Abstract:
A great deal of research has taken place in an effort
to find more economically efficient yarding systems for
commercial thinnings. Almost all of this research has
centered on tractors or small yarders with limited
capabilities in terms of long yarding distances. The
purpose of this study is to determine whether using
helicopters can be an economical alternative for commercial
thinning in steep, mountainous terrain. The study area
consists of a second-growth stand of Douglas-fir and mixed
true fir species. The stand was thinned using a Lama SA-
315B helicopter (external lifting capacity of 2500 lbs.) to
yard a total of 383 mbf (800.5 cunits) over a period of 3
weeks. Average yarding distance was approximately 2500 feet
and the average slope was 40%. The diameter of the trees
removed averaged 15 inches and the average piece size was
approximately 87 board feet (.182 cunits).
Gross production data were kept by the project manager
for the logging company. This information is used to
compare costs actually experienced during the operation with
costs that might have occurred had the stand been cable
yarded. The stand had originally been planned for uphill
cable yarding using intermediate supports. A Thunderbird
TNY 50 yarder is used as the hypothetical comparison
operation.
A detailed time study was conducted and the results are
used to evaluate the effects of turn weights and yarding
distance on the helicopter operation. Regression equations
were developed and used to predict hook time, haul time, and
total turn time for specific conditions.
A damage survey was conducted after yarding to assess
the condition of the residual stand. Results of this survey
are compared with the amount of damage predicted for a cable
system using a regression formula developed by Caccavano
(1982)
The results of the study indicate that using the Lama
helicopter can be an economically feasible alternative for
commercial thinning. An average yarding cost per thousand
board feet of $179.21 was estimated for the helicopter
operation; the cablesystem would have cost an estimated
$159.73 per mbf for yarding, with an additional $55.21 per
mbf for necessary road and landing construction. The
helicopter yarding resulted in no damage to the residual
stand. An estiniated 44.6 sq. ft. of scar area per acre
would have resulted had the stand been cable yarded.
