Algal composition of microbiotic crusts from the Central Desert of Baja California, Mexico

A total of 66 algal species representing 32 genera were recovered from soils of 10 sites in the Catavi?a region of the Central Desert of Baja California, Mexico. The most common species encountered were the cyanophytes Nostoc commune and Schizothrix calcicola , the chlorophyte Myrmecia astigmatica , and the diatoms Hantzschia amphioxys, Hantzschia amphyoxys f. capitata, Luticola cohnii, Luticola mutica , and Pinnularia borealis var. scalarts . Nine species not found in any previous studies of North American desert soils were present in our study sites, including 3 taxa new to science: Cylindrocystis brebissonii var. deserti , var. nov.; Elakatothrix obtusata , sp. nov.; and Fasciculochloris mexicana , sp. nov. Attempts to correlate species composition with soil chemical and physical parameters were unsuccessful apart from a pH effect on cyanobacterial distribution. Overall composition of the soil algal community in the Catavi?a region is distinct from other desert sites we have studies, although some cosmopolitan desert soil taxa were present.     

Ecological impacts of seed harvester ants on soil attributes in a Larrea -dominated shrubland

The influence of seed harvester ant ( Pogonomyrmex rugosus ) colonies on soil properties and soil surface and moisture characteristics was investigated through comparison of adjacent, nonnest (reference, 4 m beyond ant colony) areas in Las Vegas, Nevada. Effects of ant colonies on both terrace and slope sites were investigated. Soil moisture content and soil bulk density in a creosote bush ( Larrea tridentata )--dominated shrubland were significantly lower, while soil temperature, soil organic matter, and percent pore space were significantly higher in soils with ant nests relative to adjacent reference soils. Soil pH and texture did not differ significantly between nest and reference soils. Among soil surface characteristics, percent bare soil and rock (gravel, cobble, and boulder) cover were not significantly different between nest and reference soils. In evaluating soil moisture characteristics, soils with ant nests had a significantly higher water infiltrability and greater depth of water penetration, but a significantly lower area of water spread (surface-water runoff) at both terrace and slope sites. Between the 2 geomorphic surfaces, water infiltrability and depth of water penetration were significantly greater at the terrace than at the slope. Water-borne soil movement (fluvial erosion) was significantly greater at the slope than terrace but did not differ significantly between nest and reference soils. The presence of active P. rugosus colonies in the L. tridentata -dominated shrubland altered certain soil properties and appeared to have a protective influence on the soil by fostering more infiltration and less runoff of surface water in southern Nevada.     

Bryophytes on the calcareous soils of Mungo National Park, an arid area of southern central Australia

Bryophytes were found to be abundant as components of microbiotic soil crusts on the calcareous soils of Mungo National Park, an arid area of southern central Australia. Six sites that reflected differences in soils, topography, and vascular plant vegetation were studied. At each site bryophytes were abundant, both in terms of number of species present and percent ground cover. Number of species present did not differ significantly between sites, but percent bryophyte cover was lower at a site on sand dunes in mallee woodland and a site on a silcrete ridge than at the four other sites. Environmental factors (soil texture, pH, conductivity, nutrient status, vascular plant vegetation, light level, leaf litter, and fire frequency) appear to play a significant part in determining bryophyte distribution. Mosses that occur at Mungo are also widespread on calcareous substrates throughout arid southern Australia. Many of the bryophyte species present at Mungo also occur on limestones in high rainfall areas of eastern Australia. Environmental factors favoring bryophytic soil crusts in arid Australia are also present on limestones in high rainfall areas of eastern Australia and may account for tile presence of many arid zone bryophyte species on limestones. In Australia there appears to be a relationship between rainfall and the ratios of acrocarpous to pleurocarpous mosses, and thallose to leafy liverworts. Recognition of calcareous soils, widespread in arid areas of southern Australia, may be possible by assessing a combination of characteristics of bryophyte assemblages.     

Microbial spatial heterogeneity in microbiotic crusts in Colorado National Monument. II Bacteria

Microbial spatial heterogeneity and bacterial composition of homogeneous surface soils showing evident microbiotic crust development located under Utah juniper canopies in Colorado National Monument were studied. Four distinct homogeneous sampling sites positioned along a 12-m transect were compared on the basis of bacterial density and taxa composition. Bacterial densities showed a range differing by several orders of magnitude. In comparisons of adjacent soil samples or samples taken from two different sampling sites within close proximity, adjacent samples showed no more similarity to each other on the basis of bacterial density or taxa composition than did more widely separated samples. The bacterial composition of these soils included members of the genera Bacillus , Micrococcus , and Arthrobacter . Actinomycetes were also prevalent.     

