56 University of California Publications in Botany [Vol. 9 



feet;®® on the west side of the Rockies, in about the same latitude, 

 in the Atlin District of British Columbia, timber line runs at 3,700- 

 4,200 f in southern British Columbia, the better watered Selkirks 

 have a forest cover to approximately 6,000 feet®^ or a little higher, 

 while the drier Rocky Mountains to the east are forested about 1,000 

 feet higher, tree-line appearing at 7-8,000 feet.®^ The Purcell Range, 

 near the international boundary, has the forest limited at 7,200 feet/° 

 Along the coast in southeastern Alaska, the alpine meadows begin 

 much lower down, at approximately 3,500 feet in the Sitka region/^ 

 The mountains of British Columbia lie at the vertex of the great angle 

 formed by the south-trending mountains along the Pacific coast of 

 the United States and the southeastward extension of the Rockies. 

 The difference between the ranges of British Columbia in respect to 

 elevation of tree-line is maintained in the mountains of the western 

 United States. In Washington, Piper reports^- tree-line at 6-7,000 

 feet ; in the corresponding latitude in Montana, Rydberg'^ considers 

 71-8,100 feet the upper limit of the forest; this estimate for the height 

 of timber-line in Montana differs considerably from the figures given 

 by Gannett,'^ who found the upper forest limit in the mountains about 

 Bozeman to be about 9,500 feet, with a line at 8,800 feet in the Absa- 

 roka Mountains, and in the Flathead district, 9,000 feet as the begin- 

 ning of the alpine zone. Corroboration for Piper's estimate for Wash- 

 ington is afforded by Tansley's survey of Mt. Rainier, where the actual 

 tree-line was found to be 6,800 feet.'^^ Russell'" states that timber line 

 on the high mountains of central Idaho is near 10,000 feet. In the 

 Cascades of Oregon, Leiberg'^ reports Mts. Thielson, Pitt, and Scott 

 to have true timber lines at 93-9,400 feet. On Mt. Shasta, timber line 

 is said by Merriam®^ to average considerably under 95-9,800 feet, 

 which is the elevation of the line on the southwest slopes. In nearly 

 the same latitude, the Uintas of Utah have an alpine zone above a 

 timber line at about 11,000 feet and eastward in Wyoming and Colo- 

 rado, the same boundary between the alps and the highest of the 

 forest zones rises from 9,900 feet in the Yellowstone Park to 10,000 

 feet in the Wind River Mountains,^* 10,500 feet in the Big Horn 

 Mountains, and 11,100 feet in the Rockies of northern Colorado 

 (Longs Peak), The climatic tree-line on Lassen Peak (10,437 feet) 

 in northeastern California, is especially hard to define owing to the 

 excessively rocky nature of the slopes, which afford a soil suitable for 

 tree growth in only a few places; the line is approximately near the 

 9,200-foot contour. In the Coast Ranges of California no peaks rise 



