|Abstract or Summary
- Site preparation treatments are often used prior to the planting of clearcut
forest lands to improve planter access and to increase the number and quality of
planting spots. Most mechanical site preparation treatments alter the
configuration and material composition of surface soil materials, and can have
marked effects on soil properties important to seedling survival and growth.
Effects of some of these treatments on soil moisture, soil temperature, rates of
nitrogen mineralization, and the establishment of Picea glauca x engelmannii
seedlings were examined on fresh, moist, and wet sites in the moist cold subzone
of the Sub-boreal Spruce Zone in west-central British Columbia. Four types of
microsite alteration were investigated: forest floor removal (spot scalping), soil
mounds over inverted sections of forest floor (inverted mounds), mineral soil
mounds over a mineral soil surface, and inversion of the forest floor and mineral
soil in place.
Soil temperature was monitored continuously and soil moisture weekly at the
10-cm depth in 16 combinations of site and microsite treatment during two
growing seasons. The response of seedling height and diameter growth was
monitored for three growing seasons. Effects of altering soil temperatures
through mechanical treatments on rates of nitrogen mineralization were examined
by incubating a standard soil material in a range of microsites created by six
combinations of site and mechanical treatment. Effects of substrate quality and
soil temperature on rates of nitrogen mineralization were examined in paired
mounded and untreated spots in fresh, moist, and wet sites.
In all sites, early growing season soil temperatures in the seedling rooting
zone were substantially warmer in inverted mounds than in other treatments.
Spot scalping increased temperatures slightly relative to controls in the fresh site,
but had little or no warming effect on moist and wet sites. Inverted mounds
became substantially drier than other treatments during periods of low rainfall,
particularly in the fresh site. After three growing seasons, seedling height growth
was greatest in inverted mounds, irrespective of site. Amounts of nitrogen
mineralized in a standard soil material during incubation for 77 days in the field
were significantly greater for samples placed in inverted mounds than for those
placed in other microsite treatments. There was a significant positive correlation
between amounts of nitrogen mineralized during field incubations and degree hour
sums calculated for associated microsite treatments and sites. Both substrate
quality and soil thermal regime affected rates of N mineralization in samples
from paired mounded and untreated spots, and an interaction was observed
between the two factors.