The decline of traditional pastoral systems has highlighted the problem of managing shrub encroachment on successional shrublands in the Mediterranean region, especially in marginal habitats. A long-term study of the response of ecosystem dynamics to phosphate amelioration and shrub control was initiated in 1988 on an area of phosphorus deficient terra rossa, dominated by dwarf shrubs that had been burnt in the summer of that year. The treatments were imposed in a replicated factorial design once at the beginning of the study. The area was previously grazed yearlong by goats, but during the experiment beef cattle grazed the area during the summer of each year. Without herbicide control, shrub cover reached its preburn level within 5 years, but with shrub control after 17 years, it had not yet reached the preburn level. The average shrub cover over the whole experimental period was 41.9%–49.1% without herbicide and 13.5%–24.4% with (P < 0.0001, SE of the difference  =  3.99). The effect of phosphate application on shrub cover was not significant, but cover of herbaceous vegetation increased (P < 0.0016, SE of difference  =  5.03). A “state and transition” scheme was constructed that defines the interventions necessary to buffer any one of the states against the pressures of successional processes. Vegetation states were defined by the dominance of either herbaceous vegetation or one of two spiny shrub species, Prickly burnet (Sarcopoterium spinosum, Rosaceae) and Calicotome villosa (Fabaceae). The timing and scale of the interventions depend largely on landscape management objectives and on available economic and logistic resources. We conclude that appropriate management of grazing, periodic control of the shrub component, and occasional soil nutrient amelioration can lead to the development of attractive open woodland with a productive herbaceous understory that provides a wider range of ecological services than a landscape dominated by the undisturbed successional shrub thickets.

Ecosystem water use efficiency (EWUE) is defined as the net carbon uptake per amount of water lost from the ecosystem and is a useful measure of the functionality in semiarid shrub and grassland communities. C₄ grasses have higher water use efficiency (WUE) than do C₃ shrubs, although it has been postulated that C₄ plants have lost much of their advantage due to the rising atmospheric CO₂ concentrations. The hypothesis was that C₄-grass-dominated ecosystems have a higher EWUE than C₃-shrub-dominated ecosystems under the present CO₂ concentration and climatic variability. Evapotranspiration (ET) and CO₂ fluxes were measured with Bowen ratio systems at a shrub and grass site for 6 years in southeastern Arizona. Two different methods were used to evaluate growing season EWUE using the ET and CO₂ fluxes. The first method estimated a net daytime growing season EWUE for the grass site at 1.74 g CO₂ · mm⁻¹ ET and 1.28 g CO₂ · mm⁻¹ ET at the shrub site. The second method estimated maximum EWUE during part of the growing season at 7.35 g CO₂ · mm⁻¹ ET for the grass site and 4.68 g CO₂ · mm⁻¹ ET for the shrub site, which was considered a significant difference at P  =  0.056. Data variability of the first method precluded a statistical difference determination between sites, but the results indicated that the grass-dominated ecosystem was between 1.4 and 1.6 times more water use efficient than the shrub-dominated ecosystem. Mean annual growing season precipitation and ET were similar in the two ecosystems, but the higher EWUE of the grassland system enabled it to take up more carbon during the growing season than the shrub ecosystem. Ecosystem differences in CO₂ and H₂O flux have important management implications including primary productivity, C sequestration, and rangeland health.

We postulate that phosphorus (P) fertilization may increase above-ground net primary productivity (ANPP) of rotationally grazed rangelands without reducing the legume component, as does N fertilization. In doing so, we evaluated the effect of phosphate fertilization on the production and relative contribution of legumes and grasses of native and old tall fescue (Festuca arundinacea Schreb) grasslands; we recorded annual production, seasonal productivity, and biomass contribution of each component. The experiment was conducted in a commercial farm located in the Flooding Pampa and managed under rotational grazing. Treatments consisted of two fertilization programs (66 (P₆₆) and 29 (P₂₉) kg P · ha⁻¹ supplied as rock phosphate and/or monoammonium phosphate from 1997 to 1999) and a nonfertilized control. A paddock dominated by native grassland and another dominated by old tall fescue grassland were selected. Nine 5-ha plots were established in each paddock, and treatments were randomly assigned. During the experimental period, from October 1998 to October 1999, total above-ground biomass was harvested from each plot before and after each grazing period and separated into components: tall fescue, other C₃ perennial grasses, legumes, C₃ annual grasses, C₄ grasses, forbs, and standing dead material. ANPP of each component was estimated during the warm (October 1998–February 1999) and the cool (March 1999–September 1999) season. In native grassland, phosphate fertilization increased ANPP of C₃ annual grasses and legumes during both the warm and the cool seasons; therefore annual ANPP of the grassland under P₆₆ was 40% higher than under P₂₉ and doubled ANPP of nonfertilized plots. Phosphate fertilization didn't increase total annual ANPP of old tall fescue grassland, but it did increase ANPP of legumes during both seasons.

