Tebuthiuron was evaluated at two Wyoming locations for its effects on big sagebrush control and associated vegetation, Big sagebrush was controlled with tebuthiuron at 0.6 to 1.1 kg ai/ha. Green needlegrass, prairie junegrass, blue grama, and Douglas rabbitbrush were unaffected by tebuthiuron treatments. Western wheatgrass and downy brome increased at different study locations and were dominant grass species at the end of 7 yr.

The control of western juniper (Juniperus occidentalis Hook.) trees released shrub and herbaceous vegetation from dominance of the tree overstory. Revegetation of the woodland with desirable browse and forage species required weed control of both shrub and herbaceous species. The method of tree control (herbicidal, mechanical, or wood harvesting) influenced subsequent weed control-revegetation options in the understory. Physical restraints imposed by standing dead trees resulting from picloram (4-amino-3,5,6-trichloropicolinic acid) treatment limited the use of weed control and seeding equipment. Accumulation of litter interfered with the use of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] for annual grass control on both the picloram and wood harvest plots. Establishment of forage species was most successful on the mechanically cleared plots. Attempts to revegetate with browse species were largely foiled by native herbivores, and selective predation occurred on herbaceous species.

Survival and growth of five collections of big sagebrush were compared in reciprocal transplant gardens. The study was designed to further the understanding of seedling ecology of this important rangeland plant. Survival of transplanted seedlings was not tied to their origin, but antagonism for collection site in survival was apparent for some collections. The site with the highest environmental potential as indexed by native plant community, soil development, and precipitation had the poorest seedling survival. The site with the lowest environmental potential produced seedlings that had the highest survival across all reciprocal gardens. The average mortality level after 3 yr was 11%, indicating that seedlings of big sagebrush can be transplanted successfully. In dry years, the collection from the driest location had the highest amount of juvenile biomass accumulation. However, during a season with much above-normal precipitation this was reversed and the amount of growth for this source was below levels observed for the dry years. The relation between subspecies of big sagebrush and survival or growth of the collections used in this study was not clear. Because collections were made on arid extremes of the subspecies they may reflect introgressive populations among subspecies.

Establishment of seedlings of big sagebrush subsequent to range weed control treatments limits the economic feasibility of such treatments for increased forage production. This study investigated the dynamics of seed production by this species as one step in understanding seedling establishment. Studies were conducted on five different ecological sites along the arid extremity of big sagebrush distribution in western Nevada. Demography, physical dimensional parameters, biomass, and community structure were determined for each site and related to seed production over a 4-yr period. In addition, seeds harvested from each site were used to grow plants that were transplanted to establish reciprocal gardens at all sites. Seeds were subsequently harvested from the plants in these gardens. The average stand studied was capable of producing about 50 million seeds/ha annually. The plant characteristics most closely correlated with seed production were leaf weight, canopy density, and root crown diameter. The stand that consistently had the highest average seed production had the lowest woody biomass accumulation rate. In reciprocal gardens, plants grown from this stand had the highest average seed production. Seed production of big sagebrush plants appears to be related to site characteristics, shrub biomass characteristics, and inherent genetic potential of the plants in a given collection.

Sagebrush control has historically involved mechanical and chemical (2,4-D) treatments designed for total control and which detrimentally affect nontarget plant species, resulting in decreases in native wildlife abundance and diversity. Tebuthiuron, a potentially selective herbicide with thinning capabilities, was applied at various rates to big sagebrush plots near Ten Sleep, WY in 1979 and Hyatteville, WY in 1983. Plant and small mammal communities were evaluated in 1992 and 1993. Big sagebrush cover in untreated areas was 31 ± 1% in 1992 and 34 ± 1% in 1993 at Ten Sleep, and 44 ± 4% at Hyatteville (α = 0.10). Big sagebrush control increased as application rate increased. Productivity of herbaceous species (graminoids, forbs, or both) tended to be greatest at about 11 to 17% big sagebrush cover. In general, plant community diversity tended to be greatest where sagebrush was thinned to this level. Small mammal community diversity was least at both sites where big sagebrush cover was less than 5%, and was strongly correlated with plant community diversity at Ten Sleep (R2W = 0.99; 4 degrees of freedom). In addition, greater abundance of or better habitat quality for endemic, stenotypic (habitat specialist) species was associated with about 15% big sagebrush cover. This suggests (albeit retroductively) that biodiversity at both local (alpha) and global (epsilon) scales might be conserved by thinning big sagebrush with tebuthiuron.

