinus virginianus]. While often thought to be a strong increaser with grazing pressure, information on the actual relationship between western ragweed and grasses is contradictory. Our objectives were to 1) determine the effect of western ragweed on grass standing crop, and 2) determine the effect of vegetation type and grazing on survival and shoot morphology of western ragweed. Western ragweed did not appear to reduce grass standing crop. Instead, standing crop (40 to 620 kg ha-1) and density (6 to 41 shoots m-2) of western ragweed were positively related to grass and grass-forb standing crop in mixed prairie. Standing crop of western ragweed was not related to grass standing crop in tallgrass prairie. Competitive thresholds for western ragweed in mixed and tallgrass prairies appear to be above the levels observed in this study. Density of western ragweed shoots decreased over the growing season under both grazed and ungrazed treatments. Survival of western ragweed shoots from June to September was greater in mixed prairie (81%) than in tallgrass prairie (63%) and was greater in ungrazed (76%) than grazed plots (68%). Western ragweed shoots weighed less per unit of height in tall grassprairie. Western ragweed shoots in ungrazed plots were taller than shoots in grazed plots but weighed less per unit of height. These differences in shoot morphology are consistent with increased competition for light in tallgrass prairie and in ungrazed sites. Western ragweed may not directly reduce grass standing crop but, rather, increase only when grasses are reduced by other stresses such as improper grazing.