National Geographic : 1899 May
172 THREATENED ARIDITY ON THE PACIFIC SLOPE THE HUMID REGIONS From the subhumid tracts we come to the humid ones. These are chiefly limited to the mountain regions. When they extend into the plains or into areas of lower humidity, they do so only in the bottoms or on the northern slopes of deep canyons or the northern slopes of ridges. On the other hand, it is everywhere noticeable that the subhumid areas send long, strong lobes and extensions into the humid tracts, carrying their characteristic trees with them and indicating the coming ascendancy of drier climatic conditions. The trees which compose the forests in this zone group them selves into three divisions, according to their altitudinal range. The first group, occupying the higher elevations, contains the following species: Larix lyallii, Lyall larch; Pinus albicaulis, White-bark pine; Tsuga pattonii, Mountain hemlock. The second group contains species which most generally oc cupy areas at the lowest elevations in the zone. They are: Thuja plicata, Pacific arbor-vitae; Larix occdentalis, Western larch; Tsuga mertensiana, Western hemlock; Pinus monticola, Mountain white pine. The third group contains species which range indiscriminately from the upper to the lower areas of the humid zone and are as follows: Abies lasiocarpa, Alpine fir; Piceaengelmanni, Engelmann spruce; Pinus murrayana,Lodgepole pine. Of the species included in this group, the Alpine fir possesses the least power of adaptability, the lodgepole pine the highest. In addition to the species enumerated, there are the following whose behavior as to altitudinal extensions and limitations are not very thoroughly known. They are: Libocedrus decurrens, Incense cedar; Chamacyparisnootkatensis, Yellow cedar ; A bies amabilis, Amabilis fir; A bies nobilis, Noble fir; Abies shastensis, Shasta fir; Pinusflexilis, Limber pine; Pinus lambertiana,Sugar pine.