Japanese brome (Bromus japonicus Thunb. ex Murr.) is an introduced, annual cool-season grass adapted to the central and northern Great Plains. Japanese brome has negatively impacted perennial grasses and decreased seasonal animal gains. Prescribed spring burning and defoliation have been effective in reducing brome density or cover, but little information directly compares the two common strategies. The objectives of this study were to 1) compare annual spring burning and grazing to reduce Japanese brome populations; and 2) evaluate trends of vegetative composition and biomass in burned, grazed, and unburned rangelands infested with Japanese brome. Paddocks with Japanese brome were assigned to one of four treatments: 1) annual prescribed spring burning, 2) spring grazing, 3) a combination of annual spring burning and grazing, and 4) an idle control. Treatments were applied annually from 2000 to 2004. Japanese brome density was greatest in the idle control in all years, even when low winter and spring precipitation limited Japanese brome recruitment. Late spring Japanese brome density was similar in all treatments with grazing or burning in four of the five seasons. Spring burning resulted in less than 65% litter cover the last 3 years, whereas the idle control and spring grazing had over 80% litter cover the last 4 years. Western wheatgrass (Pascopyrum smithii [Rydb.] A. Löve) decreased with spring grazing in burned and unburned paddocks. Buffalograss (Bouteloua dactyloides [Nutt] J. T. Columbus) composition decreased in the idle control treatment. Blue grama (Bouteloua gracilis [Willd. ex Kunth] Lag. ex Griffiths) and sideoats grama (Bouteloua curtipendula [Michx.] Torr.) composition varied by year. Even though annual burning and spring grazing were equally effective in limiting Japanese brome density and biomass compared to the idle control, Japanese brome was still present after 5 years, which indicates the difficulty of eradicating Japanese brome from ecosystems where it has become naturalized.

Broom snakeweed (Gutierrezia sarothrae [Pursh] Britt. & Rusby) increases and dominates rangelands following disturbances such as overgrazing, fire, and drought. However, if cattle can be forced to graze snakeweed, they can be used as a biological tool to control it. Grazing trials were conducted in May and August 2004, 2005, and 2006 on a crested wheatgrass (Agropyron cristatum L.) seeding that had been invaded by broom snakeweed. Narrow grazing lanes were fenced with temporary electric fence and the cows were moved to a new lane each day. Forage allowance was limited to 24%–75% of the intake requirement. There were significant negative correlations (P < 0.05) between forage allowance and snakeweed utilization, suggesting it was the main factor driving snakeweed consumption. In the 2004 experiment, 7 cows in low body condition (4.6 body condition score, BCS) and 7 cows in high body condition (6.8 BCS) were grazed in separate lanes. The low body condition group grazed more snakeweed in the evening grazing period (26% of bites) than the high body condition group (20% of bites, P  =  0.03). In the 2005 experiment, one group (6 cows) received a protein/energy supplement high in bypass amino acids required for detoxification of terpenes; the second group received no supplement. There was no difference in snakeweed consumption between the supplement groups (P  =  0.63). The major difference in diets in both years occurred in grazing periods during the day. Cows grazed perennial bunchgrasses first, then turned to cheatgrass (Bromus tectorum L.), and grazed snakeweed only when all other forage was depleted (20% of bites in the evening grazing periods). Cattle grazed 62%–95% of snakeweed plants and utilized 50%–85% of snakeweed biomass. Cattle can be forced to graze snakeweed by confining them to small areas and limiting alternative forage. Grazing reduced the snakeweed population.

