African pastoral ecosystems have been studied with the assumptions that these ecosystems are potentially stable (equilibrial) systems which become destabilized by overstocking and overgrazing. Development policy in these regions has focused on internal alterations of system structure, with the goals of restoring equilibrium and increasing productivity. Nine years of ecosystem-level research in northern Kenya presents a view of pastoral ecosystems that are non-equilibrial but persistent, with system dynamics affected more by abiotic than biotic controls. Development practices that fail to recognize these dynamics may result in increased deprivation and failure. Pastoral ecosystems may be better supported by development policies that build on and facilitate the traditional pastoral strategies rather than constrain them.

This paper reports the effect of season of cutting on coppice biomass production by 5 tree species common in the semiarid caatinga woodlands of northeast Brazil. Trees were cut early and late in the wet and dry seasons and coppice biomass production was monitored for 2 growing seasons after cutting. No mortality occurred as a result of cutting in any season. The effect of season of cutting on subsequent coppice production was most pronounced in the first year but differences persisted into the second year. Production by trees cut late in the wet season lagged behind that of trees cut at any other time. This was true for all species except marmeliero (Croton hemiargyreus Muell. Arg.) during both years. Pau branco (Auxemma oncocalyx Taub.) production was maximized by cutting late in the dry season. Jurema preta (Mimosa acutistipula Benth.) and catingueira (Caesalpinia pyramidalis Tul.) production was maximized by cutting early in the dry season. The season of cutting does not affect marmeliero stem production. Except for the late wet season, no treatment significantly affected sabiá Mimosa caesalpinifolia production. Stem biomass production is affected more by season of cut than is leaf biomass production. The different patterns of response among these species could be the basis of a selective cutting scheme to achieve objectives such as browse and wood production.

Twenty-two adult, female mule deer (Odocoileus hemionus hemionus) were radio-collared with activity sensors and monitored with ground triangulation from mid-November through March, for 3 years (1982-1985) in the foothills west of Fort Collins, Colorado, to test 4 general hypotheses about habitat selection and activity: (1) The proportion of time deer spend feeding and resting varies with time of day. (2) Deer alter their activity patterns in response to environmental influences. (3) Selection of specific vegetation types for feeding and resting varies with time of day. (4) Ecotones are preferred habitats. Deer were monitored during 6-hr sampling periods: sunrise, daytime, sunset, and night. Deer fed most during sunset, night, and sunrise periods and least during the day. Feeding occupied similar proportions of an average deer's time during sunset, night, and sunrise periods. They preferred the grassland type for feeding and resting at night and the mountain mahogany (Cercocarpus montanus) type for both activities during all other periods. Preference deer showed for the ponderosa pine (Pinus ponderosa) type for feeding activity was inversely related to canopy cover. Deer rested most during daytime and night periods. During periods of daylight, deer using the grassland type showed preference for ecotones with certain types offering escape cover. No such preference was observed at night. Deer fed less and rested more when snow depth exceeded 36 cm. No significant differences (P>0.05) in the proportion of time deer devoted to feeding were found in the following comparisons: clear versus cloudy full-moon nights (-50 vs. + 50% cloud cover), full-moon versus new-moon, low versus high wind speeds (0-32 vs. 32-56 km/hr), and warm versus cold temperatures (+18 to -15 vs. -15 to -23 degrees C). No significant relationships were found for the same comparisons in proportion of time devoted to resting.

The objectives of this study were to: (1) determine the effects of temperature and water stress on germination, and; (2) evaluate effects of seeding date on emergence and survival of green and gray rubber rabbitbrush (Chrysothamnus nauseosus (Pallas) Britt. subsp. graveolens (Nutt.) Piper. and Chrysothamnus nauseosus (Pallas) Britt. subsp. nauseosus (Nutt.) Piper.). Seeds of both shrubs were incubated at 10, 20, and 30 degrees C in a gradient of osmotic potentials ranging from 0.0 to -1.5 MPa. Seedings were also made in the field on seeding dates over a period of 3 years. Total germination and germination rate declined as temperatures and osmotic potentials decreased; they were highest for both shrubs at 20 and 30 degrees C and lowest at 10 degrees C. Under field conditions seedling populations were limited by low emergence and survival relative to viable seed planted. Emergence and survival of seedlings were highest in an exceptionally wet year, declining in subsequent years that were drier. Emergence ranged from 0 to 6.9% and 0 to 7.1% and survival of emerged seedlings ranged from 6.6 to 55% and 0 to 60% for green and gray rubber rabbitbrush, respectively. Survival of green rubber rabbitbrush was highest from mid-spring plantings, but no distinctively favorable seeding date was found for gray rubber rabbitbrush. Results suggest that seeds of these shrubs should be planted prior to or during periods when seedbed temperatures are in the 20 to 30 degrees C range and soil moisture is expected near its seasonal high.

