Comparison on the soil seed bank of exclosures and free grazing areas for restoration in Tigray region, N. Ethiopia.

Abstract

An investigation of the seed composition of seed banks is ecologically important in predicting the initial composition of the pioneer vegetation in an area, particularly on exposed or cleared sites. This study was initiated with the objectives of gaining more knowledge on the role of seed banks in stimulating vegetation regeneration leading to natural dry evergreen afromontane forest restoration, by analyzing their species composition and abundance and further investigates the difference on soil seed bank in exclosures and the adjacent free grazing areas. Soil seed bank density, diversity, vertical and horizontal distribution and composition were assessed by collecting 360 soil samples. The total numbers of species recovered from the soil samples collected in the study area were 47 for the exclosure and 39 for the free grazing area and totally 62 species. The total seed density in the upper nine centimeters both from seedling emergence and seed counting method was 1868 seeds m^-2 for exclosures and 1431 seeds m^-2 for free grazing areas. The similarity between the soil seed bank and above-ground flora was also low for exclosures Sj value 0.29 and average for free grazing area Sj value 0.51. But the herbs similarities was high showing 0.75 and 0.78 similarities in exclosures and free grazing respectively. Similarity between the soil seed banks and aboveground flora was very low implying that the role of soil seed banks in the regeneration is low and dispersal of seeds from the adjacent forest areas play an important role in the process. These results support the idea that assisted natural regeneration can promote the regeneration of species and increase plant biodiversity in the area, if seed sources are available in the area or nearby sites of the restoration areas.

Key words: Exclosure, Free grazing area, Soil seed bank, Tigray (Ethiopia)