30 FOREST TREES OF THE PACIFIC SLOPE. 



OCCURRENCE. 



On dry, rocky, east slopes, summits, tops of ridges and foothills, and sometimes on 

 sides of moister canyons and banks of mountain streams. Adapted to a great variety 

 of soils and not exacting as regards depth or moisture, but grows best in moist, well- 

 drained soils. Usually in dry, rc^ky, very shallow soil, appearing to prefer dry, loose, 

 gravelly loam, with little or no humus. Reaches higher elevations on clay soils than on 

 sandy ones. 



Usually occurs singly or in small groves among other conifers, where it is of largest 

 size ; occasionally in pure, open stands, commonly stunted, on exposed slopes and ridges. 

 Apparently less frequent in Tacific tlian in Rocky Mountain range. Associated mainly 

 with lodgepole pine and black hemlock at higher elevations, and sparingly with white 

 fir and stunted sugar pine at lower altitudes. 



Climatic Conditions. — Endures a variety of climatic conditions throughout range. 

 Mean annual rainfall varies from 15 to 30 inches. Snowfall heavy, except in southern 

 Rockies and southern California. Growing season, from 3 to 4 months in north ; some- 

 what longer in south. Minimum temperature from about —60° F. in north to —13° F. 

 in south ; maximum temperature thoughout range, from 90° to 97° F. Little atmos- 

 pheric moisture. 



Tolerance. — Appears to require full light. Never forms dense stands, and does not 

 tend to crowd out other species ; only occasionally in fairly dense mixed stands. Similar 

 in light requirement to white-bark and bristlecone pines, and less tolerant than other 

 associated conifers. 



Reproduction. — Moderate seeder, varying with region and elevation. Generally bears 

 cones abundantly in open stands at low altitudes, less abundantly in denser stands at 

 higher elevations. Cones produced locally about every year. Seeds practically wingless 

 and shed only near tree ; largely eaten by birds and squirrels. Mineral seed-bed most 

 favorable for germination, which even under favorable conditions is but moderate. 



"White-bark Pine. 

 Pi it us albicaulis Engelmann. 



DISTINGUISHING CHARACTERISTICS. 



White-bark pine has a low, long-branched, twisted or crooked trunk from 15 

 to 50 feet high and from 10 to 24 inches in diameter. Taller and larger trees 

 occur in protected situations. In the high, wind-swept home of this tree it is 

 often reduced to a sprawling shrub with enormous branches spreading over the 

 ground. Young trees have distant, regular whorls of branches at right angles 

 to the trunk, but in later life some of the upper whorls develop upward into 

 long, willowy stems, giving the tree a loose, bushy crown. The branches, 

 especially near the trunk, are exceedingly tough and flexible, so that the tree 

 is characteristically able to withstand the fiercest storms. The bark, even that 

 of old trees, is little broken, except near the base of the trunk, where it is 

 rarely more than one-half inch thick. Narrow cracks divide the lower bark 

 into very thin whitish or brownish scales, which, on falling or being torn off, 

 reveal the characteristic red-brown inner bark. Elsewhere the bark is rarely 

 more than one- fourth of au inch thick. Twigs of a year's and sometimes of two 

 years' growth are slightly downy. The leaves (fig. 7). densely clustered at the 

 ends of the branches, are dark yellow-green ; 5 in a bundle : length, about 1^ to 

 2£ inches. Shorter leaves occur on trees in the most exposed situations. Leaves 

 of a season's growth remain on the tree for approximately 7 or 8 years, but 

 some of them persist only 4 or 5 years. The cones (fig. 7) are a deep purple, 

 with very thick scales, vary in length from about li to nearly 3A inches, and 

 mature by the end of August or early in September of the second year. Usually 

 they shed their seed during the latter month, but sometimes not until late in 

 October. The cones dry out and open slowly in high, cold situations where this 

 pine grows. The seeds (fig. 7, a), about one-half inch in length by one-third 



