Effects of exotic grasses on soil seed banks in southeastern Arizona grasslands

Species richness in Madrean mixed-grass prairies dominated by native or exotic species in southeastern Arizona was characterized at the community and point scales using ten 1-m 2 quadrats nested within each of eight 1000-m 2 plots. In the 1000-m 2 plots average richness was significantly higher in oak savanna (OS, 121.0 species) than in exotic grassland on mesa tops (EMT, 52.0 species), whereas native grassland on mesa slopes (NMS, 92.5 species) and native grassland on mesa tops (NMT, 77.0 species) did not differ significantly in richness from OS or EMT. When richness was partitioned by life form, EMT was notably poorer than other community types in species of perennial grasses, perennial herbs, and summer annuals. In the 1-m 2 quadrats, OS (21.2 species), NMS (20.9 species), and NMT (20.7 species) were significantly richer than EMT (5.9 species). Cover in 1-m 2 plots was significantly higher in EMT than in NMT, NMS, or OS. Species richness at the point scale showed a unimodal relation to canopy cover, with cover accounting for 30% of the variation in number of species in 1-m2 quadrats. Competitive exclusion and allelopathy have perhaps limited species richness at the point scale in exotic grassland. There was no evidence of a species-pool effect between point and community scales, but such an effect between community and landscape scales was supported. Madrean mixed-grass prairies are landscapes with high species richness in comparison to other grassland types in North America, providing a large pool of potential colonizing species at the community scale. Beta-diversity (between communities) within the landscape of the Appleton-Whittell Research Ranch was consequently high despite a relative lack of habitat diversity.     

Influence of soil water availability on competition among leafy spurge ( Euphorbia Esula ) and grasses

Some perturbations differentially influence invasive plant and grass production. For example, growth regulator herbicides and biological control agents can dramatically reduce leafy spurge production while having little or no influence on grass production, and overgrazing can reduce grass production while not substantially influencing leafy spurge production because cattle typically ingest little or no leafy spurge. To predict how grass production will respond to a perturbation that influences only leafy spurge and to predict how leafy spurge production will respond to a perturbation that affects only grasses, competitive relationships must be understood. Seeding mixtures of leafy spurge and 2 grasses were planted in experiments and grown for 127 days to determine whether different water application regimes influenced competition among these 3 species. Competition became less intense as the number of water applications increased. If this finding holds true under field conditions, then it indicates that competition is less intense in years and locations with numerous precipitation events. Competitive interactions (i.e., competition coefficients) were less variable when water was applied more frequently, but the ability of models to account for variation in plant weight (i.e., r 2 ) was not influenced by the frequency of water application. This suggests that models will predict invasive plant and grass biomass with equal accuracy in years with few or many precipitation events. Competitive effects were similar regardless of grass species, which suggests that grasses might be considered collectively in predicting response to perturbations in the field.     

Effect of salinity on seed germination of Triglochin maritima under various temperature regimes

Triglochin maritima L. (arrow grass), an herbaceous perennial in the family Juncaginacea, is widely distributed in inland and coastal salt marshes of North America. Triglochin maritima seeds from a population growing in a salt marsh at Faust, Utah, were germinated at 4 temperature regimes (12-h night/12-h day, 5-15° C, 10-20° C, and 15-25° C) and 5 salinities (0, 100, 200, 300, 400, and 500 mol m -3 NaCl) to determine optimal conditions for germination and level of salt tolerance. Ungerminated seeds were returned to distilled water after 20 d to determine whether seeds could recover from salinity treatments. Maximum germination occurred in distilled water, and increases in NaCl concentration progressively inhibited seed germination. No seeds germinated at concentrations higher than 400 mol m -3 NaCl. A temperature regime of low night (5° C) and high day (25° C) temperature yielded maximum germination; all other temperature regimes significantly inhibited seed germination relative to this optimum. Recovery of germination was highest at 5-25° C and lowest at 5-15° C. Recovery of seed germination when seeds were transferred to distilled water from salt solutions was highest at 5-25° C (72%) for seeds exposed to the 500 mol m -3 NaCl pretreatment and significantly reduced at other temperature regimes. The recovery germination response indicates a synergistic inhibitory interaction effect on germination when seeds were exposed to high salinities at suboptimal thermoperiods.     

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.     

