National Geographic : 1899 May
THREATENED A RIDITY ON THE PACIFIC SLOPE 175 is here phenomenally high-a significant fact in connection with the wide extensions of subhumid and semi-arid conditions into the interior of this range, and a possible consequent rise of the nean annual temperature. The absence of a timber-line even at the highest peaks was noted and commented upon by the various parties engaged in the first surveys for a northern trans continental railroad route, but was generally ascribed to the effects produced by a current of warm air supposed to move eastward from the plains of the Columbia in this latitude. None of the three species contained in the summit group of trees possesses any marked power of adaptation. The Lyall larch is wholly deficient in this respect. The white-bark pine ranks slightly higher, and the mountain hemlock somewhat above the latter, as shown by its occurrence within undoubted subhumid conditions in some localities, as in the middle portion of the Deschutes basin in Oregon. In the Bitter Roots we find the Lyall larch along the high crests of the main range from a point just north of Nez Perce pass to an as yet undetermined northern point. However, it does not go very far beyond the ridges which bound the north fork of Clearwater basin. It is found on both the east and west slopes of the range, extending three to four miles away from the crest on either side. The western spurs of the range present one or two outlying small groves of the species on the divide between the Lochsa and Selway forks. Its habitats in the Bitter Root range are abso lutely cut off from all connection with others elsewhere by gaps of low altitudes a hundred miles or more in width, which now cannot possibly be spanned by the species. In these regions this larch is clearly approaching extinction. Its cone and seed pro duction are extremely scanty. Its growth is excessively slow. Most of the individuals which make up the stands are far ad vanced in age. Seedlings or saplings are rare and scattered. No farther back than three centuries there must have been abundant seed production, as a majority of the trees are approximately of this age. Three centuries hence the stands, if existing at all, will show great diversity of age, unless the cone-bearing periods run in cycles, long intervals of barrenness being followed by periods of fertility. Whatever rotation may exist in this respect (and that some does occur admits of no doubt) it operates only within narrow limits of time, producing what are called " off years," and does not impress itself very strongly upon the stand of the species as a whole.