Abstract:Termites are renowned ecosystem engineers. Their mounds have been described as an important element of savanna vegetation dynamics, but little is known about their large-scale impact on vegetation composition. To investigate the influence of termite-induced heterogeneity in savannas along a climatic gradient in West Africa termite mound vegetation was compared with adjacent savanna vegetation using 256 paired plots (size of the termite mound and a corresponding savanna area) in five protected areas from northern Burkina Faso to northern Benin. On each plot vegetation and soil sampling was performed. Additionally bioclimatic variables from the WORLDCLIM database were used. The vegetation on the mounds and the surrounding savanna differed within all study sites (DCA length of gradient 3.85 SD) and showed complete turnover along the climatic gradient (DCA length of gradient 5.99 SD). Differences between mounds and savanna were significantly related to termite-induced changes in soil parameters, specifically clay enrichment and increased cation concentrations (base saturation). On a local scale, termite-induced differences in soil conditions were found to be the most important factor affecting mound vegetation, while on a regional scale, annual precipitation showed the strongest significant correlations. However, with increasing precipitation, differences between mounds and the surrounding matrix became more pronounced, and the contribution of mounds to local phytodiversity increased. Eleven plant species were identified as characteristic termite mound species. In the more humid parts of the gradient, more characteristic plant species were found that may benefit from favourable soil conditions, good water availability, and a low fire impact in the mound microhabitat.

Questions Termite mounds are important sources of local‐scale soil heterogeneity and thereby affect savanna vegetation. Studies contrasting mound and savanna vegetation usually neglect variation between savanna types. We aim to answer the following questions: (1) is mound vegetation consistently different from the surrounding savanna vegetation at landscape scale; (2) is mound vegetation homogeneous across different savanna types; and (3) are differences between mound and savanna vegetation influenced more by nutrient accumulation or clay enrichment in mounds? Location Pendjari National Park, northern Benin. Methods We analysed the vegetation in 59 pairs of mound and savanna plots in four savanna types. We examined if mounds differed in community composition between savanna types, and from savanna plots using ordinations, and tested for correlations between community composition and soil parameters. We identified characteristic plant species for mounds in each savanna type using the IndVal method. Finally, we evaluated the relative importance of different soil parameters for differences in vegetation between mound and savanna plots using projection to latent structures regression (PLSR). Results There were clear differences between savanna types for both savanna and mound plant communities, and in each savanna type, clear differences emerged between mound and savanna vegetation. Community differences correlated with differences in soil parameters in all cases. We identified ten characteristic plant species for mounds, with little overlap between characteristic species from different savanna types. Across savanna types, 63% of the variation in mound – savanna vegetation contrast was explained by variation in nine soil parameters, most importantly clay content. Conclusion Even at the landscape scale, the influence of mounds on vegetation depends on habitat context. Thus, local mound vegetation patterns can only be understood considering the influence of different soil parameters in each savanna type. However, enrichment of clay and macronutrients together explain the largest part of the differences between mound and savanna vegetation. Further variation in vegetation composition among mounds is likely driven by biotic interactions and spatial distribution of mounds.

Particularly in savannas, termites are ecosystem engineers and a keystone group in ecology. For the understanding of the savanna vegetation, mound building termites are of particular interest. Due to their special soil chemistry and physical structure, termite mounds often host other plants than the surrounding savanna. As our knowledge of the specific contribution of mound-building termites to overall savanna diversity and ecosystem dynamics doubtlessly is not complete, this paper summarises the state of the art in order to stimulate further research. According to the research interest of the authors, focus is laid on the West African savanna and on the genus Macrotermes.

Termite mounds represent abundant microhabitats of high biodiversity in tropical savanna ecosystems and are an important source of landscape heterogeneity in Sub–Saharan West Africa. Floristic composition as well as density, structure and zonation of plant cover on the mounds were investigated in northern Benin and compared to the adjacent savanna vegetation. A total of 57 abandoned and densely vegetated termite mounds of comparable size and similarly affected by erosion  located  in different types of savannas inside and outside of the W National Park and in cotton fields were studied. This study revealed that termitaria are special habitats differing in density, composition and structure from surrounding savannas. The plant cover of termite mounds showed a distinctive zonation. Succulents, geophytes, and lianas were much more abundant on mounds, the family Capparaceae was found exclusively on mounds. The floristic composition and vegetation on termitaria proved to be rather homogeneous; although those mounds located in cotton fields differed by higher abundance of Poaceae and lower species richness.