206 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA. 



grassland has a wider extension vertically and hence probably occupies a 

 broader climatic belt. The vertical range as a climax is often more than 6,000 

 feet .in the Rocky Mountains, and it is usually somewhat more in the Sierras 

 and Cascades. The corresponding range in rainfall and temperature is enor- 

 mous, and in either physical or human terms the climax contains several 

 climates. In the form of the pine consociation, the montane forest often 

 occurs in a rainfall of 20 inches or less from Colorado to Arizona and the Great 

 Basin. On the Pacific Coast, it is frequently found in a rainfall of 50 to 60 

 inches. Moreover, along the central axis of the Rocky Mountains, 50 per cent 

 or more of the rainfall occurs in the summer, while along the Sierras and Cas- 

 cades, 70 to 90 per cent of the precipitation falls during the winter. The figures 

 for temperature are less striking, but still very divergent. There is a differ- 

 ence of more than 20 degrees in the mean temperatures of the formation in 

 northern Montana and northern California, and of 60 degrees in the lowest 

 recorded minimum. In spite of this, the regular association of the three major 

 dominants throughout the formational area indicates that the climate is 

 essentially a unit from the standpoint of the dominant vegetation (fig. 9) . 



Fig. 9. — Monthly and total rainfall for representative localities in the association of the Petran 



montane forest. 



Relationship and contacts. — The closest relationship of the montane climax 

 is with the coast forest. This is best shown in northwestern Montana, north- 

 ern Idaho, and adjacent British Columbia, where the two meet to form a 

 broad transition. It is further indicated by the fact that Pseudotsuga is the 

 typical subclimax species of the cedar-hemlock forest. The most important 

 contact is with the subalpine forest. These touch each other for thousands 

 of miles along the ranges of the Rocky Mountains and of the Sierra-Cascade 

 system. They constitute a broad forest zone of fairly uniform physiognomy 

 and have even been regarded as a single formation. Gray (1878) seems to 

 have been the first to recognize their distinctness, and a similar view has been 

 maintained by Merriam (1898) and his followers, obscured somewhat by the 

 unsuccessful attempt to distinguish two zones, Canadian and Hudsonian, in 

 the subalpine climax. While the two climaxes are similar in appearance, they 

 differ fundamentally in composition, climatic and successional relations, and 

 in origin. The difference between them is clear where they occur in massive 

 zones, but is more or less hidden in regions of much topographic diversity. 



The contacts along the lower edge of the formation are varied. The normal 

 contact ecologically is with the woodland climax, and this is regularly found 

 in the southern half of the formational area in which woodland is more or less 



