An understanding of the impacts of grazing during and following drought on rangeland ecosystems is critical for developing effective drought management strategies. This study was designed to examine the effects of drought and grazing on blue grama [Bouteloua gracilis (H.B.K) Lag. ex Griffiths] and western wheatgrass [Pascopyrum smithii Rydb. (Love)] tiller growth dynamics. Research was conducted from 1993 to 1996 at the Fort Keogh Livestock and Range Research Laboratory located near Miles City, Mont. An automated rainout shelter was used during 1994 to impose a severe late spring to early fall (May to October) drought on 6 of twelve, 5- x 10-m non-weighing lysimeters. Twice replicated grazing treatments were: 1) grazed both the year of (1994) and the year after (1995) drought; 2) grazed the year of and rested the year after drought; and 3) no grazing either year. Drought had minimal impact on tiller relative growth rates of plants grazed twice, although it reduced (P less than or equal to 0.01) rates of axillary tiller emergence for blue grama (79%) and western wheatgrass (91%). Defoliation periodically increased relative growth rates (P less than or equal to 0.05) and tiller emergence (P less than or equal to 0.01) of both species. Neither drought nor grazing affected tiller densities or tiller replacement rates of either species nor did they affect productivity of blue grama. Drought, however, reduced (P less than or equal to 0.01) productivity of western wheatgrass 50% in 1994 whereas grazing reduced productivity (P less than or equal to 0.01) by 46% in 1994 and 69% in 1995. Moderate stocking levels (40-50% utilization) during and after drought did not adversely affect the sustainability of these dominant native grasses.

Presence of annual bromes (Bromus spp.), introduced annual weedy grasses, can alter seasonal patterns of forage production and quality and require management changes for efficient use of infested rangelands. We determined biological impacts of the presence of brome by comparing livestock performance on brome infested rangeland to similar sites on which brome had been suppressed by autumn application of atrazine [6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine] at 0.56 kg ha(-1) in 1992 and 1993. Each treatment was randomly assigned to three, 12-ha pastures. Vegetation was measured for 5 months (May to September) each year from 1993 to 1995. Each pasture was stocked with 8 crossbred steers of British breed origin (Bos taurus) from mid-May to mid-September 1993 and 1995 and to mid-August 1994. Initial body weights averaged 329 kg SD = 31 in 1993, 273 kg SD = 14 in 1994, and 272 kg SD = 21 in 1995. Brome suppression and environment influenced plant species in diets, diet quality, and livestock performance. Brome suppression reduced percentage of annual grasses in diets from 14% to 10%. Annual grasses were replaced in the diet by a variety of forb and grass species {western wheatgrass [Pascopyrum smithii Rydb. (Love)], and blue grama [Bouteloua gracilis [H.B.K.] Lag. ex Griffiths]}, with specific replacement depending on year and month. Steer gains were increased from 0.92 to 1.04 +/- 0.02 kg head(-1) day(-1) (P < 0.02) and from 69 to 81 +/- 2.8 kg ha(-1) (P < 0.05) with brome suppression. This experiment demonstrated that improvement in livestock performance can be expected with the suppression of annual bromes on semiarid rangelands.

Drought and herbivory frequently influence North American rangelands. While these influences may temporarily reduce vegetative cover, their mutual influence on the available seedbanks which might occupy new safe sites is unclear. We examine effects of drought and grazing upon pre- and post-drought plant root distribution and germinable seed bank to determine 1) if the response of root distributions to drought depends upon grazing use and 2) if the presence of germinable seeds is altered significantly by drought and grazing. Using twelve, 5 X 10 m nonweighing lysimeters with an automated rainout shelter, we documented root intercepts in situ using a minirhizotron from 1993-1996, Seed bank samples were incubated in a greenhouse to determine seedling emergence. Roots were fewer in shallow soil layers in grazed plots than ungrazed plots by the end of the study, irrespective of drought, Roots in deeper (Bw horizon) soil layers were fewer during drought, but were not influenced by grazing. Seed bank composition results suggest that perennial grasses were a small portion of the seed bank. Cool-season annual grass seeds accumulated after drought. Without drought, forb seed banks increased with grazing, Thus while shallow roots may decrease during drought, in the year following drought grazing may decrease aboveground net primary production, and allow Large accumulations of cool-season annual grass seed in a northern mixed grass prairie.

