Vegetation patterns in Navajo National Monument, Arizona, were studied over a five-year period from 1977 to 1981. Twelve distinct plant community types occur within the boundaries of the park. These communities are characterized and the dominant plant species of each are recorded. The relationships of parent material, soils, and moisture to plant communities are also discussed. It appears that discrete communities occupy soils of different characteristics, particularly with respect to amount of weathering of parent material.

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.

The diatom flora of Beaver Dam Creek, Washington County, Utah, was studied. The study area is in a warm Mojave Desert environment at an elevation between 810 and 850 m. A total of 99 taxa were identified from composite samples taken in the fall, winter, spring, and summer seasons. These taxa are all broadly distributed and no endemic species were encountered. Three new records for the state of Utah were identified: Gomphoneis eriense Skv. & Mayer, Navicula elginensis var. lata (M. Perag.) Patr., and Nitzschia calida Grun. The most important taxa throughout the study as determined by multiplying percent presence by average relative density (Important Species Index) were Cymbella affinis Kutz., Epithemia sorex Kutz., Navicula veneta Kutz., Nitzchia palea (Kutz.) W. Sm., and Nitzchia microcephala Grun.

Glass microscope slides were placed to span a range of temperatures in and around a warm spring in the Portneuf River, Idaho in the winter of 1987. Diatoms were allowed to colonize these slides for 8 weeks. Analysis of slides revealed that maximum species diversity and species richness were reached between 25° and 30 °C. Analysis also showed that certain diatom taxa were stenothermal, showing distinct preferences for various temperatures while others were eurythermal.

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. Thermal springs are common throughout western North America. They occur in a variety of elevations and habitat types and are popular sites for recreation. The waters of thermal systems vary widely in temperature and mineral content (Loam 1980). It is common for such springs to contain high levels of dissolved minerals, some of which should exert influence on the surrounding vegetation. The ecology of vascular plant communities surrounding thermal springs is not well known. Meadow vegetation surrounding warm springs in the Great Basin of western North America has been described by Bolan (1964). Bolan studied vegetation surrounding springs at Fish Springs National Wildlife Refuge, Tooele County, Utah, where he discussed 10 community types. The zonation patterns surrounding these springs were predominantly influenced by soil salinity. Ranwell (1973) stated that soil structure, soil particle size, and soil moisture were important factors in determining growth and zonation of vascular plants in marsh habitats. In addition, Skougard and Brotherson (1979) discussed the influence of soil moisture, pH, and soluble salts on several distinct vegetation zones in playa meadows in central Utah. They found that salinity had the greatest influence on community structure, followed by soil moisture. Shupe et al. (1986) examined the vegetation patterns surrounding several cold springs in Utah County, Utah. These authors found that soil moisture and salinity largely accounted for the observed patterns. As distance from the springs increased, salt levels in the soil increased and soil moisture decreased. Halophytic species generally increased with distance from the spring sources. Literature treating the ecology of meadow vegetation arising from thermal springs is nearly absent. This paper attempts to add information to our knowledge of these interesting and distinct ecosystems by describing the vegetative zonation patterns surrounding hot springs near Benton, Mono County, California (Fig. 1).

ABSTRACTMt. St. Helens, a volcanic peak in the Cascade Range in southern Washington erupted violently on May 18, 1980, causing enormous damage to both terrestrial and aquatic ecosystems. The initial explosion evaporated, scoured or buried all springs and streams in the blast impact area. Ash fall and erosion from defoliated hillsides subsequently filled most of the lotic habitats with organic debris and volcanic ash. Recolonization of springs and streams by algae occurred quickly in areas where erosion through the ash progressed down to bedrock. Within 15 months or less of the eruption, algal communities were established throughout the blast impact area. However, as a result of the initial and continued disturbance these communities remained in an early successional stage. Floral assemblages were highly variable except that they were composed mostly of diatoms, with Achnanthes minutissima dominating most lotic sites. Springs showed the most rapid development toward stable floras.

Saline meadows in Goshen Bay, Utah County, Utah, USA, occur interspersed among large areas of salt playa. Springs irrigate these meadows which show concentric vegetational zones surrounding each spring. Each vegetational zone demonstrates its own unique dominant vascular plant species. The central zone is dominated primarily by Scirpus americanus, the middle zone by Eleocharis palustris and the outer zone by Juncus balticus, Distichlis spicata and Muhlenbergia asperifolia. As distance increases from the springs, pH and soluble salt concentration increase, while percent organic matter, percent moisture and phosphorus decrease. With the increase in salt levels and decrease in water levels, halophytic plant species generally increase with distance from the springs.

