title: Savanna fire and the origins of the 'underground forests' of Africa.
abstract: The origin of fire-adapted lineages is a long-standing question in ecology. Although phylogeny can provide a significant contribution to the ongoing debate, its use has been precluded by the lack of comprehensive DNA data. Here, we focus on the 'underground trees' (=geoxyles) of southern Africa, one of the most distinctive growth forms characteristic of fire-prone savannas. We placed geoxyles within the most comprehensive dated phylogeny for the regional flora comprising over 1400 woody species. Using this phylogeny, we tested whether African geoxyles evolved concomitantly with those of the South American cerrado and used their phylogenetic position to date the appearance of humid savannas. We found multiple independent origins of the geoxyle life-form mostly from the Pliocene, a period consistent with the origin of cerrado, with the majority of divergences occurring within the last 2 million yr. When contrasted with their tree relatives, geoxyles occur in regions characterized by higher rainfall and greater fire frequency. Our results indicate that the geoxylic growth form may have evolved in response to the interactive effects of frequent fires and high precipitation. As such, geoxyles may be regarded as markers of fire-maintained savannas occurring in climates suitable for forests.
authors.affiliation: African Centre for DNA Barcoding, Department of Botany & Plant Biotechnology, University of Johannesburg, PO Box 524, Auckland Park, 2006, Johannesburg, Gauteng, South Africa.
authors.forename: Olivier
authors.initials: O
authors.lastname: Maurin
authors.affiliation: African Centre for DNA Barcoding, Department of Botany & Plant Biotechnology, University of Johannesburg, PO Box 524, Auckland Park, 2006, Johannesburg, Gauteng, South Africa.|Department of Biology, McGill University, 1205 Ave Docteur Penfield, Montreal, QC, H3A 0G4, Canada.
authors.forename: T Jonathan
authors.initials: TJ
authors.lastname: Davies
authors.affiliation: Buffelskloof Herbarium, PO Box 710, Lydenburg, 1120, South Africa.|Department of Plant Sciences, University of Pretoria, Private Bag X20, Hatfield, 0028, Pretoria, South Africa.
authors.forename: John E
authors.initials: JE
authors.lastname: Burrows
authors.affiliation: African Centre for DNA Barcoding, Department of Botany & Plant Biotechnology, University of Johannesburg, PO Box 524, Auckland Park, 2006, Johannesburg, Gauteng, South Africa.
authors.forename: Barnabas H
authors.initials: BH
authors.lastname: Daru
authors.affiliation: African Centre for DNA Barcoding, Department of Botany & Plant Biotechnology, University of Johannesburg, PO Box 524, Auckland Park, 2006, Johannesburg, Gauteng, South Africa.|Department of Environmental Sciences, University of South Africa, Florida Campus, Florida, 1710, Gauteng, South Africa.
authors.forename: Kowiyou
authors.initials: K
authors.lastname: Yessoufou
authors.affiliation: Department of Biological Sciences, University of Cape Town, Rondebosch, 7701, Western Cape, South Africa.
authors.forename: A Muthama
authors.initials: AM
authors.lastname: Muasya
authors.affiliation: African Centre for DNA Barcoding, Department of Botany & Plant Biotechnology, University of Johannesburg, PO Box 524, Auckland Park, 2006, Johannesburg, Gauteng, South Africa.
authors.forename: Michelle
authors.initials: M
authors.lastname: van der Bank
authors.affiliation: Department of Biological Sciences, University of Cape Town, Rondebosch, 7701, Western Cape, South Africa.|South African Environmental Observation Network, Private Bag X7, 7735, Rhodes Drive, Newlands, Western Cape, South Africa.
authors.forename: William J
authors.initials: WJ
authors.lastname: Bond
mesh_terms: D000220:Adaptation, Biological; D000349:Africa; D044822:Biodiversity; D005075:Biological Evolution; D001938:Brazil; D017753:Ecosystem; D005390:Fires; D065928:Forests; D065948:Grassland; D010802:Phylogeny
keywords: Pliocene; fire adaptation; geoxylic suffrutex; phylogeny; savanna; trees of southern Africa; underground forests