Habitat relationships of saltcedar ( Tamarix ramosissima ) in central Utah

Nineteen study sites were established in areas infested with saltcedar bordering Utah Lake in central Utah. Saltcedar cover on the sites averaged 57% but varied widely from community to community. Seventeen soil factors were measured relative to the stands studied. Cover of saltcedar was regressed against the different soil factors, but no patterns were detected. Saltcedar functioned equally well at all levels of each gradient studied and appeared able to accommodate wide variations in all factors studied. It is suggested that saltcedar has evolved a general-purpose genotype that contributes to its being a vigorous and troublesome weed. Criteria as to why it is such an aggressive weed are listed.     

Environmental attributes correlating with density of blackbrush ( Coleogyne ramosissima ) shurbs in the Spring Mountains of southern Nevada

Discovery of distinct mid-elevational bands of blackbrush ( Coleogyne ramosissima Torr.) shrublands on desert mountain slopes in the Mojave Desert caused an investigation of the relationships between environmental factors and Coleogyne distribution. Environmental factors were quantitatively examined to determine which were significant predictors of Coleogyne density at upper-elevational limits (ecotones) in the Spring Mountains of southern Nevada. Path analysis revealed significant, direct causal effects of air temperature, soil moisture, soil depth, and percent litter cover on the distribution of Coleogyne . Specifically, air temperature was a significant positive predictor, while soil moisture, soil depth, and percent litter cover were significant negative predictors of Coleogyne density, with the effects of other environmental variables parceled out. Path analysis also indicated that indirect effects of soil pH, bulk density, compaction, percent pore space, organic matter, soil temperature, salinity, cryptogam, and percent bare soil and rock cover on Coleogyne density were substantially more potent than their direct casual effects. Environmental attributes associated with elevational changes correlate with and may determine the density of Coleogyne shrubs at upper ecotones in southern Nevada.     

Variation in germination response to temperature and water availability in blackbrush ( Coleogyne ramosissima ) and its ecological significance

Blackbursh ( Coleogyne ramosissima Torr.) is a dominant desert shrub in a distinct mid-elevations vegetation belt between creosote bush-bursage ( Larrea tridentata-Ambrosia dumosa ) shrubland below and big sagebrush-pinyon pine- Utah juniper ( Artemisia tridentata-Pinus monophylla-Juniperus osteosperma ) woodland above in the Mojave Desert. Seed germination patterns of blackbrush seeds collected from 2 elevations (1200 and 1550 m) in 5 mountain ranges within the blackbrush shrublands were investigated. Morphological features of blackbrush seeds, including weight, length, and width, were not significantly different ( P > 0.05) among elevations and mountain ranges in the Mojave Desert. Germination of blackbrush seeds was optimal when preceded by a prechill period of 4-6 wk. Seeds incubated at room temperature germinated poorly. Seeds collected at warm, low-elevation sites appeared to be less dormant (required less prechill time), germinated faster, and showed a higher overall germination response; watering at 2-wk intervals revealed the greatest germination. Some ecotypic variation among populations establishing at different elevations was evident with regard to dormancy duration and germination response at certain constant temperatures.     

Habitat and community relationships of cliffrose ( Cowania mexicana var. stansburiana ) in central Utah

Cliffrose ( Cowania mexicana var. stansburiana [Torr.] Jepson) community measurements were taken in central Utah. Data revealed a high between-site similarity of 78.5%. Soil analysis for sites showed most macronutrients, and some micronutrients, relatively low. Cover of cliffrose was found to increase with increases in soil magnesium (p ≤ 0.01). Plants growing on the sites have adapted life cycles to exploit moisture and nutrients during seasons of maximum availability. Prevalent species in the community were cheatgrass ( Bromus tectorum ), cliffrose, madwort ( Alyssum alyssoides ), and bluebunch wheatgrass ( Agropyron spicatum ). Annual grasses were the most important life form to community composition; the second was shrubs. Ratios between soil nutrients and cliffrose tissue nutrients indicate active transport of some elements. Data indicated a steady decline in establishment of new cliffrose individuals on the sites since 1957. This lack of reproductive success is most likely due to a combination of factors but appears most influenced by the elevated levels of annual plants (mainly cheatgrass) on the sites. If the cliffrose communities in central Utah are to be maintained, special attention to their management must be considered and implemented.     

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.     

Habitat relationships of Glaux maritima in central Utah

Thirty-five study sites were established in the meadow communities surrounding Utah Lake in central Utah. The study sites ranged across several community types. Glaux maritima was found in all sites but varied as to its ecological importance in these communities. Sixteen soil factors were measured relative to the stands studied. Cover of Glaux maritima correlated with parts per million sodium and total soluble salts in the soil. No other factors correlated significantly with the cover of Glaux maritima. Glaux maritima occupied only those sites with high levels of moisture throughout the growing season. The high moisture levels came from springs, seeps, elevated water tables, and early seasonal inundation. High levels of Glaux maritima cover corresponded to low numbers of species in the habitat.        

