Medium-term effects of wildfire severity on soil physical, chemical and biological properties in Pinus halepensis Mill. woodland (Southern Italy): an opportunity for invasive Acacia saligna colonization?

•We still observed wildfire effects on pinewood soils four years post-fire.•Organic layers (L + F) have not recovered after four years from wildfire.•We estimate a loss of about 2 t Corg ha−1 from organic layers.•Changes in N-cycle processes occurred in burnt mineral soil, without effects of burn severity.•A. saligna density increased in a burnt site but did not affect soil.