Biotic interactions, climate and disturbance underlie the distribution of two Julbernardia tree species in miombo woodlands of Africa

Occurrence data for Julbernardia globiflora and J. paniculata at 617 sites in the miombo woodland region of central, eastern and southern Africa and forest inventory data for 512 woodland plots in Zambia were used to determine species distribution and dominance. Distribution of the two Julbernardia species overlaps in the central region of the miombo woodland range while the eastern and western range regions are exclusively for only one of the two species. In the region of co-occurrence, there is a clear spatial separation in the dominance of the two species. In old-growth woodland a significant proportion of the variation in the dominance of J. globiflora was explained by the dominance of J. paniculata while mean annual maximum temperature and tree species richness negatively affect the dominance of J. paniculata. Old-growth woodland clearing changes the local climatic conditions and alters the way Julbernardia species in re-growth stands respond to potential evapo-transpiration (PET). Climate change, especially global warming, may further reinforce the impacts of PET to differentially favour J. globiflora. Because of this altered response of Julbernardia species in re-growth miombo, preserving old-growth miombo and preventing present human disturbances in designated areas, such as forest reserves andnational parks, may be a useful climate adaptation strategy for these species.