Ametsitsi, George K. D., Van Langevelde, Frank, Logah, Vincent, Janssen, Thomas, Medina-Vega, Jose A., Issifu, Hamza, Ollivier, Laurianne, den Hartogh, Koos, Adjei-Gyapong, Thomas, Adu-Bredu, Stephen, Lloyd, Jon, and Veenendaal, Elmar M. (2020) Fixed or mixed? Variation in tree functional types and vegetation structure in a forest-savanna ecotone in West Africa. Journal of Tropical Ecology, 36 (4). pp. 133-149.

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Abstract

We analysed thirty-five 400-m(2) 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 similar to 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.

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