Depletion of soil moisture by two cold-desert bunchgrasses and effects on photoshythetic performance

This study compared the abilities of two cool-season bunchgrasses to extract moisture from a drying soil and compared photosynthetic and stomatal responses of the two species as soil moisture supplies were depleted. When grown in 49-L pots in a greenhouse, Leymus cinereus extracted more water from the soil and maintained higher gas exchange rates to lower absolute amounts of soil water than did Agropyron desertorum . The soil water content at the lower limit of extraction was 10.3% for L. cinereus and 13.3% for A. desertorum . When soil moisture was expressed as extractable soil water, there was little difference between the species in pattern of water use. Both species maintained high stomatal conductances (g w ) and photosynthetic rates (A) until extractable soil moisture was reduced to about 15%. For field-grown plants under severe water stress, A was higher in L. cinereus than in A. desertorum at comparable leaf water potentials. The relationship between A and g w was similar for the two species; higher A in L. cinereus was a consequence of higher g w . Thus, higher A in L. cinereus is achieved through some sacrifice of water-use efficiency.     

Demography of Astragalus scaphoides and effects of herbivory on population growth

Losses in fecundity due to predispersal herbivory can be large; however, the effects of this loss on long-term population viability have rarely been investigated. I conducted a demographic study of Astragalus scaphoides (Fabaceae), a long-lived perennial endemic to east central Idaho and adjacent Montana, by following mapped individuals at two sites from 1986 to 1993. Astragalus scaphoides suffers losses of predispersal fecundity averaging nearly 50% from insect seed predation and inflorescence predation by insects and livestock. Cattle reduced fecundity by 0-85%. Nonetheless, estimates from matrix projection models indicate that both sample populations had positive growth in most years. Elasticity analyses revealed that population growth occurred in spite of relatively small contributions by recruitment compared to growth and survival of nonreproductive plants. Results suggest that populations of this long-lived perennial depend little on reproduction and recruitment for growth and can persist in association with seasonal-rotation livestock grazing.     

The effects of varied densities on the growth and emigration of adult cutthroat trout and brook trout in fenced stream enclosures

We evaluated the effects of various density treatments on adult fish growth and emigration rates between Bonneville cutthroat trout Oncorhynchus clarki utah and brook trout Salvelinus fontinalis in stream enclosures in Beaver Creek, Idaho. We used 3 density treatments (low, ambient, and high fish densities) to evaluate density-related effects and to ensure a response. Intraspecific ambient-density tests using cutthroat trout only were also performed. Results indicated an absence of cage effects in the stream enclosures and no differences in fish growth between ambient-density stream-enclosure fish and free-range fish. Brook trout outgrew and moved less than cutthroat trout in the stream enclosures, especially as density increased. In all 3 density treatments, brook trout gained more weight than cutthroat trout, with brook trout gaining weight in each density treatment and cutthroat trout losing weight at the highest density. At high densities, cutthroat trout attempted to emigrate more frequently than brook trout in sympatry and allopatry. We observed a negative correlation between growth and emigration for interspecific cutthroat trout, indicating a possible competitive response due to the presence of brook trout. We observed similar responses for weight and emigration in trials of allopatric cutthroat trout, indicating strong intraspecific effects as density increased. While cutthroat trout showed a response to experimental manipulation with brook trout at different densities, there has been long-term coexistence between these species in Beaver Creek. This system presents a unique opportunity to study the mechanisms that lead cutthroat trout to coexist with rather than be replaced by nonnative brook trout.     

Plasticity and polymorphism in seed germination of Mimulus guttatus (Scrophulariaceae)

Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 /* 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;} Seeds of 12 populations of Mimulus guttatus representative of the Wasatch Mountain ecotype were incubated for 17 months (one natural season plus a year) in five artificial climates found in phytotron studies to be important to the growth of the plants of that form of monkey flower. In all but the coldest climate, germination occurred promptly (3–8 days, on average), peaked during the first three weeks, and then tapered off gradually well into the second season. Generally, the amount and timing of germination was plastic, showing much the same range of responses in widely different climates both overall and for individual populations. However, in some cases, there were significant differences between populations indicative of polymorphism within the species. For example, germination was significantly slower, more variable, and less in amount the higher the elevation of origin of the populations. The responses of the population suggest the presence of both much plasticity and much polymorphism for germination characteristics in this form of M. guttatus.     

