Weight relations for twig lengths and diameters were determined for hairy mountain mahogany plants in southern New Mexico. Both twig lengths and twig diameters were related linearly to twig weights. Twig length and twig diameters explained more than 80% of the variation in twig weight. The equation ŷ(g) = -0.68 + 0.3 (length) + 6.33 (diameter) resulted in the highest r2 (0.88) value compared to either length or diameter alone. Thus, twig length and diameter measurements could be used to determined production and utilization of hairy mountain mahogany. These relationships probably, however, vary with environmental context.

Around 1900 temperate and semidesert grassland productivity declined, soil erosion increased, and drought destabilized the livestock industry in the northern and southern hemispheres. As government leaders throughout the world began to recognize the importance of grassland productivity and soil conservation, a massive experiment began to evolve. Government and private individuals 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 (Cenchrus ciliaris L.), weeping lovegrass [Eragrostis curvula (Schrad.) Nees], kleingrass (Panicum coloratum L.), and lovegrass (Eragrostis lehmanniana Nees) plants from seed collected in Africa were easier to establish and persisted longer than other grasses. Between 1930 and 1986 scientists in many countries evaluated the establishment and persistence of these grasses, but no attempt was made to synthesize the data base and determine the effects of climate and soil on plant establishment and persistence. Our objective was to: (1) determine the climatic and edaphic characteristics of areas where the seed of each grass was collected in Africa, and where each grass has been successfully established in both hemispheres, and (2) identify characteristics which influence 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 5 degrees C, and soil texture is loamy. Weeping lovegrass can be established and plants persist when spring, summer, and fall rainfall varies from 400 to 1,000 mm on deep sandy soil and mean minimum winter temperatures rarely fall below -5 degrees C. The invasion of adjacent nonplanted sites occurs only in Africa where growing season rainfall infrequently cycles between 750 and 1,000 mm and soils remain wet in mid-summer. Kleingrass can be established where mean maximum daily summer temperatures are above 30 degrees C, mean minimum daily winter temperatures rarely fall below 0 degrees C, summer growing season rainfall varies from 400 to 990 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 rainfall in 30 to 40 days exceeds 150 mm, and soil textures are sandy or sandy loam.

Understanding the temporal response of vegetation to selected livestock grazing strategies is necessary for the continued maintenance or increased productivity of rangelands. Vegetation cover and above-ground biomass were sampled bimonthly from 1978-1984 on pastures grazed continuously (MCG) and moderately stocked (8.1 ha AU-1); continuously (HCG) and heavily stocked (4.6 ha AU-1); high-intensity, low-frequency (HILF) and moderately stocked (8-1; 17:119 day stocked at 8.1 ha AU-1); short-duration grazing (SDG) and heavily stocked (14-1; 4:50 day, stocked at 4.6 ha AU-1); and livestock exclusion (LEX). Prior grazing history, vegetation cover, soils, and slope were similar among pastures. Midgrass cover was eliminated in the HCG pasture, and declined in the heavily stocked SDG pasture. Midgrass cover was maintained under the moderately stocked HILF grazing strategy and increased under MCG or LEX. During 1984, sideoats grama (Bouteloua curtipendula (Michx.) Torr.) basal diameter in the MCG and LEX pastures was significantly greater than in the SDG pasture. By the end of the study, total organic cover and total aboveground biomass in the MCG or LEX pastures were significantly greater than in the SDG and HCG pastures. The heavy grazing intensity used in this study, regardless of the grazing strategy, does not appear suited for long-term maintenance of midgrass species.

Within the pinyon-juniper type, trees and understory vegetation are interspersed with open areas forming a mosaic of vegetational patterns. The objective of this research was to define and describe vegetational zones surrounding Rocky Mountain pinyon (Pinus edulis Engelm.) and oneseed juniper (Juniperus monosperma [Engelm.] Sarg.). Transects consisting of contiguous frames were laid out from the base of the tree and continued into the interspace area (outside the canopy) for each cardinal direction. Potential zone boundaries were located by calculating a squared Euclidean distance utilizing basal cover estimates of each frame. Zone boundaries were verified by discriminant analysis. Vegetation associated with both pinyon pine and oneseed juniper exhibited 3 zones. Zone 1 consisted of vegetation associated with the tree bole. Zone 2 was, for the most part, located beneath the tree canopy. Zone 3, consisting primarily of interspace, contained mostly perennial grasses and forbs. Mean basal cover of vegetation surrounding oneseed juniper increased from <1% in zone 1, to approximately 7% in zone 2, to about 12% in zone 3. Mean basal cover estimates of vegetation associated with pinyon pine increased from approximately 4% in zone 1, to 10 and 11% in zones 2 and 3, respectively. Differences in species composition among zones between tree species were apparent.

