Vegetation zones and soil characteristics in vernal pools in the Channeled Scabland of eastern Washington

Vernal pools are seasonal pools occurring in Mediterranean-type climates within which grow concentric zones of vegetation. We studied two vernal pools that lie within an Artemisia tridentata/Festuca idahoensis shrub-steppe landscape in the Channeled Scabland of eastern Washington to determine the relationship between vegetation zonation and soil characteristics. Abundant plant species in the pools include Elymus cinereus, Poa scabrella, Lomatium grayi, Allium geyeri, Eleocharis palustris, Epilobium minutum, Myosurus aristatis, Deschampsia danthonioides, and Psilocarphus oregonus . We surveyed topography, measured plant species frequency and cover to describe the vegetation zones, and used Sorenson's index of percent to similarity to verify our designation of plant zones as communities. In one pool we described soil profiles and sampled soils throughout the growing season according to plant communities. We analyzed soils for pH; electrical conductivity; sodium, calcium, and magnesium ions; sodium absorption ratio; particle size; organic carbon; and water matric potential. ANOVA tests of soil characteristics and topography among plant communities showed that only differences in topography are statistically significant. There are, however, trends in particle size, some soil chemical parameters, and soil moisture potential among plant communities along the topographic gradient. Electrical conductivity decreased with increasing dryness of the soil through spring and summer. Seasonal changes in soil moisture potential showed that shallower soils in the centers of pools were wetter during the wet season and drier during the dry season than are deeper soils. These changes in moisture may be the most important influence on vegetation distribution within the vernal pools.     

Does the presence of Wyethia mollis affect growth of Pinus jeffreyi seedlings?

Regeneration of Pinus jeffreyi in the Sierra Nevada is often limited on sites dominated by Wyethia mollis . Allelopathic chemicals and competition for soil moisture have been suggested as possible mechanisms for limiting regeneration. We tested the hypothesis that soil chemical and microbial properties from sites in different stages of succession influence seedling growth of Pinus jeffreyi . Soil was collected from an early-seral site dominated by Wyethia mollis , a mid-seral site dominated by the shrubs Arctostaphylos patula, Ceanothus prostratus, C. velutinus , and Purshia tridentata , and a late-seral site dominated by mature Pinus . These sites were compared for nutrient content, Pinus seedling growth capacity, and microbial population size. Soil (0-33 cm) from the early-seral site had the lowest C, microbial biomass, and fungal and bacterial populations. There were no consistent trends in soil nutrient content among sites. The early-seral site had the lowest soil Ca and Mg contents but also had a lower C/N ratio and more than twofold greater P content than either the mid- or late-seral site. Pinus seedling growth and foliar nutrient concentrations were compared at 3 harvest dates (220, 314, and 417 days after germination) in a greenhouse bioassay. The treatment design was a 3 × 2 factorial with soil from each of the 3 sites either with or without Pinus seedlings. Pots without seedlings were used as controls to assess the effects of seedlings on microbial biomass. Seedling growth in the early-seral soil was initially suppressed in comparison to growth in the mid-seral soil, but by the final harvest total seedling weight was similar between these 2 treatments. The most obvious treatment effect was a reduction in growth for seedlings planted in lateseral soil, probably due to a nutrient imbalance in the soil. Seedlings grown in late-seral soil had Fe and Al levels that were nearly twice those of seedlings grown in early- and mid-seral soils. Microbial biomass followed a temporal pattern similar to that found for seedling growth. Differences in microbial biomass between the early- and mid-seral soils, although initially large, were not detected by the final harvest. We interpret these results to indicate that allelopathy or soil nutrient deficiencies resulting from the presence of Wyethia are unlikely to be responsible for limited growth of Pinus seedlings in Wyethia -dominated stands.     

