Assessment of soil seed bank from six different vegetation types in Kakamega forest, Western Kenya

Abstract

Kakamega forest, the only rainforest in Kenya, has faced extensive fragmentation and degradation over the last decades. Slow recovery of degraded areas is due to slow or no natural regeneration. An assessment was conducted to ascertain the contribution of soil seed bank in forest regeneration within six sites in Kakamega Forest. Sites investigated were the natural forest, plantation, shrubland, secondary grassland, natural glade, and burnt glade. Soil sampling was done from three stratified depths of 0 to 5, 5 to10 and 10 to 15 cm in each site. Soil seed bank was determined by seedling emergence technique and total seed counts. Laboratory experiments on seed viability were done in a germination chamber at 20°C. Soil seed banks in all the six vegetation types were mainly dominated by herbaceous species. There was a high seed density in the upper layers for all the sites except for natural forest and burnt glade. Seed viability tests revealed low seed viability for the seeds from all the sites. It was concluded that natural regeneration is slowed by low woody species which ranged from 5.7 for natural glade to 48.4% for natural forest soil seed bank, and a low seed viability that ranged between 1.3 for plantation to 33.8% for grassland. It is therefore important to consider other ways of forest restoration other than the soil seed bank.

Key words: Seed bank, herbaceous species, seed viability, seedling emergence.