Black Grama Research Articles

Environmental controls on nitric oxide emission from northern Chihuahuan desert soils

A survey of nitric oxide (NO) emission from Chihuahuan desert soils found mean NO fluxes <0.1 ng NO-N cm−2h−1 during the dry season. These fluxes were at thelower end of the range reported for temperate grassland and woodlandecosystems. NO fluxes from wet or watered soils were higher(0.1–35 ng NO-N cm−2 h−1).Watering of black grama grassland soils produced an initial pulse of 12ng cm−2 h−1 (12-h after 1-cm watering)with high fluxes sustained over 4 days with repeated watering. Initialpulses from shrubland soils were lower (maximum 5 ngcm−2 h−1), and fluxes declined withrepeated watering. Repeated watering of creosotebush soils depleted thesoil NH 4 + pool, and NO emissions weredirectly related to soil NH 4 + concentrationsat the end of the experiment. In watered andNH 4 + -fertilized creosotebush soils, NO fluxeswere positively related to potential net nitrification rates.NH 4 + -fertilization boosted the initial NOpulse 15 times in the shrubland and 5 times in black grama grasslandrelative to watered controls. These experimental results point towardgreater substrate limitation in shrublands. In this desert basin, NOemission averaged 0.12 kg N ha−1 y−1in untreated soil and 0.76 kg N ha−1y−1 in watered soil. We multiplied these averages bythe distribution of grassland and shrubland vegetation within a58,600-ha area of the Jornada del Muerto basin to estimate regionallosses of 0.15–0.38 kg NO-N ha−1y−1 for this area of the Chihuahuan desert.

Long-term influences of shrub removal and lagomorph exclusion on Chihuahuan Desert vegetation dynamics

Cover of perennial species in long-term experimental plots in a creosotebush (Larrea tridentata Sess. & Moc. Ex DC.) dominated community in the Chihuahuan Desert was monitored for 56 years. Sixteen 21·3×21·3 m plots were established in 1938–39 to evaluate the effects of lagomorph exclusion and shrub removal. Major dominant shrubs were individually severed at ground level and removed by hand in 1939, and this process was repeated after measuring plant cover in 1947, 1956, 1960, 1967, 1989, and 1995. Lagomorphs were excluded with poultry wire fencing. Shrub removal increased (p≤0·05) the basal cover of two major desert grass species, black grama (Bouteloua eriopoda Torr.) and spike dropseed (Sporobolus contractus A.S. Hitch.) between 1939 and 1995, but differences were not evident until 50 years after initial treatment. Temporal effects of lagomorph exclusion were less pronounced than shrub removal. Clearly, shrub dominance has an extremely important and lasting role in determining vegetation community structure in this arid environment, even when above-ground shrub structures are periodically removed.

Diets of 3 Cattle Breeds on Chihuahuan Desert Rangeland

Diet botanical composition, fecal nitrogen percent, and fecal phosphorus percent were determined seasonally during 1991 and 1992 for 3 cattle breeds (Barzona, Brangus, Beefmaster) grazing late-seral Chihuahuan Desert rangeland in southcentral New Mexico. These 3 cattle breeds are considered to be well adapted to harsh environments. Cattle breed main effect was non-significant (P > 0.05) for diet botanical composition. However, season main effects (P < 0.05) did occur for some diet botanical composition components. Total grasses in cattle diets were highest in January and lowest in June. Dropseeds (Sporobolus sp.), black grama (Bouteloua eriopoda Torr.), and threeawns (Aristida sp.) were the primary grasses consumed by cattle. Forb consumption was highest in June lowest in January. Honey mesquite (Prosopis glandulosa Torr.) consumption by cattle was highest in August and lowest in January. It was the primary shrub in cattle diets. Breed X season interactions (P < 0.05) occurred for a few diet botanical composition components, but the small magnitude of the values and lack of consistency prevented drawing definite management implications. Fecal nitrogen values showed differences (P < 0.05) among breeds in some seasons. However due to lack of consistency no definite conclusions could be drawn regarding superiority of 1 breed compared to another in diet nutritional quality. Both fecal nitrogen and phosphorus concentrations showed cattle diets to be lowest in quality in winter and highest in summer. From a practical standpoint, this study showed no definite advantage of any breed studied in diet botanical composition or in diet quality.

