De I. VNER VEW D Forest Trees of the Pacific Slope

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, velldrained
soils. Usually in dry, rocky, 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 Pacific than 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 C)NDITIONs.-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; somewhat
longer in south. Minimum temperature from about -60° F. in north to -13° F.
in south; maximum temperature thoughout range, from 90° to 970 F. Little atmospheric
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.
Pinus albtcaulis 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 dianleter. Taller and larger trees
occur in protected situations. In the higlh, wilnd-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-brow'n inner bark. Elsewhere the bark is rarely
more than one-fourth of an 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 lA to
2j 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 thema persist only 4 or 5 years. The cones (fig. 7) are a deep purple,
with very thick scales, vary in length from about fl to nearly 31 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