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Get ready to go—then follow the fire
Fire is an ecological factor in several parts of the world; in regions in which fires are especially prevalent there are plant species that exhibit adaptations for living in such situations and even for making use of the effects of fire in their life cycles. Thus there are species in which seed dormancy is broken by the heat of the fire and/or by the effects of smoke. However, there are other adaptive strategies in relation to germination after fire, as described by Ooi et al. (Wollongong and Hurstville, Australia, pp. 421–430). They work with ericaceous shrubs in the genus Leucopogon. The three species investigated, L. exolasius, L. setiger and L. esquamatus, all exhibit increased germination after a fire. However, it is clear from the authors’ work that fire does not break seed dormancy. Seeds removed from freshly dispersed fruit of all three species are unable to germinate even under favourable conditions; treatment with smoke and/or heat does not break this dormancy. The authors subjected dormant seeds to several different treatments; here we concentrate on those incubated in conditions that mimicked seasonal changes in temperature, including a normal range of day–night fluctuation appropriate for each season. Although the timings over the incubation period differed between the three species, it was clear overall that the seasonal temperature changes led to breakage of dormancy. In nature, this pattern of dormancy breakage leads to seedling emergence in the autumn. What then is the role of fire? Once dormancy was broken, smoke treatment slightly stimulates germination while heat is inhibitory. In general then, despite their occurrence in fire-prone areas, germination is not significantly affected by fire itself. It may well be that for these seed banking species, it is the creation of open ground (and hence the change in the light environment) by fire that is a major stimulus for germination once dormancy is broken.
Professor J. A. Bryant
University of Exeter, UK
j.a.bryant{at}exeter.ac.uk
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