Soil properties beneath Pinus halepensis and Quercus calliprinos trees on burned and unburned mixed forest on Mt. Carmel, Israel

In order to study the effect of fire on soil properties of a mixed Pinus halepensis Mill. and Quercus calliprinos Webb. forest, pH, organic matter, total and available nitrogen [(N, NNH₄ and N(NO₃ + NO₂)] and phosphorus and soluble cations (K. Mg, and Ca) were determined from soil samples collected under these trees, in a burned and adjacent unburned forest. Samples from the latter were also collected from an open grassy patch. In addition, the responses of barley (Hordeum sativum) and alfalfa (Medicago sativa) to the different levels of nutrients of these soils were studied in pot tests. In the ash layer collected under the burned pine trees 2 months after the fire there was a significant increase in available nitrogen, phosphorus and soluble cations (K and Mg). Fourteen months after the fire, the organic matter and nutrient levels in the burned soil were less than those of the unburned. The exception was total phosphorus which was significantly higher in the upper, burned, soil layer than in the unburned. At the same time, all soil parameters measured were higher in the upper layer (0-5 cm) than in the lower one (5-25 cm). With the exception of available nitrogen [(NNH₄, N(NO + NO₂)], all soil nutrient levels measured were highest under the pine soils followed by oak soil, and lowest in the open-grass soil. No significant differences were found in pH values, which varied between 7.5 and 7.7. The measurements obtained for alfalfa and barley grown in burned and unburned soils verified the outcome of the soil analyses, showing the same trend of increase from pine to oak and open grassy. The exception was the above-ground phytomass of barley which was higher in the 'oak soil' than in the 'pine soil' due to the higher levels of nitrogen in the soil under these trees. For a thorough study, the patchiness of the vegetation affecting the upper soil layer should be taken into account.