Is Geodiversity Correlated to Biodiversity? A Case Study of the Relationship Between Spatial Heterogeneity of Soil Resources and Tree Diversity in a Western Kenyan Rainforest

Abstract

Interactions of biotic and abiotic factors are critical in determiningpopulation dynamics and maintenance of high diversity in tropicalrainforests. An investigation was conducted to test the hypothesis thattree species composition and dispersion influence spatial pattern ofsoil properties on a small scale of meters. Soil variables (pH, EC andtotal and water extractable (available) K, Ca, Mg and Mn) were highlyheterogeneous in both vertical and horizontal dimensions. Available Mnwas the most variable (coefficient of variation CV = 76%) parameter andpH the least (CV = 4%). There was an inverse relationship betweenabundant levels of available cations and heterogeneity. Plots with highheterogeneity in available cations had low tree diversity but there wasno evident pattern between total concentration of cations and treediversity. Tree diversity was negatively correlated to variability ofavailable Mn (r = -0.7). These findings indicate that tree diversityinfluences soil heterogeneity hence contributing to maintenance of highdiversity in tropical rainforests. The results show that the observedsoil patterns are caused by geogenic processes as well as processesinfluenced by vegetation. The raising effect of the vegetation on theelements is expected in the order from Mn, Ca, Mg to K. This vegetationeffect indicates the significance of maintaining a closed canopy intropical rain forests. Geodiversity is thus correlated to biodiversityand needs to be more recognized in ecological research.