Tall larkspur (Delphinium barbeyi) is a major cause of livestock death on mountain ranges. The influence of plant phenology, grazing site, and rumen fill on tall larkspur consumption was evaluated during July and August, 1987. Livestock consumption of larkspur was determined using bite counts during 4 phenological stages: bud, early flower, flower, and pod. Further, we examined larkspur ingestion in a shaded tree site and in an open sun site at 0, 50, and 100% rumen fill levels using ruminally cannulated steers. Steers on the 0, 50, and 100% fill levels consumed 9, 15, and 17% larkspur, respectively (P=0.15). There was a site effect (P=0.06) with steers eating 17 and 11% larkspur in the shade and sun sites, respectively. Over the summer, larkspur comprised 6% of cattle diets. No larkspur was consumed during the bud stage. Larkspur consumption peaked at 10% of cattle diets during the pod stage. Leaves of tall larkspur contained >3% total alkaloids (dry weight) in early July, but declined greatly with maturation. Larkspur was very nutritious, with crude protein levels 12 to 20%, and fiber levels <20% during most of the summer. Cattle diets, as determined with esophageally fistulated animals, were also high in crude protein and low in fiber during the summer. We propose a toxic window hypothesis relating larkspur palatability and toxicity. This hypothesis predicts that most cattle losses will occur during the flowering stage. We found that tall larkspur was unpalatable to cattle from the bud stage until the flowering racemes had elongated, and then consumption generally increased with plant maturation. Even though palatability and consumption increase during the grazing season, cattle can graze tall larkspur with a much lower risk of toxicosis when toxicity is low later in the grazing season.

Hand separation of roots of 2 or more plants species from soil cores is a tedious and labor-intensive task. Our objective was to determine whether near-infrared reflectance spectroscopy (NIRS) could be employed to estimate root biomass proportions in binary mixtures of alfalfa (Medicago sativa L.) with each of 4 grasses. Grasses chosen for experimentation were crested wheatgrass (Agropyron cristatum L.), intermediate wheatgrass [Thinopyrum intermedium (Host) Barkworth & D.R. Dewey], an intergeneric hybrid [Elytrigia repens (L.) Nevski × Pseudoroegneria spicata (Pursh) Love], and Russian wildrye [Psathyrostachys juncea (Fisch.) Nevski]. In the first experiment, roots from single-species field plots were washed from soil cores, dried, ground, and mechanically mixed in preselected alfalfa-grass ratios in which the percentage of grass varied from 0 to 100. Equations to measure the proportion of alfalfa or grass were developed from near infrared reflectance data using 84 randomly selected samples. In the second experiment, the 5 plant species were grown in greenhouse pots in pure stands and in binary mixtures that included all combinations of the grasses. Root systems were separated while attached to the topgrowth, dried, and ground. Tissues from single species treatments were mixed and calibration equations developed from these mixtures were used to estimate the proportion of alfalfa and the proportion of grass in samples. Samples contained either one type of root or a mixture of roots in proportions similar to those that occurred naturally in the pots. Coefficients of determination (r2) between the estimated and the actual root mass ratios ranged from 0.92 to 0.99. Determination of the proportion of grass in the samples was more accurate and precise than determination of the proportion of alfalfa. After the appropriate calibration equations have been developed, NIRS is more efficient than hand separation for estimating alfalfa-grass root mass ratios. The utility of the techniques can be increased by developing equations that encompass more complex mixtures and a wider range of environmental circumstances.

Foliar sprays of 2,4-D [(2,4-dichlorophenoxy)acetic acid]), picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid), dicamba (3,6-dichloro-2-methoxy benzoic acid), or clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) were applied in 30 or 150 L of total spray solution ha-1 to threadleaf rubber rabbitbrush [Chrysothamnus nauseosus ssp. consimilis (Greene) Hall & Clem] in Garfield County, Utah. Additional herbicide treatments were applied in 150 L ha-1 in Sevier County, Utah. Herbicides were less effective when applied in 30 L ha-1 than when applied in 150 L of total spray solution ha-1. Mortality was 74 to 87% following applications of 4.4 kg a.e. (acid equivalent) 2,4-D ha-1. Dicamba applied at 3.3 kg ha-1 resulted in 70 to 87% mortality, and picloram applied at 0.8 kg ha-1 resulted in 56 to 79% mortality. The greatest mortalities (84 to 97%) occurred on areas treated with 2.2 kg clopyralid ha-1. Mortality of threadleaf rubber rabbitbrush increased an average of 28, 17, 33, and 27% following applications of 2,4-D, dicamba, picloram, and clopyralid respectively, by using 150 L spray volume. Greatest increases were at the lowest herbicide rates. Applying herbicides in greater amounts of carrier (water) significantly increased both mortality and canopy reduction of threadleaf rubber rabbitbrush for at least 39 months.