Epicormic strand structure in Angophora, Eucalyptus and Lophostemon (Myrtaceae) -: implications for fire resistance and recovery

Epicormic bud producing structures in the eucalypts, a large group of woody plants of considerable ecological, horticultural and silvicultural importance, are described here. The outer portion of epicormic strands excised from the bark of large diameter stems of 18 Eucalyptus species, two Angophora species and Lophostemon contertus was examined anatomically in semithin sections. In the inner bark each eucalypt strand usually possessed 5-12 radially orientated strips of tissue of meristematic appearance. The meristem strips were c. 30-50 mum high, 70-110 mum wide and 2000-10 000 mum long, with a lacuna above the meristem surface. Few buds or bud primordia were associated with the strands and the strands appeared to have a reduced regenerative potential in the outer bark. In most angiosperm trees dormant epicormic buds are present in the outer bark, a position where they could be killed by fire. By contrast, in eucalypts the greatest epicormic bud initiation potential is at the level of the vascular cambium, which is protected by the maximum bark thickness. This might explain the pronounced ability of eucalypts to produce bole and branch epicormic shoots after moderate to intense fire.