Spring elk grazing may reduce forage availability for wildlife or livestock in summer and may harm forage resources on foothill rangeland. We quantified bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. Love) response to spring defoliation on foothill rangeland in southwestern Montana. Two experiments were conducted simultaneously on a foothill grassland site and a foothill sagebrush steppe site. Bluebunch wheatgrass plants (n  =  800) were selected and excluded from wild and domestic ungulates. Clipping treatments were applied in either early spring (mid- to late April) or late spring (mid- to late May), and plants were clipped to 1 of 3 residual heights (3, 6, or 9 cm) for 1, 2, or 3 successive years. Unclipped plants served as controls. Plant response was measured in late June and late July on both sites. April clipping for 3 successive years did not adversely affect bluebunch wheatgrass in June or July (P > 0.05) at either site. On foothill grassland, May defoliation to 3 cm for 2 consecutive years reduced leaf height (P  =  0.04) in July. May defoliation for 3 successive years to 3 or 6 cm reduced plant yield (P < 0.05) and leaf height (P < 0.05) in June, and May defoliation for 3 successive years to 3 cm reduced leaf height (P  =  0.02) in July. On foothill sagebrush steppe, 3 successive years of May defoliation to ≤ 9-cm stubble heights decreased leaf height in June (P < 0.05). We conclude that foothill rangelands where bluebunch wheatgrass receives moderate or light defoliation (6–9-cm residual stubble heights) in mid- to late May should be limited to no more than 2 successive years of mid- to late May grazing, whereas sites that receive heavy to severe defoliation (≤ 3-cm residual stubble heights) in mid- to late May should not be grazed for 2 successive years during mid- to late May.

Increases of velvet mesquite (Prosopis velutina Woot.) in southwestern grasslands might have been caused by livestock consumption of fuels that once burned with sufficient frequency and intensity to kill the trees. However, attempts to control mesquite with fire usually have failed. We measured fire damage and 5 years of postfire recovery for 225 mesquite trees > 1 m tall, following a 2002 wildfire that included grasslands differing in fire history, presence vs. 34-year livestock exclusion, and predominance of native vs. exotic grasses. The fire burned 100% of ground cover in ungrazed areas and 65% on grazed lands. Top-kill was 100% for trees in exotic ungrazed grasslands (the areas with highest fuel loads), 79% for trees in ungrazed native grasslands, and 28% for trees in grazed grasslands. Most top-killed trees produced ground sprouts, so that by 2006 the combined foliage volume from ground sprouts and surviving branches was 78% (± 3.2 SE) of preburn foliage volume in grazed areas, 66% (± 3.3) in ungrazed exotic grasslands, and 57% (± 4.0) in ungrazed native grasslands. Fire damage was greater among surviving trees in ungrazed areas that had burned twice (1987 and 2002) than among those that had burned only once since 1968 (in 2002), especially in native grasslands where postfire foliage recovery for twice-burned trees was only 47% (± 6.3) by 2006. Only 1 of 84 trees died in the area burned once, whereas 12 of 66 (18.2%) died in the area burned twice, including several individuals > 3 m tall. These results suggest that repeated fires likely could have prevented the historic spread of velvet mesquite into southwestern grasslands, but probably could be used to control mesquite today only in areas where abundant herbaceous growth provides sufficient fine fuels.

Wyoming big sagebrush (Artemisia tridentata subsp. wyomingensis [Beetle & A. Young] S.L. Welsh) plant communities of the Intermountain West have been greatly reduced from their historic range as a result of wildfire, agronomic practices, brush control treatments, and weed invasions. The impact of prescribed fall burning Wyoming big sagebrush has not been well quantified. Treatments were sagebrush removed with burning (burned) and sagebrush present (control). Treatments were applied to 0.4-ha plots at 6 sites. Biomass production, vegetation cover, perennial herbaceous vegetation diversity, soil water content, soil inorganic nitrogen (NO−3, NH 4), total soil nitrogen (N), total soil carbon (C), and soil organic matter (OM) were compared between treatments in the first 2 years postburn. In 2003 and 2004, total (shrub and herbaceous) aboveground annual biomass production was 2.3 and 1.2 times greater, respectively, in the control compared to the burned treatment. In the upper 15 cm of the soil profile, inorganic N concentrations were greater in the burned than control treatment, while soil water, at least in the spring, was greater in the control than burned treatment. Regardless, greater herbaceous aboveground annual production and cover in the burned treatment indicated that resources were more available to herbaceous vegetation in the burned than the control treatment. Exotic annual grasses did not increase with the burn treatment. Our results suggest in some instances that late seral Wyoming big sagebrush plant communities can be prescribed fall burned to increase livestock forage or alter wildlife habitat without exotic annual grass invasion in the first 2 years postburn. However, long-term evaluation at multiple sites across a larger area is needed to better quantify the effects of prescribed fall burning on these communities. Thus, caution is advised because of the value of Wyoming big sagebrush plant communities to wildlife and the threat of invasive plants.