Habitat requirements for Erigeron kachinensis , a rare endemic of the Colorado Plateau

Erigeron kachinensis is a rare endemic of the Colorado Plateau in southeastern Utah. This perennial composite grows in small, isolated populations at seeps and alcoves arising along canyon walls in Cedar Mesa Sandstone substrates. Characteristics of six Erigeron kachinensis sites in Natural Bridges National Monument, San Juan County, Utah, were studied to determine habitat requirements for this species. Sites were analyzed with respect to geology, soil chemistry, physical properties, and vegetational characteristics. The alcoves studied were very saline, often with soil surfaces covered with a white crust of salt. Living cover was enhanced by perennially moist soils, diminished amounts of solar radiation, soil salinity, and above-average amounts of available soil phosphorus. Kachina daisy vegetative growth appears to be favored by these same abiotic factors. The most commonly associated plant species on E. kachinensis sites were Aquilegia micrantha, Calamagrostis scopulorum, Zigadenus vaginatus, and Erigeron kachinensis . These species and the daisy accounted for more than 75% of the total living cover in the alcoves studied. A principal components analysis procedure was developed for evaluating site suitability for Erigeron kachinensis . This daisy has been successfully introduced to a site selected using that model.     

Effects of grazing exclusions on rangeland vegetation and soils, east central Idaho

Nineteen exclosures on sagebrush steppe and shadscale rangelands, varying in age from 18 to 38 years, were sampled for plant species richness, plant composition, indicators of soil erosion, ground cover, vegetative cover, and herb-low shrub layer screening cover. Features within the exclosures were compared with adjacent sites of the same size that were open to grazing by livestock and wildlife. Species richness typically was slightly greater inside exclosures than in adjacent grazed sites (median = 2 more species inside exclosures), but the difference was not significant ( P = 0.16). Similarity of plant community composition between exclosures and adjacent grazed sites ranged from 45% to 82%. Evidences of soil movement, soil pedestals, and soil flow patterns were all more pronounced outside exclosures than inside ( P ≤ 0.02), even though many sites were on flat to mild slopes (median slope = 12%). Meta-analysis of the 19 exclosure sites indicated that grazing exclusion resulted in less bare ground cover compared with adjacent grazed sites ( P ≤ 0.05). The effect of grazing exclusion on visible soil surface cryptogams was significant ( P ≤ 0.05), with generally greater cover inside exclosures. Cryptogam cover differences between grazed sites and exclosures tended to increase with the number of years of grazing exclusion ( r = 0.64, P = 0.046). Pseudoroegneria spicata , a principal livestock forage, averaged greater basal cover inside exclosures than outside on 4 of 10 sites where it occurred, although no exclosure sites had greater P. spicata cover on grazed sites. Meta-analysis of the 10 sites indicated that grazing exclusion resulted in greater P. spicata cover compared with adjacent grazed areas ( P ≤ 0.05). Poa secunda , a short-growing grass that initiates growth early in the spring and is not important livestock forage, averaged greater basal cover outside exclosures on 5 of 15 sites where it occurred. Meta-analysis of the 15 sites indicated a significant treatment effect ( P ≤ 0.05), with greater Poa secunda basal cover outside exclosures. Grazing exclusion resulted in greater screening cover in the herb-low shrub layer (0-0.5 m height; P ≤ 0.05). These results indicate that despite improved livestock grazing management over the past half century, livestock grazing still can limit the potential of native plant communities in sagebrush steppe ecosystems, and that the health of semiarid ecosystems can improve with livestock exclusion in the absence of other disturbances. A few exclosure sites were similar for the measured parameters, suggesting that these sites were ecologically stable and that exclusion of livestock grazing was not sufficient to move succession toward more pristine conditions, at least within the time periods studied. Managed disturbance such as fire or mechanical brush treatments may be necessary to restore herb productivity on these ecologically stable sites.     

