Fire reduces Russian olive seed germination and seedling survival with increasing fuel load

Elaeagnus angustifolia (Russian olive) is an invasive tree common within riparian areas in the western United States. Control methods can be expensive and regular monitoring is necessary to control stump and root sprouts, and newly established seedlings. Studies have assessed scarification and cold treatment effects on germination and establishment of Russian olive seeds. However, fire effects on seeds and newly emerged seedlings have not been documented. Russian olive seeds were subjected to fire at three fuel loads (1,500, 3,000, and 4,500 kg/ha) and a non-burned control. With no fire, 40% of seeds germinated and fire at any of the three fuel loads reduced germination. Germination was reduced to one-fifth of the non-burned level with fire at the 1,500 kg/ha fuel load and did not differ from 0% at the 4,500 kg/ha(-1) fuel load. The probability of at least one seed germinating from 50-seed lots decreased as all measures of temperature and time-temperature increased. Fire killed all but one of the 250 seedlings tested, indicating Russian olive seedlings at 10 weeks old or younger were highly susceptible to fire-induced mortality. However, some seedlings did not die immediately following fire and produced new axillary buds. Although all but one seedling died, bud production after fire was interpreted as an indicator of potential resistance to fire. Our results indicate that fire does not enhance Russian olive seed germination and is deleterious to seed viability. Fire could potentially kill most Russian olive seedlings that are less than 1 year old.