Satellite and high-altitude aerial remote sensing have been used to measure dense infestations of invasive weeds over very large areas but have limited resolution and cannot be used to detect sparsely distributed weeds. Ground-based methods have provided detailed measurements of invasive weeds but can measure only limited areas. Here we test a novel approach that uses a lightweight airplane, flying at 72 km ṡ h⁻¹ and 100-m altitude, to rapidly collect high-resolution images over relatively large areas. We obtained 1 987 images, each representing 48.5 m² of mixed-grass prairie with 2-mm resolution (ground sample distance). From these images we were able to reliably measure small patches and even individual plants of the invasive forb Dalmatian toadflax (Linaria dalmatica [L.] P. Mill.). Ground-based measurements of aboveground toadflax biomass were highly correlated (R² > 0.93) with point-intercept and visual-estimate cover measurements from aerial images. The time required to analyze images ranged from 4 to 45 seconds for presence/absence data and from 1 to 6 minutes for cover data. Toadflax was present in 795 of 1 987 images but exceeded 1% cover in only 99 images. Given the observed variation among images in toadflax cover, at least 400 images were needed to precisely estimate the mean toadflax cover of 0.2%. These results suggest that such high-resolution aerial imagery could be used to obtain detailed measurements of many invasive weed populations. It may be most useful for identifying incipient weed infestations and expanding the scale at which population-level attributes of weed populations can be effectively measured.

Concentrated herbivory by elk (Cervus elaphus) can degrade vegetative communities and alter ecosystem processes. Areas severely damaged by elk are commonly protected with woven wire fence, which can exclude other animals. Complete exclusion and prevention of large mammal herbivory might not always be necessary to restore vegetative communities. We designed and evaluated a simple fence that excluded elk, but maintained access for deer and other species. We enclosed a 1-ha stand of quaking aspen (Populus tremuloides Michaux) with our fence in an area with a high density of elk. We monitored effectiveness of the fence with trackplots, animal-activated cameras, and changes in aspen stem height and density. We documented only 1 elk within the exclosure in 2 years of monitoring. Mammals that used the exclosure included beaver (Castor canadensis), black bear (Ursus americanus), bobcat (Lynx rufus), coyote (Canis latrans), deer (Odocoileus spp.), mountain lion (Puma concolor), raccoon (Procyon lotor), red fox (Vulpes vulpes), and lagomorph (Leporidae). After 1 year of protection, mean aspen stem height increased 14.5 cm more inside the exclosure than outside, but stem density in the exclosure changed little compared to outside. Our fence design effectively excluded elk and has potential for protecting a variety of resources.

The spread of the invasive, Eurasian spotted knapweed (Centaurea maculosa Lam.) across the northwestern United States would be reduced if livestock regularly consumed it. We determined if white-face yearling ewes (n  =  36) conditioned for 12 days to fresh-cut spotted knapweed, with or without molasses, would increase their use of it during a 5-day field trial and/or a 4-day drylot trial. Ewes were assigned to one of three treatments: ewes not conditioned to spotted knapweed or molasses (NC), ewes conditioned to spotted knapweed (SK), or ewes conditioned to spotted knapweed sprayed with liquid beet molasses (SKM). During conditioning, all groups consumed high amounts of their feed. Nonconditioned ewes (NC) consumed less than ewes conditioned to spotted knapweed (SK, SKM), indicating spotted knapweed did not inhibit initial consumption. In the field, SKM ewes spent more time grazing spotted knapweed and other forbs than SK ewes. In a drylot, time spent eating and intake of spotted knapweed and bromegrass (Bromus inermis Leyss.) varied through time. Conditioning yearling ewes to spotted knapweed, with or without molasses, did not increase consumption of this invasive plant, possibly because sheep inherently graze spotted knapweed only to a certain extent, or we did not use enough spotted knapweed during conditioning.