This research addresses the hypothesis that grazing intensity during and following drought can dramatically alter community level, post-drought recovery patterns, Research was conducted during the 1993 through 1996 growing seasons at the Fort Keogh Livestock and Range Research Laboratory located near Miles City, Mont. Study plots were twelve, 5 x 10-m non-weighing lysimeters constructed in 1992 on a gently sloping (4%) clayey range site. An automated rainout shelter was constructed to control the amount of precipitation received on 6 lysimeters during the 1992 growing season. We conclude from study results that the independent and combined effects of the imposed late spring to early fall drought and associated grazing treatments were minimal relative to soil water dynamics and aboveground net primary production although both grazing treatments reduced herbage standing crops. We attribute the absence of a strong response to the drought to its timing (i.e., late growing season) in that most herbage production in these cool-season dominated grasslands is completed by early summer. Thus, annual production processes in these grasslands avoided the major impacts of the drought. The results do not provide convincing evidence, however, that would lead us to completely reject our original hypothesis. Rather, they simply provide evidence that these grasslands are well adapted to surviving late growing season drought with or without intensive grazing by ungulates.

The sustainability of natural grasslands is in large part dependent upon the successful ingress and propagation of alien plant species. We attempted to characterize the propagation potential of the dominant plant species of a southeastern Montana mixed-grass prairie community including two introduced grasses, Bromus japonicus and B. tectorum. Aboveground standing crops and densities of seeds were estimated on 10 dates between September 1991 and August 1993 and seedling densities were estimated on 21 dates between September 1991 and July 1993. Total aboveground standing crop ranged from about 110 to 340 g m(-2) and was dominated by three grasses: Bouteloua gracilis, a warm-season, perennial; Pascopyrum smithii, a fool-season, perennial; and B. japonicus, a cool-season, annual grass. Seed production was dominated by B. japonicus (similar to 10,400 seeds m(-2)). Bouteloua gracilis and P. smithii seed production was negligible with maximum densities of about 120 and 25 seeds m(-2), respectively. Density of seedlings was greatest for B. japonicus (similar to 2100 seedlings m(-2)), Festuca octoflora (similar to 1100 seedlings m(-2)), and Plantago patagonica (similar to 350 seedlings m(-2)). Maximum number of B. gracilis seedlings was 25 m(-2). No P. smithii seedlings were observed during the study. Temporal differences in seedling densities were closely tied to late summer-early fall precipitation patterns. Although community-level seed production and seedling establishment processes were dominated by B. japonicus, the overwhelming presence of herbage produced by the two vegetative propagating species, B. gracilis and P. smithii, casts doubt on a trend in ecological succession toward an annual grass-dominated community.

Japanese brome (Bromus japonicus Thunb.) has invaded many northern mixed prairie communities. Understanding how defoliation affects the life cycle of this species is critical for proper grazing management of communities infested with this annual. The objective of this study was to determine the effect of defoliation on growth of Japanese brome. Treatments included no clipping or clipping to 75- or 150-mm stubble height weekly or biweekly for 65 to 70 days in a greenhouse. Response of Japanese brome tiller numbers, leaf height, and above- and below-ground biomass were measured in 1991, 1992, and 1997. Clipping vegetative plants in 1991 reduced tiller numbers and leaf heights, whereas clipping plants with reproductive shoots in 1992 and 1997 increased tiller numbers and reduced leaf heights. Herbage accumulated during clipping, above-ground and total biomass were similar in 1991 and 1997, but lower in 1992. Accumulated herbage was reduced by reducing stubble height from 150 mm to 75 mm on a biweekly frequency and increasing the frequency of clipping from biweekly to weekly at either the 150-mm or 75-mm stubble height. Reducing the stubble height also reduced above-ground and total biomass. Increasing frequency of clipping did not generally affect total biomass. Some inflorescences were produced with even the most severe clipping treatment.