Experiments were conducted to compare the influence of production site and seed source on the germination of big sagebrush seeds in relation to incubation temperatures. Seeds of big sagebrush were collected from five plant communities located on the margin of the Carson Desert in western Nevada. Seedlings were grown from the seeds and transplanted back to the sites of collection in reciprocal gardens. Seeds from 1-yr-old gardens were tested for germination at a constant 15 C for three consecutive years. The greater quantity of seeds produced by 2- and 3-yr-old gardens were tested at 55 constant or alternating temperature regimes. Seeds of big sagebrush produced in reciprocal gardens had lower germination than seeds collected from native stands at the same locations. The reduced germination disappeared as the reciprocally transplanted plants grew older and larger, but seeds from these plants did not reach the same levels of germination as those collected from native stands at the same location. Moisture stress and/or freezing temperature conditions during flowering may have directly influenced the quality of seeds produced or interacted with the inherent genotypes of big sagebrush to trigger seed production of variable quality in relation to germination characteristics.

Our purpose is to discuss the impact of alien plants on rangeland ecosystems of the Great Basin in terms of their effects on biological functions. The sagebrush/bunchgrass ranges of western North America are used as a model ecosystem for the impact of alien plants. Alien weed species have been introduced in successive waves, with the success of each new introduction dependent on how well adapted to the environment and how competitive the new weed is with those previously introduced. Annual species have been successful across extensive areas of Great Basin rangelands. Biennial and short- and long-lived perennial introductions have been restricted to much more specific habitats. Alien plants impact rangelands through stand renewal and successional processes. Alien weeds can cause such processes to be accelerated and/or truncated depending on the species and range site.

Eight herbicides or herbicide combinations were evaluated for control of Wasatch milkvetch and other broadleaf plants. Triclopyr at 2.2 kg ae/ha controlled Wasatch milkvetch and associated mountain big sagebrush and mulesears 100%. A combination of triclopyr plus dicamba at 1.1 plus 1.1 kg ae/ha also controlled these species. When compared to untreated plots, grass production increased over 400% on plots treated with triclopyr at 1.7 and 2.2 kg/ha and more than 300% on plots treated with triclopyr plus dicamba at 1.1 plus 1.1 kg/ha.

The purpose of this study was to investigate seed dispersal and germination of seeds in the soil as factors in establishment of big sagebrush seedlings. Seed dispersal began at seed maturity in December. Under the shrub canopy the dispersal of seeds was greater to the east. Between shrubs the dispersal of seeds tended to be uniform. For 6 months of each year there were no detectable germinable seeds in the litter and surface soil at the sites sampled. Germinable seeds in the soil increased rapidly during seed dispersal but were not detected by June of the next season. Enrichment of bioassay samples with GA3 or KNO3 did not enhance emergence of big sagebrush seedlings. Big sagebrush seedlings were found at very low densities in areas previously burned in wildfires. This suggests the presence of viable big sagebrush seeds in the soil at a very low density.

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

Sprays of 2.2 kg ae/ha of 2,4-D [(2,4-dichlorophenoxy)acetic acid] and 0.5, 1.1, or 2.2 kg ae/ha of clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) were applied at three Utah sites. The 2,4-D and 1.1 or 2.2 kg/ha of clopyralid effectively controlled mountain big sagebrush (Artemisia tridentata Nutt. # ARTTR ssp. vaseyana). Applications of 2.2 kg/ha of 2,4-D resulted in 84% mortality of antelope bitterbrush [Purshia tridentata (Pursh.) DC] and killed 96% of the Saskatoon serviceberry (Amelanchier alnifolia Nutt.). Clopyralid applications of 2.2 kg/ha killed only 5% of the antelope bitterbrush and 6% of the Saskatoon serviceberry. Thus, clopyralid is an effective alternative to 2,4-D for control of mountain big sagebrush when the desirable shrubs antelope bitterbrush and/or Saskatoon serviceberry are present.