Soil loosening processes following the abandonment of two arid western Nevada townsites

Soil compaction was measured at four sites within two abandoned mining camps in the western Great Basin Desert, Nevada. Bulk density and macroporosity values were generated from soil samples collected in areas of different land use intensities in camps that had been abandoned for approximately 70 years. Results show that significant differences remain in bulk density values between abandoned roads and undisturbed areas in both towns, and that the areas around foundation peripheries are still significantly more compacted in one town. There were no significant differences between land use groups as measured by macroporosity. Estimated soil recovery, based on a linear model using bulk density values, suggests that approximately 100 to 130 years are necessary for complete loosening to occur for abandoned roads, and that 100 or fewer years are necessary for complete amelioration of the foundation periphery areas. The wetter townsite, with more freeze-thaw days, finer-grained soils, and greater plant cover, had shorter recovery estimates. These finding suggest that the results of human-use impacts in arid areas may still be apparent long after disturbances cease.     

Natural history of a saline mound ecosystem

Along the margins of playas in northwestern Nevada, a salt-tolerant plant community occupies mounds that dot a largely unvegetated landscape. In this environment we studied soil development and plant-soil relationships. The mounds, averaging 0.3 m in height, are occupied by the shrubs Allenrolfea occidentalis (iodine bush), Sacrobatus vermiculatus (black greasewood), and Atriplex lentiformis spp. torreyi (Torrey saltbush). Distichlis spicata (desert saltgrass) is the only herbaceous plant occupying this community. Soil salinity decreases with depth in this environment, and content of aqueous-extractable solutes is significantly influenced by site-specific vegetation. Content of silt, clay, and salt in mound surface horizons suggests a chronosequence of mound formation, with the youngest at the barren playa interface and the oldest at the upland vegetation border. Plant demography and mound soil stratigraphy suggest that a pulse of plant recruitment and mound building occurred during a time of neoglacial cooling. As a substrate for plant recruitment, mounds have a limited lifespan because deposition of eolian-transported salts and geochemical cycling by plants quickly render them too saline for seed germination. The apparent productivity of mound formation precludes definitive conclusions regarding those mound characteristics favorable for plant recruitment and survivorship.     

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.     

Soil characteristics of mountainous northeastern Nevada sagebrush community types

Soil physical and chemical properties were studied to identify habitat differences among 15 sagebrush dominated plant community types of the Great Basin. The sagebrush taxa studied followed an apparent gradient of increasing soil fertility, with Artemisia nova commonly occupying the lowest fertility sites. Sites of moderate soil fertility tended to support A. arbuscula , A. longiloba , and A. tridentata ssp. Wyomingensis . Artemisia tridentata ssp. Tridentata and A. tridentata ssp. Vaseyana were commonly found on sites with the highest soil fertility levels as indicated by maximum organic carbon, nitrogen, and phosphorus levels within such soils. Mollic epipedon depth, total depth, and water-holding capacity of the soil also increased as the dominant sagebrush taxon of a community type changed from A. nova to A. tridentata ssp. Vaseyana . Data from this study provide information concerning soil relationships within relatively undisturbed rangeland communities. Such data are required if future soil sampling efforts within the Great Basin are to have a basis for comparison.     

Applicability of the universal soil loss equation for southeastern Idaho wildlands

Soil physical and chemical properties were studied to identify habitat differences among 15 sagebrush dominated plant community types of the Great Basin. The sagebrush taxa studied followed an apparent gradient of increasing soil fertility, with Artemisia nova commonly occupying the lowest fertility sites. Sites of moderate soil fertility tended to support A. arbuscula , A. longiloba , and A. tridentata ssp. Wyomingensis . Artemisia tridentata ssp. Tridentata and A. tridentata ssp. Vaseyana were commonly found on sites with the highest soil fertility levels as indicated by maximum organic carbon, nitrogen, and phosphorus levels within such soils. Mollic epipedon depth, total depth, and water-holding capacity of the soil also increased as the dominant sagebrush taxon of a community type changed from A. nova to A. tridentata ssp. Vaseyana . Data from this study provide information concerning soil relationships within relatively undisturbed rangeland communities. Such data are required if future soil sampling efforts within the Great Basin are to have a basis for comparison.     

Habitat relationships of the blackbrush community ( Coleogyne ramosissima ) of southwestern Utah

Eight general study sites in the blackbrush ( Coleogyne ramosissima ) zone of southwestern Utah were examined. Soils data were gathered and plant cover was estimated. Shrubs were found to he positively correlated with shallow, sandy soil. Nonwoody plants were found to be positively correlated with deeper, silty soils. Cryptogamic soil crusts were positively correlated with silt and nitrogen in the soil and therefore may play a role in elevating soil fertility. Shrubs and grasses were negatively correlated. Management implications are discussed.         

