The conversion of sagebrush-steppe communities of the Great Basin into cheatgrass-dominated communities is one of the most dramatic ongoing land conversions in North America. Although restoration of these communities is a high priority to landowners and land management agencies, restoration of native vegetation is difficult. Several restoration treatments intended to increase the success of aerially‐seeded perennial grasses in cheatgrass-invaded sagebrush ecosystems were assessed to determine their effects on perennial seedling emergence and soil seed bank density and composition. Assessed restoration treatments were: 1) vegetation manipulation (sagebrush thinning and prescribed burning); 2) imazapic herbicide application; 3) seedbed amendments (aerial seeding with activated carbon addition, aerial seeding with sucrose addition); and 4) seeding frequency. The effects of these treatments were evaluated in two distinct sagebrush shrubland ecosystems in northern Utah. One is characterized as a remnant sagebrush stand with a cheatgrass-dominated understory and the other as a cheatgrass near-monoculture, completely lacking a sagebrush component. In the seed bank study, responses were assessed immediately and 1 year following treatment while in the seedling emergence study, they were assessed 2 and 3 years following treatment. Main effects of vegetation manipulation, herbicide application, and seedbed addition treatments and their interactions on perennial seedling emergence are described in Chapter 2. The effects of seeding frequency on perennial seedling emergence are also described in Chapter 2. Herbicide demonstrated potential for increasing native perennial grass emergence, although this response was delayed and not seen until 3 years post-application. Burning showed potential for increasing the emergence of perennial grasses 2 years post-burn. Results also suggest that potential exists to increase native perennial grass emergence through an increase in seeding frequency. In Chapter 3 I evaluated the effects of vegetation manipulation, herbicide application, and seedbed addition on seed pool dynamics. These results suggest that herbicide and sucrose may be useful tools for reducing exotic species richness in cheatgrass-invaded systems. Herbicide also showed potential for reducing cheatgrass seed bank densities. Additionally, results demonstrated that the reductions in cheatgrass seed bank densities observed immediately after fire are still observed 1 year post-burn.

Every year, millions of acres of forest and rangeland are burned in prescribed burns as well as wildfires. The costs associated with wildfires may be some of the largest we face as a society both in material goods and in life. The importance of managing fire fuels has increased with the development of the wildland-urban interface. With this increased emphasis has come the development of tools to assess, map, and simulate fuel maps at a landscape level. These fuel maps are then input into computer-aided wildfire simulation models that are used by land managers in the planning process. A current challenge for land managers is to find efficient ways to measure the amount and structure of fire fuels on a landscape level. Fuel models are one of the required inputs for software that mathematically computes wildfire rate of spread. Various methods have been used to develop fuel maps. It is the objective of this thesis to develop a method by which fuel models can be predicted and mapped on a landscape level through utilization of remotely sensed data. The proposed process for this method is: 1) develop landcover classification, 2) assess data analysis approaches for use in creation of predictive regression models, 3) correlation of data results to Natural Fuels Photo Series, and 4) translate Natural Fuels Photo Series classifications into fuel models described by Scott and Burgan.

Herbivory and plant competition affect sexual reproduction of plants in various ways. Exclusion of mule deer (Odocoileus hemionus) and cattle, removal of plant competition (both inter- and intraspecific), and all combinations of the above treatments were used to examine the individual and combined affects on Artemisia tridentata ssp. wyomingensis (Wyoming big sagebrush) reproduction. Reproduction of Artemisia tridentata ssp. wyomingensis was divided into hierarchical levels of the number of: (1) modules per current-year ' s growth (CYG), (2) nodes per module, (3) inflorescence heads per node, (4) achenes per inflorescence head and (5) percent viable achenes. Counts at hierarchical levels were made to determine the level affected by the treatments. Deer herbivory significantly reduced reproduction at the reproductive-module-per-CYG-vegetative-biomass hierarchical level, while plant competition (both inter- and intraspecific) significantly reduced reproduction at the nodes-per-reproductive-module level and at the inflorescence-heads-per-node level. Cattle presence had neither a beneficial nor detrimental influence on reproduction during this two-year study. The combined effects of release from deer herbivory and from plant competition on reproduction was more than additive because these biotic interactions affected nested hierarchical levels.

