Tropicultura (Jan 2007)
Persistent Soil Seed Banks for Natural Rehabilitation of Dry Tropical Forests in Northern Ethiopia
Abstract
Dry tropical forests are threatened world-wide by conversion to grazing land, secondary forest, savannah or arable land. In Ethiopia, natural dry forest cover has been decreasing at an alarming rate over the last decennia and has reached a critical level. Efforts like the rehabilitation of dry forests to curb this ecological degradation, need a stronger scientific basis than currently available. The aim of the present research was to test the hypothesis whether soil seed banks can contribute to natural forest regeneration in the dry forest of Ethiopia. Therefore, the composition of the seed bank in relation to vegetation and abiotic environment was analysed in four forest relics and four exclosures, i.e. demarcated land areas under strict conservation management, in the highlands of Tigray, northern Ethiopia. Results show strong relationships between natural vegetation, seed bank composition, soil chemical characteristics and environmental degradation, as evidenced through characteristics such as land use impact and soil depth. Most striking is the presence of only very few woody species in the seed bank of degraded areas. This suggests that seed banks only play a minimal role in natural forest recovery in the study area. If this is true, natural recovery will primarily depend on presence of seed trees in the vicinity and successful seed dispersal mechanisms. This result underlines the importance of sustainable management of the few remaining forest relics and trees outside these relics.
