Influence of Climatic Factors on Vegetation Distribution Along the Altitudinal Gradient in Western Kenya

Abstract

Distribution of C3 and C4 plant species in the western region of Kenya was studied along the altitude from Chwele in Bungoma through Mt. Elgon in Trans Nzoia to Baringo County. The study area experiences variable climatic conditions, and the distribution of various plant species is predicted to follow distinct patterns which reveal the adaptive advantages of the different photosynthetic pathways. Carbon isotope method was used to establish carbon isotopic values of the plant species. The values were used to distinguish between C3, C4 and CAM plant species. Vegetation was sampled along an elevation gradient and samples taken at 100 metre intervals using a nested design for trees, shrubs, and herbaceous species. Species were identified in the field and verified with taxonomic databases, while altitude, geographic coordinates, and climatic data were recorded. Species frequency was calculated per belt to evaluate distribution patterns along the gradient. The distribution of plants was strongly associated with temperature and rainfall. At 1100–1600 m a.s.l., C₃ and C₄ species occurred in similar proportions. However, C₃ species became more common as elevation increased. In contrast, C₄ species were mostly found at elevations lower than 3100 m.a.s.l. This pattern reflects cooler temperatures and higher rainfall at higher altitudes, which limit C₄ occurrence and promote C₃ dominance. Data was first recorded in a Microsoft Excel spreadsheet and later exported to the Statistical Package
for Social Sciences (SPSS) software version 26.0. Pearson correlation was used to quantify the strength of linear relationship between photosynthetic pathways and climatic variable, while regression analysis was used to express the relationship of these variables inform of an equation. The findings were presented in tables and scatter plots. Of 313 plant species in the whole area 234 were C3, 69 were C4, and 10 were CAM species. Since temperature and rainfall strongly influence the distribution of C₃, C₄, and CAM species along altitudinal gradients, long-term ecological monitoring including incorporation of climate change models should be established. This would help detect shifts in plant distribution patterns under ongoing climate change, particularly warming trends that may allow C₄ species to expand into higher elevations.