Lichens of soil crust communities in the Intermountain Area of the western United States

Lichens are common components of microbiotic soil crusts. A total of 34 species from 17 genera are reported from soil crust communities throughout the Intermountain Area. Distribution of terricolous lichens is determined by various physical and biological factors: physical and chemical characteristics of the soil, moisture regimes, temperature, insolation, and development and composition of the vascular plant community. Some species demonstrate a broad ecological amplitude while others have a more restricted distribution. All growth forms are represented; however, the vast majority of soil crust lichens are squamulose (minutely foliose). Fruticose species are least abundant. In exposed, middle-elevation sites vagrant (detached) species are common. This paper describes and discusses terricolous lichen communities of desert habitats of the intermountain western United States. Effects of various human-related activities including grazing, wildfire, air pollution, and recreation vehicles on soil crust lichens are discussed. Gypsoplaca macrophylla (Zahlbr.) Timdal, a rare squamulose lichen which occurs on gypsifersous soils, was recently collected in Emery County, Utah, and is reported as new to the state.     

Habitat and distribution of pygmy rabbits ( Sylvilagus idahoensis ) in Oregon

Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 st1\:*{behavior:url(#ieooui) } /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} An investigation to determine the location and extent of populations of pygmy rabbits ( Sylvilagus idahoensis ) in Oregon, and to describe several biotic and physical components within communities that include pygmy rabbits, was conducted from October 1981 to September 1983. Of 211 sites suspected of supporting the species based on interpretation of museum records, aerial photographs, soil maps, and interviews with biologists and area residents, 51 exhibited evidence of being inhabited when examined in summer 1982. Soil and vegetation components were sampled at 15 sites occupied by pygmy rabbits and 21 sites adjacent thereto. At inhabited sites, mean soil depth (51.0 ± 2.3 cm), mean soil strength of surface (0.8 ± 0.2 kg/cm 2 ) and subsurface (3.8 ± 0.3 kg/cm 2 ) horizons, shrub height (84.4 ± 5.8 cm), and shrub cover (28.8 ± 1.4%) were significantly greater ( P 2 ), density of forbs (3.4 ± 0.6/1,000 cm 2 ), and cryptogam cover (2.4 ± 0.5%) were not. Except for the clay component of subsurface soils, texture of surface and subsurface soils were not significantly different between sites occupied by pygmy rabbits and adjacent sites. The affinity of pygmy rabbits for areas with greater shrub cover, shrub height, soil strength, and soil depth, and, to a small degree, coarser soil texture possibly was related to availability of forage, security from predation, and ease of burrow construction. Analysis of 472 samples of sagebrush ( Artemisia tridentata ) collected at and near sites inhabited by pygmy rabbits indicated their distribution was not dependent upon the presence of specific subspecies of sagebrush. A marked decrese in evidence of occupancy of sample sites and of pygmy rabbit activity at occupied sites in 1983 indicated that populations of pygmy rabbits were susceptible to rapid declines and possible local extirpation. Fragmentation of sagebrush communities poses a potential threat to populations of pygmy rabbits, but the severity of the threat presently is unknown.     

Fertile island development around perennial shrubs across a Mojave Desert chronosequence

Spatial heterogeneity has been examined only recently as a factor in studies of ecosystem processes. The effect of this factor on desert organisms is exemplified in the ""fertile island"" a concentration of essential soil nutrients under perennial shrubs. In this study we examined fertile island patterns in undisturbed desert areas and on abandoned roadways to see at what rate and magnitude these fertile patches reappeared after disturbance. Small-scale examination of patterns of soil P, organic matter, moisture, and bulk density showed that soils beneath Larrea tridentata (DC.) Cov. shrubs on the roads lacked the tight circular gradient in these variables that was characteristic of soils beneath control shrubs, even 88 years after road abandonment. The nature of the initial soil disturbance altered both spatial patterns of soil N and temporal patterns of fertile island development. Fertile island patterns for total soil N, available P, and organic matter were more circular than patterns for bulk density, texture, or pH. We suggest that patterns of soil heterogeneity may develop first for elements that may be limiting to desert shrub growth (N, P, organic matter), followed by spatial development in other less limiting soil factors (bulk density, texture, pH).     

Influence of soil frost on infiltration of shrub coppice dune and dune interspace soils in southeastern Nevada

The influence of soil frost on the infiltration rate of shrub coppice dune and dune interspace soils was evaluated near Crystal Springs, Nevada, using simulated rainfall. The infiltration rate of the coppice dune soil was greater than the dune interspace soil under frozen or unfrozen conditions. Because of different vegetation cover and surface soil characteristics, coppice dune and dune interspace soils responded differently to freezing, thus imposing a spatial and temporal response to infiltration rate. Infiltration rate of soils with porous concrete frost increased as the soils thawed during simulated rainfall, but soils with nonporous concrete frost allowed very little infiltration to occur. Both coppice dune and dune interspace soils that were classified in January as having granular frost had a higher infiltration rate than the same unfrozen soils in March.     

