State-and-transition models (STMs) have been successfully used to
describe ecological dynamics in woodlands, shrublands, grasslands, and several other ecosystems. Changes in vegetation and soil are measured to gauge and predict plant community dynamics within ecological states and transitions between alternative ecological states. Ecological states and their boundaries are defined by...
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...
Forest stands were studied to determine if old-growth
forest structure could be mimicked in younger stands via
overstory manipulation. Cover and species composition of
understory plants were systematically sampled in sixteen
thinned second-growth stands and sixteen adjacent unthinned
second-growth Douglas fir (Pseudotsuga menziesii (Mirabel)
Franco.) stands. The stands were thinned...
I compared transpiration among different types of forest stands in the western Cascades of Oregon. The three major questions were: 1) How does transpiration compare between a young and old stand and why? 2) Does diversity of overstory trees affect transpiration? and 3) How is transpiration related to stream flow?...
Reforestation-based restoration of severely burnt plantations is one of the primary management activities following wildfire on U.S. federal lands. Restoration effects on early-seral plant and cryptogam communities have not been documented. The objectives of this study were, in severely burnt plantations two to four years post-fire, to examine the: (1)...
Native plants provide many ecosystem services while also having great beauty and are a valuable component of the landscape. As use of these plants in habitat restoration, agricultural insectary plantings, and home landscapes increases so does demand for information on the basic biology of a group of species that have...
In the Coast Range of western Oregon, some natural resource managers are converting red alder-dominated riparian areas to conifers to increase the future source of in-stream large wood for salmonid habitat. However, studies in Alaska have shown red alder-dominated riparian areas support greater invertebrate biomass compared to conifer-dominated areas. In...
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...
Vegetation diversity in the Wyoming big sagebrush/Thurber needlegrass (Artemisia tridentata Nutt. ssp. wyomingensis Beetle & Young/Achnatherum thurberianum (Piper) Barkworth. syn. Stipa thurberiana Piper) plant association was studied across a condition class gradient in southeastern Oregon. All observable vascular plant species were counted during 6 seasons and 2 years and diversity...
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...
The relation of nutria (Myocastor coypus) feeding to total abundance, species composition, and seasonal use of the marsh flora on
the William L. Finley National Wildlife Refuge was studied during
1969 and 1970. Nutria numbers were estimated by livetrapping. Food
habits data were compiled from observations of feeding nutria. Phenology,...
The Willamette Valley (Oregon) Prairie Plant Trait Dataset is a compilation of plant traits of species important in upland prairies, wetland prairies, vernal pools, and emergent wetlands, and in the restoration of prairies and wetlands of the Willamette Valley of Oregon. These species are also found widely throughout the Pacific...
Prairie-oak ecosystems in the Willamette Valley, Oregon have experienced habitat loss and degradation; most of these ecosystems are fragmented into smaller patches. Prairie-oak butterfly species, in the Willamette Valley, have decreased dramatically due to loss or degradation of habitat. More research is needed on sustaining the populations of butterflies in...
Improving vegetation management decisions in Pacific Northwest forests requires a better understanding of the interactions between
planted conifers and associated vegetation. A practical index of interspecific competition, and quantitative models predicting conifer performance from such an index are particularly needed. To meet this
need, neighborhood models of interspecific competition were...
General outcomes of this study show that early growth of planted red alder is often slowed in the presence of neighboring vegetation, and overwhelmingly by salmonberry, a common associate in disturbed Oregon Coast Range habitats. Additionally, young red alder plantations located in
riparian areas may be highly susceptible to frost...
Tree species directly and indirectly affect soil nutrient cycles. I sought to characterize soils and foliage associated with four common canopy tree species (Douglas-fir, western hemlock, western redcedar, and bigleaf maple) in mixed-species old-growth forests of the Oregon Coast Range and to determine whether and how soils differ among the...
Small remnants of 'natural' habitats exist today throughout much of the world. Upland prairies in the Willamette Valley, Oregon have been nearly eliminated by conversion to agriculture and other uses. As a result, very few prairies remain and at least four butterfly species that require this habitat appear to be...
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,...
Invasion by exotic species can pose a major challenge for developing native
plant communities in wetland restoration projects. Often native plant communities
do not develop as anticipated in restored wetlands due to colonization by exotic
species that dominate the native plant community. Despite the time and expense to
restore wetlands,...
The vast majority of terrestrial plant species live in symbiosis with arbuscular mycorrhizal fungi (AMF). AMF and plants live in complex networks, with roots of individual plants hosting multiple AMF, and single AMF colonizing multiple plants concurrently. Through the exchange of resources, the two partners of this symbiosis can have...
Fire suppression in the last several decades has resulted in unprecedented accumulations of organic matter on the landscape, leading to an increase in large, intense wildfires. This study investigated the soil microbial community (using phospholipid fatty acid analysis) across recently burned forests on the eastern slope of the Cascade Range...
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...
I examined hydrological and plant community changes associated with the implementation of a restoration management plan in two riparian meadows located within an agricultural landscape of the central Willamette Valley, Oregon. I established exclosure fencing (a form of passive restoration) in one agricultural field and established fencing and plugged a...
Historically fire has been the primary disturbance factor in the sagebrush-steppe. The settlement of the West by Euro-Americans, grazing by domestic livestock, and the concomitant spread of invasive species have altered the historical fire regime. Understanding the long-term vegetation structure and fuel succession of the various sagebrush-dominated communities of this...
Wetland restoration success in attaining wildlife conservation goals can be confounded by the presence of multiple biological invaders. Wetland management activities typically target invasive plants, but bottom-up responses of higher trophic levels in novel communities are difficult to predict. We surveyed plant and amphibian assemblages at 26 sites enrolled in...
Management practices and options to provide habitat for wildlife in the Great Basin of southeastern Oregon deal with both vegetation treatment and protection, livestock management, maintenance or distribution of water developments, protection of wildlife areas through road closures or fencing, and direct manipulation of wildlife through hunting, trapping, or other...