Jerry R. Cox

Influence of climatic and edaphic factors on the distribution of Eragrostis lehmanniana Nees in Arizona, USA.

Abstract Lehmann lovegrass (Eragrostis lehmanniana Nees) was introduced into Arizona, USA, from South Africa in 1932 and has since been sown throughout the southwestern USA and Northern Mexico. The species is well adapted in southeastern Arizona where it has been sown on over 69 115 ha and has spread by seed to an additional 76 040 ha. Where Lehmann lovegrass predominates and spreads, surface soils are sandy, summer rainfall is greater than or equal to 200 mm and winter temperatures rarely fall below 0° C. Factors contributing to the spread of Lehmann lovegrass in southeastern Arizona include fire, cattle grazing and drought.

Hydrologic characteristics immediately after seasonal burning on introduced and native grasslands.

Fire on rangelands used as a management tool or as an unwanted wildfire removes vegetation cover. Vegetation cover is thought to be a dominate factor controlling surface runoff and erosion. Vegetation removal by a burn should have an immediate effect on runoff and erosion. Surface runoff and sediment production were evaluated immediately after fall and spring season burns at 2 locations with different soil and vegetation types for 2 years in southeastern Arizona. The evaluations were conducted with a rainfall simulator at 2 precipitation intensities. Immediately after a burn there was not a significant change in runoff and erosion, therefore, vegetation cover by itself was concluded not to be a dominate factor controlling surface runoff and erosion. The increase found in surface runoff and sediment production from the burn plots was not significantly greater than the natural variability for the locations or seasons. Significantly higher surface runoff and sediment production was measured in the fall season compared to the spring at 1 location.

Biological and physical factors influencing Acacia constricta and Prosopis velutina establishment in the Sonoran Desert

Over the past century woody plants have increased in abundance on sites formerly occupied by grasslands in the Sonoran Desert. Woody plant invasion has been associated with a multitude of biological and physical factors. This study was conducted to determine temperature, soil, fire, rodent, and livestock effects on the germination and establishment of whitethorn acacia (Acacia constricta Benth.) and velvet mesquite (Prosopis velutina (Woot.) Sarg.). Optimum termination temperatures for both shrubs ranged from 26 to 31 degrees C, and seedling emergence was greatest from seed sown at 1 to 2 cm depths in sandy loam soil. Merriams kangaroo rats (Dipodomys merriami) fed seeds in the laboratory removed seed coats and planted embryos at 2 to 4 cm depths in a sandy loam soil. Prescribed fire killed 100% of seed placed on the soil surface but had no measurable effect on the germination of seed planted at 2 cm. After passage by sheep, about 6% of the A. constricta and 13% of the P. velutina seeds germinated while after passage by cattle, only 1% of the A. constricta and 3% of the P. velutina seed terminated. Embryo planting by rodents may improve survival efficiencies for these legunminous shrub seedlings, but seed consumption and passage by sheep and cattle appear to adversely affect seed germination. Dipodomys merriami, rather than domestic livestock, may be responsible for the spread of these shrubs in the Sonoran Desert.

Predicting buffelgrass survival across a geographical and environmental gradient

This research was designed to identify relationships between T4464 buffelgrass (Cenchrus 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% (r2=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 precipitation and winter precipitation correctly classified 88% (r2 = 0.8) of the seedling sites between spreads and dies. Survival regime selection prior to brush control, seedbed preparation and sowing will reduce planting failure probabilities, soil erosion and economic losses, and enhance long-term beef production.

Climatic effects on buffelgrass productivity in the Sonoran Desert.

Buffelgrass (Cenchrus cilaris L.), a perennial bunchgrass from northcentral Kenya has been successfully seeded on 400,000 ha in northwest Mexico. To determine if carrying capacity increased after buffelgrass introduction we measured live, recent-dead standing, old-dead standing and litter at 2-week intervals for three years. Live biomass was produced throughout the year but peak production, over the 3 years was in August. Peak live biomass production varied from 46S kg/ha in a summer of below-average precipitation to 3,045 kg/ha in a summer of above-average precipitation. Recent- and old-dead standing quantities were highly variable among years and transfers among components were dependent on temperature and precipitation. Buffelgrass annually produces about 3 times more green forage than native grasses.

Water balance in pure stand of Lehmann lovegrass.

Lehmann lovegrass (Eragrostis lehmanniana Nees), an introduced warm season grass, has invaded grasslands in southern Arizona, in many areas replacing the native warm-season grasses. A water balance evaluation in a pure stand of Lehmann lovegrass showed that more soil water was used through evapotranspiration than occurred as precipitation during 2 years of a 3-year study period. During the winter season, an appreciable amount of water was used by Lehmann lovegrass or lost by evaporation from the soil surface. The remaining available soil water was used in the spring dry period. In the dry early spring the soil water contents (to depths of 120 cm) were less than the traditional wilting point tension of -1.5 MPa. The invasion of Lehmann lovegrass into grasslands of southern Arizona is partially related to its ability to utilize soil water during parts of the year when the native species are dormant and also to extract water from the soil profile to very low water contents.

