6 BULLETIN 418, U. S. DEPARTMENT OF AGRICULTURE. 
SOIL AND SOIL MOISTURE. 
Western yellow pine grows and thrives on nearly every variety of 
soil within its range; it is one of the first trees to get a foothold on 
the disintegrating recent lava flows of central Oregon, and its ability 
to thrive on almost soilless steep talus slopes is remarkable. It grows 
also on loamy clay soils, on loose sand, and on the deep, light, frag- 
mental pumice stone of central Oregon; but on cold, peaty, or heavy, 
moist soils, such as those adjacent to meadows, it is usually not 
found. It grows well on land which is too dry for any of its asso- 
ciates. It seems to prefer well-drained, loose soils; but an increase 
in moisture, provided the soil is well drained, makes for more rapid 
growth. Occasionally, but not usually, it grows on situations where 
the water table is within 4 or 5 feet of the surface during the growing 
season. It is, therefore, uncommon on flats and bottom land, and is 
distinctly a tree of the slopes. Exceptions occur, notably the form 
which occurs west of the Cascades hi the Willamette Valley and 
which inhabits moist river benches. 
LIGHT. 
Stands of western yellow pine are always rather open because this 
tree is intolerant of shade. Seedlings do fairly well under the shade 
of parent trees, but saplings do not grow thriftily until they receive 
direct light. Western yellow pine is as intolerant as any of the trees 
with which it is associated in Oregon, and its reproduction can not 
compete successfully in the virgin forest with that of Douglas fir, 
white fir, or lodgepole pine on sites where the latter grow vigorously. 
With an increase in the amount of soil moisture, yellow pine becomes 
more tolerant of shade. The openness of most of the yellow-pine 
stands is probably due to the demand of the trees for soil moisture 
and the competition of the roots for ground space where moisture is 
insufficient, as well as to the demand for light and crown space. 
REPRODUCTION. 
SEED PRODUCTION. 
Yellow pine after reaching middle age produces seed fairly abun- 
dantly. Trees under 50 years old, or 10 inches in diameter, rarely 
bear any cones; and large crops are not borne except by very much 
older and larger trees. Every three years, and sometimes oftener, 
come good seed years in which most of the adult trees in the stand 
bear seed; and in the intervening years there is usually some seed. 1 
It is disseminated either by wind or by rodents that carry the cones 
or the seeds and store them. Sometimes many bushels of cones are 
1 For a full discussion of seed production of the yellow pine of the Southwest, see Forest Service Circular 
196, "The Influence of Age and Condition of the Tree upon the Seed Production in Western Yellow Pine," 
by G. A. Pearson. 