Observations on the distribution of microorganisms in desert soil

Population estimates of fungi, bacteria, and actinomycetes in desert soil were determined with respect to soil depth and distance from shrubs. In general the highest numbers of microbes were found at the shrub base; the lowest numbers were found in the interspaces. While the total number of organisms usually declined in deeper soil, the relative importance of the actinomycetes increased. These population trends are attributed to substrate availability and utilization and interspecific interactions. As the soils became drier and warmer the total number of microorganisms decreased. Mold populations remained at about the same level during the study. While the numbers of both bacteria and actinomycetes declined, the relative importance of the actinomycetes increased.        

Field observations of Irbisia pacifica (Hemiptera: Miridae): feeding behavior and effects on host plant growth

The interaction between a grass-feeding mirid, Irbisia pacifica (Uhler), and plant growth of intermediate wheatgrass, Thinopyrum intermedium (Host) Barkw. & D. R. Dewey, was examined on a field site in northern Utah in 1985. With egg hatch beginning in April, the bug completed its life cycle within two months. Ovarian development was completed by 11 June, a week after all bugs had become adults. The proportion of feeding damage per leaf (35.1%) peaked on the seventh week of the twelve-week study (18 July). Green leaf area per tiller decreased initially from bug feeding and then continued to decrease because of seasonal aging. All plants senesced within three months. Grass bugs predominantly attacked the second and third youngest leaves. Analyses of age-specific leaf cohorts demonstrated that the major effect of bug feeding was the loss of green leaf area and potential foliage production over time. Bug feeding may also exacerbate other physiological stresses on the host plants.     

Taxonomy and biology of final-instar larvae of some Eurytomidae (Hymenoptera: Chalcidoidea) associated with grasses in the UK

A comparative morphological study was made of the final-instar larval stage of 33 species of grass-inhabiting Eurytomidae belonging to four genera: Eurytoma Illiger, Tetramesa Walker, Sycophila Walker and Ahtola Claridge. Emphasis was placed upon chaetotaxy and mandibular structure. The final-instar larvae of the species are described, those of 26 species for the first time, and diagnostic characters and keys to genera and species are provided. Information, including new rearing records, is given on the larval biology of each eurytomid species, together with comments on the adult taxonomy of certain species.     

Effect of soil microtopography on seed bank distribution in the shrub-steppe

The relationship between soil surface cryptogamic crusts and seed banks was investigated in the shrubsteppe in the Lower Columbia Basin. Seventy-four percent of the seeds in a disturbed bunchgrass community were found in crevices bordering cryptogamic crust polygons. In a sagebrush/bunchgrass community, 89% of the seeds were found in crevices. In a disturbed bunchgrass community, Bromus tectorum seeds were found in both the seed bank and aboveground vegetation communities. Bromus tectorum seeds were located in the seed bank of a sagebrush/bunchgrass community, although it had a minor presence in the aboveground community. Seeds of Artemisia tridentata Nutt. were not found in either the bunchgrass or sagebrush/bunchgrass communities. The high number of seeds found in crevices bordering the cryptogamic crust suggests that crevices play a role in determining the small-scale distributional pattern of shrub-steppe plants at the Fitzner-Eberhardt Arid Lands Ecology Reserve.     

Influence of soil and site characteristics on Palouse prairie plant communties

The structure of grassland communities can vary widely in response to heterogeneous habitat variables. In this study we document plant communities, soil types, and site characteristics for 12 Palouse prairie remnants in southeastern Washington and northern Idaho. We used general linear models to test the predictive value of 6 biophysical variables (slope, aspect, distance from edge, edge type, vegetation structure, and soil type) on 3 plant community metrics: species richness, Simpson’s diversity index, and the dominance of exotic species. From full models including all variables, we used Akaike’s information criterion (AIC) to select the best model for each metric. Aspect and vegetation structure were significant predictors of species richness ( R 2 = 0.08) and diversity ( R 2 = 0.09), while aspect, soil type, distance from edge, and edge type (type of adjacent matrix habitat) influenced the dominance of exotic species ( R 2 = 0.28). Additional soil sampling determined that the depth to a restrictive layer also had significant impacts on the dominance of exotic species ( R 2 = 0.31). This study confirms that biophysical characteristics influence Palouse prairie plant communities and may help set research and conservation priorities for isolated and uninventoried remnants.     

