Assessment of ecological factors limiting tropical rain forest regeneration: case study of Kakamega forest, western Kenya

Abstract

Slow rate of regeneration poses a major challenge to our depleted tropical rain forests, however soil seed bank has been deemed as the main source of forest regeneration. This study was designed to assess various biotic and abiotic factors in the southern part of Kakamega forest to verify their contribution to regeneration. Sampling was done in six habitats using three transects of 100m and 5x5 m quadrants. Aspects looked into were soil physical-chemical parameters, micro-climate, soil seed bank, seed viability and anthropogenic impacts. The soil seed banks for all the habitats were mainly dominated by the herbaceous species. A vertical distribution of seeds in the seed bank revealed a high density in the upper soil layers for the secondary grassland, shrub-land, natural glade and plantation. However, the burnt glade and the natural forest, had small variations in seed density with soil depth. The seed viability for the six habitats was low and ranged between 1.3-33.8%. Soil fertility for all the habitats was found to be generally low and highly depleted of nutrients. The pH was generally medium (it ranged between 5.3 to 6.09), making the soils weakly acidic in nature. The soils comprised of a high sand percentage, and were well drained. Anthropogenic impacts appeared to affect the regeneration of the forest. There were significant differences in the micro-climates of the habitats. The soil seed bank was found to be inadequately reliable for the regeneration of the forest because of its low viability and being dominated by other herbaceous species. Soil nutrients were found to be low for the support of the growth and establishment of seedlings. It was found that forest regeneration does not entirely rely on the soil seed bank but is affected much by other biotic and abiotic factors. The understanding of impacts of these factors gives a clear methodology on regeneration in the various habitats.