FOREST TREES OF THE PACIFIC SLOPE. 247 



Anaktuvuk River valley (branch of Colville River), on Arctic watershed of Endicott 

 Mountains, here reaching its northmost limit (lat. 69° 20') at 75 miles from coast . 

 Abundant throughout Yukon River Valley bottoms and also on slopes. Extends, on 

 south slopes of Endicott Range, to about 1,000 to 2,000 feet, on Koyukuk River to about 

 3,000 feet, on White and Upper Tanana rivers to about 3,500 feet, on lower Stewart 

 River to about 2,500 feet; on south slopes of Alaska Range, near Cook Inlet, to about 

 1,200 feet, river bottoms on Chitina River and in Skolai Mountains, on upper Sushitna 

 and Copper rivers to somewhat higher elevations, Bkwentna River to 2. .",00 feet, on 

 north and west slopes of Alaska Range to 3,500 and 4,000 feet, valley of Kobuk River 

 (western tributary of Arctic Ocean) to 1,000 feet. 



Oregon*. — Reported from eastern part, but definite records are wanting. 



Native range of Populus balsamifera candicans unknown, but the tree is cultivated 

 and escaped from cultivation from New Brunswick to Georgia and west to Minnesota. 

 It may possibly be met with in the Pacific region. 



The detailed range of this tree east of the Pacific region will be described in 

 later bulletins. 



OCCURRENCE. 



Alluvial stream bottoms, flats, borders of lakes and swamps in moist sandy and grav- 

 elly soils, which are often rich and deep. Forms pure stands and is more or less mixed 

 with black and white spruces, birches, alders, and willows. 



Climatic Conditions. — Characterized by humidity, heavy precipitation, very low tem- 

 perature, short growing season, and long, severe winters. 



Tolerance and Reproduction. — Not determined. 



Black Cottonwood. 

 Populus trichocarpa Torrey and Gray. 

 DISTINGUISHING CHARACTERISTICS. 



Black cottonwood. the largest of our poplars, under the best conditions for 

 growth, is from 80 to-125 foot high and from :; to 4 feet in diameter; trees 

 somewhat taller and from 5 to G feet through occur much less commonly, while 

 over much. of its range it is under 50 feet and from 12 to 18 inches in diameter. 

 The pale gray, deeply and regularly furrowed trunks are clear of branches for 

 from 50 to 80 feet or more in the best grown trees, straight, or, often, with a 

 long, slight bend. Smaller trees, grown under less favorable conditions, have 

 relatively long, clean trunks, except in the open. All have rather open, short, 

 wide crowns of thick upright branches. The furrows and ridges of the trunk 

 bark, often nearly 2 inches thick, are distinctly and sharply defined. Young 

 twigs are indistinctly angled, later becoming round, shiny, and reddish yellow. 

 The similarly colored buds, from live-eighths to three-fourths of an inch long, 

 are often curved (as if bent) and covered with a fragrant, yellowish-brown .mini. 

 from which the tree gets the name, "balsam Cottonwood." .Mature leaves (tigs. 

 108, 109) are thick, leathery, and smooth; deep shiny green above, and silvery 

 White or whitish beneath, with rusty areas .and veiny. Midveins and their 

 branches, as well as the slender, round leaf-stems, sometimes very minutely 

 hairy. In dying, the leaves become a dull yellowish-brown. Wood, soft. 

 straight-grained, fine-grained in dense stands; dull grayish-brown. Large logs 

 obtainable from the best grown trees give clear, wide lumber and other mate- 

 rials which are extensively used in the range of the species, especially for coop- 

 erage stock. It is likely to he even a much more important soft wood in the 

 northwest Pacific region than it is now. owing to tEe scarcity of other broad- 

 leaf timber trees suitable for the special purposes to which this wood can 

 be put. 



Longevity. — Not fully determined. Probably attains the greatesl ace of any 

 Of our native species. Trunks from 2 to ;i feet in diameter are from 85 to 110 



