Soil seed bank study of Hirmi woodland vegetation: Implications for restoration and conservation of natural vegetation, in Tigray, Northern Ethiopia

Abstract

Soil seed bank (SSB) is an important component in the process of rehabilitating degraded lands by forecasting the future vegetation cover of a given area. The present study was conducted in Hirmidryland vegetation, Tigray, Northern Ethiopia; to investigate the soil seed bank under different land use types in the vegetation ecosystem. A total of 128 soil samples were taken from eight points of four land use types (Shrubland, forest, grassland and bare land) and four soil layers (litter layer, 0–3 cm, 3–6 cm and 6–9 cm depth). Each sample plots measured 15 cm x 15 cm (225cm2). The density, composition and vertical distribution of seedlings were computed. A total of 58 species representing 51 genera and 22 families were recovered from the soil seed bank. Of these, 86.2% of them were herbs. The total density of soil seed banks from all land-use types was 3,116.7seeds/m2. The highest species composition was recorded in the shrubland and the least number of species were recorded in the bare land. Poaceae, Asteraceae, Fabaceae and Lamiaceae were among the plant families with high species composition that accounted for 60.35% of the total. Oplismenus burmannii, Woodfordia uniflora, Rhus retinorrhoea and Pennisetum glaucifolium were among the species with high density. The highest Jaccard's coefficient of similarity was revealed between soil seed bank of forest and shrubland whereas the least similarity was recorded between forest land and bare land. The soil seed bank result from all land use types in the study area showed that the regeneration potential of the woody species were poor. Hence, this study underscores other restoration approaches such as growing seedlings of woody species and plantation, direct seeding in the degraded ecosystem and preventing selective cutting of the matured woody species are recommended.