Carbon isotopes reveal soil organic matter dynamics following arid land shrub expansion.

Over the past century, overgrazing and drought in New Mexico's Jornada Basin has promoted the replacement of native black grama (Bouteloua eriopoda Torr.) grass communities by shrubs, primarily mesquite (Prosopis glandulosa Torr.). We investigated the effects of shrub expansion on the distribution, origin, turnover, and quality of light (LFC) and heavy (HFC) soil organic matter (SOM) fractions using δ13C natural abundance to partition SOM into C4 (grass) and C3 (shrub) sources. Soil organic matter beneath grasses and mesquite was isotopically distinct from associated plant litter, providing evidence of both recent shrub expansion and Holocene plant community changes. Our δ13C analyses indicated that SOM derived from mesquite was greatest beneath shrub canopies, but extended at least 3 m beyond canopy margins, similar to the distribution of fine roots. Specific 14C activities of LFC indicated that root litter is an important source of SOM at depth. Comparison of turnover rates for surface LFC pools in grass (7 or 40 years) and mesquite (11 or 28 years) soils and for HFC pools by soil depth (∼150-280 years), suggest that mesquite may enhance soil C storage relative to grasses. We conclude that the replacement of semiarid grasslands by woody shrubs will effect changes in root biomass, litter production, and SOM cycling that influence nutrient availability and long-term soil C sequestration at the ecosystem level.

Wildlife Numbers on Excellent and Good Condition Chihuahuan Desert Rangelands: An Observation

Information is lacking on the influence of range condition on wildlife populations in the Chihuahuan Desert. Wildlife observations were made along transects on ranges in excellent and good ecological condition in south-central New Mexico (86% and 72% of climax vegetation remaining, respectively). Black grama (Bouteloua eriopoda Torr.) dominated the excellent condition range while the good condition range had a mixture of grasses, forbs, and shrubs. Plant species diversity was greater on the good compared to excellent condition range. Total mammal sightings/km2 during the study period were higher (p<0.05) on the good compared to excellent condition range (October 1991 through October 1992). More species of wildlife were seen on the good compared to excellent condition range. Sightings of important game species (scaled quail, mourning doves, pronghorn, desert cottontails) were higher on the good compared to excellent condition range. Lack of diversity in vegetation composition and structure appear to explain the lower wildlife sightings on the excellent condition range. Results from this study indicate that Chihuahuan Desert ranges in good ecological condition (51-75% of the climax vegetation) will better meet the needs of most wildlife species than ranges in climax or near climax range condition. Research shows grazing intensities that remove on average about 1/3 of current year's growth of key forage species (black grama) are effective in developing and maintaining range in good ecological condition in the Chihuahuan Desert.

Season and Sex Influences on Botanical Composition of Cattle Diets in Southern New Mexico

We conducted a study in southern New Mexico to determine seasonal variation in botanical diet composition of cattle and to compare cow and steer diets. The climate and vegetation is typical of semidesert grassland. Fecal samples were obtained from a group of cows and steers during spring, summer, fall, 1989; winter and summer, 1990. Results showed that cattle diets were highest in grass content during spring (57%), summer (78%), and winter (54%), while fortes comprised the highest proportion of cattle diets during the fall (47%). Shrubs were moderately important during winter (18%). Dropseeds (Sporobolus spp.), black grama (Bouteloua eriopoda [Torr.] Torr.), threeawn species (Aristida spp.), and leatherweed croton (Croton pottsii [Klotzch] Muell. Arg.) were key forage species for cattle. The importance of these species varied with season, availability, physiological stage, and presence of other species. Differences between cow and steer diets varied with season. The relative similarity ranged from 70% (fall) to 90% (summer). The lower fall similarity compared to that in the summer might be related to physiological variation or past differences in grazing experience between cows and steers. For practical purposes, steer diets might generally be used to represent cow diets, but caution should be exercised during periods of low forage quality.

