The heat is on: frequent high intensity fire in bracken (Pteridium aquilinum) drives mortality of the sprouting tree Protea caffra in temperate grasslands Hylton Adie • Stephen Richert • Kevin P. Kirkman • Michael J. Lawes Received: 6 January 2011 / Accepted: 21 June 2011 / Published online: 23 July 2011 Ó Springer Science+Business Media B.V. 2011 Abstract We examined the effect of fire frequency and intensity on a Protea caffra tree population in the temperate montane grasslands of north-western KwaZ- ulu-Natal, South Africa. We assessed the effect of fire by comparing the population structure of the resprouter P. caffra in discrete bracken (Pteridium aquilinum) patches with that in the surrounding grassland matrix. Fuel biomass did not differ between grassland and bracken, but bracken fuel was significantly drier than grass. Above-ground fire temperatures and fireline intensity, measured by P. caffra char height, were significantly higher in the bracken habitat. Forty-two percent of the P. caffra population in grassland and in bracken persisted by coppice resprouts, having lost their original stem to fire damage. Exposure to higher intensity bracken fire suppressed P. caffra regeneration and caused greater adult mortality compared with trees in grassland. Consequently, the P. caffra population in bracken was skewed towards old age with most trees severely fire damaged. The high incidence of small trees in grassland indicates that a regular fire interval of 2–3 years does not negatively affect regeneration of P. caffra. However, in bracken patches regular high intensity fires cause high mortality among all P. caffra size classes and will ultimately result in local extinc- tion. Bracken thus has the potential to significantly alter tree–grass interactions in these montane grasslands. Keywords Fire behaviour  Topkill  Invasive plant  Resprouter  Tree–grass interaction Introduction Fire has a considerable effect on the structure and dynamics of plant communities and is a critical selection pressure on plant persistence traits (Pausas et al. 2004; Bond and Keeley 2005; Bond et al. 2005). Understanding the response of vegetation to varying fire regimes is a prerequisite to developing management strategies for fire-prone ecosystems for both conserva- tion- and production-based activities (Richardson et al. 1994; Bond 1997). Prescribed burning is an important management tool in rangelands where it maintains grass sward vigour, suppresses and removes undesir- able woody elements and reduces the risk of wildfires by reducing fuel accumulation (van Wilgen et al. 1990; Everson et al. 2004). The relative impacts of fire H. Adie  K. P. Kirkman  M. J. Lawes (&) School of Biological and Conservation Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville 3209, South Africa e-mail: Michael.Lawes@cdu.edu.au S. Richert KZN Wildlife, P.O. Box 13069, Cascades 3202, South Africa M. J. Lawes Research Institute for the Environment and Livelihoods, Charles Darwin University, Darwin, NT 0909, Australia 123 Plant Ecol (2011) 212:2013–2022 DOI 10.1007/s11258-011-9945-8