Introduction to the symposium on soil crust communities

Soil crust communities in semiarid and arid lands around the world have received increasing attention in the past two decades. A symposium on their ecology was presented at the annual meeting of the American Bryological and Lichenological Society held in 1991 in San Antonio, Texas. An introduction to the topic and an overview of the papers appearing in the proceedings volume are given in this prologue.     

Climates of fescue grasslands of mountains in the western United States

Climates of fescue grasslands were described by summarizing USDC Weather Bureau records of representative sites. Mean temperatures of the warmest month declined from 18 to 14 C, average annual precipitation increased from 40–50 to 170 cm, and the number of arid months in an arbitrarily defined dry year declined from 3 to 1–2 as one moves from Festuca arizonica (14 stations) to F. scabrella (15) to F. idahoensis (17) to F. thurberi (6) to F. viridula (9). Climates of the grasslands are sufficiently like those of the Pseudotsuga menziesii and Abies lasiocarpa zones of the northern Rocky Mountains to make one ask what factors—wind, snow duration, soil characteristics, or fire—allow the fescue grasslands to persist in a conifer climatic zone.     

Improving national-scale invasion maps: tamarisk in the western United States

New invasions, better field data, and novel spatial-modeling techniques often drive the need to revisit previous maps and models of invasive species. Such is the case with the at least 10 species of Tamarix, which are invading riparian systems in the western United States and expanding their range throughout North America. In 2006, we developed a National Tamarisk Map by using a compilation of presence and absence locations with remotely sensed data and statistical modeling techniques. Since the publication of that work, our database of Tamarix distributions has grown significantly. Using the updated database of species occurrence, new predictor variables, and the maximum entropy (Maxent) model, we have revised our potential Tamarix distribution map for the western United States. Distance-to-water was the strongest predictor in the model (58.1%), while mean temperature of the warmest quarter was the second best predictor (18.4%). Model validation, averaged from 25 model iterations, indicated that our analysis had strong predictive performance (AUC = 0.93) and that the extent of Tamarix distributions is much greater than previously thought. The southwestern United States had the greatest suitable habitat, and this result differed from the 2006 model. Our work highlights the utility of iterative modeling for invasive species habitat modeling as new information becomes available. A menudo las nuevas invasiones, mejores datos de campo y técnicas novedosas de modelado espacial impulsan la actualización de los mapas y de los modelos existentes de especies invasoras. Este es el caso de al menos 10 especies de Tamarix, las cuales están invadiendo los sistemas ribereños en el oeste de los EE.UU. y extendiendo su distribución por toda Norteamérica. En 2006, desarrollamos un mapa nacional del tamarisco (National Tamarisk Map) utilizando una compilación de sitios de presencia y ausencia con datos de sensores remotos y técnicas de modelación estadística. Desde la publicación de este trabajo, nuestra base de datos sobre la distribución de Tamarix ha crecido considerablemente. Utilizando la base de datos actualizada de presencia de especies, nuevas variables predictoras y el modelo de máxima entropía (Maxent), hemos modificado nuestro mapa de la distribución potencial de Tamarix para el oeste de los EE.UU. El predictor más fuerte en el modelo fue la distancia al agua (58.1%), y la temperatura promedio del trimestre más cálido fue el segundo (18.4%). La validación de modelo, calculada como el promedio de 25 iteraciones del modelo, indicó que nuestro análisis tuvo una alta capacidad predictiva (ABC = 0.93), y que la distribución de Tamarix es mucho más extensa de lo que se pensaba. El suroeste de los EE.UU. tuvo la mayor cantidad de hábitat adecuado para la especie, y este resultado difirió del modelo de 2006. Nuestro trabajo enfatiza la utilidad del modelado iterativo para modelar el hábitat de las especies invasoras a medida que se disponga de nueva información.     

