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Annals of Botany 73: 33-38, 1994
© 1994 Annals of Botany Company
Do Small Myrtaceous Seed-capsules Display Specialized Insulating Characteristics which Protect Seed During Fire?
School of Botany, University of Melbourne, Parkville Victoria, 3052, Australia
The internal temperatures of the seed-capsules of four Australian Myrtaceae were measured in response to a range of external temperatures produced by two different heat sources. The pattern of moisture loss from capsules and the relationship between capsule size and insulating capacity were also examined.
Intracapsular temperatures took up to 5 min (Leptospermum myrsinoides) to reach 100 °C when capsules were heated in a furnace at 200 °C but as little as 10 (Eucalyptus regnans) to 25 s (L. myrsinoides) when heated at 600 °C. Even briefer times were recorded when capsules were exposed to convective heat at similar temperatures. Capsule size was shown to be the primary determinant of insulating capacity and the results of an experiment employing a size series of tissue cores suggest that the two are linearly related. Moist capsules are better insulators than similarly sized but drier capsules. A high moisture content may improve insulation through partial thermal arrest in the capsule wall and/or the formation of an external boundary layer by escaping water vapour.
Despite their effectiveness during fire, this and related work establishes that small myrtaceous capsules have few, if any, remarkable properties as seed insulators. The presented data suggest that survival times for encapsulated seed are more likely to be in the order of seconds than minutes, further supporting the proposition that seed survival is largely dependent on brief flame residence times.Copyright 1994, 1999 Academic Press
Myrtaceae, Kunzea ambigua, Eucalyptus regnans, Leptospermum laevigatum, Leptospermum myrsinoides, seed-capsules, insulating capacity, fire