Natural and Artificial Regeneration of Adansonia digitata L. at Elkhouyi, North Kordofan State, Sudan.

Abstract

Adansonia digitata (Tabeldi, Boabab) is an economically important tree species for rural people and at the national level for its uses and nutritional and medicinal values. The species is considered endangered with poor natural regeneration in Sudan. This study surveyed the status of soil seed bank and natural regeneration at Elkhouyi Site in North Kordofan State. Also, it investigated the effect of fruit collection date, seed planting date and seed pre-germination treatment on seed germination and seedling growth at the nursery. Effect of protection from grazing for seedling and seed on germination and seedling survival was studied at the site. Soil seed bank was surveyed according to soil depth, distance and direction from existing trees. Natural regeneration was assessed by counting young seedlings (1 m in length) according to direction and distance from the nearest tree. Seed pre-germination treatments (sulfuric acid (96%), electric burner, dry heat and control) were applied for seed collected in October, November, December and January of the following year and weighed. Treated seeds were tried in January, April and July 2006. Seed germination was recorded and seedling growth was measured weekly from week 5 to week 13 and leaves number per seedling was recorded at week 13. The results showed that there is low soil seed bank and scarce natural regeneration. Seed number per unit volume of soil is significantly higher at soil depth 5 cm than other deeper depths. Also, the seeds and seedlings were concentrated near trees. The direction from trees showed no significant effect on seed or seedling number. X Seeds collection date, planting date and scarification treatment showed significant effect on seed germination and to some extent on seedling height and leaves number. Seeds collected in January (2006), had significantly higher germination percent than those collected in October 2005, indicating importance of seed maturity and suitable fruit collection date. Seeds planted in July showed higher germination percentages and longer seedlings and more leaves than earlier planting (January and April). This also, showed the importance of seed maturity. The effect of seed treatments was significant on seeds planted in January and April. Seed coat scarification using electric burner or concentrated sulphuric acid gave higher germination percentage, especially for seeds planted in January and April. The field study showed significantly higher survival percentage for transplanted and germinating seedlings in protected site compared to unprotected one. This indicates the importance of protection from grazing animals. Accordingly, the study recommends protection of A. digitata sites and enriching the soil seed bank of A. digitata to ensure germination.