Medusahead (Taeniatherum caput-medusae ssp. asperum (Simk.) Melderis) is a Eurasian annual grass that infests large areas of U.S. rangelands, dominating former bunchgrass/shrub sites. Squirreltail (Elymus elymoides (Raf.) Swezey) is a native perennial grass that has demonstrated the ability to establish in stands of medusahead.
A study conducted on two sites...
Early and late seral tree species were compared for inter-and intraspecific competitive ability; within-population genetic variability; and allocation patterns of soluble sugars and starch seasonally and in response to shade and nitrogen fertilization. Species were Douglas-fir (early seral) and western hemlock (late
seral) from a low elevation habitat; and noble...
Experiments were conducted to determine if allelopathy is a mechanism
by which buckwheat interferes with a) the growth of Canada thistle and/or b)
mycorrhizae colonization in Canada thistle roots. In a competition experiment,
buckwheat plant biomass was only affected by the intraspecific competition
from other buckwheat plants and not by...
Understory conifer regeneration needs to occur beneath conifer-dominated
canopies if two-storied or uneven-aged structures are to be considered for western
Oregon Coast Range stand management. To ensure adequate numbers of seedlings
to meet stocking or habitat structure objectives, planting may be a solution. We
undertook a multi-level study to determine...
The amount and quality of competition among
individuals in developing plant communities is an important factor determining community structure, composition and development. In perennial plant communities, this competition is reflected by shifts in carbon allocation among plant parts and can result in long-term structural differences between neighboring individuals. This study...
Disease has been implied as an important selective
force acting in plant populations. This study was
conducted to determine the effects of stripe rust (Puccinia
striiformis) on the population dynamics of wheat (Triticum
aestivum) cultivar mixtures.
Five wheat cultivars were grown in pure stands and all
possible mixtures at three...
The use of grass cover crops is a recommended practice in
nonirrigated vineyards in the Willamette Valley, Oregon. Two
studies were initiated to investigate the competitive and
noncompetitive effects of grass cover crops on the growth and
development of Pinot noir grapevines. Two greenhouse pot culture
experiments were performed to...
This thesis examines the competitive aspects of Douglas-fir trees growing with two commonly associated competitors--red alder and grass--at varying densities. Two Nelder plots in three different environments in the Oregon Coast Range were studied. The sites represented the warm, dry climate of the Willamette Valley; the warm, moist climate of...
Effects of tanoak (Lithocarpus densiflorus) on early
growth, morphology, and physiology of Douglas-fir
(Pseudotsuga menziesii) were studied to determine
developmental characteristics of young stands and
mechanisms of competition. Growth, leaf area, and biomass
of Douglas-fir, tanoak, and shrubs / herbs were monitored
for six years after establishing a gradient of...
