- Three five acre exclosures were established in 1964 to monitor
vegetational regeneration and forage productivity on a coniferous
forest site in northeastern Oregon which was clear-cut in 1963, broadcast
burned and seeded in 1964. Fence design and construction to
facilitate controlled early summer cattle grazing trials was completed
by 1965. One exclosure, I, excluded indigenous big game species,
mule deer (Odocoileus heinionus) and elk (Cervus canadensis) as well
as cattle (Bos tarus); the remaining two, II and III, excluded cattle
only. It had become evident by 1969 that the amount of available
herbaceous forage in the game exclosure was decreasing as the
amount of browse production increased. This study was set up during
the summer of 1970 to quantitatively evaluate the amount, preference
and nutritive value of browse utilized by cattle.
Following an early summer grazing trial, five mature cows were placed in I from 19 August to 2 September, 1970. These animals
lost an average of 6.7 pounds/day. The control group on
meadow pasture lost an average of 2.3 pounds/day. The cows in I
preferred herbaceous species, but as these were utilized, they
grazed elderberry (Sambucus cerulea ), willow (Salix ssp. ), ninebark
(Physocarpus malvaceus), redstem ceanothus (Ceanothu.s
sanguineus ), and snowbrush (C. velutinus) in descending order of
preference. Browsing on conifers was negligible, and only 2% of
the trees were injured by trampling.
Frequency and density of all plant species and cover of the
shrub species were taken (in exclosures I and II) in June of 1971.
Frequency data, incorporated into an association table, confirmed
the presence of two plant communities, each displaying different
floral composition. Shrub density on the ridge type, designated a
Ponderosa pine community, was almost identical between I and U.
Exclosure II, however, contained only two-thirds the cover of I.
Shrub density in I of the slope type, a mixed coniferous forest community,
was almost twice that of II; cover in I was four times that
of II. These differences between exclosures were attributed to big
Mature cows, pre-conditioned to a browse diet, were placed
in I from 13 August to 27 August 1971. They gained .81 pounds/day,
while the control group on an adjacent forested area lost .64 pounds/day. Elderberry, willow, redstem ceanothus, snowbrush,
and ninebark was the descending order of browse preference that
year. Conifer loss was restricted to only negligible trampling
damage. To date, it appears that the number of conifer trees and
the average tree height between I and II have not been influenced
by the grazing treatments.
An indirect competition factor (similar plant species preference
but at different seasons) was found to exist between the big
game animals and the domestic livestock. Previous research indicates
that mule deer prefer such species as ninebark, snowbrush,
redstem ceanothus, oceanspray (Holodiscus discolor), and willow
during the spring and early summer. The late summer grazing cows
indicated a similar preference. The only direct competition (similar
plant species preference during the same season) observed was in
19 71 when the early summer grazing heifers made heavy utilization