Canopy gap formation, a frequent small-scale disturbance in many forests, has been hypothesized to be an important event in the structuring of many forest communities. Canopy gaps increase environmental heterogeneity by altering abundances and distributions of abiotic and biotic resources. Resources that have been demonstrated to change after gap formation are light, soil moisture, nutrients, fruit availability, seed availability, seed germination, and herbivores. Such changes in the spatial and temporal heterogeneity of resources may affect forest dynamics by altering colonization success and competitive outcomes, thereby linking natural disturbances to the maintenance of plant species diversity. Canopy gaps and their dynamics in regeneration were investigated in Gera Forest of Jimma Zone Oromia Regional State, located west of Ethiopia at an altitude range of 1600 to 2400m above sea level. The replacement probability in the Forest is low except for Millettiaferruginea, Syzygiumguineense and Prunusafricana; all the rest of the gap formers are replaced by other nongap forming species. Croton macrostachyus, one of the dominant trees in the forest, shows uniform regenerating potential compared with other species in the forest. Dominant species in the forest were not found being replaced by their own seedlings or saplings and among the ten woody dominant species only seven had sapling and five had seedling stages.

Keywords: replacement probability, gap formers, regenerating potential, Dominant species, sapling, seedlings