Geostatistical analysis of resource islands under Artemisia tridentata in the shrub-steppe

Desert plants can influence the pattern of resources in soil resulting in small-scale enriched zones. Although conceptually simple, the shape, size, and orientation of these "resource islands" are difficult to study in detail using conventional sampling regimes. To demonstrate and alternative approach, we sampled soil under and around individual Artemisia tridentata (sagebrush), a dominant shrub of cool desert environments, and analyzed the samples with univariate statistics and geostatistics. Univariate statistics revealed that soil variables like total inorganic-N, soluble-C, and microbial biomass-C were distributed with highest mean values within about 25 cm of the plant axis and significantly lower mean values at distances beyond 60 cm. However, such simple analyses restricted our view of resource islands to identically sized, symmetrical accumulations of soil resources under each plant. Geostatistics provided additional information about spatial characteristics of soil variables. Variography revealed that samples separated by a distance of less than about 70 cm were correlated spatially. Over 75% of the sample variance was attributable to spatial variability. We modeled these spatial relationships and used kriging to predict values for unsampled locations. Resulting maps indicated that magnitude, size, and spatial distribution of soil resource islands vary between individual plants and for different soil properties. Maps, together with cross-variography, further indicate that resource islands under A. tridentata are not always distinguishable from the surrounding soil by sharp transition boundaries and may be asymmetrically distributed around the plant axis.     

Nodulation and acetylene reduction by two legumes with Rhizobia indigenous to northern Great Basin soils

Medicago sativa L. and Hedysarum boreale Nutt. were grown in the greenhouse on soils representing 27 of the major soil associations of the northern Great Basin. Nodulation of Medicago sativa L. by indigenous rhizobia occurred with 25 of the soil associations and of Hedysarum boreale Nutt. with 21 of these soil associations. Nitrogen fixation, as indicated by acetylene reduction activity, was greater for Medicago sativa L. than for Hedysarum boreale Nutt. for most of the soil associations. Multiple regression functions incorporating 49 independent climatic, edaphic, and vegetation variables failed to predict acetylene reduction activity with satisfactory precision.     

Vegetation and soil factors in the relation to slope position on foothill knolls in the Uinta Basin of Utah

Vegetation and soil differences with respect to slope position were studied on foothill knolls in the Uinta Basin of Utah. Plant communities on windswept ridges (top of slope) exhibited several unique characteristics when compared to the other slope communities. These communities at the top and base of slopes were sufficiently different in respect to plant life form composition, plant cover, wind-adapted growth forms, and percent exposed rock that they should be considered separate community types. Mineral concentrations in plant tissue and soil samples declined downslope in some cases and increased in others. Diversity decreased downslope as shrubs became dominant over grasses and forbs. Management of these communities should require special consideration due to the changes in the community structure with slope position.     

Pollinators of Astragalus monoensis Barneby (Fabaceae): new host records; potential impact of sheep grazing

Important bee species inhabiting the study area are listed, including those observed and collected foraging on Astragalus monoensis , a California rare plant. The significance of each species as a potential pollinator is assessed, based on frequency of occurrence in collecting, observed and published host plant records, and morphology. Three pollinator categories are proposed: observed and/or collected on the plant, probable visitors, and possible visitors. New host plant records for these species are listed. Current sheep grazing practices in the A. monoensis habitat endanger pollinators in four ways: (1) destruction of potential nest sites, (2) destruction of existing nests and contents, (3) direct trampling of adult bees, and (4) removal of food resources. Exposure of the major bee species to each of these factors is assessed utilizing experimental data and published information.         

Some physiological variations of Agropyron smithii Rydb. (western wheatgrass) at different salinitylevels

The purpose of this study was to determine the physiological responses of Agropyron smithii Rydb. To various saline environments as evaluated in the laboratory. Agropyron smithii Rydb. (Rosana) seeds were germinated, transplanted into nutrient solutions with NaCl concentrations of 0, 50, 100, 150, and 200 m M , and grown for 80 days in a growth chamber. Results indicated that leaf water potential, relative water content of leaf tissue, and concentrations of Na, K, and Cl in plant tissue were significantly affected by increasing NaCl concentration. However, leaf chlorophyll concentration and concentrations of Ca and Mg in plant tissue were not significantly affected by the presence of NaCl.     

