226 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA. 



Picea and Abies, the slight handicap of the latter in competition with Picea 

 being offset by its abiUty to produce new plants by layering. Burn areas are 

 dominated by lodgepole pine or aspen, or by the two in varying mixture. 

 The aspen yields to the pine, and this in turn to the spruce and balsam. This 

 is Ukewise true of Pinus flexilis or P. aristata, where they occur on rocky 

 ridges or dry slopes in the heart of the association. Wheja the forest becomes 

 more open or breaks up into groups toward timber-line, the tolerance of the 

 spruce and balsam loses most of its advantage and the pines persist as per- 

 manent constituents of the community. 



SOCIETIES. 



Owing to its position, the subalpine forest has many societies in common 

 with the montane forest in its lower half and with the alpine meadow in the 

 upper. The societies are best developed in the central area, and decrease in 

 numl^er and importance toward both extremes, but especially to the north. 

 The following list for the Colorado region is fairly representative : 



Shrub layer: 



Linnaea borealis. 

 Lonicera involucrata. 

 Pachystigma myrsiiiites. 



Herbs, t emal Societies: 

 Thalictrum fendleri. 

 Polemonium pulchellum. 

 Mertensia polyphylla. 

 Aquilegia coerulea. 

 Fragaria vesca. 

 Draba aurea. 

 Draba streptocarpa. 



Herbs, Eslival Societies: 

 Sedum stenopetalum. 

 Solidago humilis. 

 Arnica cordifolia. 

 Pedicularia racemosa. 



Ribes lacuatre. 

 Shepherdia canadensis. 

 Salix nuttallii. 



Arabis drummondii. 

 Aisine baicalensis. 

 Adoxa moschatellina. 

 Zygadenus elegans. 

 Aragallus deflexua. 

 Ligusticum porteri. 

 Pirola minor. 



Carduus hookerianus. 

 Castilleia miniata. 

 Erigeron elatior. 

 Erigeron salsuginosus. 



Vaccinium caespitosum. 

 Vaccinium myrtilius. 



Mitella pentandra. 

 Mitella trifida. 

 Parnasaia fimbriata. 

 Androsace septentrionalis. 

 Pentstemon glaucus. 

 Pseudocymopterus montanus. 



Gentiana frigida. 

 Gentiana amarella. 

 Poa pratensia. 

 Featuca ovina. 



THE SIERRAN SUBALPINE FOREST. 

 PINUS-TSUGA ASSOCIATION. 



Extent. The subalpine forest reaches its northern limit along the Pacific in 

 the neighborhood of the sixtieth parallel, stretching west in Alaska from Lynn 

 Canal to Cook Inlet. It follows the summits of the Coast ranges southward 

 to southern British Columbia, where it broadens out to the eastward and 

 comes into contact with the Petran association in Alberta and Montana. It 

 occurs throughout the mountains of Washington from the Olympics to those 

 of the northeastern part of the State, but is only slightly developed in the 

 Blue Mountains. It follows the Cascade Range throughout Oregon into the 

 Siskiyou and the Sierra Nevada of California. It maintains its characteristic 

 expression throughout the latter, though Picea and Abies lasiocarpa have dis- 

 appeared. On the eastern slopes, it sometimes comes into contact with the 

 Petran association. The subalpine forest is much reduced in the San Ber- 

 nardino and San Jacinto Mountains ; its most southern outpost is probably in 

 the San Pedro Martir Range of Lower California (plate 54). 



The altitude of the subalpine zone changes greatly from Alaska to southern 

 CaUfomia. In Alaska it is chiefly at 2,000 to 4,000 feet, in southern British 

 Columbia at 3,000 to 6,000 feet, and in the Cascades at 5,000 to 8,000; while 

 in the Sierra Nevada it lies at 7,000 to 10,000, or rarely 12,000 feet. 