Grazing Influences on Watering Point Vegetation in the Chihuahuan Desert

Long-term influences of livestock grazing on vegetation around watering points was studied on 2 upland Chihuahuan desert ranges in southcentral New Mexico using regression analysis. One range had been conservatives stocked since the 1950's while the other was more heavily stocked. About 45% of the climax vegetation occurred on the heavily stocked range compared to 70% on the conservatively stocked range. During 3 years of study, both ranges were stocked conservatively so annual utilization of the key forage grasses was 30-35%. Regression analyses showed black grama (Boueteloua eriopoda Torr.), mesa dropseed (Sporobolus flexuosus Thurb, Rybd.), threeawn (Aristida sp.), and total perennial grass standing crop increased as distance from water increased on the good condition range (P < 0.05). However, black grama and threeawn standing crop showed no association with distance from water on the fair condition range. Broom snakeweed (Xanthocephalum sarothrae Pursh.), the primary poisonous plant found on both ranges, was associated (r2 = 0.35) with distance from water only on the good condition range in April. Poisonous plants other than broom snakeweed decreased as distance from water increased with the exception of the fair condition range in October. No livestock losses from poisonous plants were noted on either range over the 3 years. We attribute this to the present conservative stocking rates. Our study supports the recommendation that downward stocking rate adjustments be made for the zone more than 1,600 m from water.

Observation: Cattle Diets on Excellent and Good Condition Chihuahuan Desert Rangelands

Information is limited on the influence of range condition on cattle diets in the Chihuahuan desert. Botanical composition of cattle diets on Chihuahuan desert ranges in excellent and good condition was studied by microhistological analysis. Cattle feces were analyzed seasonally from fall 1991 through fall 1992. Excellent condition and good condition ranges supported 86% and 72% of the climax vegetation, respectively. Key species in cattle diets on the excellent condition range were black grama (Bouteloua eripoda Torr.) and threeawns (Aristida spp.). On the good condition range the key species were dropseeds (Sporobolus spp.), threeawns and black grama. Total grass and black grama content of cattle diets were greater on the excellent condition range. Seasonal trends occurred in cattle diets on good condition but not on excellent condition range. Low availability of forbs and shrubs explained the high diets similarities among seasons on the excellent condition range. Cattle on good condition range readily used forbs and shrubs when green grass was unavailable. Nitrogen and phosphorus analyses of fecal samples indicated diets were nutritionally superior on the good compared to the excellent condition range. Our research and other studies show consumption of forbs and shrubs permits cattle to maximize their nutritional welfare when grasses are dormant. The excellent condition range in our study had a different(P<0.05) mean grass standing crop (999 kg/ha) across periods compared to on the good condition range (659 kg/ha). Based on our research and other studies excellent condition Chihuahuan desert range maximizes forage quantity for cattle but good condition range appears better from a nutritional standpoint in the spring and early summer. Our research and other studies indicate Chihuahuan desert ranges dominated by black grama are most effectively used in winter while ranges with a high dropseed component are best suited for use in summer and early fall.

Functional diversity of microbial communities: A quantitative approach

Evaluating the biodiversity of microbial communities remains an elusive task because of taxonomic and methodological difficulties. An alternative approach is to examine components of biodiversity for which there exists a reasonable chance of detecting patterns that are biologically meaningful. One such alternative is functional diversity. We propose a procedure based on the Biolog identification system to quickly, effectively, and inexpensively assess aspects of the functional diversity of microbial communities. The numbers and types of substrates utilized by bacterial communities, as well as the levels of activities on various substrates and patterns of temporal development, constitute an information-rich data set from which to assess functional diversity. Data from six plant communities (black grama grassland. Sporobolus grassland, creosotebush bajada, herbaceous bajada, mesquite-playa fringe, and playa grassland) located along an elevational and moisture gradient at the Jornada Long-Term Ecological Research site in the northern Chihuahuan Desert, are analyzed to illustrate the procedure and its relevance to biodiversity. Our analyses demonstrate that the Biolog system can detect considerable variation in the ability of microbial communities to metabolize different carbon compounds. Variation in substrate use was compartmentalized differently along the moisture gradient. Differences in functional diversity were dependent upon the class of carbon sources (guild-specific results). A multifaceted approach to biodiversity that comprises both functional and taxonomic perspectives represents fertile ground for future research endeavors.

