Impact of torrential rainfall and salvage logging on post-wildfire soil properties in NE Iberian Peninsula

Abstract

Mediterranean ecosystems are prone to wildfires, subsequent to which torrential rainfall and salvage logging are liable to modify soil properties. However, few studies to date have examined the impact of both types of disturbance on the same plot. The aim of this study is to examine the joint, medium-term effects of a torrential rainfall event, immediately following a wildfire, and post-fire salvage logging on the same plot. Three days after the wildfire we established and sampled an experimental plot (72 m2). The second sampling campaign was conducted 4 days after the onset of an intense rainfall event and 7 days after the wildfire broke out. Six months after the wildfire, salvage logging was implemented using heavy machinery to extract burned logs. A third sampling campaign was conducted one year after the wildfire; and a fourth was carried out four years after the event. In each campaign, 30 points, spaced 2 m apart, were sampled at a depth of 0–5 cm. Soil properties analyzed included soil water repellency (SWR), aggregate stability (AS), infiltration rate (in mm/h), soil organic matter (SOM), total nitrogen (TN), inorganic carbon (IC), C/N ratio, pH, electrical conductivity (EC), extractable calcium (Ca), magnesium (Mg), sodium (Na), potassium (K), aluminum (Al), manganese (Mn), iron (Fe), zinc (Zn), copper (Cu), boron (B), chromium (Cr), available phosphorous (P), extractable silicon (Si), and sulfur (S). Soil extractable elements refers to ammonium acetate extractable fraction and soil available P refers to plant available P. Post-fire rainfall affected pH, EC, Ca, Mg, Zn, P, Si and S. Salvage logging modified SOM, C/N, pH, EC, Ca, Mg, K, Mn, Fe, Zn, Cr, P and Si in the short term and IC, Ca, Al, Mn, Zn, Cr and B in the medium term. The post-fire occurrence of torrential rainfall and salvage logging, in particular the human intervention, had a marked impact on soil properties, resulting in soil degradation. To date, the long-term impact of salvage logging on forest soils has yet to be verified.