Effects of salvage logging on soil properties and vegetation recovery in a fire-affected Mediterranean forest: A two year monitoring research

Highlights

• Mediterranean soils developed over marls are very vulnerable to degradation after wildfire.

• Post-fire salvage logging affects soil quality over short- and medium-terms.

• Plant recovery is also affected by salvage logging treatments after forest fire.

• Reduced plant cover and lower soil quality could increase soil erosion rates.

Abstract

Post-fire management can have an additional impact on the ecosystem; in some cases, even more severe than the fire. Salvage logging (SL) is a common practice in most fire-affected areas. The management of burnt wood can determine microclimatic conditions and seriously affect soil properties. In some cases, the way of doing it, using heavy machinery, and the vulnerability of soils to erosion and degradation can make this management potentially aggressive to soil. Research was done in “Sierra de Mariola Natural Park” (E Spain). A forest fire (> 500 ha) occurred in July 2012. In February 2013, SL treatment was applied in a part of the affected forest. Plots for monitoring this effect were installed in this area and in a similar nearby area where no treatment was done, used as control (C). Soil samplings were done immediately after treatment and every 6 months during two years. Some soil properties were analysed, including organic matter (OM) content, nitrogen (N) available phosphorous (P) basal soil respiration (BSR), microbial biomass carbon (C_mic), bulk density (BD), water repellency (WR), aggregate stability (AS) and field capacity (FC). SL treatment caused an increase in BD, a decrease of AS, FC, OM and N. In the control area, in general the soil properties remained constant across the 2 years of monitoring, and the microbial parameters (BSR and C_mic), initially affected by the fire, recovered faster in C than in the SL area. Plant recovery also showed some differences between treatments. No significant differences were observed in the number of plant species recorded (richness) comparing C versus SL plots, but the number of individuals of each species (evenness) was significantly higher in C plots. In conclusion, we can affirm that for the conditions of this study case, SL had a negative effect on the soil-plant system.

Introduction

Forest fires are part of the natural dynamic of the terrestrial ecosystem (Le Houerou, 1977, Naveh, 1975), and are also reflected in the fossil record and the great number of species adaptation due to this natural disturbance. The Mediterranean ecosystems have been and currently are very influenced by this phenomenon, as fire is a recurrent fact in the Mediterranean area, and one of the main causes of changes in these ecosystems. Fire induces changes in soil properties (e.g.: Andreu et al., 1994, Cerdà, 1996, Certini, 2005, Llovet et al., 2008), and can have an impact on soil productivity of burnt areas (Robichaud, 2009) especially when they are affected by huge and high intensity fires such as those that are frequent in some summer seasons under extreme weather conditions.

Post-fire management can have a negative impact on the soils being in some cases even more severe than the fire itself. Salvage logging (SL) is a common management technique in fire-affected areas, comprising the extraction of the burnt wood and in many cases using heavy machinery and dragging the trunks over soil, leading to a consequent increase in its vulnerability to erosion and soil degradation (Mataix-Solera et al., 2015, Mataix-Solera et al., 2016).

González-Ochoa et al. (2004), Martínez-Sánchez et al. (1999), Pausas et al. (2004), Vega et al. (2008), and Griffin et al. (2013), among others, studied the vegetation dynamic in areas affected by fires and where SL treatments were applied. All of them concluded that to a greater or lesser degree there was a negative influence on plant recovery. Wagenbrenner et al. (2016), Morgan et al. (2014) and Sexton (1998) observed, reduced vegetation cover in areas where SL treatment was used compared to unlogged areas. Vegetation recovery after post-fire SL might have been hampered by the soil compaction (Page-Dumroese et al., 2006) or lower water availability (Marañón-Jiménez et al., 2013) caused by the equipment traffic. Numerous studies have demonstrated that soil compaction in forested environments can also persist for several decades, which can impede plant development for prolonged time periods (Wert and Thomas, 1981, Froehlich et al., 1985, Vora, 1988, Reisinger et al., 1992, Brevik, 2013).

Previous studies have shown that post-fire logging can increase soil disturbance and erosion (Klock, 1975, McIver and Starr, 2001, McIver and McNeil, 2006, Slestak et al., 2015, Wagenbrenner et al., 2015, Peterson and Dodson, 2016), alter the cover and composition of recovering native vegetation (Stuart et al., 1993, Purdon et al., 2004, Keyser et al., 2009, Ritchie et al., 2013), damage natural tree regeneration (Keyser et al., 2009) and increase surface woody fuels within 2–4 years after fire and logging (Donato et al., 2006).

There are several factors contributing to the increased runoff rates and erosion after SL treatment. Wagenbrenner et al. (2016) attributed the increase in runoff after logging equipment traffic to lower infiltration rates resulting from reduced micro and macro soil porosity (Ares et al., 2005, Horn et al., 2004, Startsev and McNabb, 2000), associated it with an increase in soil compaction. Wilson (1999), in his rainfall simulation experiments found that post-fire SL did increase surface runoff and erosion in part caused by the disruption of the biotic crust by heavy equipment. However, in NE Spain Marques and Mora (1998), observed that the sediment yields in burned areas as a consequence of the SL treatment were moderately low, and recently in NW Spain, Fernández and Vega (2016) didn't find any detrimental effect of SL treatment compared to natural regeneration. These contradictory results could be due to factors such as type of soil, when and how the SL treatment is carried out, and meteorological conditions which can be decisive.

Little is known about what effect this kind of treatment has in soil properties and how this can affect the ecosystem response to the fire and post-fire managements. Marañón-Jiménez et al. (2011) observed a decrease in soil respiration after salvage logging treatment, and Serrano-Ortiz et al. (2011) a negative impact for potential carbon sequestration. Post-fire SL treatment reduces the vegetation cover (Serrano-Ortiz et al., 2011, Wagenbrenner et al., 2016), and affects soil micro-climate (Lindenmayer and Noss, 2006), decomposition, and ecosystem carbon storage capacity. Moreover, post-fire SL can reduce organic matter input to the soil by removing the standing dead trunks that would eventually fall and contribute to soil organic carbon storage (Smith et al., 2000, DeLuca and Aplet, 2008, Moroni et al., 2010, Seedre et al., 2011). All these factors can also provoke a fast response in microbial properties, producing important changes in the content of microorganisms and their activity (Burton et al., 2000, Nadelhoffer, 2000, Tang et al., 2003).

In this research we studied the immediate, short and medium–term effect (2 years of monitoring) of a SL treatment applied in a recently burned area (6 months after fire) with a soil vulnerable to degradation in physical, chemical and microbial soil properties, and also in the restoration of vegetation recovery, by comparison with no treatment (control) to study whether this management can have an impact on soil quality and the magnitude of these changes.