THE MONTANE FOREST CLIMAX. 205 



THE MONTANE FOREST CLIMAX. 



PINUS-PSEUDOTSUGA FORMATION. 



Nature. — This climax is an evergreen forest in which the dominants are 

 exclusively conifers. Broad-leaved deciduous and evergreen species occur in 

 it, such as Populus tremuloides, Quercus calif ornica, and Arbutus menziesii, 

 but they are typically subclimax in character. In contrast with the woodland, 

 this is a true forest formation. The trees are tall, usually 75 to 150 feet or 

 more in height at maturity, with massive trunks and dense crowns. In typical 

 habitats, they grow more or less closely, forming a continuous canopy. The 

 latter is less dense than in the other two forest formations and the forest nor- 

 mally exhibits a good development of layers. The number of societies of 

 shrubs and herbs is large and the aspects are well-marked. The major domi- 

 nants are few, but they have a wide range and the composition of the forma- 

 tion is exceptionally uniform. The number of more restricted and of local 

 dominants is larger, and they serve to give character to the associations. The 

 most typical as well as the most xeroid of its dominants, Pinus ponderosa, 

 possesses a striking power of adjustment and often forms savannah, which 

 extends far into the Great Plains as belts of woodland. 



Extent. — The montane forest is the most extensive and important of all 

 the western forest climaxes. In its broadest outlines it extends from the 

 foothills of western Nebraska and South Dakota and the mountains of western 

 Texas to the Pacific Coast. It reaches from the mountains of central British 

 Columbia to those of northern Mexico and Lower California. It occurs 

 throughout the mountain ranges of the Great Basin and on those of the south- 

 western deserts where the altitude permits. On the east, extensive forests of 

 Pinus ponderosa cover the Black Hills of South Dakota and a narrow strip 

 of the same forest follows the canyon of the Niobrara River as far east as the 

 ninety-ninth meridian. The southeastern limits of the formation are found 

 in the Guadalupe and Davis Mountains of trans-Pecos Texas. The southern- 

 most limit is attained by Pinus ponderosa, P. arizonica, and P. chihuahuana 

 in the ranges of Sinaloa and Durango. 



Unity of the formation. — The occurrence of the three major dominants, 

 Pinus ponderosa, Pseudotsuga mucronata, and Abies concolor, from Montana 

 to Mexico and Colorado to California leaves no question of the unity of the 

 formation. This is further emphasized by the more or less constant presence 

 of Pinus contorta, P. flexilis, and P. albicaulis in both associations. In addi- 

 tion, Pinus is represented by three species peculiar to each of the two associa- 

 tions, Picea by one species, and Cupressus by one. There is also a marked 

 agreement as to the genera of the societies, more than three-fourths of these 

 being common to both associations. With the major dominants so universal 

 and controlling, it follows that the ecologic and phylogenetic unity of the for- 

 mation is equally clear. 



Geographically, the formation is typical of the great Cordilleran system 

 from which it extends out upon the interior plateaus, such as that of the 

 Colorado, and along the minor ranges and escarpments which front the Rocky 

 Mountains on the east. Its climatic range rivals that of the grassland in so 

 far as latitude is concerned. Both formations extend several degrees north- 

 ward into Canada, and even a greater distance southward into Mexico. But 



