The cost of standing tall: wood nutrients associated with tree invasions in nutrient‐poor fynbos soils of South Africa

Tree invasions into native grasslands and shrublands are global phenomena, with alien tree invasions occurring on nearly every continent. We hypothesized that wood nutrient concentrations are a key trait to enable successful tree invasions in regions limited by soil nutrient availability, such as the fynbos vegetation of the Cape Floristic Region of South Africa. We sampled wood and bark of a height range of indigenous and alien woody species within the Cape Floristic Region. We used linear regression and phylogenetic analyses to assess associations between wood nutrients and tree height and analysis of variance to assess how wood nutrients vary across vegetation types. Alien trees had lower wood nutrient concentrations than many native trees, and nutrient concentrations, especially not only N and P, but also Mg and K, were negatively associated with tree height. These results suggest that recent tree invasions into the nutrient‐poor fynbos shrublands may be a result of low wood nutrient concentrations that allow the alien trees to successfully overtop the native vegetation. This indicates that wood nutrient concentrations may be a useful trait to predict whether an alien tree species has a greater potential of becoming invasive in regions with limited soil nutrients.