ABSTRACT Five taxa of Chaetoceros occur in inland waters of North America. These most commonly occur in waters with elevated total dissolved solids in arid regions of the western United States and Canada. Chaetoceros amanita Cleve‐Euler is characterized by consistently forming relatively long chains of cells and having very spinose primary resting spore valves. Chaetoceros elmorei Boyer also forms long chains of cells which are connected by evident valvar processes; spores are nearly always smooth. Chaetoceros muelleri Lemm. may form short chains with processes between sibling valves, but also produces solitary cells lacking processes. Chaetoceros muelleri var. subsalsum (Lemm.)Johansen et Rushforth is similar to the nominate but never produces cells with Processes. Both of the C. muelleri varieties produce spores with smooth primary valves. Chaetoceros simplex Ostenfeld is characterized by a noncolonial habit, cells lacking processes and the production of resting spores with warty to some what spinose primary valves.

—The diatom flora of Cowboy Hot Spring, Mono County, California, was studied. Two habitats, one at 37C and one at 41C, were examined. Fifty-six taxa were identified from our samples. These taxa were mostly broadly distributed forms, and no endemic species were encountered. The dominant taxon was Nitzschia frustiilum, followed by Achnanthes gibberula, Achnanthes exigua, Nitzschia hantzschiana , and Navicula cincta . Interest in natural thermal waters has increased substantially during the past few years. Early studies of these environments were generally concerned with Cyanophyta or the faunas of such habitats (Edwards 1868, Davis 1897, Tilden 1897, 1898). These authors often expressed surprise that organisms could exist in thermal environments and were interested in the upper temperature tolerance of thermophilic species. Diatoms were not studied systematically until some time later (Lacsny 1912, Oestrup 1918, Strom 1921, Famin 1933, Springer 1930), when they were found to be common in hot springs. More extensive studies were begun in the 1940s (Negoro 1940, Emoto and Hirose 1940, Emoto and Yoneda 1941, Yoneda 1942a, 1942b) and have continued to the present time (Whitford 1956, Yoneda 1962, Thomas and Gonzalves 1965a, 1965b, 1966a-e, Biebl and Kusel-Fetzmann 1966, and others). Diatoms also have recently been studied in several western North American springs (Kaczmarska and Rushforth 1983, St. Clair and Rushforth 1977, Stockner 1967a, 1967b, 1968, Rushforth et al. 1986). Cowboy Hot Spring of the Mono Basin thermal area of eastern California is one of many thermal springs in the Basin and Range Geological Province (Great Basin). This province occurs east of the Sierra Nevada Mountains, between the Snake River and the Mojave Desert, and extends across Nevada into western Utah. The Great Basin is characterized by a thinning of the earth's crust, more than 200 north/ south-oriented mountain ranges with associated valleys (Nelson 1981), an abundance of thermal springs, and a cold desert climate. These features appear to be a result of several geological phenomena, including the continued spreading of the American Plate through the center of the Great Basin, past subduction of the Pacific Plate under the American Plate (Miller 1983), and the uplift of the Sierra Ne-

The soil algae in the Tintic Mountains, Juab County, Utah, was studied over a one-year period in 1982 and 1983. Fluorescence microscopy was used to measure algal density in samples directly from the field. A total of 30 algal taxa was observed, blue-green algae being most abundant both in terms of density and number of species. Algal density showed peaks in late fall and late spring. Minima were present in September 1982 and July 1983. Several weak correlations between algal density and climatic data existed. In general algae correlated positively with precipitation and negatively with temperature. A combination of low precipitation and hot temperatures was likely responsible for the low density observed in July. The Chrysophyta followed slightly different trends than the other algal groups, having minima in early October 1982 and late August 1983. Field observations indicated that the degree of algal crusting varied noticeably over a period of one year, with highest abundance of hummocking in spring. Heavy summer thunderstorms destroyed algal crusting during July and August of 1983, though absolute density of algae increased during this time in response to the extra moisture.

Chaetoceros muelleri Lemmermann has been reported from brackish waters in Europe and North America under more than 10 different specific names. Recently we have studied specimens of C. muelleri and C. hohnii from the western USA, as well as C. wighamoides from South Africa. We have concluded that two different forms of C. muelleri exist in North America. The nominate form is characterized by the frequent presence of a small process on the valve face. We propose the combination Chaetoceros muelleri var. subsalsum for populations consistently lacking processes. C. hohnii and C. wighamoides should be considered synonyms of C. muelleri var. subsalsum. Chaetoceros muelleri is a variable. taxon, both in vegetative cells and resting spores.

Invasion of plant species onto recently exposed beaches of Mono Lake, California, was documented. Three vegetation zones were evident on these beaches. The first was formed entirely of annual species. The second was composed of annuals mixed with salt grass, and the third was formed entirely of salt grass. Stabilization of these beaches was accomplished by the aggressive growth of salt grass rhizomes.