When a tree is surrounded by many similar individuals, its mortality increases, which is probably caused by specialised pathogens or herbivores. This effect occurs in forests all over the world, but is more pronounced in rare tropical tree species, which could contribute to the astonishing tree species diversity of tropical forests. This was discovered by a team of 52 scientists led by Lisa Hülsmann, Professor of Ecosystem Analysis and Simulation at the University of Bayreuth, and Florian Hartig, Professor of Theoretical Ecology at the University of Regensburg. Their results have now been published in Nature.