Seasonal patterns of plant flammability and monoterpenoid content in Juniperus ashei

The susceptibility of Juniperus communities to prescribed fires can vary gr eatly throughout the year. The objective of this project was to determine t he relationship between the seasonal concentration and composition of volat ile oils and plant flammability in two Ashe juniper (Juniperus ashei) popul ations. Total monoterpenoid concentration was significantly affected by sea son and by plant population. Mean monoterpenoid concentration of a populati on from each central Texas was 9.16 mg/g fresh weight of juniper needles wh ile the mean concentration of a west central Texas population was 11.62 mg/ g of fresh weight. Monoterpenoid concentrations were typically lowest durin g the summer and highest during the spring and winter in the western popula tion, but there was no seasonal pattern in the eastern population. The east ern population of trees was slightly (4.8%) more flammable than the western population, and male trees were slightly (3.8%) more flammable than female trees. The concentration of limonene was positively related to plant flamm ability and could increase flammability by 30% over the range of cencentrat ions found in this species. Bornyl acetate was negatively related to flamma bility with each 1 mg/g increase in concentration resulting in a 2% decreas e in flammability. Caloric energy content and percent leaf moisture were no t significant factors in determining the percentage of the Ashe juniper pla nt actually burned. Secondary chemicals, usually considered as antiherbivor e mechanisms, may also serve an important role in determining the likelihoo d of a plant being consumed by fire.