Temporal evolution of organic carbon and nitrogen forms in volcanic soils under broom scrub affected by a wildfire

The evolution of total N, total oxidizable C, water-soluble NH4 +–N, exchangeable NH4 +–N and soluble NO3 −–N was studied in Canarian volcanic soils under mountainous legume scrub affected by a wildfire by June 2003. Three systematic soil samplings in the burned area and in neighbouring non-burned sampling points were carried out 3, 7 and 12 months after the fire event. The results showed an important mobilization of N (as total N and soluble and exchangeable NH4 +–N) in the soil within the burned area at short term, with a simultaneous depletion of nitrates. Later on, the water-soluble NH4 +–N levels remained nearly constant along the study period in the burned area, whereas the exchangeable NH4 + decreased progressively. Nitrates were found to increase inside and outside the burned area, but the increase rate was much higher for the burned samples. Total N fluctuated along the year, although its levels were generally higher in the burned area. However, such a response pattern of N to fire in this environment was insufficient to prompt the recovery of the plant cover.