|Abstract or Summary
- The effect of the abundance and rapidity of ectomycorrhiza and root tip formation on
conifer seedling survival and growth was investigated on disturbed forest sites in southwest
Oregon and northern California. Experiments were conducted over a range of
community types and environmental conditions. A range of sources of transfer soil
were evaluated to offset disturbance-related reductions in ectomycorrhiza formation.
We established different levels of native mycorrhizae by growing seedlings in soils
from either (a) a poorly restocked clearcut in southwest Oregon, or (b) forest adjacent to
the clearcut. At the time of outplanting, only 4% of root tips were mycorrhizal on
seedling grown in clearcut soils, while 42% were mycorrhizal on seedlings grown in
forest soils. There were significant differences in growth following outplanting. Seedlings
greenhouse-grown in clearcut soil averaged nearly 44% less basal area growth and
14% less height growth than those greenhouse-grown in forest soil.
Survival and mycorrhiza formation differed among Douglas-fir seedlings planted in
three adjacent community types-whiteleaf manzanita, annual grass meadow, and an open
stand of Oregon white oak. Second-year survival averaged 92%, 43%, and 12% for
seedlings planted on the manzanita, meadow, and oak sites, respectively. Growth differences
generally paralleled survival differences. Growth of seedlings on the manzanita
site was substantially increased by the addition of unpasteurized machone soil, nearly
tripling the number of mycorrhizal root tips formed.
Mycorrhiza formation and conifer seedling performance was examined over a
range of sources of transfer soils and environmental conditions on three old and unsucessfully
reforested clearcuts. At Cedar Camp, a high elevation (1720m) southerly slope
with sandy soils, transfer of plantation soils increased 1 st-year Douglas-fir seedling
survival 50%, doubled mycorrhiza formation and tripled seedling basal area growth. Soil
from mature forest did not improve growth and survival. Less dramatic effects owing to
soil transfer were evident on the other sites, which were lower in elevation had greater
water holding capacity, and where woody shrubs had apparently preserved mycorrhizal
In another study, seedlings receiving plantation soil transfer at Cedar Camp had
62% more root tips than controls six weeks after ouplanting; however differences were
no longer statistically significant 15 weeks after planting. Seedlings receiving transferred
soil had the most mycorrhizal colonization. Of seedlings receiving transfer soil, 36.6%
survived the first growing season, compared to 11.3% of control seedlings.