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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

MATERNAL REPRODUCTIVE INVESTMENT IN THE DESERT ANNUAL LESQUERELLA GORDONII: REGULATION AND PATTERNS.

Delph, Lynda Ferrell. January 1983 (has links)
No description available.
2

Regrowth of pearl millet

Stephenson, Robert John January 2011 (has links)
Typescript (photocopy). / Digitized by Kansas Correctional Industries
3

The Effect of Protective Materials on the Overwintering of Hardy Annuals, Candytuft and Stocks

Burningham, Melvin S. 01 May 1966 (has links)
Many hardy annual flowers will live through the winter if there is sufficient snow protection. Since snow cover is not consistent from year to year it has been suggested that hardy annuals planted in late summer and provided with some kind of protection before severe freezing begins will live through the winter successfully. Not only would this enable plants to bloom four to six weeks earlier, but would also enable gardeners to utilize flowers not commonly grown in northern Utah.
4

Growth characteristics and site potentials of perennial grass species

Borman, Michael M. 13 June 1989 (has links)
In this study I assessed the potentials of selected, established perennial grasses to maintain site occupancy in the foothills ecosystem of the Rogue River Valley of southwest Oregon which is currently dominated by a variety of annual plants. The first evaluation compared growth curves of the perennial grasses and contrasted them to growth patterns of residual annual plants. Periods of growth varied among the perennial grasses studied. Of the perennial grasses, Idaho fescue (Festuca idahoensis), a native, and Berber orchardgrass (Dactylis glomerata var. 'Berber'), introduced, most closely emulated the growth patterns of the majority of the annual plants. Relative to the other perenial grasses tested, they initiated growth earlier, continued some growth through the winter and matured earlier. Once established, they should be able to effectively compete with the resident annuals for resources and maintain their populatiOhs. To assess the potential for competition for available moisture, the second evaluation considered timing and extent of soil moisture extraction by the perennial grasses and the resident annual community through the periods of active growth. This verified growth analysis results. Idaho fescue and Berber orchardgrass extracted moisture earlier than the other perennial grasses. Perennial grass plots and plots dominated by yellow starthistle (Centaurea solstitialis) end of season residual soil moisture levels were similar. Resident annual grasses left considerably more soil moisture. In years with an early summer drought, the earlier growing perennial grasses should be able to satisfy growth requirements and persist. An assessment was also made of the abilities of several selected established perennial grasses to resist reinvasion by resident annual plants. Earlier growing perennial grasses such as Berber orchardgrass and Idaho fescue suppressed the annuals more effectively than the later growing perennial grasses. Of the perennial grasses studied, those emulating the growth patterns of the annuals have been the Most competitive and have maintained the most vigorous stands. / Graduation date: 1990
5

Spatial and temporal patterns of herbaceous species at Middleback Station, South Australia /

Nicolson, K January 1900 (has links) (PDF)
Thesis (Ph. D.)--University of Adelaide, 1986. / Includes bibliographical references (p. [i.e. leaves ] 267-277).
6

Physiological ecology of some spring ephemerals,

Risser, Paul G. January 1967 (has links)
Thesis (Ph. D.)--University of Wisconsin--Madison, 1967. / Vita. Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.
7

A Seed Demography Model for Finding Optimal Strategies for Desert Annuals

Wilcott, J. Curtis 01 May 1973 (has links)
A theoretical investigation of the factors that affect the population dynamics of annual plants growing in deserts was conducted through the use of computer modeling techniques. A series of three models of the yearly life cycle of desert annuals was constructed and their behavior examined. The dissertation centers around the third and most complex model, a computer simulation model with distinguishable seed cohorts in a randomly varying rainfall environment. A typical simulation run was for 80 years and cost $1.00. The five plant functions were (l} seed losses (mainly predation) as a function of seed age, (2) seed dormancy as a function of seed ages (3) percent germination of the non-dormant seeds in response to germinating rainfall, (4) percent survival from the seedling stage to maturity as a function of total rainfall over the growing season and seedling density, and (5) seeds produced per p 1 ant as a function of total rainfall over the growing season and density of mature plants. The stochasitc rainfall generator used historical rainfall probabilities from US Weather Bureau stations at Las Vegas, Nevada and Tucson, Arizona. The literature on desert annuals was carefully searched to provide supporting data for the plant functions used in the simulation model. Most of the data is for winter annuals growing on the Nevada Test Site near Las Vegas. Single species data are rare, so the model functions reflected the average plant responses for winter annuals as a group. This base run set of functions reproduced the observed data quite well. Sensitivity analysis of the simulation model indicated that in order to persist in the Las Vegas area, the seeds of annuals should have at least a one-year period of dormancy and a minimum threshold of about 15 mm of germinating rainfall. The age distribution of the seed reserves in the soil and the percent germinable is strongly influenced by the recent rainfall history of the site and the seed loss rate. The optimum balance is when the losses of older seeds from the seed reserves due to germination is the same size as the sum of the non-productive losses (e.g., predation). Several experiments are suggested -- some to cover gaps in the published data and some that became evident through the sensitivity analysis of the model itself.
8

The Influence of Biogeography and Mating System on the Ecology of Desert Annual Plants

