The role of plants in soil development has become of crucial interest in quantifying global weathering processes. On the volcanic Reunion Island (Indian Ocean), a 15-cm-thick phytolith-rich horizon (biogenic opal-A) developed at the expense of trachytic ashes between 3820 ± 85 and 335 ± 90 yr B.P. Then, 97–138 t/km2/yr of SiO2 were biogeochemically recycled from the weathering of parent rocks through a past forest of bamboos (Nastus borbonicus). This rate is in the same range as the present chemical weathering rates of silica in the area, considered to be among the highest in the world. These results demonstrate that the storage of biogenic silica in soils may be significant and may retard the output of silica to rivers and ocean.