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.     

Distributional changes and population status of amphibians in the eastern Mojave Desert

Several amphibian species historically inhabited sparsely distributed wetlands in the Mojave Desert of western North America, habitats that have been dramatically altered or eliminated as a result of human activities. The population status and distributional changes of amphibians were investigated over a 20,000-km 2 area in the eastern Mojave Desert in 2 ways. For upland sites (i.e., sites outside of major valleys and river floodplains), where wetland habitat is almost exclusively springs, encounter surveys were conducted at 128 sites in 1997-1999, and results were compared to historical (pre-1970) locality records. For lowland sites (i.e., sites within major valleys and river floodplains), locality records and field surveys in 1995-2004 were reviewed to detect changes in distribution over time. Amphibians were found at 79% of upland sites. By far the most common species was the red-spotted toad ( Bufo punctatus , 73% of sites), followed by the Pacific chorus frog ( Pseudacris regilla ), Woodhouse's toad ( B. woodhousii ), relict leopard frog ( Rana onca ), and the introduced American bullfrog ( R. catesbeiana ). Taxa observed or collected in the lowlands since 1990 were Woodhouse's toad, Pacific chorus frog, American bullfrog, and the introduced tiger salamander ( Ambystoma tigrinum ). Four taxa (Vegas Valley leopard frog [ Rana sp.], Arizona toad [ B. microscaphus ], Great Plains toad [ B. cognatus ], and Great Basin spadefoot [ Spea intermontana ]) had historical records but no evidence of occurrence in the study area within the past 5 decades. The amphibian fauna of the study area has changed dramatically in the past century, primarily at lowland sites where habitat loss and modification have been extreme. Striking changes are the nearly complete replacement of native leopard frogs (i.e., Vegas Valley and relict leopard frogs) with the introduced bullfrog, and the complete replacement of the Arizona toad in Las Vegas Valley with Woodhouse's toad or hybrids with predominantly Woodhouse's traits. In contrast, the distributions of 2 species characteristic of upland springs, red-spotted toad and Pacific chorus frog, appear to have changed little from their historical distributions, despite habitat modification at many sites.     

Competition Between Adult and Seedling Shrubs of Ambrosia dumosa in the Mojave Desert, Nevada

Seeds of the perennial shrub Ambrosia dumosa germinated in abundance following 11 days of rain during August 1983 at a study site in the northern Mojave Desert. Seedling establishment, growth, and reproduction were observed in natural vegetation and in an area that had been previously cleared of vegetation. For 5,527 A. dumosa seedlings, percent survival in April 1986 averaged 3% in the undisturbed vegetation and 58% in the denuded area. Seedlings occupying the cleared area had grown to sizes up to 0. 1 m 3 m by October 1984; some produced flowers and fruit in the spring of 1985. Surviving seedlings in the undisturbed vegetation were all smaller than 0.001 m 3 and did not reproduce. These pronounced differences in growth, survival, and reproduction associated with the presence or absence of adult shrubs demonstrated an intense competition that is incompatible with indications of mild competition from nearest-neighbor analyses. I therefore hypothesize that competition for water occurred, not by competition for water in two dimensions but by rapid use of a common resource, as if several people were drinking with straws from a common cup. This temporal mechanism would strongly favor adults over seedlings.     

Age and population structure of Joshua trees ( Yucca brevifolia ) in the northwestern Mojave Desert

Many desert perennials are long-lived, but there are few data on ages or population structures of desert plants. We used 2 methods to estimate ages of a population of Yucca brevifolia (Joshua tree) in southwestern Utah from a 14-year census of plant sizes. Plant height at the 1st census ranged from 0.08 m to 6.0 m, and trees grew in height at a mean rate of 3.75 cm ? yr -1 . Plants also increased slowly in basal diameter (0.142 cm ? yr -1 ) and branch length (0.024 m ? yr -1 ), but basal diameter varied greatly from year to year, with many plants decreasing in diameter between sequential censuses. Forms of a nonlinear growth equation (the Richards function) did not fit the data on growth in height, but a simple linear relationship fit the data well. Using height as a linear predictor of age, we estimated that ages of a sample of 69 Joshua trees ranged from 300 years old, with 75% of the trees between 20 and 100 years and 11% over 150 years old. These data support the assumption that Joshua trees are indeed long-lived.     

