Perennial pepperweed (Lepidium latifolium L.) is a creeping rooted exotic weed that has infested native hay meadows, riparian areas and agronomic fields throughout the western United States. This highly invasive species causes major losses in forage quality and creates numerous management problems. On many sites infested with perennial pepperweed, a near mono-culture exist. Sustainable suppression programs require the establishment of a competitive perennial species. You can not establish seedlings of a perennial competitive species without some initial substantial reduction in perennial pepperweed stands through weed control. Because tillage is not feasible with this creeping rooted species, herbicidal weed control is the primary option. Experience has shown, that the massive and extensive root system of perennial pepperweed can not be completely eliminated with one application of a herbicide. This means that repeated applications of a selective herbicide are required after the perennial seedlings of a competitive species are established. Perennial pepperweed is a broadleaf species that is some what susceptible to applications of 2,4-D. Therefore, the choice revegetation species is limited to a perennial grass that is resistant to 2,4-D applications at low rates as a seedlings and moderate rates once established. The saline/alkaline nature of the soils where perennial pepperweed is often found limit the adapted perennial grasses to tall wheatgrass (Elytriga elongata [Host] Nevski). The herbicide chlorsulfuron has been shown to be more effective in initially controlling perennial pepperweed than 2,4-D. We determined that applications of chlorsulfuron at rates sufficient to control perennial pepperweed resulted in herbicidal residues that severely reduced or eliminated the establishment of tall wheatgrass seedlings. Application of 2,4-D at flower budding for perennial pepperweed (June), followed by seeding tall wheatgrass in the fall (October), and application of low rates of 2,4-D over the wheatgrass seedlings the next spring (May), gave the best grass seedling establishment and suppression of the perennial weed.

Multiple generations of rhizome-connected tillers stabilize soils and produce measurable amounts of herbage on sandy rangeland throughout the world. However, little is known about the dynamics of rhizome development in these clonal plant species. Seasonal relationships between foliar characteristics and rhizomes of prairie sandreed [Calamovilfa longifolia (Hook) Scribn.] were examined on sands range sites at 30-day intervals from May through September 1989 and 1990 at the University of Nebraska, Panhandle Experimental Range near Scottsbluff. Quadrats were excavated each year from two, 5 x 5 Latin Square macroplots in each of 2 grazing histories, long-term rest or current-year deferment. Under dry conditions in 1989, a 65% reduction in the length of new rhizomes during July preceded a 64% reduction in live tillers in August. After which, rhizome length and live tiller density were unchanged and mean tiller weight increased during September. When average precipitation occurred in 1990, a 25% reduction in live tillers and concurrent increases in new rhizome length and mean tiller weight occurred during July. Rhizome bud densities increased throughout the growing season at different but predictable rates (R2 greater than or equal to 0.95) for grazing histories, regardless of precipitation. Length of new rhizomes was highly correlated (R2 = 0.91) with live herbage throughout the growing season. Measurable increases in total rhizome length did not occur until live herbage of prairie sandreed exceeded a threshold of about 50 g m(-2). Maximum increase in length of new rhizomes per unit of live herbage was about 10 cm g(-1) near 100 g m(-2). Given its dependence on vegetative reproduction and relatively high palatability to beef cattle, periodic or repeated years of full growing season deferment may be the only reliable method of obtaining measurable increases in prairie sandreed populations.

In August 1994, wildfire burned 6,500 ha of native Dry Mixed Prairie in southeastern Alberta. The following year, a study was initiated to monitor the recovery of major plant communities. Burning was followed by 3 successive years of drought, reducing total vegetative cover by 10%. Exposed soil increased to a high of 23%, three years after the fire. Litter and grass production were reduced through 1997, with the greatest decline in 1995 when grass production on burned and unburned areas averaged 890 and 1,468 kg ha(-1), respectively. Of the major forage species, Stipa spp. and Koeleria macrantha (Ledeb. J.A. Schultes f.) were affected for a single year and Agropyron spp. 2 years by burning. Both Agropyron and Stipa abundance displayed interactions with topographic position in response to fire. In 1995, Agropyron increased on uplands with burning from 90 to 143 kg ha(-1), but decreased on lowlands from 383 to 238 kg ha(-1), a pattern repeated in 1996. In contrast, Stipa declined at both positions, but only for a single year. Where livestock grazing occurred after the fire, forage removal was greater on burned areas. Drought conditions, in combination with summer wildfire, reduced Dry Mixed Prairie range productivity and ground cover for several years and intensified livestock grazing, highlighting the need for changes in rangeland management under these conditions.

