Measurement of riparian shrub twig length before and after use should yield a useful utilization index. A first step towards determining utilization is measurement of twig length. This study appraised variability between 15 observers for measuring dormant season twig length on riparian alder (Alnus incana (L.) Moench) shrubs. Ten streamside shrubs were selected on which 5 branches consisting of 5 twigs each were tagged below the fifth twig for a total of 250 twigs. Fifteen experienced people independently measured twigs on the same day after instruction in the method. Data were analyzed by hierarchical analysis of variance for length of twigs by branches, by shrubs, and by observers. Variation among observers within a branch was about twice the size of variability among shrubs and represented 20% of the total variation. Items contributing to observer variability were measurement of dieback, selecting the twig end or live bud for measurement, inclusion of short lateral leaf stubs in measurements, and selection of a crotch from where the twig is measured. These results clearly illustrate major difficulties in trying to measure riparian shrub utilization.

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.

The effects of root-plowing on soil organic carbon and nitrogen were investigated by comparing paired undisturbed native rangeland with root-plowed sites in the southern Great Plains. Time since root-plowing ranged from 4 to 22 years. We hypothesized that following root-plowing (1) soil carbon would initially drop but recover to the level of untreated range within a 5-10 year period, and (2) the permanent removal of mesquite trees, which enhance ecosystem carbon and nitrogen and provide shade that lowers soil temperature, would result in a slow decline in soil carbon and nitrogen in this ecosystem. There were not significant differences due to treatment for either soil carbon mass (g m-2) (P=0.81) or nitrogen mass (P=0.62). There were significant differences in soil carbon mass (P=0.0014) with respect to elapsed time since plowing. The upper soil layer (0-100mm) had higher carbon levels (P=0.0001) than the deeper soil layer (100-200mm)(1422 +/- 210 g m-2 vs. 1111 +/- 206 g m-2). Differences in soil nitrogen were similar to those of soil carbon. There were significant differences in nitrogen among years-since-root-plowing observations (P=0.003) and the upper soil layer had higher nitrogen levels than the deeper soil layer 138 +/- 18 g m-2 vs. 107 +/- 18 g m-2) (P=0.0001). When the data were analyzed using paired native site values as covariate to account for site differences, the sites that had been root-plowed 4 years previously had higher soil carbon (p

Delaying calving season from late winter to late spring has been suggested as a way for producers in Wyoming and other high elevation areas of the West to reduce feeding costs. We hypothesized that shifting calving season to a later date would reduce feed costs by providing a closer match between cow nutritional requirements and nutritional quality of grazable forage. The objectives of this study were to estimate the cost of feeding a cow under 5 alternative calving month scenarios (February through June) and to identify alternative lower-cost forage practices that could replace feeding hay. Mixed integer programming models were constructed for each calving scenario with the objective of minimizing the cost of providing energy and protein to a mature cow. Objective function values from each model were compared to identify the low feed cost calving month. The ration was balanced for each month of the year, with requirements dependent on the interaction between the reproductive cycle and environmental conditions. Fat reserves were included as an alternative energy source and body condition was allowed to fluctuate. Under average weather conditions, June was the lowest feed cost calving month with a reduction in annual feed costs of 43 cow-1 over February calving. The cost reduction was a result of a shift from mechanical to stock harvested forage, with the cow being maintained at a lower average body condition during the winter.

Pocket gophers are important disturbance agents in rangelands, yet little is known about how plant responses to gopher disturbances vary with grazing and topography. We measured the spatial distribution of soil mounds created by the northern pocket gopher (Thomomys talpoides attenuatus Hall and Montague) in shortgrass steppe, and sampled plant cover and species composition on gopher mounds at 3 topographic positions within 2 pastures that were lightly and heavily grazed by cattle. Measurements were taken during 1996 and 1997 in each pasture along a 75 x 900-m transect that spanned the same topographic gradient: a south-facing slope, a north-facing slope, and an upland plain. Pocket-gopher mounds were more numerous in the lightly grazed pasture but mounds were larger in the heavily grazed pasture. An estimated 1-6% of the total area was disturbed on uplands and south-facing slopes, and <1% was disturbed on north-facing slopes. Plant cover on mounds was generally higher in the heavily grazed than in the lightly grazed pasture, primarily due to a greater cover of the dominant perennial grass, blue grama (Bouteloua gracilis [H.B.K.] Lag ex Griffiths). Detrended correspondence analysis also showed that pasture had a greater effect on plant species composition on mounds than topography or yearly variation. Our results demonstrate that topography affected the spatial distribution of pocket-gopher disturbances, and pasture influenced the pool of plant species colonizing mounds. It is therefore important to assess animal-disturbance effects and plant responses to disturbances on rangelands within the broader context of topography and grazing.

The mountainous riparian corridor performs important hydrologic functions including nutrient transfers between the terrestrial (upslope) and aquatic (stream) ecosystems. Nitrate-nitrogen and ammonium-nitrogen concentrations were determined on water samples collected in 1993 and 1994 from a montane riparian zone in Northern Colorado. Soil water samples were collected from the riparian corridor and upslope systems, under both losing (summer reservoir releases) and gaining (spring snowmelt runoff) streamflow conditions. Statistical analyses using least square means contrasts were made to identify spatial and temporal differences between: 1) the upslope system and the riparian corridor, 2) the upslope system and the stream, and 3) the riparian corridor and the stream. The Sheep Creek riparian corridor may serve as a sink for nitrate-nitrogen in both gaining and losing streamflow conditions, and as a source for ammonium nitrogen in gaining streamflow conditions. The length of the source or sink period is relatively short and is not meant to suggest differences in site productivity. Streamflow generation mechanisms help determine if the riparian corridor is a nutrient sink or source.

