| Summary: | Ranchers and resource managers have become concerned about the
role and spread of Cardaria draba (L.) Desv. (whitetop) in the sagebrush
steppe of Northeastern Oregon. This area is an important natural resource
for livestock production and big game winter range.
An area near Keating, Oregon was selected to study the influence of
environmental conditions on whitetop seed germination, mode of spread and
species displacement by whitetop.
Whitetop seeds were placed in the field at four different topographical
positions (toe slope, mid-slope, north slope and south slope) and placed at
three different locations in the soil profile (0, 1, and 3 cm). Seed placed on
the toe slope position at 0 cm had the greatest germination. At the south
aspect greater germination occurred at lower soil profile locations.
Increases in whitetop populations were evaluated by establishing
permanent transects in two locations in the study area. Whitetop shoot
density increased during the three year study. Whitetop density increase was
restricted to previously infested plots and was due to vegetative reproduction.
In whitetop infested areas, crested wheatgrass density was less than in non-infested
areas.
Whitetop germination at different topographical positions was
apparently related to moisture conditions. Once established, whitetop
populations increase through vegetative reproduction. This phenomenon is
reflected in a reduction of crested wheatgrass density and production as the
level of whitetop infestation increases. === Graduation date: 1992
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