Interaction of Fire, Temperature and Light in the Germination Response of 16 Species From the Eucalyptus marginata Forest of South-Western Australia.

Abstract

Germination responses to multiple conditions related to fire, temperature and light were examined and interpreted in relation to the environment of the jarrah (Eucalyptus marginata Donn ex Sm.) forest and the mediterranean-type climate of south-western Western Australia. Eight of the 16 selected representatives required a boiling pre-treatment as a simulation of fire before subsequent germination conditions were imposed. Trial conditions included a range of constant incubation temperatures and either a constant dark or 12h light:12h dark illumination cycle. Species common to the understorey tended to have narrow optima to temperature (13-18°C) with the greatest germination being achieved in temperatures typical of winter. Eucalyptus calophylla, one of the canopy species, germinated over a wider range of temperatures than the understorey species tested. Several species (e.g. Acacia pulchella var. glaberrima, Calothamnus rupestris, Eucalyptus marginata, Trymalium ledifolium, Xanthorrhoea gracilis and X. preissii) were not affected by the different light conditions at lower incubation temperatures, but more seeds remained dormant under higher temperatures when exposed to light. Most species, however, germinated best under continuously dark conditions, which related to being buried under soil. Two species, Banksia grandis and Hakea amplexicaulis, showed much higher germination under light exposure conditions compared to continuously dark conditions. These two serotinous species are large seeded and their seed ecology favours large gap and soil surface establishment. The multiple requirements of particular combinations of fire, temperature and light are related to the ecology of these native Western Australian species.