The role of heat and nutrient supply from ash after light and hot fires on Britanny heathland soils were studied in the laboratory. The soil surface was heated either to 150°C for 15 min or 300 °C for 30 min and the effects of the percolation of two ash solutions were studied. 2. The results showed clearly that soil heating has a significant effect on soil properties only at 300°C. The organic matter content decreased during this treatment inducing a decrease in cation exchange capacity and in exchangeable bivalent cation concentrations. The nutrient inputs from ash did not compensate for these losses, except for potassium. Nearly all sodium was leached and its exchangeable concentration always remained lower than the control samples. Moreover, the major part of nutrient input by ash was immobilized as insoluble forms. 3. These results suggest that a hot burn has transient effects on the soil fertility of these heathlands. Moreover, the repetitive fires induce a loss of nutrients and an impoverishment of the ecosystem. They contribute to the maintenance of the low fertility of these soils and the maintenance of the vegetation communities.
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Forgeard et al. (1996) studied this question.