Ecophysiology of the temperate desert halophytes: Allenrolfea occidentalis and Sarcobatus vermiculatus

Numerous basins of the intermountain area often have extensive playa surfaces that are nearly devoid of vegetation. Margins of these playas support sparse communities dominated by chenopod shrubs Allenrolfea occidentalis (iodine bush) and Sacrobatus vermiculatus (black greasewood). These plants establish and persist in an environment where halomorphic soils induce extreme osmotic stress and atmospheric precipitation is very low and erratic and occurs largely during the winter when temperatures are too low for growth. We measured net CO 2 assimilation rates, leaf conductances, transpiration rates, water-use efficiencies, and stem xylem potentials for these two C3 species. Data were collected in above-average (1991) and below-average (1992) precipitation years. Net CO 2 assimilation rates for Allenrolfea were statistically similar in 1991 and 1992 but in general declined for Sarcobatus in 1992. For both species, leaf conductances and leaf transpiration rates declined significantly from 1991 to 1992, with the decline greater for Sarcobatus . Water-use efficiencies doubled from 1991 to 1992 for both plant species. Predawn xylem water potentials were -2.2 and -3.3 MPa for Allenrolfea and -1.8 and -2.6 MPa for Sarcobatus by September 1991 and 1992, respectively. Afternoon xlem water potentials were -3.1 and -2.0 MPa for Allrolfea and -2.6 and -2.2 for Sarcobatus beginning in May 1991 and 1992, respectively. Xylem water potentials dropped to -5.0 MPa for Allenrolfea and -3.4 MPa for Sarcobatus by September for both 1991 and 1992. For Allenrolfea , in general, the total soil water potential within the zone of maximum root activity is more negative than the plant's predawn xylem potential, which suggests that the plant is partially phreatophytic and/or has a large capacitance due to its extensive woody root system.     

Site characteristics and habitat requirements of the endangered dwarf bear-claw poppy ( Arctomecon humilis Coville, Papaveraceae)

Arctomecon humilis Cov. is a narrow endemic, confined to gypsiferous substrates derived from the Shnabkaib Member of the Moenkopi Formation in southwestern Utah. The characteristics of seven A. humilis sites were studied to define habitat requirements of the species. Both physical and biotic aspects of the habitat were analyzed; geology, soil chemistry, and physical properties, as well as vascular and nonvascular plant communities, were studied. Chemical and physical properties of these soils vary considerably from those supporting adjacent desert-shrub communities. The dominant vascular species on A. humilis sites are shadscale and Mormon tea. It was found that A. humilis occurred in portions of the habitat where shrubs were relatively less dense. A soil-surface, cryptogamic community contributed 84% or more of the total living cover on sites that supported A. humilis . Species composition of the cryptogamic community was highly similar among sites. Likewise, composition of the cryptogamic cover was similar when random samples were compared with samples centered on A. humilis plants. The Purgatory Flat site, which does not support the poppy, seems inseparable from A. humilis sites, in respect to soil characteristics and composition of the associated plant cover. There is reason to believe an A. humilis population could be established at the Purgatory Flat site.     

Oribatid mites (Acari: Oribatida) of the Falkland Islands,South Atlantic and their zoogeographical relationships

A total of 21 species of oribatid mites (Acari: Oribatida) are recorded from heat-extracted samples of soil and plant material collected in the Falkland Is., South Atlantic. Previous records of a further 11 species provide a total of 32 species. The distribution of each non-endemic species recorded from the Falkland Is. is figured. The oribatid mite fauna of these islands belongs to the Neotropical Region with strong sub-Antarctic elements and some similarities with New Zealand.     

