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Submitted to: Weed Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 1/8/2009 Publication Date: 5/1/2009 Citation: Vermeire, L.T., Rinella, M.J. 2009. Fire Alters Emergence of Invasive Plant Species from Soil Surface-Deposited Seeds. Weed Science 57:304-310. Interpretive Summary: 1. Fire is recognized as an important process controlling ecosystem structure and function. Restoration of fire regimes is complicated by global concerns about exotic plants invasions, yet little is known of how the two may interact. Characterizing relationships between fire conditions and the viability of invasive plant propagules is required to facilitate restoration and prevent invasions. 2. Seeds of Japanese brome, spotted knapweed, Russian knapweed, and leafy spurge were subjected to fire at six fuel loads (890-6240 lb ac-2) and a non-burned control. Fires were simulated with field-cured grass and time-temperature profiles were developed from thermocouples at the soil surface. Seeds were placed in growth chambers to determine percent emergence for each species and fuel load. Probabilities of emergence were estimated using a Bayesian approach. 3. Fuel load explained 98% of variation in mean heat dosage and fire reduced emergence for all species. Emergence was reduced 80-86% relative to non-burned treatment with 890 lb ac-2 of fuel and at least 95% with 1783 lb ac-2 of fuel. 4. Probability of emergence decreased with increasing fuel load and was less than 0•01 for all species but C. maculosa with a 2674 lb ac-2 fuel load. A small portion of leafy spurge seeds emerged at all fuel loads tested. 5. Synthesis and applications. Results indicate high potential for fire to reduce colonization and expansion of invasive plant species through seed mortality. Although fire intensity will vary with field conditions, the relationship between fuel load and seedling emergence provides good predictability of fire effects on surface-deposited seeds. Heat exposure during fire is expected be greater above the soil surface, but decrease rapidly with depth in the soil. A single fire is unlikely to eradicate many invasive species because they often produce abundant seeds, some of which will escape fire. Furthermore, perennial invasive plants may sprout from uninjured meristems and rebuild the seed bank. However, abrupt reductions in seedling emergence with relatively light fuel loads indicate fire may be an effective tool for reducing invasive plant seed availability across a broad range of habitats. Technical Abstract: 1. Fire is recognized as an important process controlling ecosystem structure and function. Restoration of fire regimes is complicated by global concerns about exotic plants invasions, yet little is known of how the two may interact. Characterizing relationships between fire conditions and the viability of invasive plant propagules is required to facilitate restoration and prevent invasions. 2. Seeds of Bromus japonicus, Centaurea maculosa, Acroptilon repens, and Euphorbia esula were subjected to fire at six fuel loads (100-700 g m-2) and a non-burned control. Fires were simulated with field-cured grass and time-temperature profiles were developed from thermocouples at the soil surface. Seeds were placed in growth chambers to determine percent emergence for each species and fuel load. Probabilities of emergence were estimated using a Bayesian approach. 3. Fuel load explained 98% of variation in mean heat dosage and fire reduced emergence for all species. Emergence was reduced 80-86% relative to non-burned treatment with 100 g m-2 of fuel and at least 95% with 200 g m-2 of fuel. 4. Probability of emergence decreased with increasing fuel load and was less than 0•01 for all species but C. maculosa with a 300 g m-2 fuel load. A small portion of E. esula seeds emerged at all fuel loads tested. 5. Synthesis and applications. Results indicate high potential for fire to reduce colonization and expansion of invasive plant species through seed mortality. Although fire intensity will vary with field conditions, the relationship between fuel load and seedling emergence provides good predictability of fire effects on surface-deposited seeds. Heat exposure during fire is expected be greater above the soil surface, but decrease rapidly with depth in the soil. A single fire is unlikely to eradicate many invasive species because they often produce abundant seeds, some of which will escape fire. Furthermore, perennial invasive plants may sprout from uninjured meristems and rebuild the seed bank. However, abrupt reductions in seedling emergence with relatively light fuel loads indicate fire may be an effective tool for reducing invasive plant seed availability across a broad range of habitats. |
