Variation of the Pinus ponderosa needle oil with season and needle age

Influence of season and needle age on the yield and composition of the Pinus ponderosa needle oil was investigated. Oil yields throughout the year averaged 0·13% on the basis of tissue green weight. The average composition was 11·9% -pinene, 70·2% β-pinene, 8·0% 3-carene, 5·0% myrcene, 1·8% limonene, 2·2% β-phellandrene and 6·4% methyl chavicol (total MONOTERPENES = 100%). The amount of methyl chavicol and total monoterpenoids was highest in summer, lower in juvenile than in mature firstyear needles, and decreasing thereafter with needle age. A significant increase in 3-carene and decrease in β-pinene was apparent in juvenile needles. The most important step towards decreasing the seasonal and age variability of needle samples in ecological or chemotaxonomic studies was found to involve exclusion of sample collections during a period between the initial appearance of young needles and the time that they reach maximum length.