. Results of a biological survey of mount Shasta, California. ranges—one restricted tothe low Transition licit ncai- the inast, the other to the high lludsoniau zone on theloftiist mountains—may ]ire\ciit the confusion that otherwise would result from thechange of name. 1899.] WHITE-B.\RK PINE BELT. 43 tbem descend in tongues considerably below the nsual lower limit ofthe belt to which they belong. The most extreme ease of the kindobserved is on the east side of the series of hills and ridges known onthe map as dray Butte/ where a gulch, sheltered from the warm after-noon sun and moisten
. Results of a biological survey of mount Shasta, California. ranges—one restricted tothe low Transition licit ncai- the inast, the other to the high lludsoniau zone on theloftiist mountains—may ]ire\ciit the confusion that otherwise would result from thechange of name. 1899.] WHITE-B.\RK PINE BELT. 43 tbem descend in tongues considerably below the nsual lower limit ofthe belt to which they belong. The most extreme ease of the kindobserved is on the east side of the series of hills and ridges known onthe map as dray Butte/ where a gulch, sheltered from the warm after-noon sun and moistened by seepage from melting snows, carries thehemlocks to a lower altitude than they reach elsewhere. On suitableslopes they usually begin about 7,1*00 or 7,300 feet and range up toabout 8,000 feet. The highest altitude at which they were observed is8,700 feet, a little east of Mud Creek Canyon, where a few stunted treeswere found among the white-bark pines. Their extreme upper limit isthus a thousand feet lower than that of the white-bark pines. This is. Fig. 25.—Group of alpine liemlocks near Deer Canyon. due, in part at least, to the character of the upper slopes, where notrees can grow except on the ridges—as explained under the head ofTimberline (pp. 27-30)—and here the ridges are too exposed and toodry for hemlocks. On Shasta the alpine hemlock does not grow in such luxurianceor attain such dimensions as in the Cascade IJange. The averageheight of mature trees seems to be 80 or 100 feet; the average diametera little less than 3 feet. Trunks 4 and 5 feet through are by no meansrare and the one shown in the accompanying photograph (tig. 20) meas-ured G feet. It is a characteristic habit of hemlocks on sloping groundto grow in clusters, 3 to 7 springing from a common base. In this way,when young, they are better able to withstand the pressure of the snow. 44 NORTH A^IERICAN FAUNA. [NO. 16. Those that grow singly usually sui)i)ort tlieniselvos by luiviug thetrunks &g
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Keywords: ., binomial=tsugamertensiana, bookcentury1800, booksubject, taxonomy
