Influence of Fire and Edaphic Factors on Germination of the Arid Zone Shrubs Acacia aneura, Cassia nemophila and Dodonaea Viscosa

Abstract

The germination of some shrub species may be enhanced following fire in shrublands and woodlands. This paper reports the germination response of Acacia aneura, Cassia nemophila and Dodonaea viscosa - common shrub species in semi-arid and arid woodlands - to laboratory fires over a range of intensities and durations.

Seeds were subjected to fires of different intensities in the controlled environment of a glasshouse. Depth of seed placement in the soil, soil moisture level and amount and type of fuel influenced the percentage of seeds that germinated. Amounts of shredded paper fuel, equivalent to typical grass fuel levels in semi-arid woodlands did not enhance the germinability of seeds of any of the species, except for A. aneura on a moist or wet soil surface. A high, dense fuel load (simulating slow burning, low- intensity litter fires) either increased or decreased the germinability of surface and buried seeds of all species, depending upon soil moisture level and depth of seeds. The germination response to the heat of fires differed significantly between species: A . Aneura germination increased substantially at low levels of peak temperature up to 60°C whereas germination of C. nemophila increased to a lesser extent and D. viscosa was not affected at all over this low temperature range. Seeds of all species were killed by slow burning litter fires when the temperature exceeded 80°C. These results confirm the view that fire- promoted germination does not result from the burning of fine fuels per se but occurs only where there is litter buildup and when the soil temperature does not exceed the lethal threshold of 70-80°C.