Factors controlling structural and floristic variation of riparian zones in a mountainous landscape of the western United States

We examined landscape patterns in the physical conditions and vegetative composition of montane riparian zones to identify their most important sources of variation. Information on plant species cover and on physical characteristics that occur at coarse, medium, and fine scales was collected for 144 riparian plots located throughout the Lake Tahoe Basin, which straddles the California-Nevada border in the western United States. Constrained and unconstrained ordination analyses were used to identify the most important correlates of physical form and plant species composition. Through multivariate analysis of environmental variables (principal components analysis), vegetation data (detrended correspondence analysis), and the combined relationship between the environmental and vegetation data (canonical correspondence analysis), we consistently found that the greatest variation occurred along a gradient of decreasing valley width, decreasing stream sinuosity, and increasing stream slope. Although surface characteristics reflected a 2nd important source of variation in physical conditions, plant species distribution was not strongly correlated with riparian surface conditions. Strong correlations among physical variables that occur at different scales, such as between valley form and geofluvial surface and between geofluvial surface and surface conditions, support the use of a physically based hierarchical framework for organizing riparian zones within the landscape. Such a hierarchical framework would be useful for interpreting patterns in riparian structure and process at different scales and could be applied to riparian zones in other mountain landscapes of the western United States and elsewhere. Moreover, our finding that riparian plant species composition is most strongly correlated with environmental variables that occur at coarse to moderate scales, most of which can be derived from existing data, supports the idea that modeling montane riparian community distribution using topographic and remotely sensed data could be useful; however, a large degree of species variation, unexplained by the variables we collected, indicates that other variables, perhaps disturbance regime, should be included in such a venture. Nomenclature: Hickman (1993).     

Nesting and predatory behavior of some Tachysphex from the western United States (Hymenoptera: Sphecidae)

The first published observations on the nesting and predatory behavior of Tachysphex antennatus Fox, T. occidentalis Pulawski, T. williamsi Bohart, T. yolo Pulawski, T. alpestris Rohwer, T. clarconis Viereck, T. apricus Pulawski, and T. cockerellae Rohwer are presented herein. Also included are host and behavioral data on T. tarsatus (Say), T. apicalis fusus Fox, T. similis Rohwer, T. ashmeadii Fox, and T. mundus exsectus Fox.         

Floristic analysis of the southwestern United States

A study was made of the distributions of native, terrestrial, vascular plants occurring in 50 local floras from throughout the Basin and Range and Colorado Plateau physiographic provinces of the southwestern United States. The objectives of the study were to objectively define and describe the floristic elements-assemblages of species with roughly coincident geographic distribution-occurring in the southwestern United States and to determine what such assemblages reveal about the floristic history of the region. The total flora (native, terrestrial species only) of the Southwest is estimated at 5,458 species, 77% of which were recorded in 1 or more of the local floras. Nearly 22% of these species are endemic to the study region. A majority of the species were found to be relatively rare. The average range of a species included only 4 floras, and 90% of the species were recorded from 11 or fewer floras; only 81 species (1.5%) were recorded from 50% or more of the floras. Trees constitute 2% of the regional flora and have the widest average distribution; perennial herbs constitute 59% of the flora and have the most restricted distributions.  Factor analysis was used to identify seven floristic elements for the region: a Great Basin element, a Mojavean element, a Colorado Plateau element, a Chihuahuan element, an Apachian element, and a Mogollon element. This factor analysis solution was shown to satisfy criteria of interpretability and consistency. The Mojavean, Colorado Plateau, and Apachian elements are believed to be autochthonous. The other four elements show high overlap in species composition with one or more adjacent regions. Each floristic element is mapped to show its geographic form and distribution. Analysis of these maps shows how the existence of objectively defined floristic elements is not contradictory to either the individualistic view of the distribution of a species or local continuity of vegetation and flora. The rarity of the majority of species and the clear association of floristic elements with rather narrowly circumscribed Holocene environments suggests that many Southwestern species have migrated little and are of rather recent, probably postglacial origin. Geographic “principles” derived from the distribution patterns of relatively few, widespread, dominant, usually woody species may not be applicable to entire, regional floras.       

