TIMBER GROWING AND LOGGING PRACTICE IN CALIFORNIA 27 
means of blocks or shear trees, the main line sometimes having sev- 
eral such angles in it. 
The machines imtil recent years have been entirely of the low- 
speed type with the main line capable of an average speed, with 
half-loaded drum, of 250 to 450 feet per minute. With the intro- 
duction of two-speed engines, the rate has been increased till at 
present a line speed up to 1,000 feet per minute is claimed. 
With the adoption of high speed, damage to both advance repro- 
duction and seed trees increases. The incoming logs drag the 
ground bare along the trails and wipe out everything except the 
largest obstacles in their path. The extent of this damage, of 
course, depends on the percentage of the ground that is dragged, 
Fig. 8.— SCARRED BY INCOMING LOGS 
Donkey yardins; can take little account of obstacles. This tree re- 
covered from having a third of its bark torn off at the base, but many 
smaller trees similarly Injured do not recover. 
which in turn depends on the stand per acre, the frequency with 
which the main line is changed, and whether timber is yarded in 
short lengths or entire trees. 
The heavy cables are also a source of damage, for as power is 
applied they slash through a horizontal segment, knocking off limbs, 
breaking small trees, raking off bark, ancl even smashing the tops 
out of seed trees. 
The more^ important variations of this general type of logging 
will be discussed in detail as to their effect on forest production, 
and their comparative efficiency as logging methods. 
GROUND-LEAD YARDING 
The effect on reproduction of the ground-lead method with low- 
speed machines, where the lead block is placed within a few feet of 
