CORK OAK-——-RYAN AND COOKE 
a rate faster than the initial growth. 
After the second stripping, a third 
growth progresses at a rate faster than 
the second. This apparent stimula- 
tion repeats itself after each successive 
stripping. The phenomenon of stimu- 
lation in relation to quantitative yield 
was carefully studied during the 6- 
year period of stripping. As a result 
of this work it has been possible to 
estimate, with a reasonable degree of 
accuracy, the cork yield per tree at 
various ages up to 100 years. Although 
the life of a cork tree in the Mediter- 
ranean region ranges from 150 to 200 
years, or slightly over, we did not feel 
justified in carrying the estimation to 
the limit because we did not have the 
fundamental data to support it. The 
estimate, shown in table 7, is based 
upon the results of stripping trees 
between the ages of 20 and 90 years. 
TasLE 7.—Relation between annual cork yield 
per tree and age in the United States potential 
cork area 
Potential area 
Positive | Quasi 
Mean rate of growth. ..} 0.9667 1. 8439 
Pounds per annum per 
tree at: 
lOkyeaxss brie. ci: . 00 . 00 
ZOMeaTsh sj fs). =): le Sy) 33105 
SOhyears lysis. jeiens 2. 83 6. 50 
AQIV CANSiy. corel ees 5. 04 IS 5) 
SOhyearsee ey. 8. 96 20. 54 
GOlvearsenn eee 15593 36. 54 
MOyearsener nies 7s}, 2 64. 97 
SOlvearshm ae os 50. 39 115. 50 
SOME Soodoapeace 89. 60 205. 40 
POM VeaTs eras «: 159.30 |365. 40 
It is felt that the estimate is fairly 
representative of average production 
conditions and that it is sufficiently 
accurate for the practical purposes of 
comparison and estimation. 
In addition to the rate of growth 
and stripping regularity, the amount 
of cork produced by a given tree is 
greatly influenced by the shape of its 
371 
various parts, such as trunk, branches, 
crotch, etc. During the stripping of 
over 500 trees of all shapes, sizes, and 
ages, it was determined that the shape 
of an individual tree may cause it to 
deviate as much as 21 percent from 
the average values in table 7. How- 
ever, when a number of trees of differ- 
ent shapes are averaged, the cork 
yield per tree agrees very closely with 
the estimate. 
In order to determine, for commer- 
cial reasons, the cork yield per acre, 
or any other unit, it is necessary to 
know the number of trees an acre will 
accommodate. Mediterranean ex- 
perience has shown that cork yield 
is at its maximum, quality at its 
highest, and fruiting (acorn produc- 
tion) at its best when the trees are 
widely spaced so that they grow in 
full light without crowding or touch- 
ing. Therefore, as the trees grow and 
their crowns spread, the acreage must 
be systematically thinned in order to 
give each tree room for free, un- 
hampered growth. The rate at which 
the crown spreads, or increases in 
diameter, depends upon the rate of 
growth of the region in which the 
tree is located; and the number of 
trees which an acre will accommodate 
depends upon the diameter of the 
crown. 
Since the first and second strippings 
are of no real commercial value and 
the cork oak is not considered to be 
commercially mature until it is 40 
years of age and has yielded its third 
stripping, there is no point in planting 
more trees originally than an acre 
will accommodate at 40 years of age. 
On this basis, in conjunction with the 
variations in crown spread with 
growth rate and age, the number of 
trees per acre in relation to age was 
computed with the results presented 
in table 8, wherein it is seen that, for 
the first 40 years, the number of trees 
per acre is constant and, after 40 
years, the number is variable, de- 
creasing by thinning as the age 
increases. 
