Preliminary results of a study on short term effects of prescribed fire in pine stands in NW Spain

Short term effects cf prescribed burning experiments carried out in P. pinaster stands in the N.W. of Spain on fuels ; soil nutrients , soil microflora and forest floor meso fauna were studied. Fire intensities range from 21 to 420 Kw.m-1. The mean maximum temperature recorded on the litter duff interface was 408 °C ; the temperature was greater than 60°C for about 5 minutes (mean value). On the duff-soil interface, 59° was reached and 21 °C was measured 2,5 cm below the top of the mineral soil. Fires consumed 32 per cent of the total fuel and 55 per cent of the available fuel. Two years after the fires, the total fuel was practically equal to the prebum load but the available fuel represented 64 per cent of its initial load. Changes in soil (0-5cm layers) nutrients were very small. Soon after the fires a little increment for the organic matter content, a small drop in pH and an increment in K, ca, Mg and P were detected. Nitrogen content was practically equal to pre-fire level. Two years later, all the nutrients remained at the same initial level, except for Ca which was 65 per cent higher than before burning. The organic matter per cent was a little smaller than before fire but pH was higher. Some groups of the soil microflora, especially aerobic free living nitrogen fixers, were enhanced by the fire. The others remained at the same level as in unbumt areas. Forest floor mesofauna populations were affected by fire and depending on groups, duff heating and duff consumption, their recovery lasted from six months to three and a half years.