Phalacropsis dispar (Coleoptera: Phalacridae), an element in the natural control of native pine stem rust fungi in the western United States

Larvae of the phalacrid beetle Phalacropsis dispar (LeConte) consumed aeciospores and the underlying sporogenous mycelium, thereby destroying the aecia of all native western pine stem rust fungi studied. Aecia of the introduced white pine blister rust fungus ( Cronartium ribicola ) were not found to be infested by the beetle. A close, if not obligate, biosis of the beetle apparently exists with the native rust fungi, and their geographic distributions closely coincide. Laboratory tests and field observations indicate that the beetle completes its life cycle in 30 to 40 days and apparently overwinters as an adult. Quantitative data on aeciospore inoculum destruction were beyond the means of this study; however, observations over a 12 - year period evidenced widespread and extensive destruction of aeciospores. The beetle may be an effective element in the natural control of native pine stem rust fungi. Natural control by secondary organisms could significantly reduce the selective pressure for high host resistance in a naturally evolving host - parasite population.     

Status of white pine blister rust in the Intermountain West

During 1995-1997 we conducted a white pine blister rust (WPBR) disease survey in white pines of the Intermountain West. Incidence of WPBR in white pines was 59% overall, 73% in the northern Rocky Mountains, 55% in the middle Rocky Mountains, and 67% in the Sierra Nevada sample stands. Intensity within infected stands averaged 35% and ranged from 2% to 100%. Southward spread of the disease along the western slopes of the Rocky Mountains appears to have slowed or stopped, and the disease was found at the northern and western edges of, but not within, the Great Basin region. Smaller-diameter trees infected with WPBR sustained more severe damage than larger-diameter trees. Mortality and top kill caused by WPBR were very low across the entire study area, but incidence and intensity of the disease appear to have increased substantially in the northern and middle Rocky Mountains since the 1960s.     

Checklist of the mosses of the Intermountain West, USA

A revised list of the mosses of the Intermountain West, including all of Utah and Nevada and parts of surrounding states, is presented. Recorded are 342 species in 122 genera and 39 families in this region. Nomenclatural and taxonomic changes as well as floristic additions since the publication of Seville Flowers's book are included.     

Spider fauna of selected wild sunflower species sites in the southwest United States

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;} Fifteen genera representing nine families of spiders were collected in the southwestern United States in 1980. Thomisidae, Araneidae, Dictynidae, and Salticidae were the most commonly collected spider families. Ten genera of spiders not previously reported on sunflowers are reported for the first time.     

Habitat evaluation procedure for Rocky Mountain bighorn sheep in the Intermountain West

Several habitat evaluation procedures have been developed for bighorn sheep. However, none of these procedures specifically addresses the Rocky Mountain subspecies nor analyzes both the quantity and quality of potential bighorn habitat with regard to minimum viable population (MVP) criteria. This bighorn habitat evaluation procedure combines (1) a quantitative assessment of bighorn range to determine if there are adequate quantities of resources to support an MVP of bighorn sheep, and (2) a qualitative assessment of a range to predict the probable density of bighorns the range can support. Extensive literature review, intensive bighorn research, and a modeling tool, pattern recognition (PATREC), facilitate critical analysis of proposed bighorn reintroduction sites. The resultant stepwise approach to bighorn habitat evaluation enhances the ability of wildlife biologists to make timely and accurate bighorn habitat assessments.     

Monoterpene concentrations in litter and soil of singleleaf pinyon woodlands of the western Great Basin

Mean monoterpene content of singleleaf pinyon ( Pinus monophylla [Torr.] Frem.) litter from stands growing on two soil series was 340 ± 310 ug/g air dry weight (adw). Individual monoterpene hydrocarbons suggested as potential allelopathic compounds occur in extremely small amounts, 0.5-1.10 ug/g adw. Mineral soils contained 50 times less total terpene, 6.6 ug/g ± 4.8 adw, than the litter immediately above. Results suggest that allelopathic effects would more likely occur in litter than mineral soil. These findings are substantiated by previous reports of decreased emergence and growth of herbaceous species in pinyon litter but not mineral soil.     

New grass distribution records for New Mexico and the United States

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