Vegetation responses to 35 and 55 years of native ungulate grazing in shrubsteppe communities

Ungulate populations are managed in shrubsteppe ecosystems around the world, but relatively few long-term datasets are available that test the impacts of these grazers on shrubsteppe structure and function. This study evaluated 8 exclosures in 4 shrubsteppe communities to determine the effects of deer and elk over 35 or 55 years on (1) plant biomass and species composition, (2) soil nitrogen (N) mineralization and net nitrification rates, Olsen extractable phosphorus (P), and C:N ratios, and (3) arthropod diversity and abundance. The site with deer, the highest ungulate densities, and coldest climate (Sinlahekin Wildlife Area, WA) had greater vegetative biomass and cover inside the exclosures than outside. The sites with elk, moderate ungulate densities, and intermediate climatic conditions (Oak Creek and Wenas Wildlife Areas, WA) had no effects of exclosures on vegetative biomass or cover. The site with elk, the lowest ungulate densities, and driest climatic conditions (L.T. Murray Wildlife Area, WA) had greater shrub cover outside of the exclosures. Ungulates significantly increased net N mineralization and nitrification rates, providing a potential explanation for compensatory growth by grazed plants. Our data suggest that arthropod herbivory does not substitute for ungulate herbivory. To the contrary, arthropod diversity reflected ungulate-induced changes in plant biomass. In addition to effects on standing biomass, ungulates were associated with increased exotic plant species richness at all 4 sites. Our results suggest that there may be a balance between indirect positive and direct negative effects of herbivory on plants that varies with ungulate densities and site characteristics, and that arthropod herbivory does not functionally replace ungulate herbivory.     

Influence of soil and site characteristics on Palouse prairie plant communties

The structure of grassland communities can vary widely in response to heterogeneous habitat variables. In this study we document plant communities, soil types, and site characteristics for 12 Palouse prairie remnants in southeastern Washington and northern Idaho. We used general linear models to test the predictive value of 6 biophysical variables (slope, aspect, distance from edge, edge type, vegetation structure, and soil type) on 3 plant community metrics: species richness, Simpson’s diversity index, and the dominance of exotic species. From full models including all variables, we used Akaike’s information criterion (AIC) to select the best model for each metric. Aspect and vegetation structure were significant predictors of species richness ( R 2 = 0.08) and diversity ( R 2 = 0.09), while aspect, soil type, distance from edge, and edge type (type of adjacent matrix habitat) influenced the dominance of exotic species ( R 2 = 0.28). Additional soil sampling determined that the depth to a restrictive layer also had significant impacts on the dominance of exotic species ( R 2 = 0.31). This study confirms that biophysical characteristics influence Palouse prairie plant communities and may help set research and conservation priorities for isolated and uninventoried remnants.     

Soil-site relationships of white locoweed on the Raft River Mountains

White locoweed ( Oxytropis sericea Nutt.) is restricted to the top and windswept ridges of the Raft River Mountains. Elevation and soil characteristics have the greatest effect on its occurrence. It is most abundant on the subalpine windswept ridge ecological site (9.2 plants/m 2 ) above 2,380 m. White locoweed apparently can tolerate the extreme environmental stresses of the shallow, rocky, windswept ridges where it is one of the dominant species. White locoweed also occurs in the deep, subalpine loam site (3.8 plants/m 2 ) above 2,865 m, but it is a minor component of this plant community. It is apparently less competitive on the deeper soils, and its population fluctuates more. It exhibits an opportunistic survival strategy on the subalpine loam site by having a large reserve of viable seeds in the soil ready to germinate and establish when environmental conditions are favorable, and then declines with competition from more robust species.     

Movements by small mammals on a radioactive waste disposal area in southeastern Idaho

Average linear movement by populations of Dipodomys ordii, Microtus montanus, Perognathus parvus, and Peromyscus maniculatus   was investigated over a 15-month period by live trapping on a low-level, radioactive waste disposal area in Idaho. No significant differences in movement among habitats were observed seasonally, excepting M. montanus in spring. Average linear movements within habitats ranged from 20 to 70 m for all species, but some patterns varied seasonally and among age classes for individual species. Although predation on contaminated small mammals from the disposal area is a vector of radionuclide transport, local movements by these rodents do not appear to be of sufficient magnitude to contribute significantly to redistribution of radioactive particles.     

