The Indonesian island of Sulawesi is comprised of a mosaic of soil types including the largest ultramafic outcrops in the tropics (ultramafic soils are macronutrient low and phytotoxic heavy metal rich). The island’s ontogeny is also distinctive, whereby it has formed only recently < 2 million years ago via agglomeration from a number of proto-islands. How the island’s phytogeography is influenced by the dual impact of edaphic heterogeneity and island ontogeny is unknown. Equally, how the numerous metal elements influence plant-soil interactions scale up to determine phytogeography is not well understood. I show here that tree communities in Sulawesi are both influenced by dynamics of island formation and edaphic chemistry. I identify the effect of soils upon foliar metal concentrations of tree communities. This manifests as many species existing within a similar/core stoichiometric niche space (defined by leaf metal axes) irrespective of soil chemistry, but on heavy metal rich soils, species also occupy distinctive niche space far from most other members of the community. As such, I find that soil metals drive the differences in niche space occupied by communities rather than plant macronutrients. I also find that species found across both different soil types and regions in Sulawesi tend to occupy a broader stoichiometric niche than those species restricted to a region and or soil type. Conversely, clades that are overrepresented across different soil types and regions do not show greater niche breadth than those overrepresented on a single soil type and or region, indicating that occupying both a conserved and broad niche can promote dispersal. This work provides evidence for the interacting roles of island ontogeny and edaphic heterogeneity upon biogeography and the interrelationship with the plant stoichiometric niche.
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