Soil compaction from human trampling, biking, and off-road motor vehicle activity in a blackbrush ( Colleogyne ramosissima ) shrubland

Soil compaction from human trampling, biking, and off-road motor vehicle traffic was quantitatively investigated in a blackbrush ( Coleogyne ramosissima ) shrubland in Kyle Canyon of the Spring Mountains in southern Nevada. A significant difference was detected in soil compaction, bulk density, and percent pore space at a particular frequency of visits in each of 4 disturbance types. On average a single vehicle pass was equivalent to 10 human footprints. Ten and 100 footprints were equivalent to 1 motorcycle pass and 10 vehicle passes, respectively. Soil compaction is a product of increased bulk density and decreased pore space. The degree of soil compaction is a function of disturbance type and visit frequency when examining these 2 factors independently. However, interactive effects of disturbance type and visit frequency on soil bulk density, compaction, and percent pore space were not significantly different. The greatest effects occurred during the first few passes, with changes per pass decreasing as the number of passes increased in all 4 trails. Results of this study suggest that the effects of hiking and biking slowly increase over time relative to the effects of motor vehicle traffic in the Coleogyne shrubland of Kyle Canyon in southern Nevada.     

Habitat and spatial relationships of nesting Swainson's Hawks ( Buteo swainsoni ) and Red-tailed Hawks ( B. jamaicensis ) in northern Utah

A total of 28 Swainson's Hawk ( Buteo swainsoni ) and 30 Red-tailed Hawk ( B. jamaicensis ) nests were found in Cache Valley, Utah, during the summers of 1992 and 1993. All nests were in trees, but only Red-tailed Hawks nested in dead trees (30%). In the intensive study area, nesting densities were 0.10 nests/km 2 for Swainson's Hawk and 0.08 nests/km 2 for Red-tailed Hawk. Nearest-neighbor nest distances were significantly shorter among Swainson's Hawks (1.74 km) than among Red-tailed Hawks (2.83 km). Congeneric nearest-neighbor distances were significantly shorter than conspecific distances for Red-tailed Hawks (1.59 vs 2.83 km) but not for Swainson's Hawks (1.52 vs. 1.74). GIS analysis of habitat types was made for 2-km radii around nest sites. Cropland was the dominant land cover type at nest sites of both species and no significant difference was found between species. Swainson's Hawk nest sites contained significantly more pasture, whereas Red-tailed Hawk nest sites contained significantly more juniper, maple, and sagebrush. Only Red-tailed Hawk nests ( n = 8; 27%) were found on the periphery of the valley at the base of foothills of the Cache Mountains. This preference resulted in a significantly higher elevation for Red-tailed Hawk nest sites. Swainson's Hawk nests occurred only on the valley floor on level terrain. Distance to the nearest paved road and building was very similar for both species, implying that little difference exists in tolerance levels for human activities. Overall, multivariate niche overlap for habitat was high (0.89), indicating a lack of habitat partitioning between these 2 Buteos in Cache Valley.     

Effects of salinity on establishment of Populus fremontii (cottonwood) and Tamarix ramosissima (saltcedar) in southwestern United States

The exotic shrub Tamarix ramosissima (saltcedar) has replaced the native Populus fremontii (cottonwood) along many streams in southwestern United States. We used a controlled outdoor experiment to examine the influence of river salinity on germination and first year survival of P. fremontii var. wislizenii (Rio Grande cottonwood) and T. ramosissima on freshly deposited alluvial bars. We grew both species from seed in planters of sand subjected to a declining water table and solutions containing 0, 1, 3, and 5 times the concentrations of major ions in the Rio Grande at San Marcia, NM (1.2, 10.0, 25.7 and 37.4 meq 1 -1 ; 0.11, 0.97, 2.37, and 3.45 dS m -1 ). Germination of P. fremontii declined by 35% with increasing salinity ( P = .008). Germination of T. ramosissima was not affected. There were no significant effects of salinity on morality or above- and belowground growth of either species. In laboratory tests the same salinities had no effect on P. fremontii germination. P. fremontii germination is more sensitive to salinity outdoors than in covered petri dishes, probably because water scarcity resulting from eavaportion intensifies the low soil water potential associated with high salinity. River salinity appears to play only a minor role in determining relative numbers of P. fremontii and T. ramosissima seedlings on freshly deposited sandbars. However, over many years salt becomes concentrated on floodplains as a result of evaporation and salt extrusion from saltcedar leaves. T. ramosissima is known to be more tolerant of the resulting extreme salinities than P. fremontii . Therefore, increases in river salinities could indirectly contribute to decline of P. fremontii forests by exacerbating salt accumulation on floodplains.     

