Original article Temperature thresholds for germination and survival of Pittosporum undulatum: implications for management by fire 5 Roslyn M. Gleadow a,b, *, Indira Narayan a a School of Botany, The University of Melbourne, Melbourne, Victoria 3010, Australia b School of Biological Sciences, Monash University, Clayton, Victoria 3800, Australia article info Article history: Received 2 September 2005 Accepted 25 July 2006 Published online - Keywords: Invasion Fire Heat Environmental weed Seed Seedling Eucalyptus Pittosporum abstract One consequence of human-induced changes in fire regimes has been the invasion of fire- prone Mediterranean ecosystems by weeds from more mesic habitats. In southern Australia, the tree Pittosporum undulatum Vent. has established in new areas, causing a serious reduc- tion in floristic and structural diversity. Pittosporum undulatum has a high competitive ability and creates an environment that favours its own progeny at the expense of other species, making control difficult. We tested the hypothesis that fire effectively disrupts this invasion cycle by (1) eliminating the soil and canopy seed bank, (2) reducing the competitive ability of adults, and (3) minimising the number of sites favourable to invasion. To test this, the ability of P. undulatum to re-establish after a prescribed burn was estimated in a field study. The field data were then compared with the experimentally determined sensitivity of seeds and seed- lings to elevated temperatures. The experimentally determined combination of temperatures and exposure time required for seed mortality (90–120  C, depending on duration) was such that most seed stored in the canopy would be killed by prescribed burning. In addition, 90% of seedlings (ca. 0.4 m tall) were killed when heated to 180  C for 5–10 min in the laboratory, consistent with the observed 100% seedling mortality in the burnt plots. Of the adult trees, 20% resprouted within 6 months of the fire. We conclude that the temperatures associated with wildfires are sufficient to act as a circuit breaker on the invasion cycle allowing other control measures, such as poisoning and weeding to be employed to greater effect. ª 2006 Elsevier Masson SAS. All rights reserved. 1. Introduction Episodic fire is a key factor in maintaining diversity in most ecosystems which have a pronounced summer drought (Grubb and Hopkins, 1986). The impact of fire has been partic- ularly well studied in Mediterranean ecosystems on various continents (e.g. Tyler, 1995; Hanley and Fenner, 1998; Mills and Fey, 2005). Over the past 50,000 years there have been 5 This paper is dedicated to the late Dr David Ashton who inspired a generation of ecologists in Australia and initiated the research on Pittosporum undulatum in the 1970s. * Corresponding author. School of Biological Sciences, Monash University, Clayton, Victoria 3800, Australia. Tel.: þ61 3 9905 1667; fax: þ61 3 9905 1450. E-mail address: ros.gleadow@sci.monash.edu.au (R.M. Gleadow). available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/actoec ARTICLE IN PRESS 1146-609X/$ – see front matter ª 2006 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.actao.2006.07.003 acta oecologica xxx (2007) 1–7 Please cite this article in press as: Roslyn M. Gleadow, Narayan, I., Temperature thresholds for germination and survival of Pit- tosporum undulatum: implications for management by fire, Acta Oecolo. (2007), doi:10.1016/j.actao.2006.07.003