Fire and invasive species: Modifications in the germination potential of Acacia melanoxylon, Conyza canadensis and Eucalyptus globulus

This study attempts to understand the effect of the main fire factors (smoke, ash and heat) on the germination of three invasive species widely distributed in many countries: Acacia melanoxylon, Conyza canadensis and Eucalyptus globulus. Fifteen simple treatments were tested: 3 of Smoke, 3 of Ash, 8 of Heat, and 1 Control (Control 1). In addition, in C. canadensis a second test was performed using 4 combined treatments: Smoke-Ash, Smoke-Heat, Ash-Heat, Smoke-Ash-Heat and Control 2.The seeds were incubated in a germination chamber with a photoperiod of 16 h of light at 24 °C and 8 h of darkness at 16 °C.Three species showed different responses from fire factors. Smoke and ash treatments did not modify the germination percentage of A. melanoxylon, but moderate heat increased germination and severe heat significantly decreased it. Moreover, some treatments significantly decreased germination rate. C. canadensis germination was increased by moderate levels of all the factors tested, whilst high levels of fire delayed and reduced germination. The combined action of the fire factors did not modify the germination percentage, but did reduce the germination rate. E. globulus had low germination in Control 1 and none of the tested treatments modified either percentage or rate of germination. Finally, regenerative aspects of the three species are discussed.

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► The germination behaviour is related to regeneration strategies of each species.
► Conyza canadensis germination is stimulated by fire.
► Moderate heat shocks increase Acacia melanoxylon germination.
► Eucalyptus globulus has low germination and it is independent from fire.