Effects of planting depth and soil texture on the emergence of four lovegrasses.

We studied the emergence of 4 lovegrass accessions planted at 0.0,0.5,1.0,1.5, and 2.0 cm depths in Pima silty clay loam, Sonoita silty clay loam, and Comoro sandy loam soils in a greenhouse. Catalina boer lovegrass (Erugrostis curvulu var. confertcr Nees) emergence was superior to A-84 boer lovegrass, A-68 Lehmann lovegrass (Eragrostis lehmanniana Nees) and Cochise lovegrass (Eragrostis lehi however, the clay fraction of the Pima was 60% montmorillionite and the Sonoita was 80% Authors are range scientist, USDA, Agr. Res. Serv., Arid Land Ecosystems Improvement, 2000 E. Allen Road, Tucson, Ark 85719; and graduate student, range management, School of Renewable Natural Resources, University of Arizona, Tucson. Ark. 8572 I. Manuscript received April I, 1983. 204 kaolinite (USDA-Soil Conservation Service, personal COmmUnications). Soils were screened to 5 mm, thoroughly mixed and added to 15 X 15-cm tapered plastic pots to 12.7, 12.2, 11.7, 11.2, and 10.7 cm depths above the pot base. Twenty-five pure live seed of one lovegrass accession were sown on the soil surface on each pot. Soils were added to 12.7 cm depths in all pots; thus, seed were planted at 0.0, 0.5, 1.0, 1.5, and 2.0 cm depths below the soil surface. Pots were subirrigated with distilled water to insure that the soil surfaces were moist and undisturbed during the 1Cday study. Emergence was considered complete when the first leaf was 1.5 cm above the soil surface in those pots planted at depths of 0.5 to 2.0 cm, or when the first leaf was 1.5 cm above the soil surface and the seed radicle had penetrated the soil in those pots in which seed were sown on the surface. Seedlings were counted daily and summed for the 14day experiment. The study was a completely randomized block design, with 6 blocks. Each block contained 60 pots, 4 accessions, 3 soils, and 5 planting depths. Data were subjected to analysis of variance and a Duncan’s new multiple range test (Steel and Torrie 1960) used to separate means (B.05). Results and Discussion Germination of the lovegrass accessions on soil surfaces ranged between 92 and 96%. The emergence of Catalina boer lovegrass was greatest, Cochise lovegrass was intermediate, and A-68 Lehmann and A-84 boer lovegrass were least on soil surfaces (Table 1). Table 1. Mean’ emergence (%) of four lovegrass accessions sown at five soil depths (cm). Emergence from depths Accession 0.02 0.5 1.0 1.5 2.0

Seasonal burning and mowing impacts on Sporobolus wrightii grasslands.

Land managers have recommended burning or mowing big sacaton (Sporobolus wrightii) grassland in either fall or winter for 100 years. The greatest potential for natural flre would have occurred when lightning strike frequency peaked in summer. The objective of this study was to determine how burning and mowing in fall (October), summer (July) and winter (February) influences big sacaton forage quantity and quality. Plants defoliated in fall produced leaves within 215 to 245 days, those defoliated in summer within 3 days, and those in winter within 20 days. Green and dead forage that accumulated after the burning and mowing in the same seasons were similar, but differences occurred among seasons. Green and dead forage following summer treatments were similar to that on untreated areas within 2 or 3 summer growing seasons, but were reduced on fall and winter treatments. Crude protein in green forage was 3 to 5% greater in treated plants than in untreated plants for 6 weeks after treatment, but forage quality increases were temporary. Burning or mowing at any season removes green forage available to livestock and reduces the amount of green forage that may accumulate for at least 2 summer growing seasons.

SPITTLEBUG AND BUFFELGRASS RESPONSES TO SUMMER FIRES IN MEXICO

Summer burning was used to reduce spittlebug (Aeneolamia albofasciata Lall.) populations in buffelgrass [Cenchrus ciliaris (L.) Link] on the Carbo Livestock Research Station in Sonora, Mexico. Five treatments included (1) an untreated control; (2) burning 7-14 days before the summer rains when the insect and the plant were inactive; (3) burning after the accumulation of 50 mm of summer precipitation during insect egg hatch or the second leaf stage; (4) burning between the second and third instars or early culm elongation; (5) and burning between the fifth instar and adult stages or active plant growth during the summer growing season. Summer burning after the accumulation of 50 mm of precipitation and between the egg hatch and the third instars or between the second leaf stage and early culm elongation reduced spittlebug nymph and adult populations by 100% and appeared to stimulate buffelgrass growth for 3 and 4 years post treatment. Burning at the peak of buffelgrass live biomass production effectively controlled spittlebug populations but reduced plant production by almost 50% for 4 years post-treatment. Equally detrimental was the untreated control where nymph and adult spittlebug populations killed more than 50% of the buffelgrass population. Summer fires conducted after 50 mm of precipitation were easier to control than fires conducted before the growing season when plant material was dry.

Density and production of seeded range grasses in southeastern Arizona (1970-1982).