Range Condition Influences on Chihuahuan Desert Cattle and Jackrabbit Diets

Knowledge of comparative diet selection by cattle and black-tailed jackrabbits (Lepus californicus) would permit better estimation of grazing capacity on Chihuahuan desert ranges. Cattle and black-tailed jackrabbit diets were evaluated seasonally on good and fair condition ranges over a 2-year period. Fecal samples analyzed by the microhistological technique were used to determine diets of both animals. Key forage species in cattle diets were dropseeds (Sporobolus sp.), black grama (Bouteloua eriopoda Torr.), leatherweed croton (Croton pottsii Lam.), and bush muhly (Muhlenbergia porteri Scribn.). Key forage species in jackrabbit diets were honey mesquite (Prosopis glandulosa Torr.), cactus (Opuntia sp.), dropseed, broom snakeweed (Gutierrezia sarothrae Pursh.), and black grama. Overall diet botanical composition data showed cattle consumed 58% grass compared to 22% for jackrabbits (P < 0.05). Forb consumption was similar between the 2 animals and averaged about 31%. Shrub consumption averaged 47% and 12% for jackrabbits and cattle, respectively (P < 0.05). Range condition did not influence total grass consumption by either animal. Both animals, however, had lower forb and higher shrub consumption on fair compared to good condition range. Overall dietary overlaps between jackrabbits and cattle were 40 and 42% on good and fair condition ranges, respectively. Poisonous plants contributed up to 14 and 36% of cattle and jackrabbit diets, respectively. Data from this study show little forage competition occurs between cattle and jackrabbits when stocking rates and jackrabbit numbers are moderate. Several plants poisonous and unpalatable to cattle were important jackrabbit foods. These plants were more prevalent on the fair compared to the good condition range.

Responses of Bouteloua eriopoda to irrigation and nitrogen fertilization in a Chihuahuan Desert grassland

The response of Bouteloua eriopoda, black grama, to irrigation and nitrogen fertilization was examined to test the hypothesis that, in desert grasslands, nitrogen availability is greater than in adjacent shrublands. Tiller growth was greater in irrigated plots ( P < 0·05) while nitrogen had no significant effect on growth ( P > 0·05). Nitrogen induced early flowering but water had a greater effect during the various phenological stages. Water affected flowering, mortality, insect damage, and biomass production. Nitrogen and nitrogen plus water reduced root length of the experimental plants ( P < 0·05). The short and mat-like roots of fertilized plants may allow use of the small rainfall events more efficiently than the plants which received only irrigation (46 out of 61 precipitation events were < 6 mm in size). There were no differences in the total biomass production of nitrogen-treated or water-nitrogen-treated subplots compared to controls. There was a higher nitrogen content of stems and leaves on plants from the irrigated-fertilized plots, but no significant differences among other treatments. Based on the large effects of irrigation in a third wet year (> 300 mm year -1) and marginal nitrogen effects, we conclude that productivity in Chihuahuan Desert Bouteloua eriopoda grasslands is less nitrogen limited than that of the Larrea shrublands. Further, productivity in this perennial desert grassland appears to be closely linked to rainfall with no temporal lags due to nitrogen immobilization.

Litter Decomposition in a Chihuahuan Desert Playa

Mass loss rates were compared for several types of litter in a flooded desert ephemeral playa. Most nonwoody types of organic matter, including black grama grass, creosotebush leaves and rabbit feces decomposed rapidly. Creosotebush twigs and wood decomposed slowly. About 25% of the mass was lost due to abiotic leaching. Predator exclusion significantly increased decomposition of creosotebush leaves, but reduced mass loss rate of creosotebush twigs and black grama grass. Decomposition rates were within the range of those found in lakes, and much lower than rates typical of streams. Our data suggest that organisms have little effect on mass loss of debris transported into a desert playa.

Changes in Grass Basal Area and Forb Densities over a 64-Year Period on Grassland Types of the Jornada Experimental Range

Between 1915 and 1932, permanent 1 X 1-m quadrats were established on grasslands of the Jornada Experimental Range in southern New Mexico. Quadrat records accumulated from 1915 to 1979 on grasslands dominated by black grama [Bouteloua eriopoda (Torr.) Torr.], poverty threeawn (A ristida divaricata Willd.), tobosa [Hilaria mutica (Buckl.) Benth.], and burrograss (Scleropogon brevifolius Phil.) were used to examine changes in perennial grass basal area and forb densities. Quadrats originally dominated by black grama had large reductions in basal area during droughts, and basal area increased slowly following droughts. By 1979, black grama no longer occurred on 77% of the quadrats. Quadrats originally dominated by poverty threeawn changed to a mesquite (Prosopis glandulosa Torr. var. glandulosa) type. Perennial grass basal area on quadrats dominated by tobosa and burrograss decreased during droughts, but recovery was relatively rapid. Antecedent precipitation was associated with only 10 to 38% of the variation in perennial grass basal area. Perennial forb densities were low and fluctuated among years in all types. Annual forbs and grasses displayed large fluctuations in densities among years. The necessity of basing management of Chihuahuan Desert ranges on the perennial grass component is borne out by the low densities of palatable perennial forbs, and the extreme fluctuation and unpredictability in densities of annual forbs and grasses.

