Comparing germination stimuli of two alien invasive species and a native analogue: Towards sustainable management of invasives

Abstract

Invasive alien plants that have seeds with innate dormancy, and thus large, persistent soil-stored seed banks, are particularly difficult to manage. Dormant seeds typically require specific stimuli as cues for germination, resulting in mass recruitment. Sound understanding of germination stimuli may provide options to aid the management of invasives. We investigated the response of two invasive trees, Acacia mearnsii and A. melanoxylon, and an indigenous ecological analogue, Virgilia divaricata, to different germination stimuli (chipped (manually), hot water exposure, dry heat pulse, smoke, and no treatment) at two temperature regimes (winter ~12°C and summer ~20°C) to explore how their germination requirements may be used to favour V. divaricata in areas cleared of the invasives. Chipped and hot water exposure resulted in the highest germination in all three species. Virgilia divaricata responded marginally better than the invasives to the dry heat pulse, particularly at 20°C. However, the three species mostly responded comparably to the stimulus–temperature combinations, suggesting that manipulation of stimuli is not a feasible option for management of the invasives at a large scale. In the absence of any stimulus (~akin to conditions associated with aboveground clearing of alien vegetation cover), germination was poorer in V. divaricata than in the invasive species especially at 20°C, providing motivation for focusing Acacia management operations in cooler seasons in areas where V. divaricata seed banks occur. Another option is to sow V. divaricata seeds that have been chipped or exposed to hot water in areas cleared of the invasives of which the seeds would not have received stimuli.