TIMBEE GROWIXG AXD LOGGIXG PRACTICE IX CALIFORNIA 35 
used as motive power for a special type of big wheel. Bunching is 
done by 5-ton tractors. On grades up to 30 per cent, even with con- 
siderable loose rock, this system has proved its superiority to both 
big-wheel and donkey yarding. On slopes from 30 to 45 per cent 
logs are commonly skidded on the ground by tractors. 
The operating advantages of tractor logging are low yarding cost 
compared to other methods, reduced amount of railroad construc- 
F- 169273 
Fig. 14.— SKIDDER YARDING RESULTS IN A CHARACTERISTIC PATTERN 
The California type of steam skidder. used only along railways, benefits the cut- 
over land by its mobility, as shown in this bird's-eye view. 
tion, flexibility of operation, particularly in logging open and scat- 
tered forests, very low fire danger, and small amount of swamping 
required for roads. 
Damage to young growth and seed trees appears to be little greater 
than with the big-wheel method. On one operation 20 per cent of 
the total area was covered by yarding roads on which nearly all 
young growth was destroyed. Between the roads, damage was 
slight, and for the area as a whole, not over 30 per cent of the re- 
production was wiped out. 
