262 Part II. Chapter 3. 
Pinus monticola Dougl. Abies concolor Lindl. & Gord. 
»  flexilis James. Thuja plicata Don. 
» albicaulis Engelm, Juniperus occidentalis Hook. 
» Balfouriana Murr. » californica Carr. 
» aristata Engelm. Taxus brevifolia Nutt. 
»  arizonica Engelm. Salix amygdaloides Anders. 
» ‘ ponderosa Laws. » lasiandra Benth. 
»  chihuahuana Engelm. »  fluviatilis Nutt. 
» Murrayana Oreg. Com.(=P.con- »  sitchensis Sanson. 
torta var. Murrayana Engelm.). | Populus trichocarpa Torr. & Gray. 
Larix occidentalis Nutt. Betula occidentalis Hook. 
» Lyallü Parl. Alnus rhombifolia Nutt. 
Picea Engelmanni Engelm. Prunus emarginata Walp. SR 
Tsuga Mertensiana Bong. (=T.hetero- | Acacia Greggii Gray. I 
phylla Sarg.). Acer glabrum Torr. 
»  Pattoniana Jeffr. (= T. Merten- | Cornus Nuttallii And. 
siana Sarg.). Arbutus Menziesii Pursh. is 
Pseudotsuga Douglasii Carr. (=P.mu- | Chilopsis saligna Don. & 
cronata Nutt., = P. taxifolia Poir.), | Sambucus glauca Nutt. 
Abies subalpina Engelm. (= A. lasio- 
carpa Nutt.). 
Many of these trees such as Pinus ponderosa, Pseudotsuga Douglast j 
form an important element in the Pacific coast region reaching their greatest ® 
size there. The enumeration above proves that the Rocky Mountains ae 
comparatively poor in the size of its trees and the number of species; that se 
few of the species are peculiar, and those mostly in the southern part, = $ 4 
of the Mexican plateau type; that most of the Rocky Mountain trees ae 
identic in species with those of the Pacific forest. The Pacific forest in the = 
widest sense extends from central Alaska southward. a: 
Alaska Forests. The Alaska forest has a simple composition, for the bulk ” 
is made up of a mixture of two species, Picea sitchensis and Tsuga Mertensiana 
(T. heterophylla), with which dominant trees occur: Pinus contorta, Abies er ER 
alpina (A. lasiocarpa), Alnus oregana, Acer glabrum, Populus balsamıferh 
Thuja gigantea, Cupressus (Chamaecyparis) nootkaensis, while near the timber” 
line and farther west, on the lower level grows 7suga Pattoniana (7. Mertae 
siana). Numerically the coast hemlock seems to be the most common PB 
forming usually 70 to 80 per cent of the composition of the forest, the spruce 
only occasionally preponderates, especially along water-courses and on newly a 
forested moraines, until the western limit of the hemlock is reached at Prinee 
William Sound. Farther west, the spruce alone continues to form forest$ n 
open groves, as on the shores of Cook Inlet and Kadiak Island, the weste 
limit of tree growth. : 
Why trees are limited at this point, it is difficult to say for th 
ample and the climate a little more severe than at Sitka. Perhaps two cauf 
e rainfall 5 5 
