INVASIVE PLANT MANAGEMENT IMPROVED BY FIRE
Restoration of historic fire regimes is complicated by concerns about exotic plant invasions, yet little is known of how the two may interact. Seeds of Japanese brome, spotted knapweed, Russian knapweed and leafy spurge were subjected to fire at six fuel loads (100 to 700 g m22) and a nonburned control. Fires were simulated with field-cured grass and time- temperature profiles were developed from thermocouples at the soil surface.
Emergence was determined by species and fuel load in growth chambers. Fuel load explained 98 percent of variation in mean heat dosage and emergence decreased with increasing fuel load across species. Emergence was reduced 79 to 88 percent relative to nonburned treatment with 100 g m22 of fuel and at least 97 percent with 200 g m22 of fuel. Emergence probabilities were less than 0.01 for all species but spotted knapweed with a 300 g m22 fuel load. Results indicate high potential for fire to disrupt the life cycle of invasive species through direct seed mortality. The relationship between fuel load and seedling emergence provides good predictability of fire effects on surface deposited seeds. A single fire is unlikely to eradicate many invasive species because they often produce abundant seeds and some will undoubtedly escape fire.
However, abrupt reductions in seedli emergence with relatively light fuel loads indicate that fire may be an effective tool for increasing mortality of invasive plant seed across a broad range of habitats.