Temporal Impact of Mulch Treatments (Pinus halepensis Mill. and Olea europaea L.) on Soil Properties after Wildfire Disturbance in Mediterranean Croatia

Abstract

On 28 July 2019, in the hinterland of Šibenik City, 900 ha were affected by wildfire of moderate to high severity. This study aims to evaluate the effects of two mulch treatments—needles of Pinus halepensis Mill. (PM) and leaves of Olea europaea L. (OM), as compared to an unmulched control (UM)—on soil quality. The study was conducted over 15 months, and soil samples were collected every 3 months. The studied soil properties were soil water repellence (SWR; composite, 1–2, 0.5–1, 0.5–0.25, <0.25 mm), soil hydraulic conductivity (SHC), mean weight diameter (MWD), water stability of aggregates (WSA), soil pH and electrical conductivity (EC), soil organic matter (SOM), total sulphur (TS), total carbon (TC), total nitrogen (TN), extractable phosphorus (P2O5), and available potassium (K2O). Six principal component analyses (PCA) were applied to observe the temporal dynamics of the soil properties studied for each sampling date. Mulching increased the aggregate stability (MWD and WSA) and improved SHC. SWR was only indicated on the first sampling date. Soil pH and EC showed high variability due to natural soil processes and vegetation regrowth. PM showed higher efficiency in increasing the TS, TC, and SOM, while OM increased soil P2O5 and K2O. Both mulch treatments increased the soil nutrient content, but the effect was variable due to the different chemical compositions of the material. Using native mulch is recommended because it improves soil quality.