Astragalus diaphanus is a rare plant endemic to the
John Day River drainage of north-central Oregon. This
species has several interesting features, including the
dimorphism of its fruit and its geographical isolation from
the two nearest taxonomically related species, which occur
in Colorado. This study addressed the species' distribution
and...
The purpose of this study was to determine plant species composition, community structure, successional relationships, vegetational development and plant distributions in estuarine salt marshes on the Pacific Coast of Oregon.
Quadrat and transect samples of plant presence and cover, collected from April 1971 - June 1974, were subjected to phytosociological...
The seasonal duration of snow cover is a primary factor influencing the patterns of vegetation in high subalpine and alpine environments, but little is known concerning the responses of plant reproduction and
seedling recruitment to gradients of snow-release. Vegetation patterns of a high subalpine site in the Oregon High Cascades...
Growth and replacement patterns of four successionally important
species occurring on Douglas fir clear-cuts were investigated
from September 1964 to June 1967. The study was carried out
on the Marys Peak watershed located near Corvallis, Oregon.
Species used in the study include Holcus lanatus, Senecio
jacobaea, Lotus crassifolius var. subglaber,...
I studied the water relations traits, twig conductivity, C'3 isotopic composition,
and wood density of three conifer and five angiosperm species in western Oregon. This
study took place from spring 2002 to fall 2003 on four sites. Species were selected to
represent the diversity of drought tolerance of woody plants...
With little previous research on Astragalus peckii (Fabaceae), a state-listed
Threatened species in Oregon, I investigated three facets of its biology which are
integral to the conservation and management of the species. First, a four-year
demographic study of two large populations revealed increasing population growth at
one site (Chiloquin) and...
Soil moisture depletion trends under five plant species growing
on the clear-cuts of the Marys Peak Watershed near Corvallis,
Oregon, were followed during the summers of 1963 and 1964. The
species were Holcus lanatus, Lotus crassifolius var. subglaber,
Gaultheria shallon, Berberis nervosa, and Acer circinatum; and
were dominant plants of...
This thesis examines factors limiting understory herb presence and flowering in young second-growth Douglas-fir (Pseudotsuga menziesii) forests on the west side of the Cascade Mountains, Oregon, USA. I studied the belowground effects of canopy trees on understory herbs and shrubs in old-growth forests using trenched plots from which tree roots...
This study describes the soils, vegetation and age structure
of the Pinus contorta forests of Crater Lake National Park. Growth
rates of P. contorta, and levels of infection and impact of dwarf
mistletoe (Arceuthobium americanu1r) on growth of P. contorta
individuals are compared among communities.
Vegetation description is based on...
Population dynamics, plant communities, and abiotic environments of three narrowly endemic, allopatric mariposa lilies (Calochortus Pursh) are described and compared. All were restricted to ultramafic soils in southwestern Oregon with high concentrations of nickel, zinc, and chromium, and low calcium to magnesium ratios. Soils inhabited by the three species differed...
The diverse lichen flora of the Pacific Northwest is being impacted by
population growth and by forest management practices. Accumulating information
about our lichen flora will improve our conservation strategies. This dissertation first
collects information to improve our understanding of how lichen communities vary
among forests of differing structure, and...
This research examines the community composition of biotic soil crusts at nine sites in central and eastern Oregon, U.S.A. At each site, data were collected in one pair of livestock-grazed and excluded transects. Variables recorded included: cover of biotic soil crusts and vascular plant species, soil surface pH, electrical conductivity,...
In an effort to describe the plant communities and
succession of the Oregon coastal grasslands, vegetation
and environmental data were collected from 75 stands at
24 separate locations ranging from Cape Falcon in Tillamook
County to Cape Ferrelo in Curry County. The vegetation
data consisted of cover and frequency values...
Many studies suggest that weedy plant species are most successful when
soil nitrogen in abundant. Consequently, I used soil nitrogen manipulations to
determine if altering nitrogen would affect the establishment of both weedy and
native plant species in a western Oregon wetland prairie. In two studies, we
added carbon amendments...
A necrosis at the tip of cones was observed on hop (Humulus lupulus), cultivar "Nugget", grown in Oregon in the early 1990's. Fusarium sambucinum and F. avenaceum were recovered from symptomatic cones in 1998 and preliminary inoculation experiments suggested both Fusarium species could cause hop cone necrosis. Studies were carried...