Abundance and Diversity of Surface-active Collembola along a Watershed in the Northern Chihuahuan Desert

Jackknife diversity estimates (N2 = inverse Simpson diversity index) for surface-active Collembola were examined along a watershed in the Chihuahuan desert of southern New Mexico. Chord distance measures indicated low similarity in collembolan species composition among the six sites. However, assemblages at the top (black grama grassland) and bottom (mesquite fringe of playa) of the gradient were similar to each other, possibly reflecting available soil nitrogen. There was no significant correlation between Collembola and either weekly or long-term precipitation patterns. Populations of truly epigeic Collembola appeared unaffected by rainfall but were significantly, though weakly, correlated with long-term temperatures. INTRODUCTION Temporal and spatial distributions of soil microarthropods in desert ecosystems have been studied by several workers (Wood, 1971; Wallwork, 1972; Santos et al., 1978; Franco et al., 1979; Greenslade, 1981; Santos and Whitford, 1983; Steinberger and Whitford, 1984; Kamill et al., 1985). Considerably less work has been done examining the distribution and activity patterns of epigeic microarthropods in arid environments. Greenslade and Greenslade (1973) reported that some epigeic Collembola (e.g, Entomob7ya spp.) in semiarid Australia were active on sand dunes throughout the hottest part of the year. Comparing the taxonomic similarities of, and adaptations by, collembolan faunas in arid areas of Australia and Africa, Greenslade (1981) found several genera which were resistant to desiccation and concluded that populations of many species are underestimated in arid or semiarid areas. Pefaur (1981) showed that the abundance of epigeic microarthropods varied along an altitudinal gradient (300-1000 m) in a Peruvian desert, though there was little correlation between elevation and abundance of each species. Pefaur (1981) hypothesized that the abundance of epigeic species populations should increase in response to the increase of surface litter, which would provide greater shade and humidity. Except for Hypogastruridae (= Poduridae), he collected most Collembola from moist areas. In the Chihuahuan Desert of southern New Mexico, differences in soil type and drainage patterns produce distinct plant communities. Some of these produce more organic litter than others. Our objectives in this study were to examine the composition of epigeic collembolan communities associated with different plant communities along a watershed and to determine the seasonal activity of epigeic Collembola in this system. MATERIALS AND METHODS The study was conducted at the Jornada Long Term Ecological Research Site (LTER) located 40 km NNE of Las Cruces, New Mexico. The LTER area encompasses a watershed extending from the base of Mt. Summerford down a drainage slope (bajada) to a temporary lake basin (playa) 2850 m distant. Soils vary from coarse gravels on the bajada to sandy loam on the playa edge and clay silt on the playa basin. Pitfall traps were placed in six plant communities distributed along the watershed. From the bottom to the top of the drainage slope, these were: 1) playa, dominated by

The effects of nitrogen, water and sulfur amendments on surface litter decomposition in the Chihuahuan Desert

The effects of nitrogen, water and sulfur amendments on the decomposition rates of three types of surface litter in the northern Chihuahuan Desert were evaluated. The amendments had no effects on the decomposition rates of leaf litter from black grama (Bouteloua eriopoda) and creosote bush (Larrea tridentata). The rate of fluff grass (Erioneuron pulchellum) litter decomposition was increased by water and decreased by sulfur. Water affected fluff grass decomposition by increasing termite (Gnathamitermes tubiformans) above-ground activity. Sulfur decreased termite activity. These data suggest that the decomposer microflora and microfauna of the northern Chihuahuan Desert are more limited by quantity of organic matter than by water and nitrogen. Hence they do not respond opportunistically to increased availability of such resources.