Plant community patterns in unburned and burned blackbrush ( Coleogne ramosissima Torr.) shrublands in the Mojave Desert

The blackbrush vegetation type is dominated by Coleogyne ramossisima , which is thought to preclude the coexistence of many other plant species. Fire can remove blackbrush cover and possibly increase plant species richness and evenness. Fire also may increase the frequency and cover of alien annual grasses, thereby intensifying landscape flammability. We tested these predictions in unburned and burned (6-14 years postfire) blackbrush at 3 sites spanning the range of this vegetation type in the Mojave Desert. Species richness in unburned blackbrush was similar to published values for vegetation types in western North America, bur richness varied significantly among the 3 sites and 4 spatial scales (1, 10, 100, and 1000 m 2 ). Richness values declined in order from annual forbs, woody perennials, herbaceous perennials, annual grasses, cacti, to perennial grasses. Fire reduced Coleogyne cover, thus boosting species evenness. In contrast, species richness decreased after burning, although the results varied among spatial scales. Total cover was unaffected by fire because cover of wood perennials decreased, while cover of annual forbs, annual grasses, herbaceous perennials, and perennial grasses increased. Native species richness and cover decreased, whereas alien richness and cover increased after burning especially where the alien forb Erodium cicutarium was present. Fire had no effect on frequency and variable effects on cover of alien annual grasses. These results indicate that in blackbrush species richness can vary among sites and local spatial scales, and effects of fires can vary among plant life-forms and between natives and aliens.     

Late Pleistocene-early Holocene history of coniferous woodlands in the Lucerne Valley region, Mohave Desert, California

The composition of four radiocarbon-dated, late Pleistocene woodrat middens is reported and analyzed. A date of 11,850 ±550 BP records the first reported macrofossil occurrence in this region of late Pleistocene Pinus monophylla-Juniperus osteosperma woodlands. A 7,800 ±350 BP date documents the most recent J. osteosperma woodlands in this presently coniferless desert area, while a date of 12,100 ±400 BP is the oldest record of juniper woodlands among the four middens. Other juniper and creosote bush desert flora radiocarbon dates along with six pollen profiles were obtained. The research suggests that as recently as 7,800 BP this part of the Mohave Desert was subject to a cooler, moister climate than at present, and that the aboriginal food resources of pinyon seeds and juniper berries were probably available to early prehistoric man in this area.     

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.     

Dynamics of rodent populations in semiarid habitats in Lassen County, California

From 1996 to 2004, we studied population dynamics of a rodent assemblage in semiarid habitats in Lassen County, California. Abundances of rodents appeared affected by fluctuations in precipitation from a high in 1996 to average and slightly below-average levels in subsequent years; perhaps reflecting this, assemblage composition also changed dramatically during the study period. California kangaroo rats ( Dipodomys californicus ) declined from abundant to extremely rare, abundances of deer mice ( Peromyscus maniculatus ) fluctuated greatly during the study period, and, perhaps most notably, populations of dusky-footed woodrats ( Neotoma fuscipes ) appeared to decline to local extinction, possibly allowing for the subsequent colonization of desert woodrats ( N. lepida ). These changes appeared to represent natural variation in numbers and composition in an ecologically dynamic ecotonal region in response to multiyear changes in precipitation.     

RCLUS, a new program for clustering associated species: a demonstration using a Mojave Desert plant community dataset

This paper presents a new clustering program named RCLUS that was developed for species (R-mode) analysis of plant community data. RCLUS identifies clusters of co-occurring species that meet a user-specified cutoff level of positive association with each other. The "strict affinity" clustering algorithm in RCLUS builds clusters of species whose pairwise associations all exceed the cutoff level, whereas the "coalition" clustering algorithm only requires that the mean pairwise association of the cluster exceeds the cutoff level. Both algorithms allow species to belong to multiple clusters, thus accommodating both generalist and specialist species. Using a 60-plot dataset of perennial plants occurring on the Beaver Dam Slope in southwestern Utah, we carried out RCLUS analyses and compared the results with 2 widely used clustering techniques: UPGMA and PAM. We found that many of the RCLUS clusters were subsets of the UPGMA and PAM clusters, although novel species combinations were also generated by RCLUS. An advantage of RCLUS over these methods is its ability to exclude species that are poorly represented in a dataset as well as species lacking strong association patterns. The RCLUS program also includes modules that assess the affinity of a given species, plot, or environmental variable to a given cluster. We found statistically significant correlations between some of the RCLUS species clusters and certain environmental variables of the study area (elevation and topographical position). We also noted differences in clustering behavior when different association coefficients were used in RCLUS and found that those incorporating joint absences (e.g., the phi coefficient) produced more clusters and more even numbers of species per cluster than those not incorporating joint absences (e.g., the Jaccard index). In addition to the species association application described in this paper, the RCLUS algorithms could be used for preliminary data stratification in sample (Q-mode) analysis. The indirect link between sample plots and RCLUS species clusters could also be exploited to yield a form of "fuzzy" classification of plots or to characterize species pools of plots.     

