SEED VIABILITY OF AFROMONTANE TREE SPECIES IN FOREST SOILS

The fate of seeds of eight tree species was followed during 4 y of sto rage in the soil of an Afromontane forest at Gara Ades in the eastern highlands of Ethiopia. Seeds were enclosed in nylon mesh bags and buri ed at 5 cm soil depth. The bags were exhumed at intervals and the viab ility of the seeds was assessed by germination and cutting tests. Seed s of Bersama abyssinica and Ekebergia capensis germinated in the soil almost completely within a year after burial. The seeds of Juniperus p rocera, Olea europaea and Podocarpus falcatus also germinated to a sub stantial degree in the soil but with a distribution over several years , and some seeds of these species remained Viable at the end of the 4- y period. Germination in the soil was very low in seeds of Acacia abys sinica and Croton macrostachyus throughout the whole burial period and the seeds kept their viability. In C. macrostachyus fresh seeds were highly dormant, but after 3 y or more in the soil they germinated read ily in the laboratory suggesting an altered dormancy with time in the soil. Dormancy in seeds of A. abyssinica and Indigofera rothii was not altered throughout the study period as evidenced by marginal or no ge rmination during incubation in the laboratory. The differential seed b ehaviour observed during storage in the soil can be an indicator of th e regeneration strategy of the species studied. B. abyssinica, E. cape nsis, J. procera, O. europaea and P. falcatus form seedling banks on t he forest floor and lack persistent soil seed reserves in contrast to A. abyssinica, C. macrostachyus and I. rothii which accumulate reserve s of long-lived seeds in the soil. The generally high levels of dorman cy and somewhat extended viability in the soil, even in several of the species producing seedlings in undisturbed forest, may have been sele cted for under a climate of seasonal drought and unreliable rainfall t hat characterizes this region.