Bark thickness determines fire resistance of selected tree species from fire-prone tropical savanna in north Australia Michael J. Lawes • Anna Richards • Josefine Dathe • Jeremy J. Midgley Received: 20 May 2011 / Accepted: 4 August 2011 / Published online: 19 August 2011 Ó Springer Science+Business Media B.V. 2011 Abstract We investigated the fire resistance con- ferred by bark of seven common tree species in north Australian tropical savannas. We estimated bark thermal conductance and examined the relative importance of bark thickness, density and moisture content for protecting the cambium from lethal fire temperatures. Eucalypt and non-eucalypt species were contrasted, including the fire-sensitive conifer Callitris intratropica. Cambial temperature responses to bark surface heating were measured using a modified wick-fire technique, which simulated a heat pulse comparable to surface fires of moderate inten- sity. Bark thickness was a better predictor of resistance to cambial injury from fires than either bark moisture or density, accounting for 68% of the deviance in maximum temperature of the cambium. The duration of heating required to kill the cambium of a tree (s c ) was directly proportional to bark thickness squared. Although species did not differ significantly in their bark thermal conductance (k), the thinner barked eucalypts nevertheless achieved similar or only slightly lower levels of fire resistance than much thicker barked non-eucalypts. Bark thick- ness alone cannot account for the latter and we suggest that lower bark moisture content among the eucalypts also contributes to their apparent fire resistance. Unique eucalypt meristem anatomy and epicormic structures, combined with their bark traits, probably facilitate resprouting after fire and ensure the dominance of eucalypts in fire-prone savannas. This study emphasises the need to take into account both the thermal properties of bark and the mecha- nism of bud protection in characterising the respro- uting ability of savanna trees. Keywords Cambium  Bark thermal conductance  Bark density  Resprouting  Topkill Introduction Fire is an important driver of savanna tree dynamics worldwide. To recruit to reproductive size in fire- prone savannas juvenile trees especially, must avoid Electronic supplementary material The online version of this article (doi:10.1007/s11258-011-9954-7) contains supplementary material, which is available to authorized users. M. J. Lawes (&) Research Institute for the Environment and Livelihoods, Charles Darwin University, Darwin, NT 0909, Australia e-mail: Michael.Lawes@cdu.edu.au A. Richards CSIRO Ecosystem Sciences, PMB 44, Winnellie, NT 0822, Australia J. Dathe University of Applied Science, Eberswalde 16225, Germany J. J. Midgley Botany Department, University of Cape Town, P/Bag Rondebosch, Cape Town 7701, South Africa 123 Plant Ecol (2011) 212:2057–2069 DOI 10.1007/s11258-011-9954-7