School of Geography - Theses
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ItemGermination response of species with soil seed banks to heat treatment and fuel reduction burning( 1996)The effects of heat on seed germination were tested for a broad range of taxonomic groups and life forms of plants growing in fire prone open woodland/heathland communities of northwestern Victoria. Thirty-two species characterised by storage of seeds in the soil (soil seed bank) were tested for germination response to temperatures of 20 (i.e. control), 40, 60, 80, 100 and 120C. Germination response to heat treatment varied between species. Heat stimulated germination was important for a broad range of taxa and life forms. Twelve species ranging across the families Fabaceae, Mimosaceae, Myrtaceae, Proteaceae, Asteraceae, Sterculiaceae and Iridaceae required heat for seed germination. Maximum germination in these species occurred at temperatures between 60 and 120C. Twelve further species ranging across the families Mimosaceae, Liliaceae, Myrtaceae, Asteraceae, Proteaceae, Juncaceae, Fabaceae, and Poaceae could germinate without heat, but were also tolerant of heat. Only one species (Bursaria spinosa; Pittosporoaceae) was adversely affected by heat, showing maximum germination at 20C. Seven species showed no germination response to any treatment. Heat induced mortality occurred at 100C for some species and at 120C for others, however, twelve species could tolerate temperatures of at least 120C. In an attempt to link seed germination requirements to conditions experienced in the field during fire, soil temperatures at depths of 1, 3 and 5 cm were measured during spring and autumn prescribed burns (i.e. fuel reduction burns). Temperatures that were found to stimulate seed germination in the laboratory were experienced in the surface layers of the soil, but to varying degrees, depending on the plant community and season of burn. Soil temperatures were highly spatially variable. Temperature maxima declined with increasing soil depth, such that temperatures were almost always <65C at 5 cm. As such species requiring temperatures z60C are unlikely to germinate from this depth. Autumn fires were hotter and more uniform than spring burns. Temperatures likely to stimulate germination (i.e. z60C) were experienced at 5 cm during autumn fires in some vegetation types, while heat-stimulated germination would be limited to the top 1 cm of soil during spring burns. Fires in autumn are more likely to provide suitable germination temperatures for species requiring heat for seed germination, and since many species could tolerate seed heating, these are unlikely to be adversely affected by the hotter autumn burns. Soil temperatures during spring burns generally remained <65C regardless of depth. Thus, seed germination would be limited to species requiring temperatures lower than this. These results have important implications for fire management in relation to seed germination and post-fire recruitment from the soil seed bank.