Accessions A-68, L-11, L-19, L-28, and L-38 of Lehmann lovegrass (Eragrostis lehmanniana Nees); P-15608 Cochise lovegrass (E. lehmanniana Nees X E. trichophora Coss & Dur.); A-84 and Catalina boer lovegrass (E. curvula var. conferta Nees); Palar Wilman lovegrass (E. superba Peyr.) and P-15630 blue panicgrass (Panicum antidotale Retz.) were seeded at a study site near San Simon, Ariz., in spring 1970 and 1971. Seedbeds were prepared by root plowing and furrow pitting immediately before planting. Growing season precipitation was 136 mm in 1970 and 218 mm in 1971. Mean accession densities in the fall after the initial growing seasons were 18 plants/M2 for both the 1970 and the 1971 plantings. Between fall 1971 and 1972 mean accession densities declined 44% and forage production was unchanged on the 1970 plantings. Accession densities declined 22% and forage production increased 250% on the 1971 plantings. Between fall 1972 and 1982 the majority of seeded plants died and forage production declined 90% on the 1970 plantings. Accession densities declined 78% and forage production declined 84% on the 1971 plantings. Southeastern Arizona and southwestern New Mexico rangelands were overutilized and deteriorated rapidly between 1880 and 1900. Griffith (1901) documented the deterioration and corresponding livestock losses. Cooperative studies to restore these rangelands were initiated in the early 1900s by the Division of Agrostology (USDA) and State Experiment Stations at Tucson, Ariz., and Las Cruces, N. Mex. Blount (1892), Griffith (1907), Keefer (1899), and Thornber (1905) seeded native and introduced grasses on irrigated and rangeland sites and evaluated emergence and survival. Teff [Eragrostis abyssinica (Jacq.) Link.] emerged on irrigated and nonirrigated sites, but long-term survival occurred only at irrigated sites. Native grass either failed to emerge or to survive at southwestern revegetation sites between 1910 and 1934 (Barnes et al. 1958, Cassady 1938, Glendening 1937, and Hendricks 1936). Numerous grass, forbs, and shrub species were introduced after 1930 (Cox et al. 1982). These introduced species were screened for germination, drouth tolerance, and seed production potential at Soil Conservation Service Plant Materials Centers, and a few promising grasses were released for rangeland plantings. Among these were A-68 Lehmann lovegrass and A-84 boer lovegrass; both were introductions from southern Africa. Lovegrass species and newly developed accessions were sown in summer (Bridges 1941 and Herbel et al. 1973) and fall (Bridges 1941) at desert sites in southern New Mexico. A-68 Lehmann and A-84 boer lovegrasses emerged in moist summers, and A-68 emerged in wet winters at lower elevations. Jordan (1970) conducted studies for 9 years to determine the best combinations of mechanical brush control, seedbed preparation, The authors are range scientist, USDA, Agr. Res. Serv., Arid Land Ecosystems Improvement, 2000 East Allen Road, Tucson, Ariz. 85719; and professor, range management, School of Renewable Natural Resources, University of Arizona, Tucson 85719. This paper is published with approval of the Director, University of Arizona College of Agriculture, Agricultural Experiment Station, as Paper No. 3705. The paper reports on work supported by the U.S. Department of the Interior, Bureau of Land Management, and is a cooperative investigation of Agr. Res. Serv., USDA, and the Arizona Agr. Exp. Sta., University of Arizona. Manuscript received January 20, 1983. and time of seeding for emergence and survival of forage grasses at 3 sites in southeastern Arizona. A-68 Lehmann lovegrass emergence and survival was optimized when root plowing and pitting were used to control brush and prepare the seedbed in spring, and when seed were sown immediately after a mechanical treatment. Comparative seedling trials were conducted to select adapted lovegrass and blue panicgrass accessions at a study site near San Simon, Ariz., in 1970 and 1971. The purpose of this paper is to quantitatively document and compare initial and long-term plant densities and forage production for these seeding trials. Study Site and Methods The study site is located 25 km southwest of San Simon, Ariz., near the Arizona-New Mexico State Line in southeastern Arizona. Average annual precipitation is 280 mm, and 30 to 40% occurs in winter. Winter months (November to March) are cold, dry, and windy, and typical of the Chihuahuan Desert (Mabry et al. 1977). Winter precipitation is either evaporated or transpired by shrubs, and apparently not used by seeded grasses (Jordan 1970). Effective summer precipitation falls in late July through October and varied from 98 to 230 mm at San Simon between 1972 and 1982 (National Oceanic and Atmospheric Administration, Annual Climatological Data Summaries 1972-1982). Mean summer precipitation was 165 mm over the 10 years. Figure 1 shows the departure of annual summer precipitation from the 10-year average. Average annual air temperature is 17?C and the frost-free period is 220 days. Soils are deep, well drained, and formed in old alluvium from mixed sources. Soils are classified as Eba gravelly sandy loam, mixed, thermic Typic Haplargids (Vogt 1980). Native perennial grass forage production was 2.5 to 5.0 g/ m2 on