Observations on Double-crested Cormorants ( Phalacrocorax auritus ) at sportfishing waters in southwestern Utah

Counts of Double-crested Cormorants ( Phalacrocorax auritus ) were made at 13 reservoirs and lakes in southwestern Utah during 1989-91 to determine current abundance of that species. Food habits of cormorants were studied at three of the reservoirs in 1989. Data were also collected on trout abundance during standardized gill-netting to make comparisons between cormorant numbers and trout abundance. Cormorants were observed at all waters studied except one and were generally most numerous during the spring as they migrated through the area. Estimated cormorant abundance ranged from 0 to 34 bird-days per ha and was highest at the larger, lower-elevation reservoirs. Cormorants were summer residents at several of the larger reservoirs and nested successfully at Piute Reservoir. Trout accounted for 24-81% of the diet of cormorants, with Utah chubs constituting most of the remainder of the diet. Estimates of the annual consumption of fish by cormorants ranged from 0 to 15.8 kg per ha. The index of trout abundance was inversely related to cormorant abundance ( P < .01) at the waters studied. Cormorants apparently have increased in numbers and extended their range in southwestern Utah during the past decade. This change may be the result of factors that have led to similar changes throughout North America as well as some factors unique to Utah. Methods to mitigate the impact of predation by piscivorous birds of sportfisheries are discussed. The Utah Division of Wildlife Resources has initiated a new management plan at Minersville Reservoir that incorporates piscivorous birds into sportfish management at that reservoir.     

Distribution and abundance of native Bonneville cutthroat trout ( Oncorhynchus clarki utah ) in southwestern Utah

The Bonneville cutthroat trout ( Oncorhynchus clarki utah ; BCT) was once abundant throughout the Bonneville Basin. In southwestern Utah, however, only 3 local populations of the subspecies were known to exist in 1977, when conservation efforts to protect and replicate them began. By 1995 remnant populations were known in 6 streams, and replicate populations had been established in an additional 16. Populations of BCT in southwestern Utah streams were survey by electrofishing in 1994 and 1995 to describe the subspecies' status. Estimated densities of age-1 and older BCT ranged from 118 to 546 fish per km. Biomass estimates ranged from 8 to 64 kg per ha. Several age groups of BCT were collected at most locations. Six populations were classified as self-sustaining, 9 as expanding through natural recruitment, 6 as new, and 1 as hybridized. Overall status of BCT in southwestern Utah has improved since 1977, but conservation measures must continue to maintain a positive trend.     

Comparative habitat and community relationships of Atriplex confertifolia and Sarcobatus vermiculatus in central Utah

Thirty-four study sites were established in shadscale ( Atriplex confertifolia [Torr. & Frem.] Wats.) and greasewood ( Sarcobatus vermiculatus [Hoov. Torr. in Emory) communities bordering Utah Lake in central Utah. Differences in species composition, vegetation, and soil characteristics were assessed. Significant differences in soil factors between the two communities were found for sand, calcium, manganese, zinc, and copper. Soluble salts and sodium concentrations were generally higher in the greasewood type, but differences were not significant. Major differences were found in understory species, with burr buttercup ( Ranunculus testiculatus Grantz) showing significantly greater cover in the shadscale community and cheatgrass ( Bromus tectorum L.) showing significantly greater cover in the greasewood community.     

Habitat characteristics of small mammals in southeastern Utah

We describe habitat characteristics of 8 small mammal species occurring in the Manti-LaSal National Forest in southeastern Utah. Thirty-seven grids across 7 vegetation types were sample by live-trapping from May through October 1994 and 1995. Logistic regression models of habitat measurements correctly classified small mammal presence 36%-87% of the time. Except for 1 instance, 4 Peromyscus species present in a specific vegetation type were negatively associated with forb or grass cover. Microtus montanus was present primarily on mesas and was positively associated with tall tree and low shrub cover. Neotoma mexicana was present only in canyons and was found primarily in the pinyon-juniper ( Pinus edulis-Juniperus osteosperma ) vegetation type. Tamias spp. was present in all vegetation types. Our results allow better management of these species by providing greater understanding of their use of habitat within vegetation types.     

Naturalization and habitat relationships of bitter nightshade ( Solanum dulcamara ) in central Utah

Ten plant communities containing bitter nightshade ( Solanum dulcamara ) were studied and the ecology and naturalizing relationships of bitter nightshade in central Utah area were investigated. Biotic and abiotic factors from each area were statistically analyzed. The data indicated that bitter nightshade was negatively correlated (P &nbsp;     

Rodent populations, biomass, and community relationships in Artemisia tridentata, Rush Valley, Utah

Three desert Artemisia tridentata communities in Rush Valley, Utah, were trapped for small rodents during the summer of 1970, and population densities were estimated for each population category using Lincoln's index. Animals were weighed and rodent biomass calculated by species throughout the summer. Population, biomass, and other data were then analyzed to gain an understanding of the community relationships of the three study areas to each other as well as to the A. tridentata community types of the Great Basin. Peromyscus maniculatus, Eutamias minimus, and Reithrodontomys megalotis were common to area 1, whereas P. maniculatus, E. minimus, and Perognathus parvus were common to areas 2 and 3. The peak estimated standing crops were 182.8 (74.0). 143.1 (57.9), and 129.7 g/acre (52.5 g/ha) for areas 2, 1, and 3 respectively. The population and biomass of area 2 peaked in midsummer, area 1 early summer, and area 3 late summer.