IntensIve sIlvIculture - Forest Science Labs - Research Network ...

Abstract: A study was conducted on steep, south-facing slopes in southwest Oregon to
assess the effect of two common reforestation practices on the soil thermal environment. Three
clearcut sites and three shelterwood sites were instrumented to measure soil temperature at five
depths in the vicinity of shaded and unshaded Douglas-fir seedlings. Since the soils studied were
skeletal, heat capacities of both fine and coarse soil fractions were determined for each site. These
data were used to estimate soil heat fluxes. Shelterwoods decrease soil temperatures
approximately 6 K when compared with clearcuts. This result holds at both 20- and 320-mm
depths. Shelterwoods also decrease the depth of diurnal heating and decrease maximum hourly
heat loss and gain values by 73 and 80 W/msuperscript 2, respectively. Shadecards, cardboard
rectangles placed to the southwest of seedlings, generally have little effect on the soil temperature
regime of skeletal soils but are effective in reducing daily heat flux. The dominant shadecard
effect is a decrease in average daytime heat flux by 22 W/msuperscript 2, but shadecards also
decrease average nighttime fluxes. Shelterwoods ameliorate seasonal soil temperature conditions
significantly and may be an appropriate technique in situations where cumulative soil heating
limits reforestation success. Shadecards should be useful in situations where heat stress events of
only a few days are a problem. Over a season, shadecards exert little control, and their influence
on stress is limited. Since all soils studied had high heat capacities due to large rock fragment
content the conclusions of this study may be limited to soils with large soil heat capacity.
101. Christiansen, E.C. and S.G. Pickford. 1991. Natural abatement of fire hazard in Douglas-fir
blowdown and thinning fuelbeds. Northwest-Science 65(4): 141-148.
Keywords: thinning
precommercial thinning
tree/stand health
Abstract: The changes over time in fuelbed loading and depth in precommercially thinned
and windthrown low altitude stands of Douglas fir (Pseudotsuga menziesii) were investigated in
the Bull Run Watershed, Oregon, using standard fuel inventory techniques. Non-linear least
squares regressions were fitted to the resulting data. Slash from precommercial thinning lost half
of its original loading and depth within 2 yr. No foliage was retained on twigs and branches after
1 yr. Changes in fuels from windthrown trees were similar to those in slash, except that more
material was present initially. Fine fuels (