Hip glands in a natural population of montane voles ( Microtus montanus )

Average linear movement by populations of Dipodomys ordii, Microtus montanus, Perognathus parvus, and Peromyscus maniculatus   was investigated over a 15-month period by live trapping on a low-level, radioactive waste disposal area in Idaho. No significant differences in movement among habitats were observed seasonally, excepting M. montanus in spring. Average linear movements within habitats ranged from 20 to 70 m for all species, but some patterns varied seasonally and among age classes for individual species. Although predation on contaminated small mammals from the disposal area is a vector of radionuclide transport, local movements by these rodents do not appear to be of sufficient magnitude to contribute significantly to redistribution of radioactive particles.     

Occurrence, persistence, and expansion of saltcedar ( Tamarix spp.) populations in the Great Plains of Montana

Saltcedar ( Tamarix spp.), a shrub native to Eurasia, is associated with major alterations to wetland and riparian systems in the southwestern United States. Since the 1960s saltcedar has been naturalized in northern states of the U.S. where its growth potential and impacts are not well known. Here, we describe the occurrence, age, size, and relative cover of saltcedar populations in several river basins in central eastern Montana, USA, to identify potential patterns of spread across the region and changes in individual populations as they age. Stands were aged according to the oldest saltcedar individuals and were sampled for dominant plant cover and soil properties. Multiple introductions appear to have occurred in Montana, with the oldest stands occurring on the Bighorn River in southern Montana. Saltcedar absolute and relative cover and stand area increased significantly with stand age, while native tree and shrub relative cover remained low across all stand ages. These results suggest that saltcedar stands establish where woody natives are not abundant and that they persist and expand over time. Although soil salinity remained constant, soil pH decreased with saltcedar stand age, indicating a possible effect of organic matter inputs. An analysis of annual wood increment of saltcedar and sandbar willow (a native with analogous growth form) stems along a latitudinal gradient showed that stem growth of both species did not differ significantly among regions. Stem growth decreased inversely with elevation for both species while growth responses to elevation did not differ between species. Our results show an increase in number of populations and continued viability of these populations. Mechanisms of saltcedar increases in this region are yet to be determined. Anthropogenic influences, such as saltcedar plantings, watershed alterations (e.g., river flow control), and habitat disturbances (e.g., cattle grazing or habitat clearing) may facilitate its spread in similar climates of the Great Plains.     

Plant adaptation in the Great Basin and Colorado Plateau

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.     

Natural history and ecology of foraging of the Camponotus crassus Mayr, 1862 (Hymenoptera: Formicidae)

ABSTRACT

Ants are abundant in terrestrial ecosystems, especially in the Brazilian Cerrado, where they can play several roles at different levels of the food chain, including protection of plants against herbivores. Although there are many studies that evaluate the ant–plant interaction in the Cerrado, little is known about the natural history of most species of ants. Camponotus crassus Mayr, 1862, for example, is considered one of the main agents of plant biotic defence in Cerrado. But there are no studies specifically focused on this species, which hinders the understanding of how arthropod–plant interactions are structured in Cerrado. Here, we describe the natural history and ecology of the foraging of the C. crassus. We conducted the study from January 2013 to December 2014 in 10 quadrants of 40 m² to measure: the abundance, density and distribution of nests, location of the nests, the internal structure of the nests, the daily foraging of workers out of the nest, the food items they collect and the existence of territoriality and dominance of the workers on the soil and vegetation. We found 18 nests, 13 in the soil and 5 in hollow trunks on the ground with variable internal structures. The distribution of nests is aggregate, with density of 0.045 nests/m² and average distance of 3.73 m between nests. The foraging activity occurs on the daytime during the rainy and dry season. Extrafloral nectar and honeydew were the resources most collected, comprising 83.33% of the resources in the rainy period and 30% in the dry period. Camponotus crassus is a dominant species, especially on vegetation, although it also forages on the soil. This is the first study to evaluate in detail the natural history and foraging ecology of C. crassus, a diurnal, aggressive and territorial ant that mainly forage climbing onto the plants.