Around 1900 temperate and semidesert grassland productivity declined, soil erosion incrensed, and drought destabllixed the live stock industry in the northern and southern hemispheres. As government leaders throughout the world began to recognize the importwee of grassiaad productivity nnd soil conservation, a massive experiment began to evolve. Government and private hrdividurls collected seed from every continent, and planted seed at experimental stations and ranches in their respective countries. Hundreds of individuals who conducted thousands of seeding trials observed that buffelgrass (Cenekrur c&u& L.), weeping lovegrass [Erugrostts curv& (Schrad.) Neesl, kleingrass (Pun&urn coiivatwn L.), and Lehmann lovegrass (Eragrostts l&mum&no Nees) plants from seed coiiected in Africa were easier to establish and persisted longer than other grasses. Uetween 1930 and 1986 scientists in many countries evaluated the estabiishment and persistence of these grasses, but no attempt was made to syntbesixe the data base and determine the effects of climate and soil on piant estab-Ushment and persistence. Our objective was to: (1) determine the climatic and edapbic characteristics of areas where the seed of each grass was collected in Africa, and where each grass has been successfuliy established in both hemispheres, and (2) identify characteristics which infiuence long-term persistence. Where buffelgrass predominates and spreads, summer rainfall varies from 150 to 550 mm, winter rainfall is less than 400 mm, mean miminum winter temperatures rarely fall below 50 C, and soil texture is loamy. Weeping lovegrass can be established and plants persist when spring, summer, and fail rainfall varies from 400 to 1,000 mm on deep sandy soil end mean minimum winter temperrtures rarely fall below -50 C. The invesion of adjacent nonplanted sites occurs only in Africa where growing season reinfall infrequently cycles between 750 and 1,000 mm and soils remahr wet in mid-summer. Kleingrass can be established where mean maximum daily summer temperatures are above 300 C, mean minimum daily winter temperatures rarely fall below 00 C, summer growing season rainfall vuies from 400 to 999 mm, and soils are clayey or silty. Kleingrass, like weeping lovegrass, spreads to nonplanted sites only in Africa where a mid-summer drought does not occur. Lehmann lovegrass predominates and spreads only in southern Africa, southeastern Arizona, and northern Mexico when summer r&fail in 30 to 40 days exceeds 150 mm, and soil textures are sandy or sandy loam.

Thii research was designed to identify relationships between T-4464 buffelgrass (Ce&zrus ciliaris L.) survival and climatic and soil characteristics. At 167 buffelgrass seeding sites in North America we collected climatic and soils data where the grass: 1) persisted over time and increased in area covered (spreads), 2) persisted over time but does not increase in area covered (persists), and 3) declined over time and all plants eventually died (dies). At 30 sites in Kenya we collected climatic and soils data in the area where T4464 seed was originally collected. Only total soil nitrogen and organic carbon differed among survival regimes. Total soil nitrogen and organic carbon concentrations were least where buffelgrass spreads, intermediate where the grass persists and greatest where the grass dies. To predict buffelgrass survival among the 3 survival regimes, and between areas where the grass spreads or dies, we used discriminant function analyses. A model including organic carbon, total soil nitrogen, sand, clay, potassium and cation exchange capacity correctly classified 78% (13=0.8) of the seeding sites in the 3 survival regimes. A model including sand, total soil nitrogen, calcium, mean minimum temperature in the coldest month, annual pre-The authors acknowledge the financial suppon provided by USDA-Agricultural Research Service (Drs. Plowman. Knipling and Child). We thank Dr. N.J. Chatterton (USDA-ARS) for laboratory f&ilitk. Drs. Gary Richardson (USDA-ARS) and D.V. Sisson (Utah State University) for statistical advice. We also appreciate support and financial assistance provided by Consejo National de Ciencia y Tecnologia,

Creosotebush (Lurrea tridrntato [Sesse & Moe. ex DC.] Cov) 8nd other shrubs have spre8d into semidesert gmssl8nds of the southwestern United States urd northern Mexico; and 8s creosotebush increases, perennial gmssea decre8se. This study evalu-8ted 3 rates of tebuthiuron 8nd 4 mechanierl treitments in 1981 and 1982 for creosotebush coqtrol at 4 locations, 3 in Chihuahu8, Mexico, and 1 in Arizona, U.S.A., md compared forage production 8fter treatment with untreated checks. Creosotebush mort8lities 8veraged across ioc8tions 8nd ye8rs were 75,87,93,3,33,68, and 66 for the 0.5,1.0, and 1.5 kg ri/hr tebuthiuron (N-(5-(l,l-dimethylethyl)-1,3,4-thi8dlazol-2-yl~N,N'-dhnethylurea), l8nd lmprinting, 2-way r8iling, disk plowing, 8nd disk plowing with contour furrowing treatments, respectively. Forage production averaged across locations and years was 529,524,606,303,344,290,330, 8nd 302 kg/ha for the 0.5,1.0, nnd 1.5 kg rijhr tebuthiuron, land imprinting, 2-W8y railing, disk plowing, disk plowing with furrowing, and untreated check tre8tments, respectively. Precipitation ~8s below long-term me8ns at rli Chihuahuan lo&ions in 1983, and forage production was significantly greater on most treated plots where brush was controlled thrn on untre8ted checks. At the Arizon8 location precipit8tion ~8s above the long-term meln in 1983 8nd ail plots treated in 1981, except the disk plowing 8nd disk plowing with furrowing which destroyed perennirl gnsses, produced signific8ntly more grass for8ge than the untreated checks. Precipitation was 8bove the long-term me8ns rt all loc8tions in 1984 and about hrlfof the plots tre8ted with tebuthiuron produced significantly more forage than the untre8ted checks but not any mechanic8lly treated plots. When treatments reduced shrub density and remnants of native forage grasses were present, forage production increased in both wet and dry years.

Perennial grasses were seeded by drilling or broadcasting on 4 mechanical and 3 herbicidal weed control and/or seedbed preparation treatments at 4 semidesert grassland sites invaded by creosotebush (Zarrea tridcnutu) in the Chfuahuan and Sonoran Deserts. The cultivars 'Cochise' Atherstone lovegrass (Eragrostis lehmanniana X Eragrostis trichophera) and 'Catalina' Boer lovegrass (Effrgrostis curvuIo var. coqferta) lovegrasses were initially established and persisted in 6 of the 8 plantings on disk plowed and disk plowed plus contour furrowed seedbeds. These grasses were established and persisted in 2 of the 5 plantings made in creosotebush stands treated with tebuthiuron [JV-(S-(l,l-dimethylethyl)-1,3,4-thiadizol-2-yl)imethylurea] at 0.5, 1.0, and 1.5 kg a.i/ha rates. Grasses established initially on two-way railed and land imprinted areas usually died within 3 or 4 years. Creosotebush (Larrea tridentata), a woody perennial shrub, has invaded the semidesert grasslands within the Chihuahuan and Sonoran Deserts of North America (Humphrey 1958, Buffington and Herbel 1965, Hastings and Turner 1965). As creosotebush densities increase, perennial grass densities decline (Anderson et al. 1957). Therefore, it is desirable to replace creosotebush with perennial grasses to reduce soil erosion, increase infiltration, and provide forage for domestic livestock. Jerry COY. and Howard Morton are range scientist and supervisory plant physiologist, respectively; USDA, Agricultural Research Services Aridland Watershed Man

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