Mineralogical and chemical modifications in soils affected by a forest fire in the Mediterranean area

We studied the mineralogical and chemical modifications in four soils in Spain produced by a forest fire: two of the soils developed under Quercus pyrenaica and two under Juniperus oxycedrus. Samples were taken 2 and 8 months after the fire. Increases in soil pH, electrical conductivity, exchangeable-bases and total Ca occurred in both soils, but were more evident under Juniperus oxycedrus. The presence of calcite and alteration of vermiculite, were observed in soils beneath Juniperus oxycedrus, but not Quercus pyrenaica. This was due to lower temperatures reached during the fire in the mineral soil under this species. By heating plant and soils samples in the laboratory to 300, 400 and 500°C, the formation of calcite during the burning of Quercus pyrenaica (500°C) and Juniperus oxycedrus (300°C) was confirmed. According to the chemical and mineralogical modifications observed in-vitro, the temperature in the mineral soil under Juniperus oxycedrus reached during the fire was close to 300°C.