Plagiobothrys hirtus (Boraginaceae) is a state and federally listed endangered plant found only in Douglas County, Oregon. This vernal pool endemic has historically been threatened by agricultural conversion of seasonal wetlands in the Sutherlin area, and is currently being eradicated as habitat is lost due to the rapid urban development...
Pleuropogon oregonus Chase is a rare wetland grass endemic to eastern Oregon. The species is composed of two widely separated populations, one in Lake County and one in Union County. In order to reduce the risk of extinction, the Oregon Department of Agriculture Native Plant Conservation Program initiated several reintroduction...
In ecological restoration, species that are sown to increase the native plant
diversity range in establishment ability. Some species readily establish, while others
rarely do. This study set out to investigate some of the potential processes influencing
species establishment, as well as the traits that are associated with the success...
Identifying mechanisms that determine who lives and dies is the first step in developing successful restoration techniques for rare species and endangered habitats. We studied interactions that affect establishment of native plant forbs of conservation concern at the seedling stage to support the theoretical basis for restoration activities in Pacific...
A study consisting of three parts was undertaken to investigate how variation in species interactions, population genetic structure, epidemiological parameters, and plant breeding system may influence the ecology and biological control of an apomictic invasive plant, Chondrilla juncea (Asteraceae). Interactions between natural enemy species may modify their net effect on...
Disease is often overlooked as a natural disturbance agent in plant communities. This study examines what effects, if any, a disease-mediated disturbance has on the plant community as a whole in old-growth and mature forests of western Oregon. Phellinus weirii (Murrill) Gilbertson (Family: Hymenochaetaceae) is a native root-rotting pathogen that...
Golden paintbrush (Castilleja levisecta Greenman) historically inhabited the prairies of the Willamette Valley, Oregon. However, this Pacific Northwest endemic is currently restricted to eleven sites in the Puget Trough of Washington and British Columbia. Recovery criteria call for the establishment of new populations throughout the species historic range, including the...
I focus on addressing knowledge gaps relating to management of cryptogams in Oregon's public lands in Pseudotsuga menziesii-Tsuga heterophylla forests on the west side of the Cascade Range and dryland steppe in the Cascade Range's rainshadow.
While a great deal of research has illustrated the importance of late-successional forests for...
There are over 35 known virus and virus-like diseases of sweet cherry (Prunus avium), some with potential to cause severe economic impact by reducing vegetative growth, vigor, and/or quality of fruit. Oregon is the second-ranked state for sweet cherry production in the United States with 13,000 acres and $70.8 million...
The effects of fenamiphos on soil and root populations of Pratylenchus penetrans were evaluated in four red raspberry cv. Willamette fields in Northwestern Oregon. Field 1 was a silty clay loam with 53% organic matter (OM). Field 2 and 3 were silty loam soils with 3.25 and 2.55% OM, respectively...
The sudden oak death pathogen, Phytophthora ramorum, is present in southwestern Oregon, and while an eradication effort is underway, the potential impact of the polyphagous pathogen on surrounding vegetation is unknown. Plant communities in the area are substantially different from those affected in California, although tanoak (Lithocarpus densiflorus), evergreen huckleberry...
The objective of this study was to characterize an unknown agent associated with decline in black raspberry (Rubus occidentalis) in Oregon. A virus was found consistently associated with decline symptoms of black raspberries and was named Black raspberry decline associated virus (BRDaV). Double stranded RNA extraction from BRDaV-infected black raspberry...
Wetlands and wet prairies are economically and environmentally valuable ecosystems, but many have been degraded or converted to other uses. As human understanding of wetlands' value has increased, restoration efforts have grown correspondingly. Restoration attempts use a diversity of methods, which often include seeding with native plant species. This thesis...
Increased temperatures due to anthropogenic-induced climate change may raise the threat of extinction for taxa with sessile life histories (e.g., plants) in the near future. Linking climate change models to demographic models may provide useful insights into the potential effects of environmental changes on rare plants, and therefore aid in...
