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 persistency, 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 



