The overall goal of this research was to assess the fundamental controls on BSi soil pools in grass-dominated ecosystems.  Our major research question was to assess if the climatic controls identified in North America are similar in South Africa despite differences in parent material, soil age, and evolutionary history.  To assess precipitation and parent material controls on BSi, we sampled grasses and soils (pedons) at 3 sites in Kruger National Park of South Africa that receive on average ca. 400, 600 and 750 mm of rainfall each year. We sampled plots on both fine (basaltic) and coarse (granitic) textured soils as these parent materials can be found side-by-side along a north-south precipitation gradient. We measured plant and soil pools of BSi from all sites and found that basalts contribute greater amounts of Si from weathering into the soil than do granites.  This lithologic control, however, is accompanied by soil age.  In sites with similar MAP and ANPP both the total Si and BSi in the older savanna grasslands of South Africa are lower relative to North American sites.  A greater proportion of BSi remains in the North American soils where the percent Si out flux is lower. In terms of the response of Si mobility to ecological drivers and evolutionary history on both continents, it is clear that frequent fire results in increased Si uptake by plants although the same relationship is not apparent in soils.  In both cases (plant and soil), BSi concentrations are higher in South African relative to North American sites.