Journal of Vegetation Science && (2013) Investigating potential determinants of the distribution limits of a savanna woody plant: Colophospermum mopane Nicola Stevens, Anthony M. Swemmer, Leanne Ezzy & Barend F.N. Erasmus Keywords Climate change; Kruger National Park; MAXENT; Mopane; Range limits; Savanna; South Africa; Species distribution modelling Nomenclature Arnold & De Wet (1993) Received 12 July 2012 Accepted 6 May 2013 Co-ordinating Editor: David Ward Stevens, N. (corresponding author, nicolastvns@gmail.com): Natural Resources and the Environment, CSIR, PO Box 395, Pretoria, 0001, South Africa Stevens, N. : Department of Botany, University of Cape Town, Private Bag X3, Rondebosch, 7701, South Africa Swemmer, A.M. (tony@saeon.ac.za): South African Environmental Observation Network (SAEON) Ndlovu Node, Private Bag x1021, Phalaborwa, Kruger National Park, South Africa Ezzy, L. (leanne.ezzy@gmail.com): Queensland Parks and Wildlife, PO Box 5597, Townsville, Qld, 4810, Australia Erasmus, B.F. (Barend.Erasmus@wits.ac.za): Centre for African Ecology, School of Animal Plant and Environmental Sciences, University of the Witwatersrand, Private Bag 3, Wits, 2050, South Africa Abstract Questions: Early bioclimatic models predict that climate change in southern African savannas will cause a huge southward and westward range shift of the savanna tree Colophospermum mopane (Kirk ex Benth.) Kirk ex J.L eon. C. mopane is an economically and ecologically important subtropical savanna tree that forms mono-dominant stands across 30% of southern African savannas. We investigate the validity of these initial range expansion predictions to answer the following questions: what are the regional-scale drivers of the distribution of C. mopane in southern African savannas; and what are the landscape-scale distri- bution patterns of this species? Location: Central Lowveld, Kruger National Park, South Africa. Methods: We investigate the validity of very early range expansion modelling predictions using a regional-scale, climate envelope niche model, and fine-scale field mapping of the current boundary, to understand which environmental variables may determine the distribution limit of this signature species. Results: Our findings indicate that both non-climatic (dry season day length) and climatic (minimum temperatures) variables limit the regional distribution of C. mopane. At the landscape scale, the distribution of this species is restricted to the warmer parts of the landscape, suggesting minimum temperature appears to be the primary factor determining its landscape-scale distribution. Conclusions: This study provides the first detailed model of environmental fac- tors that may limit the regional distribution of C. mopane, and allows us to for- mulate testable hypotheses regarding the determinants of the range of a keystone species. Introduction The global distribution of plants is frequently attributed to climate, as it reflects the availability of moisture and energy for plant growth (Polis 1999; Gaston 2003; McInnes et al. 2009). This general understanding is often assumed to extend to plant communities occurring in subtropical savanna regions of the world, particularly at regional and continental scales. Recent research, however, indicates that non-climatic environmental factors (e.g. day length, fire and competition) can also significantly affect the distri- bution of plant communities at both regional and land- scape scales (Chuine & Beaubien 2001; Bond et al. 2005; Gaston 2009; Staver et al. 2011). We therefore investigated the regional determinants and landscape distribution pat- terns of an economically and ecologically important sub- tropical tree, Colophospermum mopane (Kirk ex Benth.) Kirk ex J. L eon, that occurs in semi-arid savannas of South Africa. We aim to understand the determinants in driving range limits of this keystone species as a necessary first step in improving the predictive understanding of its response to global climatic change. Colophospermum mopane is a dominant leguminous tree or multi-stemmed shrub in the Caesalpinoideae sub-fam- ily, which occurs in hot, low-lying regions of subtropical southern Africa. It is estimated to dominate, often in mono-specific stands, 30–35% of the 1.5 million km 2 (White 1983) of savanna in southern Africa (Mapaure Journal of Vegetation Science Doi: 10.1111/jvs.12098 © 2013 International Association for Vegetation Science 1