Microhabitat-specific controls on soil respiration and denitrification in the Mojave Desert: the role of harvester ant nests and vegetation

Seed harvesting ants ( Pogonomyrmex rugosus ) concentrate organic matter and nutrients near their nests and create biogeochemical hotspots in desert soil. We examined factors regulating denitrification and soil respiration in a Mojave Desert ecosystem to determine the role harvester ant colonies play in nitrogen loss and carbon mineralization. Organic matter and nutrient storage were significantly greater in colonies than under the dominant vegetation (i.e., Pleuraphis rigida , a bunch grass) and in bare soil, with standing stocks of inorganic nitrogen in colonies nearly 4-fold greater than in the other microhabitats. Soil respiration, measured with laboratory incubations, was below detection limits under ambient soil conditions. Respiration rate in soil from bare patches and under grass was limited by water and labile organic carbon, with secondary nitrate limitation evident only once carbon limitation was alleviated. Soil respiration in ant nest soil was limited by water and labile organic carbon only. Denitrification, measured by the acetylene block technique, was elevated in bare soil and under grass with the addition of nitrate. Ant nest soil also responded to a nitrate addition; however, denitrification rate was greatest with addition of glucose. Ordinarily desert soil has low rates of respiration and denitrification due to dry ambient conditions. However, ant colonies likely function as important sites for nitrogen loss and carbon mineralization following rain storms, especially if storms coincide with seed set and the temporally pulsed input of organic matter into colonies.     

Effects of land clearing on bordering winter annual populations in the Mohave Desert

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;} Construction of a 10-MWe solar thermal power plant in Daggett, California, involved clearing and leveling 53 ha of desert land. Transient offsite effects of this construction were apparent as a reduced density of annual plants within 100 m downwind of the edge of the cleared area. Schismus arabicus populations recovered within four years, but Erodium cicutarium populations did not. The effects appeared to be related more to an interaction of seed-dispersal mechanisms with the large, open space than to the obvious sand movement and deposition associated with the clearing operations.     

Notes on Viscainopelmatus davewerneri (Orthoptera: Gryllacrididae; Stenopelmatinae) from the Viscaino Desert, Baja California Sur, Mexico

A male nymph in stadium 3 of Viscainopelmatus davewerneri Tinkham is reported and illustrated. The specimen was taken near Laguna Scammon, Baja California Sur, Mexico.     

Floristics of the upper Walker River, California

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;} A checklist of the vascular flora of the upper Walker River is presented. Listed are 1078 taxa from this 4000 km 2 area. The upper Walker River encompasses a portion of the boundary between the Intermountain and Sierra Nevada floristic regions, and hence displays much floristic diversity within a relatively small area. Due to its location along the east slope of the Sierra Nevada, the Walker River drainage is unique in that it contains much elevational variation eastward into the Intermountain Region. This elevational extension is due to the presence of large mountain ranges including the Sweetwater Mountains, the Bodie Hills, and the Wassuk Range. As a result of this elevational variation, there is much overlapping of the two floristic regions. Additionally, the easternmost exposures of the Sierran granodiorites occur within the Walker River basin and may enhance the eastward migration of Sierran plants. The 90 percent floristic similarity (Sorenson’s) between the Sweetwater Mountains, lying to the east of the Sierra, and the east slope of the Sierra Nevada (within the Walker River drainage) indicates the Sweetwaters to be more affiliated with the Sierran flora instead of the Intermountain flora.       

High-elevation records for Neotoma cinerea in the White Mountains, California

New records for bushy-tailed wood rat ( Neotoma cinerea ) on the White Mountains of eastern California increase the elevation from which this animal is known on the White Mountains, outside of human habitation, from 3,120 to 3,648 m. These records, coupled with archaeological data, suggest that the isolated bouldery outcrops occupied by bushy-tailed wood rats above timberline here are true habitat islands, occasionally colonized by dispersing individuals and characterized by frequent local extinction.     

