Kimball T. Harper

Differential Resource Utilization by the Sexes of Dioecious Plants

The distribution of male and female plants was examined in five dioecious, wind-pollinated species representing five plant families and two classes (gymnosperms and angiosperms). The arid to semiarid habitats occupied by these species in northern Utah were stratified for sampling into two categories: chronically xeric and seasonally moist. The results show that for all species, males are more abundant on xeric microsites, while females are over represented on the moister parts of each local environment. Differential distribution of the sexes along a soil moisture gradient is a strategy that maximizes seed set of females and pollen dispersal of males; it also tends to minimize intraspecific competition between the sexes.

A role for nonvascular plants in management of arid and semiarid rangelands

Blue-green algae, lichens and mosses are common features on soil surfaces of arid and semiarid rangelands worldwide. Such plants often cover as much or more of the soil surface as vascular plants and make useful contributions to arid and semiarid ecosystems via enhanced soil stability against wind and water erosion and greater availability of nitrogen. In some situations, cryptogamic plants roughen soil surfaces and increase water retention and eventual infiltration. Situations are documented in which cryptogamic covers (particularly those with blue-green algae) have improved establishment and growth of vascular plant seedlings. Responses of various cryptogamic species to a broad array of environmental challenges are discussed. Evidence is presented that cryptogamic plants complement the effects of vascular plants relative to soil stability and water infiltration. It is suggested that cryptogamic cover usually does not develop at the expense of higher plant cover. Data indicate that some range management practices are damaging to cryptogamic plants, while others permit those plants (particularly blue-green algae) to persist in the ecosystem. It is recommended that future management practices on arid rangelands be designed to retain at least blue-green algae and lichens having blue-green phycobionts in the system.

Influence of Biological Soil Crusts on Soil Environments and Vascular Plants

The presence of biological soil crusts can significantly change the physical and chemical soil environment. Such alterations can affect the germination, survival, and nutritional status of vascular plants. Some landscape surveys have found a negative relationship between biological soil crusts and vascular plant cover (West 1990; Johansen 1993; Eldridge 1993). Based on this, some authors have concluded that crust organisms limit vascular plant cover (Savory 1988). However, it is also possible that soil crusts merely occupy all soil surfaces not first covered by vascular plants. In support of this, numerous authors have reported that vascular plant cover either shows no correlation with crust cover (Anderson et al. 1982; Beymer and Klopatek 1992; Jeffries and Klopatek 1987; Kleiner and Harper 1972, 1977) or that there is a positive correlation between vascular plant and crust cover (Carleton 1990; Dadlich et al. 1969; Graetz and Tongway 1986; Ladyman and Muldavin 1994; Lesica and Shelley 1992; Mucher et al. 1988).

Influence of cryptobiotic soil crusts on elemental content of tissue of two desert seed plants

Soil surface growths dominated by cyanobacteria and the lichen Collema in southeastern Utah are shown to be associated with greater tissue content of several bio‐essential elements in two co‐occurring seed plants (Festuca octoflora, Poaceae, and Mentzelia multiflora, Loasaceae). The elements N, P, K, Ca, Mg, and Fe were present in significantly greater concentrations in Festuca growing on soils heavily encrusted with cyanobacteria and cyanolichens than in plants on the same soil where foot traffic had destroyed the cryptobiotic crusts. With Mentzelia, N, Mg, and Fe were present in significantly greater concentrations in plants from sites with encrusted soil surfaces than on blow‐sand sites. The cryptobiota appeared to compete vigorously with Mentzelia for available P: Mentzelia plants from crusted sites contained significantly smaller concentrations of P than plants grown on soils where wind action precluded development of surface crusts. These cryptobiotic crusts fix considerable amounts of N, which appa...

Surface disturbance of cryptobiotic soil crusts: Nitrogenase activity, chlorophyll content, and chlorophyll degradation

Cryptobiotic soil crusts are an important component of semiarid and arid ecosystems. An important role of these crusts is the contribution of fixed nitrogen to cold‐desert ecosystems. This study examines the residual effects of various intensities and combinations of different surface disturbances (raking, scalping, and tracked vehicles) on nitrogenase activity, chlorophyll content, and chlorophyll degradation in these soil crusts. Nine months after disturbance chlorophyll content of disturbed soils was not statistically different from undisturbed controls, except in the scalped treatments, indicating recovery of this characteristic is fairly quick unless surface material is removed. Differences in chlorophyll degradation among treatments were not statistically significant. However, nitrogenase activity in all treatments showed tremendous reductions, ranging from 77–97%, when compared to the control, indicating this characteristic is slow to recover. Consequently, assessment of crustal recovery from distu...

Ecology of plant dioecy in the intermountain region of Western North America and California

SummaryData from 44 plant communities of the arid zone of western North America and from the entire California flora suggest that the dioecious habit (separate sexed individuals) is best developed among wind pollinated woody plants. A rationale is presented for the ways in which wind pollination and large plant size have favored the development of the dioecious habit. Based upon the patterns examined, it is concluded that inbreeding depression alone is insufficient to account for the evolution of the dioecious habit in many temperate species.

