Abstract Physiological groups of soil microorganisms were investigated in a forest ( Pinus pinaster Sol.) to asses their response to wildfire-induced soil changes. Microbial fluctuations were recorded 1 month and 1 year after the fire, both in the field and during controlled soil incubations. In both the burned and the unburned soil, starch-mineralizing microbes predominated over cellulose-mineralizing microbes; there were a relatively high number of ammonium-producers, whereas nitrite and nitrate producers were scarce. In the short term, burning produced a decreasing to nearly undetectable number in cellulase-producers whilst amylase-producers, and especially, ammonifying microbes increased, and the nitrifying groups did not change. One year after the wildfire, the burning effect was slightly overcome by cellulolytic microorganisms and the amylolytic population was slightly decreased; the improvement of ammonifiers was reduced, ammonium oxidizers were positively affected and nitrite oxidizers continued to be unaffected by the fire. The trends of populations during soil incubation indicated that, in the long term, the effect of burning will probably be nil on ammonifiers, somewhat negative on cellulolytic and amylolytic microbes and slightly positive on nitrite- and nitrate-formers.