Impacts of Wildfire Frequency On Plant Recovery, Soil Properties And Water Storage In Pine Woodlands of North-Central Portugal

Abstract PurposeIncreasing wildfire frequency in Mediterranean-basin together with drought periods expansion could affect plant-soil-water dynamics processes. The goal is to assess the effects of wildfire frequency on plant recovery, soil properties, soil moisture content (SMC; %) and effective soil water content (ESWC; %) during the first hydrological year after a 2012 moderate-severity-wildfire.MethodsThis study was conducted in pine woodlands of North-central Portugal affected by 1-, 4-wildfires and unburnt (1975-2012). Soil samples were gathered from plant/bare microsites at top-mid-bottom hillslope positions to determine bulk density, soil texture, soil moisture, soil organic matter content-SOM, pF-curves (available water content-AWC, field capacity-FC, permanent wilting point-PWP) (n=54) during four dry/wet periods. Soil cover, plant recovery and soil water repellency were measured. On the burnt areas 72 sensors daily/seasonal monitored SMC and ESWC at two depths (2.5/7.5 cm) and two microsites (plant/bare). ResultsThe 1 fire hillslopes showed higher plant recovery than the 4 fires hillslopes. SOM was higher in the burnt soils (17-20%) than in the unburnt ones (12-14%). Wildfire frequency: i) increased the water stress for plants and led to both maximum and minimum values of SMC/ESWC, respectively, for the wet-/dry-seasons; ii) reduced the capacity of the soils to retain water (decreased FC/AWC, increased PWP), being more accentuated in bare microsites. ConclusionThe increasing wildfire frequency and the predicted expansion of drought periods promotes lower water availability for plants in the more frequent bare soil patches. The water-stress window of the dry season happened sooner and extended for longer as increasing wildfire frequency.