Harvester ant colonies (Pogonomyrmex owyheei Cole) in southern Idaho were monitored periodically for 9 years. Mortality rates indicate that established colonies live 14-30 years (mean = 17). Mounds were commonly reactivated after the death of an old colony; consequently, some may be utilized for many decades. Clearings with active mounds showed almost no change after 9 years of observations while those without active mounds were rapidly filled by annual herbs and then gradually by perennial shrubs. Harvester ants are clearly a very persistent component of cold desert shrub communities.

Desert saltgrass [Distichlis spicata var. stricta (Torr.) Beetle] is the dominant herbaceous forage on many saline rangelands. The ability to direct-seed this grass would permit revegetation of disturbed saline soils. Seeding guidelines must be based on an understanding of germination requirements in relation to seedbed conditions. Germination responses to alternating temperatures in relation to sodium chloride (NaCl)-reduced osmotic potentials were studied in the laboratory and seedbed salinity and water potentials were measured in a typical saltgrass stand in Nevada. Optimum conditions for saltgrass germination were at -0.1 MPa osmotic potential and a 20 degrees C differential in cold and warm period temperatures with warm period temperatures above 30 degrees C. Decreasing osmotic potentials from 0 to -2 MPa decreased the rate of germination from 4.5 to 0.3 and total germination from 60 to 9% across all temperature regimes. Water potentials in the lower topographical positions of a typical saltgrass stand after an unusually wet winter were high enough for germination (>-2MPa) in June when temperatures were optimum for germination. In most years and on xeric sites, optimum temperature and moisture conditions would not overlap to result in high germination. Some germination occurs at cooler than optimum temperatures and low osmotic potentials. Some seeds may eventually germinate in saline seedbeds under these conditions but highest germination would be expected when unusually high precipitation or topographic position results in high seedbed water potentials during late spring and early summer when temperatures are optimum. Consequently, irrigation during late spring and summer should produce the best stands of saltgrass from direct seeding. Where irrigation is not possible, saltgrass should be seeded in the fall to permit germination during early spring when temperatures are suboptimum but the seedbed is still moist. Success of nonirrigated seedings will be highly dependent on seedbed salinity and moisture conditions in the spring.

Chemical and botanical analyses of feces provide information on diet quality and composition that is not easily collected directly from a grazing animal. However, fecal excreta is readily available in the pastures the animals are grazing. This study was conducted to determine the feasibility of collecting fecal samples from the pasture for chemical (nitrogen) and botanical analysis. Two experiments were conducted to determine the effects of method of drying (oven-dried vs. freeze-dried) and duration of fecal pat exposure on chemical and microhistological analyses. Concentration of nitrogen was not affected by method of drying or by duration of exposure in the field. Samples <72 hours during the winter and <24 hours during the summer may be used for nitrogen analysis. However, we recommend that samples be collected as soon as possible following defecation to reduce possible negative effects of precipitation, insect damage, and trampling. Method of drying had no significant (P<0.05) effect on percentage of identifiable fragments or subsequent forage class determination. Bleach, as a blending medium reduced pigment masking of epidermal fragments resulting in an increase in the percentage of identifiable epidermal fragments. Duration of exposure did not affect identification of most of the forage classes. The proportion of identifiable fragments, was lower during winter than summer.

The predation by selected arthropod predators on immature and adult black grass bugs (BGB), Labops hesperius and Irbisia brachycera, on Utah ranges was investigated. Adult Nabis alternatus was found to be the most important predator of BGB; this species is particularly abundant in early spring and was observed preying on BGB both in the field and in laboratory feeding tests. Immature nabids consumed the bugs but preyed mostly on leafhoppers, smaller plant bug nymphs, and other immature nabids. Nabis vanduzeei showed potential as a predator of adult BGB in the laboratory feeding tests. Spiders were important predators of BGB. Based on predation of BGB in field and laboratory studies, the spiders observed were ranked as follows from greatest to least importance as predators: Xysticus cunctator, Misumenops lepidus, Tibellus sp. (Thomisidae), Castianeira sp. (Clubionidae), and Tetragnatha sp. (Araneidae). Spiders attacked any prey of a size similar to themselves, but they also preyed on beneficial arthropods, including nabids and other spiders.

A stochastic (Monte Carlo) simulation model was developed to evaluate the influence of prescribed burning on the expected value and variability of net returns from a representative stocker cattle enterprise. The model was applied to both shallow prairie and eroded prairie range sites in eastern Oklahoma. Prescribed burning is shown to be an economically feasible means of improving the productivity of eastern redcedar infested rangeland. Implementation of an annual burning program resulted in a $69.00 and $4.80 per hectare increase in the net present value of the 10-year return stream generated from stocker cattle production on shallow prairie and eroded prairie range sites, respectively. Prescribed burning does not increase the variability of annual income from stocker cattle production. However, when risk is measured in terms of relative variability (coefficient of variation) or the probability of annual returns below zero, prescribed burning is determined to be a risk-reducing practice.