COMPARATIVE STUDY OF COMPOSITION AND DIVERSITY BETWEEN SOIL SEED BANK AND ABOVEGROUND VEGETATION IN GARDULA-SHOKOLO FOREST, GARDULA ZONE, SOUTH ETHIOPIA: AN IMPLICATION FOR ECOLOGICAL RESTORATION

Abstract

Soil seed banks might have a great potential for degraded forest restoration. This research compared the species composition and abundance resemblance between soil seed banks and aboveground vegetation in the Gardula-Shokolo natural forest in the Gardula zone, South Ethiopia. A systematic sampling technique was used to collect the data. Sixty (20m×20m) quadrats were laid across seven transects. Woody species (DBH ≥ 2.5cm) were counted in each quadrat. Two hundred forty composite soils were sampled from four different soil layers. Overall, 72 and 20 woody plant species were identified from the aboveground vegetation and soil seed bank, respectively. The density of aboveground woody vegetation was 489.2ha-1 while it was 567.9m-3 in the soil seed bank with a mean of 6.79ha-1 and 28.39m-3, respectively. The five most abundant species in aboveground vegetation were Myrica salicifolia: A. Rich. Syzgium guineense: (Willd.) DC. Pittosporum viridiflorum: Sims, Nuxia congesta: R.Br. ex Fresen. and Olinia rochetiana: A. Juss. While the least abundant species were Justicia shimperiana: T. Anderson, Vernonia myriantha: Oliv. & Hiern and Ficus vasta: Forssk. On the other hand, the five most abundant woody plant species in the soil seed bank were Pittosporum viridiflorum: Sims, Allophylus abyssinicus Jacq, Galiniera saxifraga L, Hoffmannanthus abbotianus Bullock and Syzgium guineense DC. while the least abundant species were Psidium guajava and Rubus apetalus. Sorensen similarity coefficient between the soil seed bank and the aboveground vegetation was 41.3% implying less matching. The Pearson correlation coefficient of the species abundance between the aboveground vegetation and the soil seed bank was 0.425 revealing weak relationship. There are 19 species common to both floras while 53 species were unique to the aboveground vegetation and one species was unique to the soil seed bank. Aboveground vegetation revealed high diversity (H’=3.65) than the soil seed bank flora (H’=2.52). A large number of seeds were recorded in the upper (0-3cm) layer of the soil but a few seeds were recorded in the bottom layer, showing significant differences among the different soil layers (p<0.05). The seedling emergence experiment revealed the overall mean percentage of 50.4 with a maximum record for G. saxifraga with a relative density of 24.6%, the minimum for Lippia abyssinica, Ocimum lamiifolium, Psidium guajava, and Rubus apetalus each with a relative density of 0.04%. It’s more likely that the soil seed banks will play a smaller role in recovering the degraded forest due to the low composition similarity and the weak abundance link between the aboveground vegetation and soil seed bank. Therefore, supporting the restoration of forest ecosystems from the combined approaches including protection of the forest from unwise exploitation, and enrichment plantation, besides the natural restoration from the soil seed banks is crucial for sustainable development of the society.