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

2020

English

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 nonspecialized species grouping also potentially important in understanding ecotonal responses to climate change.

Ametsitsi, G. K. D.; Langevelde, F. V.; Logah, V.; Janssen, T.; Medina-Vega, J. A.; Issifu, H.; Ollivier, L.; Hartogh, K. D.; Adjei-Gyapong, T.; Adu-Bredu, S.; Lloyd, J.; Veenendaal, E. M.