Production, losses, and germination of Ceanothus fendleri seeds in an Arizona ponderosa pine forest

I quantified seed production and ovule losses for Ceanothus fendleri Gray (Fendler ceanothus) plants protected from large ungulate herbivores in a ponderosa pine ( Pinus ponderosa [Laws]) forest of northern Arizona. I also tested seed germination responses to cold stratification and heat treatments in the laboratory. Fruit production on fecund stems ranged from 7.4 to 38.2 fruits per stem, which equated to 22.2-118.2 potential seeds based on 3 ovules per fruit. Stems that produced fruit were significantly large relative to their expected sizes. Predispersal ovule losses ranged from 70.7% to 91.4% across the 2 years studied. A chalcidoid seed parasite ( Eurytoma squamosa Bugbee) consumed 11%-28% of the total number of seeds produced. Postdispersal seed predation varied from 0% to 24% and was significantly affected by forest floor substrate in 1 study year. Cumulative ovule losses were estimated to be 71%-92%. Cold stratification did not significantly affect seed germination, and exposure to 90°C resulted in the highest germination percentage. Both dormant and nondormant seeds suggested a bet-hedging life history strategy. This study provides basic ecological information important for management of ponderosa pine forest and nursery production of C. fendleri .     

Effects of osmotic potential, potassium chloride, and sodium chloride on germination of greasewood ( Sarcobatus vermiculatus )

Greasewood ( Sarcobatus vermiculatus [Hook.] Torr.) (Chenopodiaceae) typically grows on salt-affected soils where its germination requirements may reflect characteristics necessary for establishment in saline environments. The objective of this study was to determine the effect of osmotic potential and specific ions on the germination of seeds from three populations of greasewood. Seeds were germinated at 20 C in solutions of polyethylene glycol with water potentials ranging from –0.3 to –2.2 MPa that contained 0 to 68480 µmol·L –1 sodium chloride (NaCl) or 0 to 53640 µmol·L –1 potassium chloride (KCl). Germination of two populations was reduced by increasing salt concentration and decreasing osmotic potential; germination of one population was reduced by declining osmotic potential. No seeds germinated at an osmotic potential lower than –1.6 MPa. For all populations, days to 50% of final germination increased and abnormal germination decreased as osmotic potential declined. Comparison of our results with those from other studies suggests geographic ecotypic development in response to osmotic potential and NaCl and KCl concentrations during germination.     

Population cycles of Wahweap Milkvetch on the Henry Mountains and seed reserve in the soil

A population outbreak of Wahweap milkvetch ( A. lentiginosus var. wahweapensis Welsh) occurred in the Henry Mountains area of southeastern Utah in 1985 and 1986, causing extensive locoweed poisoning in cattle grazing these winter ranges. Weather conditions supporting this population outbreak included above average precipitation in the fall of 1984 and 1985, which presumably allowed germination of seed lying dormant in the soil. Above average spring precipitation in the subsequent year supported the population growth. Part of the population died in the summer of 1985, and nearly all plants died in the summer of 1986. Historically, population outbreaks occurred every six to eight years: 1949, 1957, 1965, 1973, 1979, and 1985-1986. Correlation with weather records indicated that population outbreaks occurred in years of high spring and total annual precipitation. Wahweap milkvetch seed lying dormant in the soil ranged from 940 to 4,346 seed/m 2 where old stands occurred, and 20 to 40 seed/m 2 where old plants were not evident. Sufficient seed remains in the soil to cause future population outbreaks.     

Effects of dwarf mistletoe on growth and mortality of Douglas-fir in the Southwest

The effects of dwarf mistletoe ( Arceuthobium douglasii ) on growth and mortality of Douglas-fir ( Pseudotsuga menziesii ) were studied on 387 plots in mixed-conifer stands in three national forests in New Mexico and two in Arizona. Analyses of 8,570 trees showed that low infection ratings (dwarf mistletoe classes 1 or 2) had no significant effect on tree growth, but that losses increased markedly as infection severity increased. Average volume growth losses for trees over 10 inches in diameter were: dwarf mistletoe class 3, 10%; class 4, 25%; class 5, 45%; and class 6, 65%. Mortality of Douglas-fir in stands severely infested with dwarf mistletoe was three to four times that of healthy stands. These high losses confirm the need for silvicultural control of Douglas-fir dwarf mistletoe in the Southwest.     

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.     

Observations on woundfin spawning and growth in an outdoor experimental stream

The response of woundfin to different substrates and current speeds was investigated in an outdoor experimental stream. Fish spawned in groups of 15 – 20 over 5 – 10 cm rock substrate in a .06 to .09 m/sec current at a depth of 10 cm. Eggs were adhesive on the undersides of the rocks. Fish spawned under these conditions grew to approximately 55 – 60 mm TL in 5 months.