Japanese brome (Bromus japonicus Thunb,) and downy brome (Bromus tectorum L,), introduced annuals, have invaded many northern mixed-prairie plant communities. This study determined the effect of removing Japanese brome and clipping western wheatgrass [Pascopyrum smithii Rydb, (Love)] on aboveground forage production of a western wheatgrass dominated northern mixed-prairie community. During early spring 1993, a wet year, and 1995, a drier year, western wheatgrass tillers were clipped to ground level in May or June and Japanese brome seedlings were left undisturbed or removed in circular, 1-m(2) plots on a clay-pan field site. Western wheatgrass standing crop and tiller densities were estimated by clipping and counting in May and June, and these plus community standing crops were estimated in all plots after Japanese brome matured in mid July. Year effects were significant for standing crop and tiller density due to annual variation in amount and distribution of fall, spring, and early summer precipitation. Conditions were most favorable for tiller initiation of western wheatgrass and germination of annual brome seed in fall 1994 and for herbage production in 1993, Clipping western wheatgrass tillers reduced accumulated standing crop 230 to 350 kg ha(-1) and reduced tiller weight by 17 to 58%. Standing crop of western wheatgrass was increased 102 kg ha(-1) with removal of Japanese brome, while total standing crop was reduced 284 kg ha(-1) with brome removal. Increased standing crop of western wheatgrass appeared to result from increased tiller density rather than increased tiller weight. Removal of Japanese brome from northern mixed-prairie plant communities may increase production of associated perennial grasses, but managers should also expect a short-term decrease in total standing crop.

Mismanagement of livestock can result in herbivory on Pinus seedlings with potential for growth loss. From 1986 to 1990 on a conifer plantation in the Mixed-Conifer Zone of southwestern Oregon we measured the aboveground growth of ponderosa pine (Pinus ponderosa Douglas ex Lawson & C. Lawson var. ponderosa) seedlings that had sustained (1) removal of terminal stem or bud tissue by cattle, and (2) no removal (control). In 1990 (year 5 of the plantation), cumulative, absolute height and stem volume on seedlings that sustained terminal tissue removal were similar to control seedlings. In 1988, relative height growth was comparable between control seedlings and seedlings sustaining tissue removal in May 1987. In contrast, 1988 relative height growth was -22% (P < 0.05) for seedlings sustaining tissue removal in August 1987, compared with control seedlings. Relative stem volume growth in 1988 ranged from -21 to -26% (P < 0.05) for seedlings sustaining tissue removal in (I) August 1987, (2) April or May 1988, and (3) 1987 and 1988, compared with control seedlings. Reduced relative growth was short-term. Relative growth rates for seedlings sustaining tissue removal were comparable to control by the first or second year after removal. Seedlings sustaining tissue removal before winter bud set (April and May) were more likely to recover by the first year than seedlings sustaining tissue removal after winter bud set (August). We propose that if silviculturists prescribe cattle grazing early in the growing season and terminal tissue is removed at that time, they can still achieve understory vegetation control and enhanced soil water availability without jeopardizing longterm aboveground growth of ponderosa pine. The lack of spatial replication of treatments (terminal tissue removal dates) limits spatial extrapolation of our findings. The credibility of our findings should be tested with additional research on the growth response of ponderosa pine seedlings subsequent to actual livestock herbivory, conducted with spatially replicated treatments.

Japanese brome (Bromus japonicus Thunb.) has invaded many northern mixed-prairie plant communities, Understanding interactions of population dynamics of this and associated species is critical for proper management of communities infested with this annual, Objectives of this study were to determine the effect of Japanese brome removal on aboveground forage production and daily plant water relations of western wheatgrass [Pascopyrum smithii Rydb, (Love)] and Japanese brome in a western wheatgrass dominated northern mixed grass prairie community, During early spring of 1991, a wet year, and 1992, a dry year, 2 treatments, undisturbed and complete (total) removal of Japanese brome seedlings, were applied by hand at silty clay loam and clay field sites in circular, l-mz quadrats, Vegetation in additional quadrats was left undisturbed or Japanese brome was removed to assess plant water relations at each site in 1992, Total standing crop was reduced 500 kg ha(-1) with removal of Japanese brome, while standing crop of western wheatgrass was increased 220 kg ha(-2) with Japanese brome removal, Increased standing crop of western wheatgrass appeared to result from increased tiller density of 153 tillers m(-2) rather than increased weight per tiller. Western wheatgrass water relations were essentially unaffected by Japanese brome removal in 1992, Removal of Japanese brome from Northern Great Plains plant communities may increase production of associated perennial grasses, but managers should also expect a short-term decrease in total standing crop.

