220 CLIMAX FORMATIONS OF WESTERN NORTH AMERICA. 



The first five species represent the coastal association, the others the mon- 

 tane forest. Pseudotsuga, however, belongs to both, and Picea engelmanni is 

 normally a dominant of the subalpine zone. Pinus monticola is also more or 

 less montane in character, ranging far south into the Sierra Nevada. Like 

 Larix occidentalis, it reaches its optimum development in northern Idaho and 

 the adjacent regions, and these two may well be regarded as the most typical 

 dominants of the transition forest. While Abies grandis ranges from the 

 Coast to northwestern Wyoming, it too is more characteristic of the transition 

 forest, largely perhaps because of the absence of the more tolerant species. 

 Tsuga and Thuja occur generally throughout the region, but are usually of 

 minor importance. Tsuga drops out first toward the boundaries of the 

 forest, leaving Abies and Thuja to represent the final stage of the climax. 

 Pinus ponderosa, P. contorta, and Picea engelmanni are all of the widest range 

 and play a part in at least two formations. 



Groupings. — The groupings of the dominants of the larch-pine forest are 

 numerous and complex. The drier areas are generally controlled by Pinus 

 ponderosa and Pseudotsuga, with more or less P. contorta, Abies grandis, and 

 Larix. The moister ones are dominated by Pinus monticola and Larix, with 

 varying amounts of Thuja, Tsuga, and Picea engelmanni. In the Priest 

 River region Leiberg (1899:246) gives the abundance of the dominants as 

 follows: yellow pine zone Pseudotsuga 70 per cent, Pinus 10 per cent, Abies 

 15 per cent; white pine zone Pinus monticola 42 per cent, Larix 35 per cent, 

 Thuja 8 per cent, Picea engelmanni 6 per cent, Tsuga 3 per cent, Abies 2 

 per cent. In the Bitterroot Mountains where the western species are im- 

 portant, the percentages are: Pinus contorta 25, Picea engelmanni 19, Pseu- 

 dotsuga 14, Pinus monticola 12, Abies grandis 9, Larix 6, and Thuja 4. Where 

 the montane element predominates the values are: Pseudotsuga 34, Pinus 

 ponderosa 21, P. contorta 17, Picea engelmanni 11, Thuja 5, Abies 4. In the 

 Flathead region of Montana Larix and Pseudotsuga are often the most im- 

 portant, with all the other dominants present here and there in some degree. 

 In the Selkirks Thuja and Picea usually occupy the valleys and Pseudo- 

 tsuga and Tsuga the slopes, while Pinus monticola, Larix, Pinus contorta, and 

 P. ponderosa also occur. In eastern Washington Pinus and Pseudotsuga are 

 controlling, with considerable Larix, Pinus contorta, P. monticola, and a small 

 amount of Tsuga and Thuja. The dominants of the Blue Mountains are 

 Pinus ponderosa, Pseudotsuga, Abies grandis, Larix, and Pinus contorta. 



Factor and serai relations. — The general climatic relations of the larch-pine 

 forest have already been pointed out (p. 216). Larsen (1916:437) has indi- 

 cated the general water and fight relations of the dominants in the following 

 fists: 



Water-content, on wet ground : Picea engelmanni, Tsuga heterophylla, Thuja 

 plicata. 



Water-content, moist or intermediate ground : Pinus monticola, Abies grandis, 

 Larix occidentalis. 



Water-content, dry ground : Pinus contorta, Pseudotsuga mucronata, Pinus 

 ponderosa. 



Tolerance: Pinus ponderosa, Larix occidentalis, Pinus contorta, Pseudotsuga 

 mucronata, Pinus monticola, Picea engelmanni, Abies grandis, Tsuga hetero- 

 phylla, Thuja plicata. 



