SPRUCE AND BALSAM FIR TREES. 13 
of the tree's altitudinal range of from 8,500 to 12,000 feet in the 
South to 6,000 feet in the North, with increasing latitude. This vari- 
ation, however, is not consistent throughout the tree's range, because 
local climatic factors often have a modifying influence. Trees of 
merchantable size occur at the middle and lower levels, while chiefly 
stunted growths are found at timber line. Engelmann spruce shows 
little preference regarding the character of soil if there is sufficient 
moisture. It grows fairly well on dry soils, but usually gives way 
on porous soils to lodgepole pine, Douglas fir, and to other trees 
requiring better drainage. It thrives on retentive, fine, loamy soils, 
but attains the largest size on deep, rich, moderately moist soils of 
gulches and high river valleys. A shallow root-system enables this 
species to maintain itself on thin soils of slopes and on the wet mar- 
gins of rivers, lakes, and swamps. 
Engelmann spruce forms extensive pure forests and occurs also 
in mixed stands. Pure stands are somewhat more frequent in the 
South than in the North, where it chiefly meets trees of similar sil- 
vical requirements but of less extended southern range. In mixed 
stands it is found most frequently with alpine fir, Douglas fir, and 
lodgepole pine; occasionally it is associated with bristle-cone pine, 
white fir, and limber pine. 
Picea engelmanni is very tolerant of shade, especially in youth, 
in this respect surpassing most of its associates. It endures years 
of shading and makes good growth when released from suppression. 
Owing to its great tolerance of shade this spruce forms close stands 
of many ages, thus preserving good forest conditions. 
Engelmann spruce is a prolific seeder over most of its range. Large 
crops of seed are produced locally at intervals of about three years. 
The seed has a high rate of germination and remarkably persistent 
vitality. Seed so stored as to preserve its moisture and to prevent 
molding may show a germination of from 30 to 50 per cent after 
being kept four or five years. Trees begin to produce seed from about 
the twenty-fifth year and continue bearing it to an advanced age. 
Seeds germinate best in moist mineral soil, seedlings being rarely 
found in humus. Notwithstanding prolific seed production, seed- 
lings are not generally abundant. Reproduction appears to pro- 
ceed rather slowly but persistenly, seedlings being most numerous 
in small protected openings in the forest. Low branches of isolated 
trees also favor germination and protect seedlings, through which 
groups of trees are built up, and these combine with other near-by 
groups finally to form continuous stands. 
LONGEVITY. 
Engelmann spruce is a very long-lived tree, even in the most un- 
favorable situations. Trees from 16 to 22 inches in diameter are 