Distribution and abundance of birds in the White Mountains, California

This paper quantifies the distribution and abundance of birds in the White Mountains, Inyo and Mono counties, California, during spring-summer 1989-91, to establish a baseline for monitoring the area's avifauna. Overall 58 species were encountered in the single-leaf pinyon-Utah juniper ( Pinus monophylla-Juniperus osteosperma ) zone, and 61 species in the bristlecone-limber pine ( P. longaeva-P. flexilis ) zone. The bristlecone-limber pine zone had a significantly greater overall bird abundance relative to the pinyon-juniper. Both zones were characterized by few very abundant species, a few moderately abundant species, and numerous rare species. The Black-throated Gray Warbler (scientific names in tables), Gray Flycatcher, and Pinyon Jay were the most abundant species in the pinyon-juniper whereas the Clark's Nutcracker, Mountain Chickadee, and Cassin's Finch were the most abundant species in the bristlecone-limber pine. There were few ecological or taxonomic replacements of species between zones, with the differences in distribution and abundance related primarily to the interaction between elevation and vegetation. Significant inter-year variation in abundance was found for about 20 species in each zone—more species showed declining rather than increasing trends. The Mountain Chickadee and White-breasted Nuthatch declined, whereas the Gray Flycatcher and Rock Wren increased across years in both zones. Reasons for declines in some species might be the severe drought that continued throughout this study.     

Diets of nesting Northern Goshawks in the Warner Mountains, California

Diets of Northern Goshawks ( Accipiter gentilis ) in western and eastern North America show regional differences. This variation may be explained by the opportunistic feeding behavior of Northern Goshawks and the greater number of potential prey species in western North America. We predicted that a population of Northern Goshawks in the Warner Mountains of California would take significantly more mammals than birds as prey. Goshawk diet in the Warner Mountains was determined by pellet analysis and prey remains. A total of 33 samples from 23 nest sites was collected and analyzed. Diets were quantified by determining the minimum number of individuals per sample at each nest site. As predicted, Warner Mountain Goshawks preyed more heavily on mammalian than avian prey species. Of the 221 individuals identified, 126 (57%) were mammals, while 95 (43%) were birds. These results are in accord with the suggestion that there are potentially more mammalian prey species in western North America than in eastern North America.     

Terrestrial vertebrates of the Mono Lake islands, California

We compared vertebrate populations between the two major islands (paoha and Negit) in Mono Lake, California and the adjacent mainland to further elucidate the mechanisms underlying island colonization. Deer mice ( Peromyscus maniculatus ) and montane voles ( Microtus montanus ) were captured on Paoha, but only deer mice were captured on Negit. In contrast, eight species of rodents were captured on the mainland. Overall rodent abundance on Paoha and the mainland was similar, but on Negit it was about three times greater than on Paoha or the mainland. Adult deer mice from Paoha were significantly ( P Canis latrans ) and one or two species of lagomorphs were observed on the islands and the mainland. No amphibians or reptiles were found on the islands; both occurred in low numbers on the mainland. Rafting and human transport are probable means of colonization for mice and voles. The occurrence of coyotes on the islands may have modified historic predator-prey relationships, and thus the population of rodents and lagomorphs.     

Locality, Habitat, and Elevation Records for the Desert Shrew, Notiosorex crawfordi

Two specimens of Notiosorex crawfordi (Coues) were obtained from Rincon Mountains in southeastern Arizona. Elevations were 2,438 and 2,618 m. At the lower-elevation site the habitat was a meadow in a ponderosa pine forest.     

Zonation patterns in the vascular plant communities of Benton Hot Springs, Mono County, California

Vascular plant communities surrounding Benton Hot Springs, Mono County, California, were studied. The springs complex is comprised of two thermal springs, a thermal stream, and a cooling pond. Water temperatures varied from 57 C in one hot spring to 45 C at the cooling pond. The vegetation showed concentric zones about the springs and cooling pond and parallel zones beside the stream. Each zone demonstrated its own dominant plant species with some species being present in two or more zones. A total of six zones were identified plus an algal mat on the springs themselves. Soil factor patterns varied from spring to desert as did vegetational parameters. Soil moisture appeared responsible for most of the patterns observed.