Factors influencing the distribution and abundance of black-tailed prairie dog (Cynomys ludovicianus) colonies are of interest to rangeland managers because of the significant influence prairie dogs can exert on both livestock and biodiversity. We examined the influence of 4 prescribed burns and one wildfire on the rate and direction of prairie dog colony expansion in shortgrass steppe of southeastern Colorado. Our study was conducted during 2 years with below-average precipitation, when prairie dog colonies were expanding throughout the study area. Under these dry conditions, the rate of black-tailed prairie dog colony expansion into burned grassland (X ¯  =  2.6 ha · 100-m perimeter⁻¹ · y⁻¹; range  =  0.8–5.9 ha · 100-m perimeter⁻¹ · y⁻¹; N  =  5 colonies) was marginally greater than the expansion rate into unburned grassland (X ¯  =  1.3 ha · 100-m perimeter⁻¹ · y⁻¹; range  =  0.2–4.9 ha · 100-m perimeter⁻¹ · y⁻¹; N  =  23 colonies; P  =  0.066). For 3 colonies that were burned on only a portion of their perimeter, we documented consistently high rates of expansion into the adjacent burned grassland (38%–42% of available burned habitat colonized) but variable expansion rates into the adjacent unburned grassland (2%–39% of available unburned habitat colonized). While our results provide evidence that burning can increase colony expansion rate even under conditions of low vegetative structure, this effect was minor at the scale of the overall colony complex because some unburned colonies were also able to expand at high rates. This result highlights the need to evaluate effects of fire on colony expansion during above-average rainfall years, when expansion into unburned grassland may be considerably lower.

Simulated browsing treatments were imposed on an important browse species of the North American moose (Alces alces L.) to see if the development and extent of subsequent stem dieback in trembling aspen (Populus tremuloides Michx.) could be used to determine the time of browsing during the growing season. Two hundred naturally growing aspen saplings of similar size and form were randomly selected in a 20-ha area near the endowment lands of the University of Northern British Columbia, Prince George, British Columbia, Canada. Plants were randomly assigned to treatment categories so that the apical meristems of 50 plants each were assigned to a control or were clipped on one of the following dates 6 weeks apart: 1 June, 16 July, and 30 August 2005. The leader of each aspen was clipped and dieback was left to progress until the onset of winter dormancy. Our results showed that the earlier the simulated browsing occurs in the growing season, the greater the length of stem dieback, up to the maximum of the subapical axillary node below the point of clipping. The average rate at which dieback progressed varied between treatments and decreased throughout the growing season. Our results suggest that the ratio of the actual length of stem dieback to the overall length of stem between the clip point and the subapical axillary node serves as a good indicator for estimating the time at which aspen meristems have been browsed during the growing season.

Landscapes with structural heterogeneity or patchiness can support diverse and stable wildlife populations. Visual obstruction methods (i.e., Robel pole and Nudd's coverboard) are common and useful techniques for quantifying vegetation structure; however, both rely on ocular estimations, which can be highly variable between observers. Our objectives were to 1) compare measurement and observer variation for visual obstruction among the two standard methods and the digital image method we developed using a digital camera; and 2) compare the performance of the Robel pole and digital image to estimate standing crop. The mean variation across the five observers using the digital image method (6.8%) was significantly lower (P < 0.05) than both the Nudds' coverboard (32.1%) and the Robel pole (52.2). There were no significant differences among locations for the digital image method; however, there were for both the Robel pole and Nudds' cover board (P < 0.05). The digital image method provided a better estimate of standing crop (r²  =  0.89) compared to the Robel pole (r²  =  0.68), accounting for 21% more of the observed variation in biomass. Long-term research programs that utilize seasonal field technicians to quantify habitat structure with a visual obstruction method could benefit from implementing use of the digital image method we developed. The low measurement error observed with this technique relative to the more traditional methods compared in this study might limit year-to-year and within-year variability of habitat structure data collected by numerous technicians with a high annual turnover.

Saltcedar (Tamarix spp.) is a widespread invasive plant found in riparian corridors and floodplains in 16 western states. In addition to being associated with such problems as increased soil salinity and decreased plant diversity, saltcedar has been reported to be a prolific water user. Popular press articles widely report that each individual saltcedar tree can use as much as 757 L (200 gallons) per day. Consequently massive control and removal efforts are underway to reduce transpirational water loss and increase water salvage for arid and semiarid environments. Although the potential economic benefits of these control efforts are touted, it has not been proven whether such water savings are possible on a stream level. The original citation for the 757-L estimate does not list the experimental design or techniques used to arrive at this value. We use three lines of evidence—peer-reviewed scientific literature, sap flux rates and sap wood area, and potential evaporation rates—to demonstrate the improbability that saltcedar, or any other woody species, can use this much water per tree on a daily basis. A more realistic estimate of maximum tree-level daily water use derived from sap flux measurements would be < 122 L · d⁻¹ (32.2 gallons). Estimates of water salvage would be grossly overestimated using the popular water use value (757 L · d⁻¹), and economic benefits from saltcedar control based solely on water salvage are questionable.