Evaluation of field survival and growth to support the restoration of four valuable Miombo tree species

Abstract

Understanding of right nursery practices is important for the production of high quality seedlings and successful restoration of trees with limited natural regeneration and/or on-farm tree planting. We evaluated the effects of nursery practices on field tree survival and growth in two trials in Morogoro, Tanzania: 1) shading regime, polythene tube size with four Miombo tree species i.e. Albizia harveyi, A. versicolor, Diplorhynchus condylocarpon and Pterocarpus angolensis; and 2) soil mixture and mycorrhizae/rhizobia inoculation with three Miombo tree species i.e. A. versicolor, D. condylocarpon and P. angolensis. There were no significant effects of the shading regime and polythene tube size on the survival, root collar diameter and height for all studied tree species. Almost all P. angolensis trees died after one year but the overall tree survival was good (>80 %) for the other tree species. Tree survival was always higher in nursery soil mixture S5 (0: 0: 1 sand: cow manure: soil) for D. condycarpon and at the early stages for P. angolensis. Mycorrhizae/rhizobia inoculation reduced tree survival of D. condylocarpon but not for other tree species. Interactions of soil mixture and mycorrhizae/rhizobia were only significant for D. condylocarpon and only with soil mixture S6 (1: 2: 3 sand: cow manure: soil). The advantages of medium and large polythene tubes on tree survival and growth in the field are dismissed in favour of small polythene tubes (10 x 10 cm). Nursery forest top soil alone is recommended for P. angolensis and D. condylocarpon. Albizia harveyi and A. versicolor can be grown in any of the soil mixtures tested. Testing the effect of nursery techniques on the field performance of these tree species in dry areas or poor soils, and for enrichment planting is recommended to enhance restoration of Miombo woodland.