BLACK COTTONWOOD 



(Populus Trichocarpa) 



THIS member of the cottonwood group is a strong tree that holds 

 its ground in various latitudes and at many elevations, ranging 

 from sea level up to eight or nine thousand feet, and in latitude from 

 Alaska to southern California, a distance of nearly three thousand 

 miles. Its east and west extension is more restricted and seldom 

 exceeds four hundred miles. Its habitat covers an area of half a 

 million square miles, and in that space it finds conditions which vary 

 so greatly that the tree which can meet them must possess remarkable 

 powers of adaptation. 



Beginning in Alaska and the interior of Yukon territory, it has an 

 arctic climate. It there not only grows on the coast, but it strikes the 

 interior. It appears on the headwaters of several streams which flow 

 into the Mackenzie or Hudson bay. It passes south through British 

 Columbia and enters the United States west of the Rocky Mountains. 

 It has been reported as far east as Idaho and Montana, but further 

 information is needed before its limits in that direction can be definitely 

 fixed. 



When it enters California it prefers the elevated valleys and can- 

 yons of the Sierra Nevadas, though it occurs sparingly among the coast 

 ranges. It is generally found in the Sierras at elevations of from 3,000 

 to 6,000 feet, though it occurs between 8,000 and 9,000. Among the 

 San Jacinto mountains of southern California it grows at an altitude of 

 6,000 feet. 



When it occurs at low levels it is usually found on river bottoms 

 and sand bars, in sandy and humous soils, and there the largest trees 

 are found. At higher elevations it is more apt to occur in canyon bot- 

 toms and gulches, in moist, sandy or gravelly soil, and in such situations 

 the black cottonwood is smaller. The best growth occurs where the 

 climate is humid and the precipitation is great. Beyond the reach of 

 sea fogs, where the tree depends on soil moisture chiefly, it is smaller. 



It is an intolerant tree. It must have light. When it is crowded a 

 tall, slender trunk is developed and the small crown is lifted clear above 

 its competitors into the full light. If it cannot succeed hi gaining that 

 position its growth is stunted or the tree meets an early death. 



The black cottonwood is the greatest of the cottonwoods. This 

 country produces no other to match it, and, as far as known, the 

 whole world has none. The Pacific coast is remarkable for the giant 

 trees it produces, but most of them are softwoods the redwoods, the 



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