Diversity and distribution of wild terrestrial orchids of Mt Elgon Forest National Park, eastern Uganda

Abstract The diversity and distribution of wild terrestrial orchids of Mt Elgon National Park was studied between November 2003 and November 2004. The vegetation types investigated were grasslands, montane, bamboo, heath and moorlands. Sampling was done along Piswa and Sasa trails in the rainy and dry seasons. Altitude, slope gradient position, vegetation disturbance, burning and percentage canopy were assessed to find their influence on species diversity and distribution. Eighteen terrestrial orchids’ species were recorded. These represented four tribes and eight genera. Habenaria was the most frequent and dominant genus accounting for 44.4% of all the species encountered. Species dominance was more pronounced in the dry season. Along Sasa trail, Disa stairsii Kraenzl dominated the bamboo and heath vegetation zones. Epipactis africana Rendle dominated the montane vegetation zone. Along Piswa trail, Eulophia angolensis Rchb.f. dominated the grassland vegetation zone, while D. stairsii dominated in the montane and heath vegetation zones. Species diversity, frequency of occurrence and density were higher in the rainy season than in the dry season in all vegetation types. Canonical correspondence analysis revealed that altitude, slope gradient position and percentage canopy cover were important factors that influenced orchid species richness and distribution.