Propagation and regeneration of important indigenous tree species in Kakamega forest Kenya

Abstract

The African cherry (Prunus africana (Hook.f.) Kalkm.) regenerates poorly both naturally and artificially because of its recalcitrant seed. There is therefore a great need to conserve this species to ensure it does not become extinct. This study evaluated regeneration potential of the African cherry, identified the appropriate stage of collecting seeds for propagation and suitable sowing media that gives optimum germination and sought to identify other tree species with potential commercial uses which could be used as alternative to P. africana and hence ease the exploitation pressure that it currently faces. An experiment was set to evaluate the regeneration potentials of P. africana Vis a Vis Olea capensis and Croton megalocarpus. It also identified the best stage of seed collection and sowing media that can give good germination results. The experimental design used was randomized complete block design (RCBD) in split plot arrangement with the main plots as the stage of seed collection while the subplots as the different media type replicated three times. Seeds were collected at two stages: when fruits are green and mature and when ripe. These seeds were prepared, germinated under the different media types and germination percent monitored. The media used included: {(soil: sand), (soil: sawdust), (sand: sawdust) in ratio 1:1}, {(soil only), (sand only), (sawdust only)} and the normal nursery media of (sand: soil) in the ratio 1:3 was used as a control. The study also identified the effects of site on natural regeneration where by a sample of 10 trees per species was identified and deliberate vegetative disturbance underneath was carried out, and regeneration monitored and compared to undisturbed sites. The data was collected on mean germination percent and statistical analyses conducted at 95% significant level. The results indicated that There was significant difference in the timing of the collection of seeds for C. megalocarpus (F 2, 60, f=24.47, P<0.001). A post-hoc test (Tukey test) showed that germination rate was lower in mature green seeds compared to the other two seed collection stages – mature ripe and stored seeds. There was significant seed timing effect (Chi-square test = 32.90, d. f= 2, p < 0.001) for P. africana. Germination rate was significantly lower in stored seeds compared to the other two seed collection stages i.e. mature green seeds and mature ripe. There was a significant ‘medium’ effect on the germination of C. megalocarpus (F6, 62, f=4.84, p<0.001), Prunus africana (Chisquare test = 14.10, d. f= 6, p = 0.029) and O. capensis (Chi –square test = 18.33, d. f= 6, p = 0.005). Seeds in sand &sawdust 1:1 and sand had higher germination rate compared to those in sawdust. Soil sand 3:1 and soil had moderate germination rate. There was a significant site effect on C. megalocarpus, (F1, 18, f=10.09, p=0.005), P. africana (F1, 18, f=53.42, p=0.001) and O. capensis (W=155, p<0.001) among the three species. Disturbed sites had a higher wildling regeneration compared to non-disturbed site. From the results, it was concluded that the best seed for propagation of P. africana is seed freshly harvested; mature and ripe even without any pretreatment, while O. capensis and C. megalocarpus seed need to be harvested and dried well before sowing. It is therefore recommended that P. africana seed should be sown using this medium-sand: sawdust 1:1 immediately after harvesting without pre-treatment for optimum germination per cent. The best medium recommended for optimum germination of seed of all the three species is sand: sawdust in the ratio 1:1. It is also recommended that more P. africana seedlings should be used to rehabilitate degraded areas of the natural forests due to its shade intolerance nature. Proper tending of the seedlings after germination should be advocated as well as protection of mature P. africana trees in the wild.