Increasing calcium scarcity along Afrotropical forest succession Bauters, M., Janssens, I.A., Wasner, D., Doetterl, S., Vermeir, P., Griepentrog, M., Drake, T.W., Six, J., Barthel, M., Baumgartner, S., Van Oost, K., Makelele, I.A., Ewango, C., Verheyen, K., & Boeckx, P.