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 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...
Coast redwood (Sequoia sempervirens) (D. Don) Endl. is a host for Phytophthora ramorum but it was unclear if the pathogen represents a significant disease risk to this tree species. In this study the susceptibility of coast redwood seedlings and the likelihood of sporulation on redwood were examined. Two methods were...
North America, with over 400 species of Astragalus (Fabaceae), is one of three major centers of diversity, all of which comprise the majority of the nearly 1750 species of Astragalus worldwide. One of the most diverse species, Astragalus lentiginosus of Section Diphysi, is a polymorphic complex of over 40 varieties,...
Epiphytic, planktonic and benthic diatom assemblages were investigated in Netarts Bay, Oregon. Samples were collected for a
one-year period from February 1980 to March 1981. A planktonic flora was observed only during periods of offshore enrichment when marine neritic species were abundant and were transported into the bay by tidal...
The sagebrush steppe ecosystem of the northern Great Basin is severely degraded and continues to decline due in large part to the invasive, non-native annual grasses Bromus tectorum L. (cheatgrass) and Taeniatherum caput-medusae (L.) Nevski (medusahead). Restoration of invasive-dominated areas is difficult, but can be enhanced by adding a carbon...
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...
A 22 ha, 1S yeas old, diked permanent pasture in the Salmon River estuary in Lincoln County, Oregon, was chosen for a study to determine the potential for natural salt marsh restoration with dike breaching. Two undiked fragments of relatively undisturbed salt marsh, one at each end of the study...
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...
Although terrestrial lichens and bryophytes are common in upland plant communities of the Blue Mountains in northeast Oregon, research on cryptogam communities in this region is wanting. Studies have shown that lichens and bryophytes can reduce soil erosion and increase soil fertility in other semiarid habitats of North America. Understanding...
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...
The main objective of this thesis was to determine the influence of tree vigor on susceptibility to Armillaria root disease. First, the effect of thinning, fertilizing and pruning on tree vigor of four young Douglas-fir (Pseudo tsuga menziesii var. menziesi,) plantations was explored. Tree vigor was calculated by measuring wood...
Decomposing logs in Douglas-fir - western hemlock forests in the Pacific Northwest are systems in which many organisms interact. Fungi in these systems include both mycorrhizal fungi associated with hemlock seedlings and many species of saprotrophic wood decomposer fungi. It is very likely that these two groups of fungi interact...
Podosphaera macularis causes one of the most important diseases, powdery mildew, of Humulus lupulus (hop). If left unmanaged, hop powdery mildew can cause total crop loss due to disease or browning of hop cones rendering the cones unmarketable to buyers. The Hop Powdery Mildew Infection Risk Index (HOPS) is heavily...
The chlamydospore is a survival spore produced by 35 of the 75 described species of Phytophthora. Phytophthora ramorum Werres, de Cock & Man in't Veld, the causal agent of Sudden Oak Death (SOD), produces abundant chlamydospores in artificial culture and plant tissue. The chlamydospore is likely the most important survival...
A fossil-calibrated phylogenetic framework based on exemplars from each of the four taxonomic sections within Pinus was created using multiple nuclear and chloroplast loci. Calibration at the well-defined subgeneric split within Pinus with either fossil leaves and cones (ca. 45 million years ago) or fossil wood (ca. 85 million years...
Pollination ecology may play an important role in the maintenance of selfing in populations of self-compatible hermaphroditic plants where both selfing and outcrossing occur (mixed mating). Behavior and abundance of pollinators can influence the two major modes of selfing; autogamy (selfing within a flower) and geitonogamy (selfing between flowers on...
Sweet corn (Zea mays L.) yields in the Willamette Valley of Oregon have been declining since the early 1990’s. Studies were done to determine if there is a relationship between ear weight and several disease parameters including necrotic crowns or stalk nodes, nodal root rot, radicle root rot, and sub-crown...
More than 4,000 specimens of fruits and seeds were extracted
from the matrix removed from inside the skulls of sabre-tooth cats
excavated from various pits in the Rancho La Brea deposits. Of this
number, spproximately 1,445 specimens are involved in this study.
Many comparisons with modern fruits and seeds made...
The specificity of quantitative host resistance to plant disease has long been a controversial issue. We examined interactions between wheat (Triticum aestivum) and Mycosphaerella graminicola, causal agent of Septoria tritici blotch, to determine whether specific interactions occur between host and pathogen genotypes that could be involved in eroding quantitatively expressed...