Indian ricegrass (Achnatherum hymenoides [Roem. &Schult.] Barkw. = Oryzopsis hymenoides [Roem. & Schult.] Ricker = Stipa hymenoides Roem. &Schult.) may buffer its seed banks over time via morphological (lemma and palea) and physiological (seed coat) seed dormancy. However, Indian ricegrass seed dormancy has usually not been examined from a genetic perspective. Because a positive relationship between seed dormancy and seed size has long been noted within Indian ricegrass populations we wanted to determine if genetic variation for seed dormancy was present among seed morphs. We also wanted to determine if genetic variation for seed dormancy was present in material without polymorphism. The T-593 population from McKinley Co., N.M., has 3 seed morphs produced on genetically distinct plants, 'elongate' (2.24 mg/seed), 'globose' (3.00 mg/seed), and 'jumbo' (8.70 mg/seed). Following a 3-week prechill, elongate seed showed higher germination (66%) than globose seed (20%) over 6 tests (pairs of seed lots), while jumbo seed did not germinate without scarification. Jumbo seed had thicker (181 microgram) lemmas than globose (93 microgram) or elongate (52 microgram) seed. Individual plants of the nonpolymorphic cultivar, Rimrock, were selected for high or low germination following a 3-week prechill. The spring following seed harvest, germination with prechill was greater for progeny lines of the high-germination selections (45.5%) than low-germination selections (3.8%) with Rimrock intermediate (11.8%). This heritable difference in germination was accompanied by only small differences in lemma and palea thickness and no difference in seed mass. Genetic variation in seed dormancy may be found both between morphs (interpreted as variation for morphological dormancy) and within morphs (interpreted as variation for physiological dormancy). Genetic variation for seed dormancy can be as great within a population as between populations.

Preventing the invasion of uninfested rangeland is central to managing spotted knapweed (Centaurea maculosa Lam.). Intensity, frequency, and season of grass defoliation determine the ability of grasses to tolerate grazing and resist weed invasion. We hypothesized that as grass defoliation intensity increases, spotted knapweed cover, density, and biomass would increase, that increasing defoliation frequency would increase the intensity effect, and that spring defoliation would cause a greater increase in spotted knapweed than summer defoliation. We hand clipped grasses in 1 m2 plots at 2 spotted knapweed infested Idaho fescue (Festuca idahoensis Elmer) sites in western Montana. Clipping treatments were 4 intensities (0, 30, 60, and 90% of the foliage), 3 frequencies (1, 2, and 3 at 14-day intervals), and 2 seasons (spring beginning in mid-May and summer beginning in mid-July), factorially arranged in a randomized-complete-block design with 4 replications for a total of 24 treatments per replication. Treatments were applied in 1995 and 1996. By 1997 grass cover and density were reduced by defoliation intensity of 90%. Defoliation frequency greater than once caused a reduction in grass cover and density at the 60% intensity. Spring defoliation caused a greater reduction in grass cover and density than summer defoliation. Grass biomass was reduced by the 30% defoliation treatment. Grass defoliation intensity greater than 60% caused an increase in spotted knapweed cover and density. Defoliation more than once increased spotted knapweed cover. Spring defoliations increased spotted knapweed cover compared to summer defoliations. Spotted knapweed biomass was not affected by defoliation treatments. Our study suggests that an annual single grass defoliation of 60% or less, regardless of the season, will not increase spotted knapweed invasion on rangeland.

The recent expansion of juniper into sagebrush steppe communities throughout the semiarid Intermountain West is most frequently attributed to the reduced role of fire, introduction and overstocking of domestic livestock in the late 1800s, and mild and wet climate conditions around the turn of the century. This hypothesis has, however, limited quantitative support. There are few studies of fire history in the sagebrush steppe and none that examine the chronosequence of changes in mean fire intervals, introduction of livestock, and coincident climatic conditions with the initiation of post-settlement juniper expansion. This study was undertaken to test the hypothesis that the postsettlement expansion of juniper was synchronous with the introduction of domestic livestock, reduction in fire frequency, and optimal climate conditions for plant growth. We documented the fire history and western juniper (Juniperus occidentalis Hook). woodland chronology for a sagebrush steppe in a 5,000 ha watershed in south central Oregon. Regional tree ring data were used as proxy data for presettlement climatic conditions. Western juniper age distribution was determined by coring trees across the study area. Fire history was constructed from several small clusters of presettlement ponderosa pine (Pinus ponderosa Laws.) scattered across the study area. Samples were crossdated to determine fire occurrence to the calendar year. Mean fire intervals were computed for each cluster based on cumulative fire history of each tree sampled within the cluster. Fire events in low sagebrush (Artemisia arbuscula Nutt.) were documented by determining death dates of fire-killed western juniper trees. Records dating the introduction and buildup of livestock during the late 1800s and dates of initial fire suppression were summarized. Western juniper expansion began between 1875 and 1885, with peak expansion rates occurring between 1905 and 1925. The fire record spans 1601 to 1996. Before 1897, mean fire intervals within individual clusters ranged from 12 to 15 years with years between fires varying between 3 to 28. Nearly one third of the fires in the basin were large and usually proceeded by one year of above-average tree ring growth. Two fire events were recorded in the sparsely vegetated low sagebrush site, 1717 and 1855. The last large fire occurred in the study area in 1870 and the last small fire in 1897. The time sequence of wet climatic conditions between 1870 and 1915, introduction of livestock, and the reduced role of fire support the hypothesis that these factors contributed to the postsettlement expansions of western juniper.