Managing Wyoming Big Sagebrush (Artemisia tridentata ssp. wyomingensis) systems biologically with grazing can potentially reduce costs and increase both biodiversity and understory production as well as rejuvenate Wyoming Big Sagebrush (ARTRWY). Sheep were provided a protein-energy supplement to facilitate use of the secondary metabolites found in ARTRWY forage. Phytomass ( ) was estimated for the following plant categories: total phytomass, current annual growth (CAG) of ARTRWY, the woody portion of ARTRWY, CAG of other shrubs, the woody portion of other shrubs, grasses, forbs, litter, and standing dead material. I also measured plant species richness and abundance, as well as estimates of the age class structure of sagebrush. One year following grazing, total phytomass decreased by 43%, due primarily to the reduction of ARTRWY. The CAG of ARTRWY decreased by 66%, while grasses increased by 43%, forbs increased 60%, and the number of species encountered in the grazed plots increased 42%.

Plant spatial patterns have been studied to gain insight into plant interactions such as competition and facilitation (positive plant interactions). The stress gradient hypothesis predicts that as environmental stress increases facilitation dominates, while competition dominates in less stressful conditions. Beneficial plants (nurses) can create favorable abiotic conditions for subanopy plants. Additionally, palatable herbaceous species growing under nurse shrub canopies benefit from physical protection. I investigated spatial associations between Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) and three native grasses (Poa secunda, Elymus elymoides, and Pseudoroegneria spicata) across a rainfall gradient in the Great Basin, USA. I also explored the effect of grazing on grass-shrub spatial associations. I hypothesized that positive shrub-grass spatial associations would become more frequent at lower rainfall levels; I further hypothesized that 1) at intermediate levels of stress, positive grass-shrub spatial associations would dominate and 2) at extreme levels of stress, positive grass-shrub spatial associations and interactions would no longer dominate. At high moisture stress, the addition of grazing stress may limit the nurse’s ability to provide to benefits to subcanopy plants. Cover of P. secunda was greater in shrub canopy microsites than interspaces at low to moderate levels of rainfall. Cover and density of E. elymoides were greater in sagebrush canopies over most rainfall levels. Elymus elymoides and P. spicata were taller and narrower in basal width and less likely to be grazed in canopy versus interspace microsites. I next investigated the effects of grazing intensity over a rainfall gradient and found a significant interaction of rainfall and microsite on P. secunda cover. Poa secunda formed positive interactions with A. tridentata at lower rainfall levels, regardless of grazing intensity. Its cover was significantly greater in interspaces at high rainfall compared to low rainfall sites. Elymus elymoides density was greater in canopy vs. interspace microsites, regardless of rainfall level or grazing intensity. Plant spatial associations can indicate which nurse microsites are favorable to plant growth and may improve seeding or planting success during ecological restoration. My results suggest that exploiting sagebrush canopy microsites for restoration of native perennial grasses would improve plant establishment, growth or survival particularly in drier areas.

The objectives of this research were to investigate the ecological importance of soil seed reserves and seed rain on regeneration of a good condition sagebrush- grass range vegetation after a wildfire and draw conclusions leading to better understanding and management of such ecosystems. Investigations were conducted for two successive years on a community where major plants were neither rhizomatous nor sprouting. In such cases soil seed reserves and seed rain have to be the main source of regeneration. In addition to monitoring soil seed reserves and seed rain, vegetation changes during the past two years and the historical conditions of the study area were examined. Study of germinable soil seed reserve dynamics showed that fire can have a destructive effect on this portion of the community. Cheatgrass soil seed reserves were high even in good condition sagebrush-grass vegetation. Although fire reduced the Bromus tectorum seed bank by half, the cover of this grass increased to almost twice the level observed on the control (unburned) plots a year later. This shows the enormous reproductive capacity of this highly competitive weed species following a wildfire. Even though the pre-burn vegetation contained a high proportion of native perennial plants, soil seed reserves and seed rain had very small proportions of their germinable seeds. Timing of the fire is likely important in controlling undesirable range plants and their seeds. Had the fire occurred earlier when more seeds were attached to the culms, greater reduction in cheatgrass probably would have been obtained. Timing of the fire was just right to control sagebrush, because it occurred before their seed set and complete destruction of this species was achieved. Mormon tea was the only shrub to reestablish its cover relatively rapidly. This was related to its strong ability to sprout from root crowns. Greater germinable soil seed reserves were found under shrub canopies than in the inter spaces. This is probably related to the semi-logarithmic dispersal of seed where seed fall is greatest closest to mother plants (Harper 1977). Since flammable fuel follows the same pattern, it was found that fire has a serious impact on soil seed reserves at "hot" points, but temperatures were apparently not hot enough to cause much damage on seed banks at "cold" points in the former interspaces. Since soil seed reserves accumulate in significantly higher proportions in the surface 0-2 cm, fire has a more serious impact on the seeds in surface soil than those lower lower down. Variance of the germinable seed rain was so high that none of the grand totals, life forms totals and species values were statistically significant at alpha

