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Fixed or mixed? Variation in tree functional types and vegetation structure in a forest-savanna ecotone in West Africa

Published online by Cambridge University Press:  23 July 2020

George K.D Ametsitsi ,
Frank Van Langevelde ,
Vincent Logah Open the ORCID record for Vincent Logah [Opens in a new window] ,
Thomas Janssen Open the ORCID record for Thomas Janssen [Opens in a new window] ,
Jose A Medina-Vega ,
Hamza Issifu ,
Laurianne Ollivier ,
Koos den Hartogh ,
Thomas Adjei-Gyapong  and
Stephen Adu-Bredu
...Show all authors
George K.D Ametsitsi
Affiliation:
Plant Ecology and Nature Conservation Group, Wageningen University, 6700 AAWageningen, the Netherlands Forestry Research Institute of Ghana, P.O. Box 63, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana
Frank Van Langevelde
Affiliation:
Wildlife Ecology and Conservation Group, Wageningen University, 6700 AAWageningen, the Netherlands School of Life Sciences, Westville Campus, University of KwaZulu-Natal, Durban4000, South Africa
Vincent Logah
Affiliation:
Department of Crop and Soil Sciences, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana
Thomas Janssen
Affiliation:
Plant Ecology and Nature Conservation Group, Wageningen University, 6700 AAWageningen, the Netherlands Department of Earth Sciences, VU Amsterdam, Boelelaan 1085, 1081 HVAmsterdam, the Netherlands
Jose A Medina-Vega
Affiliation:
Plant Ecology and Nature Conservation Group, Wageningen University, 6700 AAWageningen, the Netherlands Forest Ecology and Forest Management group, Wageningen University, 6700 AAWageningen, the Netherlands
Hamza Issifu
Affiliation:
Plant Ecology and Nature Conservation Group, Wageningen University, 6700 AAWageningen, the Netherlands Department of Forestry and Forest Resources Management, University for Development Studies, P.O. Box 1882, Tamale, Ghana
Laurianne Ollivier
Affiliation:
Plant Ecology and Nature Conservation Group, Wageningen University, 6700 AAWageningen, the Netherlands
Koos den Hartogh
Affiliation:
Plant Ecology and Nature Conservation Group, Wageningen University, 6700 AAWageningen, the Netherlands
Thomas Adjei-Gyapong
Affiliation:
Department of Crop and Soil Sciences, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana
Stephen Adu-Bredu
Affiliation:
Forestry Research Institute of Ghana, P.O. Box 63, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana
Jon Lloyd
Affiliation:
Department of Life Sciences, Imperial College London, Silwood Park Campus, AscotSL5 7PY, UK School of Marine and Environmental Sciences, James Cook University, Cairns, 4870Qld, Australia Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, 14040-900Ribeirão Preto, Brazil
Elmar M Veenendaal*
Affiliation:
Plant Ecology and Nature Conservation Group, Wageningen University, 6700 AAWageningen, the Netherlands
*
Author for correspondence: *Elmar M Veenendaal, Email: Elmar.Veenendaal@wur.nl
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Abstract

We analysed thirty-five 400-m2 plots encompassing forest, savanna and intermediate vegetation types in an ecotonal area in Ghana, West Africa. Across all plots, fire frequency was over a period of 15 years relatively uniform (once in 2–4 years). Although woodlands were dominated by species typically associated with savanna-type formations, and with forest formations dominated by species usually associated with closed canopies, these associations were non-obligatory and with a discrete non-specialized species grouping also identified. Across all plots, crown area index, stem basal area and above-ground biomass were positively associated with higher soil exchangeable potassium and silt contents: this supporting recent suggestions of interplays between potassium and soil water storage potential as a significant influence on tropical vegetation structure. We also found an average NDVI cover increase of ~0.15% year−1 (1984–2011) with plots dominated by non-specialized species increasing more than those dominated by either forest- or savanna-affiliated species. Our results challenge the traditional view of a simple forest vs. savanna dichotomy controlled by fire, and with our newly identified third non-specialized species grouping also potentially important in understanding ecotonal responses to climate change.

Keywords

Alternate stable statescanopy coverforest-savanna ecotonesoil propertiesvegetation structure
Type
Research Article
Information
Journal of Tropical Ecology , Volume 36 , Issue 4 , July 2020 , pp. 133 - 149
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Copyright
© The Author(s), 2020. Published by Cambridge University Press

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