Vegetation Dynamics in the Forest-Savanna Boundary

During my MSc studies, the theory that forest and savanna represent alternative stable biome states (ABSS) was emerging. I knew little about savanna ecology back then! It is actually surprising that savanna occupies about 70% of the land area in Ghana yet there was hardly any savanna ecology course during my bachelors. There was no better way to transition from my forest ecology biased perspectives to savanna ecology than to study the vegetation dynamics in the forest-savanna boundary (FSB). The FSB is particularly interesting because this is where forest and savanna meet and often occur under similar climatic conditions. Two feedback systems maintain dry forest and savanna vegetations in the FSB. Fire, carried by grass, limit tree establishment in savannas thereby maintaining an open vegetation. In forest, closed canopy cover constrains grass growth and hence preclude frequent and intense fires thereby creating an environment conducive for establishment of forest species. These alternative feedback systems are known to drive divergence in species composition between forest and savanna.

For my master’s thesis research (supervised by Dr. Elmar Veenendaal and Dr. Frank van Langevelde), I was interested in establishing if neighbouring forest and savanna in the FSB in Ghana contained distinct species and traits (as was being elegantly demonstrated by William Hoffmann for South America). Further, I investigated whether these contrasting feedbacks also lead to compositional decoupling of the overstorey and understorey woody communities in forest and savanna vegetations. We showed that although forest and savanna species dominated the over- and understories of their respective environment, only few (< 35%) of the dominant species were present in both strata. Our results indicated that juveniles of dominant overstorey forest and savanna species face significant establishment and recruitment bottlenecks even in their respective environments. This work is published in Plant Ecology & Diversity and can be found here.

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