6 BULLETIN 418^ TJ. 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 ahihty 

 to thrive on almost soilless steep talus slopes is remarkable. It grows 

 also on loamy clay soils, on loose sand, and on the deep, hght, 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 weU 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 in the Willamette Valley and 

 which inhabits moist river benches. 



LIGHT. 



Stands of western yellow pme 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 hght. 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 yeUow-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 m which most of the adult trees in the stand 

 bear seed; and in the intervening years there is usually some seed.^ 

 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. 



