Coexistence and bush encroachment in African savannas: The role of the regeneration niche

Globally there is increasing concern over the biodiversity and economic losses associated with bush encroachment. The dominant species responsible for encroachment in Africa belong to mimosoid genera Senegalia Vachellia, previous research identifying Vachellia as more aggressive invader. We asked whether these have evolved different traits enable germination establishment among competitively superior grasses. hypothesised that coexistence at local scales underpin differences invasiveness. conducted a large greenhouse pot experiment quantify functional trait between two during seedling both presence absence of also examined seed morphology tested co-occurrence plot scale greater than expected by chance. Our results showed grew faster taller competition from In grasses, however, increased root tissue density while did not. coats were thicker those Senegalia, their seeds spherical discoid. coexist (plot) scale. speculated coat shape reflect its primarily endozoochorous dispersal mode, thinner discoid use wind dispersal. Since animal directed, promoting movement into sites frequented animals, which grasses fire has been removed, may contribute invasiveness Vachellia. Once established such sites, facilitated low-density allowing rapid resource acquisition growth high-density enabling slower but persistent Senegalia. Where focussed on environmental filtering, competition, predation or facilitation explanations plot-scale phylogenetic overdispersion, our work suggests potential role regeneration niche structuring co-occurrence. A free Plain Language Summary can be found within Supporting Information this article.