Soil seed banks in plantations and adjacent natural dry Afromontane forests of central and southern Ethiopia

The soil seed bank was investigated in plantation stands and adjacent natural forests at Menagesha-Suba and Munessa-Shashemene forest sites in central and southern Ethiopia, respectively. The total numbers of species identified in the 0-9 cm soil layer were 58 at Menagesha-Suba and 52 at Munessa-Shashemene with the corresponding soil seed bank densities ranging between 27,200 and 82,600, and 4,500 and 36,900 seeds m -2 , respectively. Herbs dominated both in the number of species and densities of seeds while the contribution of woody species was generally low. The horizontal distribution of seeds in the soil exhibited con- siderable variation at both sites. However, the overall vertical distribution of seeds in the soil was similar in all stands with the highest densities occurring in the upper three centimeters of soil with gradually decreasing densities with increasing depth. The similarities in species com- position of the soil seed bank was generally low in stands both within and between the two sites. In general, the results provide further evidence that consolidate the conclusions of previ- ous studies on soil seed banks in Ethiopia. The dry Afromontane region, in which the two study sites are located, can be characterized as possessing large numbers of buried seeds of forbs, grasses and sedges. Only a few woody plants are represented, and these by few seeds, in the soil seed bank, suggesting that most woody plants rather use the seed rain, seedling banks or coppicing from stumps as alternative regeneration routes. These results imply that the herba- ceous flora has a better chance of natural recovery in the event of disturbances owing to the di- verse soil seed banks while the regeneration of woody species, particularly trees and shrubs, would be prevented by removal of mature individuals and their seedlings on the forest floor since most of them lack seed reserves in the soil. This, in turn, indicates that future existence of the woody flora characteristic of dry Afromontane areas in Ethiopia depends on the conser- vation and sustainable utilization of the few remnant natural forests. Resumen: Se estudio el banco de semillas en el suelo en plantaciones y en rodales foresta- les naturales adyacentes en Menagesha-Suba y Munessa-Shashemene, en el centro y sur de Etiopia, respectivamente. En la franja de suelo de 0-9 cm se identificaron en total 58 especies en Menagesha-Suba y 52 en Munessa-Shashemene; las correspondientes densidades de semi- llas variaron de 27,200 a 82,600, y de 4,500 a 36,900 semillas m -2 , respectivamente. La distri- bucion horizontal de las semillas en el suelo vario considerablemente en ambos sitios. Sin em- bargo, la distribucion vertical general de las semillas fue similar en todos los rodales: las den- sidades mas altas se presentaron en los tres centimetros superiores del suelo y decrecieron gradualmente hacia mayores profundidades. La similitud en la composicion de especies en el banco de semillas del suelo fue en general baja en los rodales, tanto dentro de los sitios como entre ellos. En general, la evidencia proporcionada por los resultados apoya las conclusiones de estudios previos sobre bancos de semillas en el suelo en Etiopia. La region Afromontana seca, donde se localizan los dos sitos de estudio, se caracteriza por poseer grandes numeros de semi- llas enterradas de subarbustos, pastos y ciperaceas. Solo unas cuantas plantas lenosas estan representadas, y estas a su vez por pocas semillas, lo que sugiere que la mayoria de las plantas