A Comparison of Season of Cambial Growth in Different Geographic Races of Pinus ponderosa

Abstract

1. Radial growth was studied in forty-one trees including Pinus ponderosa Laws. and its var. scopulorum Engelm., during the calendar year 1948. These trees represented populations obtained from known sources over a wide area in the western United States and had been growing on the same habitat at Priest River Experimental Forest in northern Idaho since 1911-1917. 2. Median dates for completion of 5%, 50%, and 95% of total radial growth were May 23, June 21, and August 22. Although there was considerable variation in growing seasons within populations, there was but little difference among the populations. Susceptibility to frost damage does not appear to be correlated with radial growth that continues late in the season. In these fourteen populations representing nearly 14⚬ of latitude, daylength appears to exert no influence upon the growing season. Duration of cambial activity is not related to grouping of the populations into races on the basis of morphology and anatomy.