Mined-land reclamation practices in shrub-steppe ecosystems can be augmented by planting seedlings of locally dominant shrubs, e.g., mountain big sagebrush. Dispersion pattern could affect sagebrush performance by influencing amounts of windborne snow, soil and litter which accumulate around shrubs and by influencing water withdrawal by roots. Mountain big sagebrush seedlings were planted in plots on a reclaimed coal strip mine in two dispersion patterns: singly and in clumps of four at the same overall density. Performance of mountain big sagebrush was monitored during two growing seasons. Measures included plant survival, end-of-growing season aboveground biomass, leaf water potential components, soil water potential, twig and ephemeral leaf survival and reproductive allocation. Most measures of performance were similar for single and clumped plants. However, single plants had a greater twig elongation rate than clumped plants, and roots of plants in clumps removed less soil water to 50 cm than roots of single plants. In order for shrub dispersion pattern to affect plant performance via differential snow, soil or litter accumulation, the plants would have to respond to the added resources, probably water and nitrogen. An experiment was conducted to test if a small extra increment of water and nitrogen would affect mountain big sagebrush plants. The same plant performance indices listed above were monitored. The added water and nitrogen, either alone or in combination, had no effect except on reproduction. In 1983, there was a significant water* fertilizer interaction observed for some of the reproductive metrics, while in 1984 there was a significant water effect. While a significant main effect of nitrogen was expected under the prevailing wet conditions, the large reservoir of soil nitrogen evidently provided sufficient nitrogen. Reproduction was more sensitive to added water and nitrogen resources than was vegetative growth. The nearly equal performance of mountain big sagebrush in the two dispersion patterns may have resulted from several factors. Water availability to the experimental shrubs was very high throughout the study due to abnormally heavy precipitation and to removal of weeds from the plots. During drier years, dispersion pattern may have greater influence on the shrubs.

The conversion of sagebrush-steppe communities of the Great Basin into cheatgrass-dominated communities is one of the most dramatic ongoing land conversions in North America. Although restoration of these communities is a high priority to landowners and land management agencies, restoration of native vegetation is difficult. Several restoration treatments intended to increase the success of aerially‐seeded perennial grasses in cheatgrass-invaded sagebrush ecosystems were assessed to determine their effects on perennial seedling emergence and soil seed bank density and composition. Assessed restoration treatments were: 1) vegetation manipulation (sagebrush thinning and prescribed burning); 2) imazapic herbicide application; 3) seedbed amendments (aerial seeding with activated carbon addition, aerial seeding with sucrose addition); and 4) seeding frequency. The effects of these treatments were evaluated in two distinct sagebrush shrubland ecosystems in northern Utah. One is characterized as a remnant sagebrush stand with a cheatgrass-dominated understory and the other as a cheatgrass near-monoculture, completely lacking a sagebrush component. In the seed bank study, responses were assessed immediately and 1 year following treatment while in the seedling emergence study, they were assessed 2 and 3 years following treatment. Main effects of vegetation manipulation, herbicide application, and seedbed addition treatments and their interactions on perennial seedling emergence are described in Chapter 2. The effects of seeding frequency on perennial seedling emergence are also described in Chapter 2. Herbicide demonstrated potential for increasing native perennial grass emergence, although this response was delayed and not seen until 3 years post-application. Burning showed potential for increasing the emergence of perennial grasses 2 years post-burn. Results also suggest that potential exists to increase native perennial grass emergence through an increase in seeding frequency. In Chapter 3 I evaluated the effects of vegetation manipulation, herbicide application, and seedbed addition on seed pool dynamics. These results suggest that herbicide and sucrose may be useful tools for reducing exotic species richness in cheatgrass-invaded systems. Herbicide also showed potential for reducing cheatgrass seed bank densities. Additionally, results demonstrated that the reductions in cheatgrass seed bank densities observed immediately after fire are still observed 1 year post-burn.

Thesis (M.S.)--Oregon State University, 1994. / Typescript (photocopy). Includes bibliographical references (leaves 140-143). Also available on the World Wide Web.

Thesis (Ph. D.)--Oregon State University, 2011. / Printout. Includes bibliographical references (leaves 123-135). Also available on the World Wide Web.