THE EFFECTS OF INCREASING SNOWPACK ON A SUBALPINE MEADOW IN THE UINTA MOUNTAINS, UTAH, U.S.A.

Sampling sites were established along naturally occurring snowdrifts in order to assess the long-term impacts of increased snowpack on a subalpine meadow in the Uinta Mountains of Utah. The study area was divided into three zones (light, moderate, and heavy snowpack) based on snow depths measured on 1 April. The sites were sampled from 1976 through 1979. Several abiotic variables (slope, exposure, soil texture, and pH) did not differ significantly between snowpack zones in the study area. The variables sampled which decrease with increasing snowpack are soil depth, organic matter, plant moisture stress, total plant cover, and plant production. Four variables (snow release date, number of species per macroplot, exposed rock, and total flowering period) increase with increasing depth of the snowpack. Relative decline in plant cover and plant production are predicted for additional increases in snowpack. The vegetation of the meadow is described and prevalent species are noted. Individual species responses show that 14 species achieve maximum cover in the heavy snowpack zone while only six reach maximum cover in the light snowpack zone. Ten species show no preference for snowpack zones. Production data for the 4 yr of study show considerable variation between years. The differences in the yearly production figures are primarily due to the response of the graminoids which increase with increased growing season precipitation and decrease with greater snowpack. Forb production did not change significantly among the 4 yr of study.

Floral Ecology in Relation to Plant Species Diversity in the Wasatch Mountains of Utah and Idaho

An analysis of the relative abundance of the prevalent species in 25 major plant com? munities of the Wasatch Mountains demonstrates that variation in species diversity is significantly correlated with many floral characteristics. Wind-pollinated flowers decrease in abundance whereas animal-pollinated flowers increase along the diversity gradient. The relationship is statistically signif? icant. Color diversity and species diversity are significantly and positively correlated in open com? munities but are unrelated in forest communities. The percent sum frequency of yellow flowers decreases with increasing species diversity whereas blue flowers increase. Also, zygomorphic flowers and flowers in which access to the nectar supply is restricted by morphological barriers are positively correlated with species diversity. It is shown that species with wind-pollinated flowers and zoo- philous species having open flowers are significantly better represented in the higher-frequency classes than animal-pollinated species whose nectaries are morphologically restricted. The results suggest that many floral characteristics impart a reproductive advantage to species growing in com? munities of high diversity. That the relationships observed can be predicted with reasonable confi? dence within a small geographic area implies that the selective forces are local and strong.

Genetic diversity and gene flow in the endangered dwarf bear poppy, Arctomecon humilis (Papaveraceae)

Arctomecon humilis is a critically endangered species endemic to the Moenkopi shale of Washington County, Utah. Recovery plans for the species would be improved by an understanding of genetic diversity and gene flow among its remaining populations. Ten variable isozyme loci were used to calculate genetic diversity statistics for study populations. Westerly populations possessed higher levels of genetic variability than other populations at the same isozyme loci. Three of the populations exhibited significant deviations from Hardy-Weinberg expectations. No correlation existed between genetic distance and geographic distance. Most of the genetic diversity was distributed among populations with little gene flow between populations, suggesting that observed genetic differences may arise from genetic drift. For the westerly populations, similar genotypes were observed in the seedling and old age classes, while intermediate age classes typically possessed an alternate set of genotypes at Pgi-2. Mean heterozygosity increased with age class across populations. Westerly populations of A. humilis shared more alleles with the nearest geographic population of A. californica than other populations. Since the westerly populations contained more genetic variability and more alleles in common with a near relative, they may be relictual. Other populations may contain less genetic diversity due to founder effects and/or genetic drift.

Effects of a Coal-fired Power Plant on the Rock Lichen Rhizoplaca melanophthalma: Chlorophyll Degradation and Electrolyte Leakage

Chlorophyll degradation and electrolyte leakage were measured for the umbilicate desert lichen Rhizoplaca melanophthalma (Ram.) Leuck. & Poelt in the vicinity of a coal-fired power plant near Page, Arizona. Patterns of lichen damage indicated by chlorophyll degradation were similar to those indicated by electrolyte leakage. Regression analyses ofchlorophyll degradation as well as electrolyte leakage on distancefrom the power plant were significant (p < 0.001), suggesting that lichen damage decreased with increasing distance from the power plant. Mean values for both variables at the two sites closest to the power plant (7 and 12 km) differed significantly from values for the two sites farthest from the plant (21 and 42 km; p < 0.001). Mean values within each group (7 and 12 km; 21 and 42 km) do not differ significantly for either parameter. It is suggested that effluents from the power plant combine with local weather factors to produce the observed levels of damage. Lichens have long been used as indicators of air pollution, especially species with fruticose growth forms. In the deserts of the western United States, however, the majority of the lichen flora is crustose or foliose, forms regarded by some as more resistant to pollutants (Fenton 1964; Nash 1974). This, along with the aridity of the environment which results in shorter periods of time of metabolic activity for lichens, has led some researchers to suggest that desert species may not be useful as indicators of air pollution (Marsh & Nash 1979). Field studies with lichens have generally used patterns of species oc- currence or cover values, or both, to measure pol-