The Growth of Conifers

Abstract

MY friend, Mr. D. M. Andrews, has communicated to me an observation which seems to deserve comment. At the Government nursery near Monument, Colorado, at an altitude of 7000 ft., there are two beds of two-year-old seedlings of Engelmann spruce (Picea Engelmanni), a common tree of the Rocky Mountains. Each lot is shown to be hardy in the locality, having passed a winter in the open, protected only by a covering of oak branches. The seedlings in one bed, raised from seed gathered in the Pike's Peak, Colorado, region, were, when examined, about 2½ in. high, and had matured their buds and ceased growing for the year in the latter part of August. The seedlings in the other bed, from Arizona seed planted at the same time, were about 4 in. high, and had not yet completed their growth for the year. The Arizona seedlings were green, those from Colorado strongly bluish. Seeking an explanation for this difference, it appears probable that the Colorado trees became adapted to a more severe climate during the waning of the last glacial period, and have not yet lost the physiological characters appropriate to past conditions. The Arizona trees, the ancestors of which lived in a milder, more southern region, did not develop such adaptations, and now that our climate has changed they are actually better fitted for Colorado conditions than trees of Colorado ancestry.