Western North American Naturalist 

About: Western North American Naturalist is an academic journal published by Brigham Young University Press. The journal publishes majorly in the area(s): Population & Species richness. It has an ISSN identifier of 1944-8341. Over the lifetime, 1498 publications have been published receiving 14661 citations. The journal is also known as: The Western North American Naturalist.

Woody riparian vegetation response to different alluvial water table regimes.

Abstract: Woody riparian vegetation in western North American riparian ecosystems is commonly dependent on alluvial groundwater. Various natural and anthropogenic mechanisms can cause groundwater declines that stress ripar- ian vegetation, but little quantitative information exists on the nature of plant response to different magnitudes, rates, and durations of groundwater decline. We observed groundwater dynamics and the response of Populus fremontii, Salix gooddingii, and Tamarix ramosissima saplings at 3 sites between 1995 and 1997 along the Bill Williams River, Arizona. At a site where the lowest observed groundwater level in 1996 (-1.97 m) was 1.11 m lower than that in 1995 (-0.86 m), 92-100% of Populus and Salix saplings died, whereas 0-13% of Tamarix stems died. A site with greater absolute water table depths in 1996 (-2.55 m), but less change from the 1995 condition (0.55 m), showed less Populus and Salix mortal- ity and increased basal area. Excavations of sapling roots suggest that root distribution is related to groundwater history. Therefore, a decline in water table relative to the condition under which roots developed may strand plant roots where they cannot obtain sufficient moisture. Plant response is likely mediated by other factors such as soil texture and stratig- raphy, availability of precipitation-derived soil moisture, physiological and morphological adaptations to water stress, and tree age. An understanding of the relationships between water table declines and plant response may enable land and water managers to avoid activities that are likely to stress desirable riparian vegetation.

Effects of cattle grazing on North American arid ecosystems: a quantitative review

Abstract: A quantitative review was conducted of the effects of cattle grazing in arid systems on 16 response variables ranging from soil bulk density to total vegetative cover to rodent species diversity. Various studies from North American arid environments that used similar measures for assessing grazing effects on the same response variables were used for the review; each study was assigned to serve as a single data point in paired comparisons of grazed versus ungrazed sites. All analyses tested the 1-tailed null hypothesis that grazing has no effect on the measured variable. Eleven of 16 analyses (69%) revealed significant detrimental effects of cattle grazing, suggesting that cattle can have a negative impact on North American xeric ecosystems. Soil-related variables were most negatively impacted by grazing (3 of 4 categories tested were significantly impacted), followed by litter cover and biomass (2 of 2 categories tested), and rodent diversity and richness (2 of 2 categories tested). Vegetative variables showed more variability in terms of quantifiable grazing effects, with 4 of 8 categories testing significantly. Overall, these findings could shed light on which suites of variables may be effectively used by land managers to measure ecosystem integrity and rangeland health in grazed systems.

Plant adaptation in the Great Basin and Colorado Plateau

Abstract: Adaptive features of plants of the Great Basin are reviewed. The combination of cold winters and an arid to semiarid precipitation regime results in the distinguishing features of the vegetation in the Great Basin and Colorado Plateau. The primary effects of these climatic features arise from how they structure the hydrologic regime. Water is the most limiting factor to plant growth, and water is most reliably available in the early spring after winter recharge of soil moisture. This factor determines many characteristics of root morphology, growth phenology of roots and shoots, and photosynthetic physiology. Since winters are typically cold enough to suppress growth, and drought limits growth during the summer, the cool temperatures characteristic of the peak growing season are the second most important climatic factor influencing plant habit and performance. The combination of several distinct stress periods, including low-temperature stress in winter and spring and high-temperature stress combined with drought in summer, appears to have limited plant habit to a greater degree than found in the warm deserts to the south. Nonetheless, cool growing conditions and a more reliable spring growing season result in higher water-use efficiency and productivity in the vegetation of the cold desert than in warm deserts with equivalent total rainfall amounts. Edaphic factors are also important in structuring communities in these regions, and halophytic communities dominate many landscapes. These halophytic communities of the cold desert share more species in common with warm deserts than do the nonsaline communities. The Colorado Plateau differs from the Great Basin in having greater amounts of summer rainfall, in some regions less predictable rainfall, sandier soils, and streams which drain into river systems rather than closed basins and salt playas. One result of these climatic and edaphic differences is a more important summer growing season on the Colorado Plateau and a somewhat greater diversification of plant habit, phenology, and physiology.

Seed banks of Bromus tectorum-dominated communities in the Great Basin

Abstract: —Many shrub-steppe communities of the Great Basin have been converted to Bromus tectorum–dominated communities. Seed production and seed bank traits of native perennials may be poorly suited to conditions of communities dominated by this introduced annual, and native perennials may be lost from the seed banks. Seed banks of former shrub-steppe communities now dominated by annuals were quantified on 3 sites in western Utah to determine if seeds of native perennials were present and to track changes in Bromus tectorum seed densities and species composition of seed banks after fire. Burned and unburned plots on 1 site were sampled for 3 years after a wildfire. Plots consisted of grids of 5.2-cm-diameter soil cores. Seeds were quantified by monitoring seedling emergence from these cores over an extended period of time in the greenhouse. On unburned plots introduced annuals, mainly Bromus tectorum, constituted >99% of the seed bank, with Bromus densities of 4800–12,800 seeds m–2. Immediately after the fire, Bromus seed density was <3% of unburned plots, but its seed bank density recovered in 2 years. The major change in species composition of the seed bank following fire was a shift in proportional abundance between Bromus and 2 other introduced annuals immediately after the fire. One native annual and a native annual/perennial (Oenothera pallida) increased in the seed bank the 1st year after the fire. Of all samples, only 4 perennial-plant seeds representing 3 species (excluding Oenothera) were found, for a total perennial-plant seed bank of 2–3 seeds m–2. Lack of perennial-plant seeds in annual-dominated communities impairs the reestablishment of native perennials. Because perennial-plant seeds are so few, the reduction of Bromus seed banks by fire provides no opportunity for reestablishment of native species.