THE SUBALPINE FOREST CLIMAX. 



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4 



3 



2 



1 





 Fig 



Frances, Colorado 



It 



a 



11. — Monthly and total rainfall for represent- 

 ative localities in the Petran subalpine forest. 



tinct forms which replace each other. The two other most typical dominants 

 are Tsuga mertensiana and Larix lyallii. These are essentially Coastal in 

 character, but both occur in the transition area of northern Montana and 

 Idaho and Larix reaches the Rocky Mountains in southern Alberta. The 

 other characteristic dominant is Abies ?nagnifica, which is found only in Cali- 

 fornia and southern Oregon, and may well be regarded as the ecological rep- 

 resentative of A . lasiocarpa. 



The ecological unity of the formation is well shown by the behavior of the 

 individuals as well as of the community in the upper part of the zone and at 

 timber-line, as already noted. This is emphasized by its constant relation to 

 the montane forest below it and the alpine climax above. Geographically, 

 the formation is consistently one of high mountain ranges and peaks or of 

 northern ones. The geographic and topographic relations serve to explain 

 the uniformly boreal climate in which it flourishes. This is characterized by a 

 short growing season, high precipi- 

 tation, largely in the form of snow, 

 and wide diurnal and seasonal range 

 of temperatures. The long winter 

 is often marked by high winds and 

 excessive transpiration in relation 

 to the chresard, and these have a 

 controlling influence in determin- 

 ing the timber-line (fig. 11). 



Relationship and contacts. — The subalpine climax shows some relationship 

 to three different formations, viz, the boreal forest, the Coast forest, and the 

 montane forest. Its closest relationship appears to be with the first, since the 

 chief dominants in both belong to the two genera, Picea and Abies, and the 

 species are also more or less related. It seems probable that the boreal forest 

 represents a Tertiary spruce-balsam climax from which the subalpine forma- 

 tion was differentiated. The relationship to the Coast forest is shown by the 

 species of Abies in the latter, and by the presence of Tsuga and Larix in each, 

 though represented by different species. An additional relation is found in the 

 fact that Picea engelmanni is common and Abies lasiocarpa not infrequent in 

 the lower levels of the transition association of the Coast forest. Finally, several 

 dominants of the latter, such as Abies amabilis, A. nobilis, and Chamaecyparis 

 nootkatensis occur frequently in the subalpine zone, and the former especially 

 may often form the timber-line. The relationship to the montane forest is 

 shown chiefly by the presence in each of closely related species of Picea and 

 Abies, though the two genera play a much less important r61e in the montane 

 zone. Pinus contorta and Populus tremuloides are common to the two zones, 

 and Abies concolor, Pinus jeffreyi, and Pinus monticola form a broad ecotone 

 with the subalpine dominants. 



The lower contact of the subalpine formation is with the montane forest 

 in the Rocky Mountains from New Mexico to Alberta and in the ranges of the 

 interior. This is the case also in the mountains of southern California, the 

 Sierra Nevada, and the Cascades to northern Oregon. From here to the 

 Kenai Peninsula in Alaska, and to Idaho and northwestern Montana, the 

 subalpine forest touches the Coast climax. In northern British Columbia 