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.     

Weed control and soil amendment effects on restoration plantings in an Oregon grassland

The restoration of perennial grasslands in western North America often depends on effective weed control. We took advantage of a grassland restoration site on the Nature Conservancy's Agate Desert Preserve in southern Oregon (TNC 1997), where 3 sites had been previously burned, mowed, or both. At these sites we carried out a series of controlled, replicated experiments designed to test the effectiveness of 3 weed control measures: (1) sawdust, (2) glyphosate herbicide, and (3) herbicide plus an alfalfa mulch. All plots were seeded with a mix of 3 native perennial grasses. The soils of the 3 areas differing in previous vegetation management were similar, with the exception of total available soil nitrogen, which was significantly lower in the 2 burned sites. The sawdust treatment reduced total available soil nitrogen, but only in the unburned site, and only in the first few months after application. In all 3 areas the alfalfa mulch significantly increased total available soil nitrogen. However, none of these soil nitrogen differences significantly affected the success of weeds or planted perennial grasses. The herbicide treatment reduced exotic annual grasses and forbs and greatly increased the success of native forbs and the planted perennial grasses. The herbicide increased both initial establishment of the native grasses and their absolute cover and biomass. These results suggest that neither nitrogen impoverishment nor nitrogen enrichment was a useful restoration technique at this site, but weed control by herbicides can be of considerable assistance in restoring native perennial grasses.     

Arbuscular mycorrhizae in thermal-influenced soils in Yellowstone National Park

Mycorrhizae are common plant-fungal symbioses occurring in most land plants. Despite their ubiquity, little is known about the distribution of arbuscular mycorrhizae (AM) in extreme environments. We surveyed for the presence of AM in thermal sites in Yellowstone National Park (YNP) where soils are characterized by extreme pHs, elevated temperatures, and toxic element concentrations. Plants at 5 sites, growing in soils with rooting-zone temperatures up to 48°C and soil pH values as low as 3.4, were mycorrhizal (colonization levels from 4% to 34%). Soils from a sparsely vegetated thermal area and an adjacent, continuously vegetated transition area differed significantly in rooting-zone temperature (35°C vs. 26°C), acidity (pH 3.8 vs. 5.4), electrical conductivity (2.22 vs. 0.49 mmhos cm -1 ), Fe (181.3 vs. 48.5 mg kg -1 ),Mn (7.2 vs. 98.2 mg kg -1 ), and Zn (2.3 vs. 4.5 mg kg -1 ). Mycorrhizal infectivity potential (MIP) was 77% greater in the transition soils, with colonization levels of 26% and 46% in thermal and transition soils, respectively. Furthermore, colonization of Agrostis scabra , Dichanthelium lanuginosum , and Mimulus guttatus was found to be consistently high throughout the growing season (from 48% to 72%). It is possible that AM are essential for plant life on the edge of thermal areas, and that either or both symbionts are specifically adapted to their environment. Further research is required to elucidate AM function in and specific adaptations to YNP's thermal areas.     

Experimental manipulations of fertile islands and nurse plant effects in the Mojave Desert, USA

In a mixed desert shrub community we removed and added shrub canopies to examine above- and belowground influences of 3 species of shrubs on islands of soil fertility and the survival of transplanted Ambrosia dumosa seedlings. Soils sampled under shrubs in the wet season had higher pH, water content, organic matter, and both total and mineralizable nitrogen than soils in adjacent open areas, confirming a widely established pattern in arid lands. However, we also found species differences in soil parameters. Soils under Coleogyne ramosissima had highest pH, soils under A. dumosa had highest water content and nitrogen mineralization rates, and soils under Larrea tridentata had lowest water content. Soils sampled under shrubs in the dry season, 7 months after experimental shrub removal, maintained higher organic matter and total and mineralizable nitrogen content than adjacent open soils, but pH and water were altered by shrub manipulations. Species differences persisted only in soil water levels ( A. dumosa soils were driest). Over a 1-year period, transplanted A. dumosa seedlings had highest survivorship in shrub removal and open treatments and died most rapidly under control shrubs of all 3 species, suggesting that shrubs had a strong negative effect on seedling survival, even in the presence of higher organic matter, nutrients, and (initially) higher water content of fertile islands. Our results suggest that nurse plants and islands of soil fertility have the potential to facilitate growth of other species by nutrient additions, but that the net effect of nurse plants can be negative due to shading and/or root competition.