Early spring prescribed burning in mixed Pinus halepensis Mill. and Pinus pinaster Ait. stands reduced biological soil functionality in the short term

This study evaluates the effects of prescribed burnings on soil physico-chemical and biological properties in the short term. This practice is still in the process of evaluation and its effect on Mediterranean pine forests is not understood completely. Prescribed burning was carried out in three plots of mixed Pinus halepensis and Pinus pinaster stands in Castilla-La Mancha (Spain) while monitoring soil temperature. Vegetation coverage was measured and soil samples were taken before, immediately after and 1 year after burning. Texture, pH, soil electrical conductivity, cation exchange capacity, soil organic carbon, total nitrogen, available phosphorus, magnesium, calcium, potassium, basal soil respiration, microbial biomass carbon content and enzymatic activities of urease, dehydrogenase, phosphatase, and beta-glucosidase were evaluated by generalized linear models, and a principal component analysis was used to reveal the relations between variables. The vegetation cover was reduced by 85% after fire. Soil organic carbon increased immediately after burning to return to the previous values one year later. Phosphorous and cationic exchange capacity increased immediately after burning and remained high one year later, while electrical conductivity and sodium were significantly lower after a year. Basal soil respiration and glucosidase were not affected by prescribed burning. Microbial biomass carbon, urease, phosphatase, and dehydrogenase had significantly lowered one year after burning. Our results show that prescribed burning managed to decrease the vegetation cover of the understory while it also reduced soil biological functions in areas with poorly developed soil and a dry climate, where recovery periods can be longer than expected.