OLEORESIN PRODUCTION. 43 
Chipping should progress up the tree at the rate of not more 
than one-half inch a week. In experiments in which chips of an 
average height of 0.40 ** to 0.34 45 inch were actually cut, a higher 
sustained yield was produced than in comparable workings in which 
the chip averaged one-half inch high. In the case of the double 
chipping at Columbia, Miss., an average height of chip of 0.32 inch 
was obtained with a 00 hack in 1916, and an average 0.26-inch chip 
with a puller during 1917. During the second year these trees, 
under this treatment, showed a smaller relative reduction in yield 
of turpentine, when compared to the first year yield, than did the 
half-inch chipping (standard). Using such a narrow streak means 
chipping in the light-wood or region of maximum stimulation, at 
least for a part of the season. It is yet to be determined whether the 
height of the chip can be further reduced. 
Sufficient experiments to determine the most advantageous depth 
of chipping have not been carried out. It appears probable that 
the significant factor in this case, however, is the width of the sap- 
wood, since, as has been shown, a considerable yield is obtained from 
many of the outer sapwood rings. A layer of healthy moist sap- 
wood should always be present behind each face to maintain at the 
maximum the vital activities of the sapwood layers exposed at the 
streak. With wide sapwood and deep chipping (about three-fourths 
inch) very high yields may be obtained. 
The advantages to be gained by the practice of conservative nar- 
row chipping were shown to be the following : 
1. Higher yields (40 to 50 per cent) per inch of height of chipped 
surface. 
2. Higher sustained yields — that is, less reduction in yield from 
year to year, approaching the optimum condition, confidently to be 
expected, when the yields of subsequent years will surpass that of 
the first year. 
3. Total annual yield approximating or even surpassing the yield 
from heavier chipping. 
4. Little reduction, on the average, below the wood formation 
of the round timber, either in amount or quality. 
5. Very high production of resiniferous tissue. ThisJ for a 
given year, was markedly greater about one foot above the early 
streaks made that year. Hence narrow chipping enables the opera- 
tor to reap the full benefit from this region of maximum stimula- 
tion and response by the practice known as chipping in the lightwood 
instead of wasting the wood containing the greatest number of resin 
passages by cutting it away with high chipping. 
44 Early Forest Service Experiments, page 27. 
45 Narrow chipping, Columbia, Miss., page 21. 