Mineral concentrations of range grasses are often below that required by grazing livestock. Limited information is available on forage mineral concentrations for the Northern Great Plains and there is little data on factors influencing concentrations of forage minerals throughout the year. Therefore, a study was conducted to evaluate spacial and temporal variations in mineral concentrations of major forage species in the Northern Great Plains. Herbage was sampled from 4 replicates on each of 2 soils in July, August, and September 1991, April, June, July, August, and September 1992, and April 1993. Herbage was sorted by species grouping and by live and dead tissue classes. Analyses on herbage included Ca, P, Mg, K, Na, Zn, Cu, Mn, and Mo. For western wheatgrass [Pascopyrum smithii (Rydb.) Love] and annual bromes [Bromus spp.], Zn and all macrominerals except Na were greater in live than in dead tissue. Live tissues of all other species groupings contained greater amounts of P and K than did dead tissue. Live tissue Mg concentrations were greater than dead tissue concentrations for other cool-season and warm-season grasses. Manganese concentrations were greater in live than dead annual brome tissues, while Cu was greater in dead than five tissue. Dead sedge tissue contained greater concentrations of Ca than five tissue. Soil type affected several nutrients but this was partially related to soil effects upon composition of species groupings and live:dead ratios. Minerals most likely to be found in quantities less than required for animal production were P, Na, K, Zn, and Cu.

Quantity and quality of forage produced are primary determinants of level of livestock production derived from grazing lands, Moreover, species composition of herbage is often considered a primary determinant of the ecological condition of rangelands, The broad objective of this study was to quantify the productivity, growth dynamics, and quality of herbage growing on 2 Northern Great Plains range sites and to concurrently relate magnitude and composition of production to the ecological condition of the sites, Using frequent harvest techniques, the 2-year study showed herbage production on the highly productive silty range site averaged 219 g m(-2) as compared to 218 g m(-2) on the supposedly less productive Clay pan range site. The primary reason the clay pan site proved to be as productive as the silty site was attributed to the greater amounts of introduced annual grasses on the clay pan (148 g m(-2)) than the silty site (104 g m(-2)), The annual grass component on the clay pan was a near equal mix (71 vs 51 g m(-2)) of Japanese brome (Bromus japonicus Thunb,) and cheatgrass (B. tectorum L,) whereas the ovenwhelming dominant on the silty site was cheatgrass (73 g m(-2)), Western wheatgrass [Pascopyrum smithii Rydb, (Love)] was the dominant perennial grass on both sites averaging 49 g m(-2) on the clay pan site and 57 g m(-2) on the silty site, There were minimal differences between sites in terms of nutrient quality values (i.e., crude protein, acid detergent fiber, neutral detergent fiber) with results showing clearly that age of tissue was the major factor altering seasonal forage quality values, Range condition analyses revealed the clay pan site was in fair ecological condition and the silty site was in good condition, Study results demonstrate the need for land management agencies to continue to refine productivity estimates as well as adopt new techniques for assessing the ecological condition of rangelands.

Japanese brome (Bromus japonicus Thunb,), an introduced annual grass, is now common in some northern mixed-prairie communities, This species has the potential to alter both the seasonality of standing crop and forage quality, We sought to gain a greater understanding of Japanese brome seed germination by subjecting seed to a series of 55 constant or alternating temperature regimes following 3 to 9 months of dry laboratory storage, Cold and moderate temperature regimes provided optimum germination conditions (defined as not lower than the maximum observed minus one-half its confidence interval at the 0.05 level of probability), Extremely cold or warm temperatures suppressed germination, Germination of afterripened seed over a wide range of temperature combinations, many of which occur during fall in the Northern Great Plains, should enhance establishment and perpetuation of Japanese brome on rangelands.

The forage disk meter, a double sampling device used to predict forage biomass, has been used extensively on improved pastures, but its use on rangelands has not been investigated thoroughly. Efficiency of the forge d&k meter was investigated in predicting yields of forage biomass on different range sites in western Kansas. Using le8st sqtmres regression methods, resting heights (forage buik) and dry matter yields were used to calibrate the disk meter for eachsiteands8mplingd8te.HighiysignKiantregressiom(F<0.ooo1) were obtained on l U tbe shortgrass sites, where several factors that had unfavorable effects on the regression relationship between fornge bulk and forage biomass were not apparent. These factors, although not quantified, included l ccumul8tion of litter, microrelief, lodged vegetation, and presence of broadleaf species. Regression coeffkients (b) and intercepts (a) varied between sites and dates, thus the forage disk meter should be calibrated for every range site. If 8 forage disk meter is calibrated for a specific range site, regression coefficients utd intercepts might not differ from yeu to year if grazing pressure and species composition are temporally consistent, which implies that recalibration might be unnecessary. The forage disk meter was useful as a double sampling device on range sites dominated by sbortgrawes, but its use was limited on areas dominated by mual forbs or midgrasses.