372 
TABLE 8.—Relation between the number of trees 
per acre and age in the United States potential 
cork area 
Potential area 
Positive | Quasi 
Mean rate of growth...| 0.9667) 1.8439 
Trees per acre at: 
Initial planting.......} 43.53 8. 85 
AQEY Cates cr Cremite cts 43. 53 8. 85 
SOR CALS tlesta sca tint PASS OH 6. 09 
GOlyearsiersst il. ).teear 2210 4.49 
OB ears). thks cmv: eos 17.09 3. 47 
BOlyearste pater e 13. 68 Phe: 
D0 tv.eaTsnise assem 123 228 
NOOhvearseee aac st: 9. 43 1e9t 
The cork yield per acre per annum 
at any given age may now be deter- 
mined by multiplying the yield per 
tree per annum (table 7) by the 
number of trees per acre (table 8) 
with the results shown in table 9. 
TABLE 9.—Relation between annual cork yield 
per acre 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 acre at: 
10) SHEE Ayo doc . 00 . 00 
20) yearseetien ee 69. 21 32530 
J Ohyearseterrerscce 122. 89 Nh SW 
AQlivearsaecciscy 219. 39 102. 22 
KOM EEIRotoo ce of 268. 53 125309 
GO yearstine. sr 352m 21 164. 06 
OW ECATS ira ster: 483. 99 225. 45 
SOlveatsacoeiseir 689.34 | 321.10 
SOky.earsrerpeier 1006. 21 468. 31 
1OOkyearsieee st 1502.20 | 697.91 
A marked peculiarity shown in 
table 9 is the fact that, at a given rate 
of growth, the cork yield per acre in- 
creases with age but, at any given age, 
the yield decreases as the mean rate 
of growth increases. In other words, 
the region in which the cork tree grows 
the fastest produces the least amount 
ANNUAL REPORT SMITHSONIAN INSTITUTION, 1948 
of cork per acre. This phenomenon 
is readily explained by the fact that 
the number of trees per acre (table 8) 
decreases at a faster rate than the 
cork yield per tree (table 7) increases. 
The net result of this situation is 
nothing to cause undue alarm. It is 
not only a perfectly normal condition, 
but it is also a typical Mediterranean 
characteristic. Table 6 shows that 
Spain has the lowest rate of growth 
(0.842) in the Mediterranean region, 
while, in table 1, it is shown to have 
the highest cork yield per acre (212 
pounds). 
This evidence considerably strength- 
ens the argument in favor of limiting 
the growth of commercial cork to the 
positive potential area which is the 
only region in the United States with 
climatic environments and growth 
rates identical with those of the 
Mediterranean region. This does not 
mean that the quasi-potential area 
is to be neglected. In addition to its 
hog-raising possibilities, this area can 
render a valuable service to the Nation 
by planting to cork trees the vast 
amount of lands which it contains 
that are now out of agricultural pro- 
duction due to the depleted condition 
of their soils. Since the scarcity of 
food-producing land is a problem not 
only in the United States but all over 
the world, any land that has food- 
producing potentiality should not be 
planted to cork oaks. 
The Cork Forest 
The most desirable cork-forest in- 
dustry for the United States is one 
which will produce sufficient cork to 
meet our yearly requirement of ap- 
proximately 160,000 tons. A forest 
which will produce at this rate must, 
as will be shown, contain at least 
28,000,000 trees planted on almost 
1,000,000 acres. Such a planting, 
however, could not be made in any 
one year because the acorns are not 
available. It would require 84,000,000 
acorns, since common practice is to 
plant three acorns to a hill in order to 
assure the germination of one. 