Population Age Structure and Its Relationship to the Maintenance of a Semidesert Grassland Undergoing Invasion by Mesquite

Data from long-term chart quadrats recorded from the Jornada Experimental Range in south-central New Mexico were used to develop demographic measurements for black grama and mesa dropseed. These measurements included mean and maximum lifespans, survival proba- bilities, and rates of establishment and were used to derive the stable age structure for black grama. They were combined with factors such as climate and grazing in a model designed to sim- ulate the long-term dynamics of a stable perennial grassland. Using the stable age structure as a starting point, the model was perturbed by differentially lowering the age-specific survival rates in an effort to mimic the effect of mesquite competition. A stable age structure for black grama was achieved after a period of 40 years. A similar structure for mesa dropseed could not be derived. Output of the model run over a 47-year period in the absence of mesquite shows that stability of numbers in each class can be achieved over the entire time period. Grazing does not appear to disrupt this stability, but only decreases the number of plants established each year. Simulation of increased mesquite competition showed that in the first 12 years there may be a concomitant decline in the number of new individuals. By the 25th year, the survival rates for all but the oldest individuals have been adversely affected and there are few individuals alive.

Foraging Ecology of Seed-Harvesting Ants, Pheidole spp. in a Chihuahuan Desert Ecosystem

Seasonal activity, factors affecting foraging activity and forage selection were studied in three species of Pheidole (Hymenoptera: Formicidae) on a watershed in the southern New Mexico Chihuahuan Desert. Pheidole spp. exhibited a seasonal pattern in numbers of active colonies with most colonies active in July coincident with onset of summer rains and seed drop by annual plants. Pheidole militicida occurred only on the deeper soils of the lower watershed while Ph. rugulosa and Ph. xerophila occurred on the entire watershed. The three Pheidole spp. were active only at soil temperatures between 15-35C and were most active at sunrise. Analysis of factors affecting foraging intensity using a stepwise discriminant function and regression showed evaporation and soil surface temperature to be the strongest influences and seed availability to rank second. However, the factors included in the analysis accounted for less than 50% of the variance in all three species. Pheidole militicida collected mostly forb seeds while Ph. xerophila utilized primarily grass seeds, especially the seeds of fluff grass Erioneuron pulchellum. Introduction Seed-harvesting ants (Pogonomyrmex sp., Veromessor pergandii (Mayr) and Pheidole sp.) are important components of desert ecosystems (Whitford, 1978; Davidson, 1977). The ecology of Pogonomyrmex sp. has been studied extensively by Whitford (1976, 1978), Whitford et al (1976), Whitford and Ettershank (1975) and Rogers (1974). Tevis (1958), Went et al. (1972), Clark and Comanor (1973), Wheeler and Rissing (1975a, b,) and Rissing and Wheeler (1976) reported on aspects of the ecology of Veromessor pergandii. However, studies on the foraging ecology of desert-inhabiting species of Pheidole are limited (Davidson, 1977). Studies of Pheidole are necessary to assess the relative impact of seed-harvesting ants in desert ecosystems. Brown and Davidson (1977) showed that the density of Pheidole sp. increased in areas where seed-eating rodents were excluded, indicating that these seed harvesters responded quickly to the removal of competitors whereas the large-bodysize, seed-harvesting ants of the genus Pogonomyrmex appeared not to be affected. The work of Brown and Davidson suggests potentially important differences between Pheidole and Pogonomyrmex and point to a need for information concerning the foraging ecology of desert species of Pheidole. Our studies were designed to examine the foraging ecology of Pheidole militicida (Wheeler), Pheidole rugulosa (Gregg) and Pheidole xerophila (Wheeler), the most numerous species of Pheidole in several plant communities on a Chihuahuan desert watershed. Methods Studies were conducted on the Jornada Validation Site watershed 40km NNE of Las Cruces, Dona Ana Co., New Mexico. The watershed is an alluvial fan to the ? and E of Mt. Summerford, Dona Ana Mountains, which drains into a small ephemeral lake. The upper portion of the watershed at the base of the mountain (elevation ca. 2000 m) is a black grama (Bouteloua eriopoda) (Torr.) grassland which shifts abruptly to a creosote bush (Larrea tridentata) (DC)-dominated desert pavement community on shallow soils. On the highly dissected slopes of the watershed, the creosote bush community supports a variety of annual plants which occur at low densities during summer rainy periods (ca. lO^OO'ha-1) (Whitford, 1973). 1 Permanent address : Department of Zoology and Entomology, Monash University, Clayton, Victoria, Australia.

