The number of tree species growing in regions close to the equator is significantly higher than in regions further north and south of the earth. An international study published in „Nature Ecology and Evolution“ investigates the causes of this with a precision never before achieved. It emphasizes that the diversity of tree species in the tropics does not depend solely on bioclimatic factors. The study is based on a cooperation of 222 universities and research institutions. On the part of the University of Bayreuth, PD Dr. Andreas Hemp, who has been researching vegetation in mountainous regions of East Africa for more than 30 years, was involved in this international research.