Evidence for direct effects of fire-cues on germination of some perennial forbs common in grassy ecosystems

In grassy ecosystems of south-eastern Australia, fire maintains richness of native forbs. It is commonly thought that fire promotes regeneration indirectly by reducing competition for light and providing gaps for recruitment, rather than directly stimulating germination. However, physiological dormancy and morphophysiological dormancy are common, and few studies have explored responses to fire-cues among dormant or hard-to-germinate forbs. Recent studies from other fire-prone ecosystems suggest that in some cases, fire-cues may not alleviate physiological or morphophysiological dormancy, but instead promote germination in combination with treatments which alleviate dormancy. We experimentally tested the prevailing hypothesis that perennial forbs common in south-eastern Australian grassy ecosystems do not germinate in direct response to fire. Responses to fire-cues both inherently and in combination with treatments which alleviate dormancy were investigated for seven species. Two fire-cues (smoke and heat) plus a treatment of both heat + smoke were applied to fresh seed at three temperatures (35/25 degrees C, 30/20 degrees C and 25/15 degrees C). Following this, the effect of fire-cues on seed that had undergone warm stratification, cold stratification and dry-after-ripening was investigated. Three species - Arthropodium strictum, Cheiranthera cyanea and Dianella revoluta - responded to fire-cues inherently, although germination in C. cyanea was low. High germination of D. revoluta was found when fire-cues were combined with warm stratification. Fire-cues had no effect on germination of Brunonia australis, Burchardia umbellata and Eryngium ovinum. Germination of Stypandra glauca was zero following all treatment combinations. Our finding that fire-cues promote germination of three of the seven study species did not provide sufficient evidence to reject the current hypothesis that germination of perennial forbs is not typically promoted by fire-cues. However, this study highlights the important direct role fire-cues can play in promoting germination of some perennial forbs both inherently and in combination with treatments used to alleviate physiological dormancy.