Research and Publications
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This study quantitatively characterized the floral guilds of 17 prevalent wildflower species of the Great Basin that are, or could be, available for restoration seed mixes. More than 3800 bees representing >170 species were sampled from >35,000 plants. Species of Osmia, Andrena, Bombus, Eucera, Halictus, and Lasioglossum bees prevailed. The most thoroughly collected floral guilds, at Balsamorhiza sagittata and Astragalus filipes, comprised 76 and 85 native bee species, respectively. Pollen-specialists dominated guilds at Lomatium dissectum, Penstemon speciosus, and several congenerics. In contrast, the two native wildflowers used most often in sagebrush steppe seeding mixes—Achillea millefolium and Linum lewisii—attracted the fewest bees, most of them unimportant in the other floral guilds. Successfully seeding more of the other wildflowers studied here would greatly improve degraded sagebrush steppe for its diverse native bee communities.
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Annual growth-ring analysis was used to determine the year of establishment and the relationship between recruitment and weather events. Results indicated stand ages and locations were different (P > 0.001) among species and subspecies, and years of recruitment were strongly correlated with local and hemispheric weather patterns. Linear and multiple regressions modeled recruitment pulses for all four species. Weather-based predictor variables indicated complex interactions between recruitment and climatic controls. Pacific Decadal Oscillation index variables were prominent predictors for all four species at their associated sites. Other important local weather variables included total annual precipitation the year before recruitment, the year of recruitment, and the year following recruitment. In Nevada and the Great Basin, it is imperative that successful sagebrush seeding technologies are discovered and implemented.
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In this study, a multivariate dataset was analyzed using principal components analysis to identify “defining factors” that best explained variation among sites. Variation was primarily attributed to an inverse relationship between crested wheatgrass and sagebrush abundance (R2 = 0.69; P < 0.0001) and their affinity for either silty or sandy soil textures, respectively, as well as a negative association between crested wheatgrass abundance and species diversity (R2 = 0.67; P < 0.0001). These results do not support the assumption that crested wheatgrass seedings uniformly remain in vegetation states with low diversity and poor sagebrush reestablishment over the long term (i.e., 43 − 63 yr). We suggest that a broader interpretation of plant community dynamics is needed while avoiding generalizations of how historically seeded Wyoming big sagebrush sites will respond over time.
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In this study, exotic annual grass cover and density were greatly reduced in all treatments where perennial seedlings were planted compared with the control (no seedlings planted). Treatments including crested wheatgrass (Agropyron desertorum) generally limited annual grasses more than other treatments. Most notably, forage kochia (Bassia prostata) reduced exotic annual grasses less than crested wheatgrass and crested wheatgrass planted with forage kochia. This suggests that if forage kochia will be planted, it should be used in conjunction with perennial bunchgrasses in efforts to revegetate exotic annual grass − invaded sagebrush steppe. Established native vegetation also greatly reduced exotic annual grass reinvasion. Though some differences existed among established vegetation treatments, our study highlights that established perennial vegetation prevents redomination by invasives after exotic annual grass control.
View Chapter 12 of the book, Exotic brome-grasses in arid and semiarid ecosystems of the western US: causes, consequences, and management implications.
Invasive annual grass research and management in arid and semiarid ecosystems of the Western United States (USA) have historically focused on reducing weed abundance as opposed to ecosystem restoration, which addresses the underlying processes responsible for their persistence. Given the current impact of invasive annual grasses and their continued spread in this region, we identified common characteristics responsible for persistence of the most problematic exotic annual Bromus. For heavily invaded areas, these include transient, yet typically large seed banks, altered soil resource availability and litter production, displacement of native species, and frequent disturbance from fire. To better address these common characteristics for future management, we illustrate how an adaptive management framework can reduce existing uncertainty associated with the restoration of arid and semiarid ecosystems.
View Chapter 11 of the book, Exotic brome-grasses in arid and semiarid ecosystems of the western US: causes, consequences, and management implications.
Human land uses are the primary cause of the introduction and spread of exotic annual Bromus species. Initial introductions were likely linked to contaminated seeds used by homesteading farmers in the late 1880s and early 1900s. Transportation routes aided their spread. Unrestricted livestock grazing from the 1800s through the mid-1900s reduced native plant competitors leaving large areas vulnerable to Bromus dominance. Ecosystems with cooler and moister soils tend to have greater potential to recover from disturbances (resilience) and to be more resistant to Bromus invasion and dominance. Warmer and drier ecosystems are less resistant to Bromus and are threatened by altered fire regimes which can lead to Bromus dominance, impacts to wildlife, and alternative stable states.
View Chapter 10 of the book, Exotic brome-grasses in arid and semiarid ecosystems of the western US: Causes, consequences, and management implications.
The factors that determine plant community resistance to exotic annual Bromus species are diverse and context specific. They are influenced by the environmental characteristics and attributes of the community, the traits of Bromus species, and the direct and indirect interactions of Bromus with the plant community. Environmental factors, in particular ambient and soil temperatures, have significant effects on the ability of Bromus to establish and spread.
View Chapter 9 of the book, Exotic brome-grasses in arid and semiarid ecosystems of the western US: causes, consequences, and management implications.
A prominent goal of invasive plant management is to prevent or reduce the spread of invasive species into uninvaded landscapes and regions. Monitoring and control efforts often rely on scientific knowledge of suitable habitat for the invasive species. However, rising temperatures and altered precipitation projected with climate change are likely to shift the geographic range of that suitable habitat. Here, we review experimental and modeling studies of climatic limits to exotic annual Bromus distribution in the Intermountain West in the context of projections of future climate change.
View Chapter 8 of the book, Exotic brome-grasses in arid and semiarid ecosystems of the western US: causes, consequences, and management implications.
Abiotic factors have a strong influence on where annual Bromus species are found. At the large regional scale, temperature and precipitation extremes determine the boundaries of Bromus occurrence. At the more local scale, soil characteristics and climate influence distribution, cover, and performance. In hot, dry, summer rainfall-dominated deserts (Sonoran, Chihuahuan), little or no Bromus is found, likely due to timing or amount of soil moisture relative to Bromus phenology. In hot, winter-rainfall-dominated deserts (parts of the Mojave Desert), Bromus rubens is widespread and correlated with high phosphorus availability. It also responds positively to additions of nitrogen alone or with phosphorus.
View Chapter 7 of the book, Exotic brome-grasses in arid and semiarid ecosystems of the western US: causes, consequences, and management implications.
Bromus tectorum presents a rich resource for soil microorganisms because of its abundant production of biomass, seeds, and surface litter. These organisms interact dynamically with abiotic factors such as interannual variation in weather, with other soil microorganisms, with their hosts, and with each other to create spatially and temporally varying patterns of endemic or epidemic disease. Five principal soil borne pathogens, Ustilago bullata, Tilletia bromi, Pyrenophora semeniperda, Fusarium, and a new species in the Rutstroemiaceae (bleach blonde syndrome pathogen), are known to have sometimes major impacts on B. tectorum seed bank dynamics, seedling emergence, and seed production. Naturally occurring fungal pathogens that can have a strong negative impact on B. tectorum success have also been considered as candidate organisms for B. tectorum biocontrol using an augmentative mycoherbicidal strategy.