FRUIT CLUSTERING IN THE MYRTACEAE - SEED SURVIVAL IN CAPSULES SUBJECTED TO EXPERIMENTAL HEATING

The effect of the natural clustering of capsules on seed insulation was investigated by heating mature capsules of Kunzea ambigua in a muffle furnace at 250-degrees-C for up to 5 min. Survival of the encapsulated seed of K. ambigua was higher when capsules were retained in their natural aggregates than when individual fruits were heated. Seed within clustered K. ambigua fruits also survived heating for longer periods than in individual capsules of both Leptospermum laevigatum and Eucalyptus regnans, species which depend heavily on encapsulated seed for post-fire regeneration. The clustered arrangement of sessile K. ambigua capsules reduces exposure to external heat sources by protecting the base and sides of the capsule. Given that any delay in heat penetration may be critical to seed survival, fruit clustering could be an important adaptation to fire by K. ambigua and other similar small-fruited Myrtaceae. The limited survival times of seed within individual capsules of the three species tested support evidence that survival of encapsulated seed during fire is largely possible due to brief flame residence times in individual shrub and tree canopies.