182 PAUL C. STAND LEY 



is said to appear, coming in from the south, but the writer did 

 not visit that region. The two zones are well marked in most 

 places, except along the rock slides and rarely on the slopes at 

 middle elevations, where there is sometimes an intricate associ- 

 ation of plants which makes it impossible to refer a certain area 

 definitely to either zone. The Canadian and Transition zones 

 are not as sharply separated in New Mexico as are the Transition 

 and Upper Sonoran, or the Upper Sonoran and Lower Sonoran; 

 but, on the other hand, they are much more clearly differentiated 

 than the Canadian and Hudsonian. The two latter zones in 

 New Mexico are distinguished only artificially, even on the 

 highest peaks where there is a broad expanse ofthe Arctic-Alpine 

 Zone. 



CANADIAN ZONE 



The vegetation of this area consists of heavy forest, frequently 

 interrupted by open grassy meadows. The trees are Picea 

 parry ana, Abies concolor, Pseudotsuga mucronata, Pinus flexilis, 

 Negundo interior, and Populus aurea, the first three being most 

 abundant. Picea parry aria forms almost pure stands at the 

 higher elevations and scattered trees extend far down along the 

 small valleys. It is conspicuous inside the canyon, especially 

 on the faces of the cliffs, where many individuals manage to 

 secure a foothold in small pockets or crevices. The white fir 

 and Douglas spruce grow on the lower slopes and are often 

 mixed with yellow pine. Pinus flexilis occurs only occasionally, 

 and at the higher levels. The box-elder is rare, along the banks 

 of the streams. Aspen is the most abundant tree in number of 

 individuals, occurring everywhere as an undergrowth where the 

 shade is not too dense, and forming nearly pure stands over 

 large areas where the timber has been destroyed. 



Of the shrubs several are common: along the streams Alnus 

 tenuifolia, Sorbus scopulina, Amelanchier sp., and Dasiphora 

 fruticosa are most abundant; in the Picea forests on the plateau 

 above the canyon one finds Distegia involucrata and Sambucus 

 microbotrys, the latter with small clusters of bright red fruit; 

 while among the aspens there is an abundance of Rubus arizoni- 