The influence of night grazing on feeding behavior, nutrition and performance of cattle was studied. Twenty-four steers weighing 367 kg (SD = 76) grazed either from 0900 to 1900 (day grazers), 2100 to 0700 (night grazers) or 0900 to 1900 and 2400 to 0400 (day-and-night grazers) during 13 weeks. Four esophageally fistulated steers were used in a cross-over design to sample the diet selected during the day and at night. No differences (P > 0.05) were observed in the diet selected in the day or at night. As the season progressed the fiber components of the diet increased (P < 0.01) significantly while nitrogen and in sacco dry matter disappearance declined (P < 0.01). Actual grazing time (min day(-1), SE = 16) were 352, 376, and 476 for day, night, and day-and-night grazers, respectively. Day-and-night grazers had a higher intake of organic matter than either day or night grazers. Night grazers had the lowest forage intake and also the slowest rate of consumption. Steers that grazed in the night had the lowest water intake: 22.7 liter day(-1) (SE = 1.5) in week 4; 19.9 liter day(-1) (SE = 1.1) in week 8. Average weight changes (g day(-1), SE = 62) were -435, -548 and -239 for day, night, and day-and-night grazers, respectively. These results show that during the dry season, grazing exclusively in the night cannot substitute for day time grazing, but that it is rather complementary to the latter. Timing (day or night) of grazing did not affect diet selection but nocturnal grazing decreased the need for water.

A 3-year study was conducted to evaluate grazing strategies for production of growing cattle during summer on Northern Great Plains rangeland. Crossbred yearling steers (N = 123 per year, avg initial weight = 275 kg) were allotted to 1 of 2 treatments replicated in 3 pastures. Treatments were season-long grazing of pastures at recommended stocking rates assuming a 4-month grazing period or intensive-early grazing of pastures stocked at the same rate assuming only a 2-month grazing season. Precipitation in 1993 was 169% of normal resulting in greater forage quality than in other years and no differences were observed in weight gains between treatments during 1993. In 1994 and 1995, steers in the intensive-early stocked pastures gained less weight during the 2 months of grazing than did those in the season-long stocked pastures; however, gain per hectare was greater in the intensive-early stocked pastures. Intensive-early stocking with growing steers may be a viable means to overcome limited forage quality during late summer in the Northern Great Plains and to maximize forage utilization in years of abundant forage.

Computer simulation was used to determine the effects of wild elk (Cervus elaphus) on available forage, cattle herd size, and ranch gross margin in southwestern Montana beef cow-calf production systems. Data collected from 5 southwestern Montana ranches were used to develop input parameters for bio-economic models of elk forage harvest and beef production. Input parameters described ranch resources, animal inventories, and animal management. Cattle herd size ranged from 241 to 1147 head. Elk numbers varied by season within ranch and ranged from 49 to 421 head. Ranches were simulated as currently managed with elk present and with 10, 20, 30, and 100% of the elk removed. Simulated management scenarios were replicated 10 times. Data from each ranch were analyzed by one-way analysis of variance. Cattle herd size, gross margin, and available forage significantly (P < 0.05) increased when all elk were removed; however, the magnitude of these effects differed among ranches. Removal of all elk permitted cattle herd size to increase from 7 to 32% across ranches. Annual costs of elk on the 5 ranches (i.e., increase in gross margin from elk removal) ranged from 5,949 to 21,152. On an AUM basis, elk costs ranged from 8.55 to 14.51. Three management alternatives were evaluated for their potential to recover elk costs: Montana's Block Management Program, coordinated exchange of forage use, and leasing of hunting access. For each ranch, at least one of these management strategies could recover all estimated costs of providing elk habitat. Elk can significantly reduce profits for cow-calf ranches in southwestern Montana. Elk impacts on beef enterprise profits are closely associated with efficiency of resource use by cattie-i.e., ranches with lower unit costs of production lose more gross margin by providing forage for elk compared to ranches with higher production costs.

Airborne infrared thermal radiography has been proposed as a tool which may be used to monitor the water temperature along the network of streams and rivers which compose a watershed. The proponents of this method correlate vegetative shadows on a stream channel with reduced infrared radiation (IR) reception in the radiographic data to suggest that the water temperature is reduced in such areas. Two methods are employed to demonstrate that this interpretation of the data is in error. First, the fundamental principles of thermodynamics are employed to show that if the stream is in fact flowing, the water affected by any cooling process cannot remain in the vicinity where it was cooled. Second, temperature data taken from a stream channel are used to show that the water flowing in the channel is essentially unaffected by the patterns of vegetative shade on the surface of the channel.