THE EFFECT OF FIRE ON EUCALYPTS RESERVED FOR SEEDING

Abstract

SUMMARY This paper discusses the effects of fire on the ability of specially reserved trees of Eucalyptus regnans, E. obliqua, and E, delegatensis (syngigantea) to produce a useful supply of seed for the regeneration of logged areas with a dense understorey of rain forest or wet sclerophyll scrub. Observations are given on the fire resistance of these eucalypts at different ages and in different environments. The ecological consequences of various combinations of fire resistanos and types of fire are discussed. The surface of the ground, in the moist cool forests of Tasmania, usually accumulates much raw humus. At the butts of mature eucalypts the humus forms a mound of amorphous, peaty, combustible material at least.several inches, and commonly several feet, deep. The humus can burn only after an unusually dry summer. A fire which consumes it will kill or severely injure all local tree species almost irrespective of bark thickness. Death is due to the killing of the cambium where the humus was burnt in contact with the bark. On the other hand, a fire which consumes only the surface fuels and leaves the humus intact will be much less injurious, especially to trees with thicker bark. Even a complete scorching of the crown is rarely lethal without trunk girdling. Fire may accelerate the abscission of twigs, leaves, capsules and immature floral parts. The abscission of capsules is accompanied by accelerated seed shed. Immature floral parts do, however, often survive in good numbers provided the twig subtending them survives. Twigs may be killed either from girdling of the tree or by being directly scorched by radiant heat. The leaves and floral parts on killed twigs die, but are not abscissed. Seed shed occurs as soon as the capsules dry out. Seeds inside the capsules on the tree often survive in good numbers. Because of these findings and because burnt ground becomes relatively unreceptive to eucalypt seed after 1–2 years, owing to excessive weed growth, it is unwise to rely on regeneration from any.seed crop which is not mature at the time of the fire.