Edaphic specialization in relation to termite mounds in Katanga (DR Congo): A reciprocal transplant experiment with congeneric tree species

Abstract

Question: Do termitophilous and non-termitophilous trees of dry tropical woodlands show local adaptation?. Location: Region of Lubumbashi, Upper Katanga, DR Congo. Methods: Three pairs of congeneric tree species showing strict edaphic specialization with respect to termite mounds, Combretum molle (termitophilous, T)/C. collinum (non-termitophilous, NT); Strychnos potatorum (T)/S. spinosa (NT), Ziziphus mucronata (T)/Z. abyssinica (NT), were used in a reciprocal transplant experiment in situ. Seedlings were reciprocally transplanted on termite mounds and in the surrounding matrix in a miombo woodland. Growth (height and number of leaves) and survival were monitored for 30 months. Soil physical and chemical properties, and available water, were assessed on and off mounds. Results: Growth was little affected by habitat; only one species showed better growth in its home habitat (S. spinosa in the matrix). Survival was strongly affected by habitat, in opposite directions consistent with species’ habitat specialization. Termitophilous species experienced a very high mortality rate in the matrix, especially during the dry season. Available water content was higher in termite mound soil than in the matrix soil. Conclusions: Termitophilous and non-termitophilous tree species show local adaptation at the seedling stage, expressed mostly as different patterns of mortality in the dry season. The results point to water supply as a critical factor in the edaphic specialization of termitophilous species. In contrast, the higher mortality of non-termitophilous species on termite mounds is not explained by water stress.