Gerst, Katharine Laura January 2011 (has links)
A major challenge in plant ecology is in understanding how species strategies mediate interactions between the environment and fitness. Variation in niche strategies that affect phenological, physiological, and reproductive traits will allow species to partition resources differently in space and time, allowing for coexistence of many species and strategies within a community. How species differentially respond to variable environments will ultimately influence their population dynamics and geographic distribution. This dissertation approaches this topic from two perspectives: (a) examining the interaction between biogeography and variable demographic strategies in desert annual plants, and (b) examining the costs and benefits of contrasting reproductive strategies in co-occurring selfing and outcrossing desert annuals. Firstly, I tested the abundant center model to determine the role of range position on plant population dynamics. I examined how the geographic and climatic position of 13 desert annuals found at a common location, the Desert Laboratory at Tumamoc Hill in Tucson, Arizona, related to their demography over a 25-year time span. I found that species for which the Desert Laboratory was close to the center of their geographic range have less variable long-term survival and fecundity compared to species for which the Desert Laboratory was further from the center of their range. Secondly, I studied how related species with contrasting mating systems respond to variable environments to affect plant performance. In a three-year field study I investigated how inter-annual variation in plant reproductive phenology affects synchrony with pollinators and herbivores. Since selfing species are guaranteed to reproduce in the absence of pollinators, seasonal and annual variation in phenology resulted in less variable plant reproductive success compared to outcrossing species. Greater variation in reproduction in outcrossing species resulted from asynchrony in some years between plants and pollinators. In a greenhouse study examining the interaction between mating system and drought, I found that the physiological functioning and survival of outcrossing species was more strongly negatively affected by drought conditions, suggesting that selfing species have an advantage in more arid environments. These studies demonstrate how plant reproductive and physiological strategies can play a critical role in influencing fitness, population dynamics and geographic distribution.
9

Facilitative Interactions Among Native Perennial Shrubs and Native and Exotic Annuals in Recovering Coastal Sage Scrub

Miranda, Courtney Elizabeth 18 May 2013 (has links)
Facilitative interactions can have a powerful influence on the structure of plant communities and must be accounted for in efforts to restore disturbed and invaded habitats, such as the now rare coastal sage scrub (CSS) of California. In this study, I tested for evidence of facilitative effects by the native shrubs Eriogonum fasciculatum var. foliolosum and Artemisia californica on germination and survival of the CSS native annual forb Phacelia distans. P. distans seeds were planted near patches of native shrubs, both under the shrub canopy where any facilitative effects should be strongest, and 0.5 m away in the more exposed grassland. To determine whether the shrub-forb relationship was affected by the presence of invasive annuals, E. fasciculatum sites were assigned either invasive annual removal or non-removal control treatment; no removal treatments were carried out for A. californica. P. distans had significantly higher germination but lower survivorship under the canopy of E. fasciculatum. The results showed no overall effect of invasive removal, but there was a weak interaction effect with location; in shrub-canopy plots, invasive species further lowered survivorship. A. californica showed neither facilitative nor negative effects of this shrub species on either germination or survivorship of P. distans, in contrast with the results for E. fasciculatum. Although E. fasciculatum appears to facilitate the germination of native forbs under its canopy, it also seems to have a negative effect on survival. The weak interaction between location and removal to further decrease survival under the canopy when invasives are present, and the abundance of grasses growing under the canopy, suggest that native shrubs may facilitate the growth of invasive annuals as well as the germination of natives. Consequently, controlling invasive grass abundance may be necessary to capture the benefits of shrub facilitation for the restoration of native CSS herbs.
10

Facilitative Interactions Among Native Perennial Shrubs and Native and Exotic Annuals in Recovering Coastal Sage Scrub

Miranda, Courtney Elizabeth 01 January 2013 (has links)
Facilitative interactions can have a powerful influence on the structure of plant communities and must be accounted for in efforts to restore disturbed and invaded habitats, such as the now rare coastal sage scrub (CSS) of California. In this study, I tested for evidence of facilitative effects by the native shrubs Eriogonum fasciculatum var. foliolosum and Artemisia californica on germination and survival of the CSS native annual forb Phacelia distans. P. distans seeds were planted near patches of native shrubs, both under the shrub canopy where any facilitative effects should be strongest, and 0.5 m away in the more exposed grassland. To determine whether the shrub-forb relationship was affected by the presence of invasive annuals, E. fasciculatum sites were assigned either invasive annual removal or non-removal control treatment; no removal treatments were carried out for A. californica. P. distans had significantly higher germination but lower survivorship under the canopy of E. fasciculatum. The results showed no overall effect of invasive removal, but there was a weak interaction effect with location; in shrub-canopy plots, invasive species further lowered survivorship. A. californica showed neither facilitative nor negative effects of this shrub species on either germination or survivorship of P. distans, in contrast with the results for E. fasciculatum. Although E. fasciculatum appears to facilitate the germination of native forbs under its canopy, it also seems to have a negative effect on survival. The weak interaction between location and removal to further decrease survival under the canopy when invasives are present, and the abundance of grasses growing under the canopy, suggest that native shrubs may facilitate the growth of invasive annuals as well as the germination of natives. Consequently, controlling invasive grass abundance may be necessary to capture the benefits of shrub facilitation for the restoration of native CSS herbs.

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