Fire is often used in northern grasslands to control invasive grass species but has unknown effects on Tamarix spp., more recent invaders. Temperature (using an oven as a fire surrogate) and duration combinations that would be most lethal to Tamarix seeds and seedlings were determined. Tamarix seeds were sown in soil-lined dishes, water added to saturation, and seedlings grown for 1 to 5 d. Seeds were also placed in water-saturated or dry soil just before temperature exposure (79 to 204 C [175 to 400 F]) by duration (1 to 5 min) treatments. After treatment, soil water loss was measured by weight difference, and surviving seedlings were counted for 6 d. Tamarix seedling establishment and survival decreased with increasing temperature and duration. The 5-d-old seedlings were the most affected. No 5-d-old seedlings survived 1- and 2-min exposures to 204 C, whereas 1-d-old seedlings had greater than 25% survival. If soils were saturated, two to four times more seedlings established following seed exposure to 177 and 204 C. Longer durations at lower temperatures were required to reduce Tamarix survival. Increasing duration from 2 to 5 min at 121 C decreased 5-d-old seedling survival from more than 80% to less than 10% and eliminated those seedlings at 149 C. Five minutes at 149 C decreased dry-soil seed viability to about 15%, whereas germination on saturated soils remained high (∼75%). No seeds survived the exposure to 177 and 204 C. Soil moisture loss values associated with 90% mortality of 5- and 1-d-old seedlings were 1.7 and 2.2%, respectively. On saturated soils, 90% of seeds died with 2.5% water loss. Under suitable conditions, fire can decrease Tamarix seedling survival. Fire may be useful for controlling Tamarix seedlings in northern grasslands and should be considered for management of new invasions.
Nomenclature: Tamarix spp.: Chinese tamarisk, Tamarix chinensis Lour. TAACH; saltcedar, Tamarix ramosissima Ledeb. TAARA.
Management Implications: Tamarix can invade moist-soil grasslands in the Northern Great Plains, and it is necessary to treat seedlings before they become well-established. Fire is an important management tool used to control nonnative grasses in northern grasslands, but this practice may also minimize Tamarix spread from seed. Although temperatures and durations associated with prescribed grassland fire are reported to be minimal, under appropriate conditions controlled burns in northern grasslands can provide soil surface temperatures and exposure periods lethal to most Tamarix seeds and developing seedlings. Deposited seeds are more likely to survive elevated temperatures than newly emerging seedlings but because seeds germinate rapidly upon wetting, fire will more likely encounter seedlings. To effectively control new infestations, Tamarix seedlings should be treated before they develop belowground perennating buds that generate new shoots following dormancy or disturbance. Repeated burning regimes are less likely to increase nonnative invasions in grasslands than other habitats suitable for Tamarix establishment because these ecosystems have evolved with this disturbance. Fire is, therefore, a viable option for Tamarix seedling control in northern grasslands, but burn programs should not target this species until more information is available.