Impacts of repeated fuel reduction burning on tree growth, mortality and recruitment in mixed species eucalypt forests of southeast Queensland, Australia

Abstract

The long-term effects of repeated prescribed burning on diameter growth of trees in mixed species dry and wet sclerophyll forest sites in southeast Queensland, Australia were assessed. In addition, fire effects on tree mortality and recruitment in the wet sclerophyll site were evaluated. The results show that growth responses of species to fire were variable. Nevertheless, for most species, recurrent burning had no deleterious effect on tree growth. At the dry sclerophyll site, annual burning since 1952 did not affect growth rates of Eucalyptus drepanophylla and E. acmenoides. On the other hand, E. tereticornis responded positively to annual burning. Smaller Corymbia variegata (formerly Eucalyptus maculata) trees appeared to respond positively to annual burning, while larger trees appeared to respond negatively but this response lessened over time. Periodic burning (every 2–3 years) since 1973 did not significantly affect the growth rates of any tree species. At the wet sclerophyll site, biennial burning since 1972 has enhanced the diameter growth of Lophostemon confertus but depressed that of Syncarpia glomulifera. Quadrennial burning did not affect the diameter growth of L. confertus but depressed that of S. glomulifera. The diameter growth of E. pilularis, C. intermedia, E. microcorys and E. resinifera was not affected by either burning treatment. Basal area growth of most eucalypts at this site was unaffected by burning. However, basal area growth of both S. glomulifera and L. confertus was adversely affected by burning due to tree mortality. For most species, tree mortality was both diameter-dependent and fire-related, that is, smaller trees have a lower chance of survival than larger trees and frequent burning further reduces this probability. Without fire, recruitment was dominated by S. glomulifera and to a lesser extent by L. confertus. Recruitment of these species was adversely affected by burning. This result and the greater mortality of smaller trees with frequent burning suggest that if these trends continue, future stand growth and hence productivity of these species could be jeopardized because of the reduction of the regenerative capacity of the forest. Recruitment was negligible for other tree species in this forest regardless of fire treatment.