Prairies were once the dominant vegetation type in Oregon's Willamette Valley. Land use conversion, fire suppression, succession, and invasive species have reduced Willamette Valley prairies to less than 1% of their historical area. The remnant prairies that persist today are small in size and are highly fragmented. Marginal strips of...
Crater Lake, located in the southern Cascade mountains of Oregon, is the seventh deepest lake in the world. Unlike a majority of the deepest lakes in the world, found in continental rift valleys, Crater Lake is in the caldera of a volcano. For the young at heart and mind, those...
The showy biennial to short-lived perennial Oenothera wolfii (Munz) Raven, Dietrich & Stubbe (Wolf’s evening primrose) occurs in only a small number of isolated populations on the southern Oregon and northern California coast. This rare species is currently listed as Threatened in Oregon, and is considered a Species of Concern...
Quercus garryana dominated plant communities are found in
the interior coastal valleys and on foothills from southeastern
Vancouver Island, British Columbia, south to San Francisco,
California. They occur as savannas, intermixed with a variety of
conifers, and in almost pure stands. The diversity of habitats
occupied by the species and...
Kincaid's lupine (Lupinus oreganus Heller) is a federally listed threatened species native to remnant grassland of western Oregon and southwestern Washington, and is the primary larval host plant of a once thought extinct butterfly, Plebejus icarioides fenderi Macy. Past studies concerning Kincaid's lupine reproduction
suggested that populations may suffer reductions...
Research on the population genetics of microbial organisms requires the use of specialized analyses designed for clonal organisms to avoid violating the assumptions of traditional population genetic models. The tools necessary for performing these analyses existed as a set of unrelated software with non-overlapping capabilities and did not cover all...
Soil food webs process the majority of terrestrial carbon, and influence overall ecosystem function. A primary distinction among soil food webs is based on fungal versus bacterial pathways of decomposition; these lead to fundamentally different soil function, and are expected to differ in dominance between meadows and forests. This assumption...
Prior to European settlement, native prairie dominated the landscape of the
Willamette Valley. Today, due to urbanization, agriculture, and the cessation of
burning, only isolated remnants of these grasslands still exist. In response to
conservation concerns, there has been a move to restore the remaining prairies in the
Willamette Valley,...
The efficiencies of wet sieving/sucrose
centrifugation (WS/SC) recovery of Pratylenchus penetrans
(59 %), Paratylenchus sp., (80 %), and Criconemella
xenoplax (66 %) were established. Baermann funnels (BF)
recovered significantly more P. penetrans (p = 0.01) and
significantly less (p = 0.01) C. xenoplax than did WS/SC.
While densities of P....
Since around 1923 Port-Orford-cedar (Chamaecyparis lawsoniana (A. Murray) Parl.) has been affected by Phytophthora root disease caused by the virulent introduced pathogen Phytophthora lateralis. A systematic resistance testing and breeding program located at the USDA Forest Service Dorena Genetic Resource Center in Cottage Grove, Oregon was initiated in 1997 with...
Knowledge of post-dispersal seed fates and other regeneration characteristics is
crucial for predicting abundances and distributions of populations and, ultimately,
community species composition and diversity. Seed fate studies, however, are rare
primarily due to the difficulty of determining seed fates and causes of mortality.
This thesis investigated post-dispersal seed fates...
Preservation of rare plant species often requires establishment of new populations. Survivorship surveys are the most common method of post-introduction monitoring. However, they provide an incomplete picture of establishment success. This study is an attempt to develop a model for determining establishment success by determining the factors affecting recruitment in...
The role of unusual geologies in plant distribution and form is well-known. Serpentine (ultramafic) soils exert a particularly strong influence on plants, as evidenced by a high level of endemism and the morphological and physiological traits displayed in adaptation to the extraordinary chemistry of these substrates. Adaptation may lead to...
The Pacific Northwest is an internationally important region for the production of Brassica seed and other seed crops including grass seed. Oregon lawmakers mandated research into the co-existence of canola (Brassica napus) with other Brassica production in the Willamette Valley and House Bill 2427 was signed into law in 2013,...
For the past several years vegetable growers in Oregon's Willamette Valley
have experienced reduced yields in their sweet corn plantings. We conducted
studies to 1) describe the symptomology and etiology of the disease, 2) test a root
rot rating system we developed to evaluate factors in the disease syndrome, and...