Response of Bouteloua eriopoda (Torr.) Torr. and Sporobolus flexuosus (Thurb.) Rybd. to Season of Defoliation

Production, total nonstructural carbohydrates, and crown diameters were measured to evaluate the effects of season of clipping on black grama and mesa dropseed. Vegetative reproduction was also monitored for black grama. Early defoliation of both black grama and mesa dropseed had less impact on plant vigor than ‘continuous defoliation or defoliation during the last half of the growing season. Black grama plants clipped during or after flowering, or continuously through the growing season, produced less herbage in the following year than those plants clipped during the vegetative stage. Removal of 65% of the current year’s growth any time during the growing season significantly reduced stolon numbers on black grama. Mesa dropseed clipped during maturity, during flowering, or clipped continuously throughout the growing season was negatively affected on one or more of the plant parameters measured. Clipping during the vegetative state had little apparent effect on plant vigor. Knowledge of plant responses to defoliation during various seasons, frequencies, and intensities is essential for proper management on rangelands. Limited data exist on season, frequency, and intensity of use on native plants occurring on Southwestern rangelands. Nelson ( 1934) and Canfield ( 1939) concluded that persistent heavy grazing significantly reduced the vigor of black grama (Bouteloua eriopodu (Torr.) Tot-t-.), an ecological dominant of much of the Southwest. Valentine (1970) found the number and length of stolons per black grama plant were closely correlated with intensity of winter grazing. Paulsen and Ares ( 1962) reported cyclic changes in black grama basal area were closely correlated with precipitation during the growing season. Paulsen and Ares ( 1962) reported that temperature requirements for mesa dropseed (Sporobofus flexuosus (Thurb.) Rybd.), another important Southwestern range plant, were less limiting than for black grama. Mesa dropseed seedlings establish well on open areas (Nelson 1934), especially during the first favorable growing season following drought (Dittberner 197 1). While ecological relationships and limited information on grazing tolerance are available, the impact of defoliation at different stages of phenological development on physiological and morphologcal characteristics have not been established for this area. Similarly, time necessary for recovery of vigor of

Drought Effects on a Semidesert Grassland Range

A vegetational survey on the Jornada Experimental Range in southern New Mexico, taken annually from 1941 through 1957, is the basis for a study of the effects of the great drought of 1951 through 1956. Both cover and yields were studied. Observations were stratified into seven classes based on a consideration of land form and soil characteristics. Seasonal and annual precipitation during the drought averaged 55% of the pre—drought average. The most severe drought years were 1951, 1953, and 1956. Both the cover and yield of Bouteloua eriopoda (Torr.) Torr., the dominant species on the upland sandy soils, were greatly reduced by drought. However, drought damage was much more severe on the deep than on shallow sands. When the impermeable caliche layer occurred at shallow depths, moisture relations during drought were apparently much better than when caliche occurred at greater depths. Another result of drought was the invasion of Prosopis juliflora (Sw.) DC. in areas where grass stands have been thinned by drought. Sporobolus spp. and Aristida spp., minor components of the climax, were more susceptible to drought damage than Bouteloua eriopoda. Yields of perennial grasses per unit cover were as great during the drought as prior to the drought. Both winter—spring and summer precipitation are important in preventing death losses of black grama. In arid areas it seems necessary to consider both cover and species composition in arriving at a potential for a site.

Pre-Emergence Herbicides for Seeding Range Grasses

CAMPBELL, R. S. 1931. Plant succession and grazing capacity on clay soils in southern New Mexico. J. Agr. Res. 43:1027-1051. CLEMENTS, F. E., AND V. E. SHELFORD. 1939. Bioecology. Wiley gc Sons Inc., N.Y. GONZALEZ, M. H. 1957. Grazing value and management of tobosa grass (Hilaria mutica (Buckl.) Benth.) on the Texas Range Station near Barnhart. M. S. Thesis, Texas A8cM Univ., College Station, Texas. 94 p. PAULSEN, H. A., AND F. N. ARES. 1962. Grazing values and management of black grama and tobosa grasslands and associated shrub ranges of the southwest. U.S. Dep. Agr. Tech. Bull. 1270, 56 p.