Elsevier

Geoderma

Volumes 221–222, June 2014, Pages 131-138
Geoderma

Forest fire effects on soil chemical and physicochemical properties, infiltration, runoff, and erosion in a semiarid Mediterranean region

https://doi.org/10.1016/j.geoderma.2014.01.015Get rights and content

Highlights

  • Infiltration rate, runoff, and soil loss under forest fires were studied.

  • Chemical soil properties were altered under different fire and heat conditions.

  • Heat increased aggregate stability and decreased runoff and soil loss.

  • Differences in runoff and soil loss were decreased in consecutive rainstorms.

Abstract

Forest fires are a major environmental concern, especially in the semiarid Mediterranean regions, where the long dry and hot summers and mild winters favor outbreaks of wildfires. The objective of this work was to study the effects of different fire treatments on physical, chemical, and physicochemical properties of Pale rendzina, and their impact on infiltration rate (IR), runoff and soil loss under consecutive rainstorms. After a wildfire in a forest located in northern Israel, soil samples were taken from an area that was directly exposed to fire (direct fire treatment) and from adjacent unburned (unburned soil treatment). Part of the unburned soil was heated in a muffle at 300 °C (heated soil treatment). Runoff, soil loss and IR values were measured for the various samples using a laboratory rainfall simulator, and aggregate stability was determined using slaking and dispersion values. The organic matter, clay, and sand content, and cation exchange capacity were significantly lower in the heated soil than in the unburned soil. The CaCO3 content in the heated soil was significantly higher than in the unburned and direct fire soils. In general, the IR values were highest, intermediate, and lowest and the runoff and soil loss amounts were lowest, intermediate, and highest in the heated, direct fire, and unburned soils, respectively. However, these differences decreased with progression of the consecutive rainstorms. Heating the soil to 300 °C enhanced soil-structure stability, most likely due to increased dehydration of 2:1 clay minerals and transformation of iron and aluminum oxides which acted as cementing agents. In addition, soil heating increased the electrical conductivity (EC) and decreased the sodium adsorption ratio in the heated soil solution in the first rainstorm. These processes limited clay dispersion and seal formation in the heated soil, leading to high IR values and low runoff and soil loss. In the second and third rainstorms, EC of the soil solution decreased, which in turn increased clay dispersion. This lessened the differences in the IR values and runoff and soil loss amounts between the fire treatments in these rainstorms compared to the first rainstorm.

Introduction

Semiarid Mediterranean regions are characterized by long, dry and hot summers and short, wet, mild winters (Hötzl, 2008). These conditions are favorable for wildfires and indeed, there has been an increase in the number of wildfires and total burnt area in the Mediterranean region since the 1960s (Kliot, 1996, Pausas and Vallejo, 1999, Wittenberg and Malkinson, 2009). The rise in the number of wildfires is ascribed mainly to the accumulation of combustible fuels in abandoned areas (Pausas and Fernández-Muñoz, 2012, Shakesby, 2011), afforestation of mono-specific flammable tree species (Shakesby, 2011), and climate change (Pausas, 2004, Pausas and Fernández-Muñoz, 2012). Possible harmful effects of forest fire include total or partial loss of vegetation and litter cover in the forest (e.g., Ben-Hur et al., 2011, Shakesby, 2011, Soto et al., 1997), increases in surface runoff, soil erosion, and downstream flooding (Ben-Hur et al., 2011, Wagenbrenner et al., 2006), and export of sediments, organic matter, nutrients, and pollutants that can endanger downstream aquatic and flood-zone habitats and associated human infrastructures (Ferreira et al., 2008, Shakesby and Doerr, 2006).

Reduction of infiltration rates (IRs) and an increase in surface runoff and soil erosion following forest fires have been widely reported (e.g., Benavides-Solorio and MacDonald, 2001, Benavides-Solorio and MacDonald, 2005, Inbar et al., 1997, Inbar et al., 1998, Martin and Moody, 2001, Mayor et al., 2007, Moody and Martin, 2001, Shakesby, 2011, Wittenberg and Inbar, 2009). The increase in runoff and soil erosion has been attributed mainly to: (i) increasing soil water repellency that can decrease the IR (DeBano, 2000, DeBano et al., 1998, Letey, 2001, Neary et al., 1999); (ii) a decrease in transpiration as a result of vegetation losses in the forest which, in turn, alters the soil–water relationships (Ben-Hur et al., 2011); (iii) amplification of soil proofing by transport and accumulation of ash particles (Cerdà and Doerr, 2008, Etiégni and Campbell, 1991, Larsen et al., 2009, Mallik et al., 1984, Martin and Moody, 2001, Neary et al., 1999, Pannkuk and Robichaud, 2003, Woods and Balfour, 2010).

Soils in semiarid regions are characterized by low organic matter and high expandable clay mineral contents (Singer, 2007), properties that can decrease the stability of soil structure (Ben-Hur, 2008). When these soils are exposed to the impact of raindrops, a structural seal develops at the soil surface (Ben-Hur, 2008, Morin et al., 1981). This seal is thin (a few millimeters) and is characterized by greater density, higher strength, finer pores, and lower saturated hydraulic conductivity than the underlying soil (Chen et al., 1980, Gal et al., 1984, McIntyre, 1958, Onofiok and Singer, 1984, Wakindiki and Ben-Hur, 2002, West et al., 1992), leading to a decrease in IR (Assouline, 2004, Ben-Hur et al., 1985a, Morin et al., 1981). McIntyre (1958) found that the structural seal consists of two distinct parts: an upper skin seal and a “washed-in” zone with decreased porosity attributed to the accumulation of dispersed clay particles. Its formation is a result of two complementary mechanisms: (i) physical disintegration of aggregates at the soil surface caused mainly by the impact energy of raindrops and fast wetting of the soil, and (ii) chemical dispersion of clay particles, which migrate into the soil with the infiltrating water and clog the pores immediately beneath the surface, forming the “washed-in” zone (Agassi et al., 1981, Lado et al., 2004b, Morin et al., 1981). Soil erosion involves two major processes: (i) detachment of soil material from the soil surface, and (ii) transport of the resulting sediments, mainly by surface runoff (Watson and Laflen, 1986).

Soil detachment and seal formation depend on aggregate stability, and therefore on soil components and soil-solution properties. Clay minerals, iron and aluminum oxides, CaCO3, and organic matter in the soil can act as cementing materials that hold the particles together in the aggregate against the impact energy of raindrops and fast wetting of the soil, leading to higher aggregate stability (Lado et al., 2004b, Oades and Waters, 1991, Rimmer and Greenland, 1976, Singer, 1994, Six et al., 2000). An increase in sodium adsorption ratio (SAR) and a decrease in electrical conductivity (EC) in the solution of the upper soil layer might enhance chemical dispersion of the clay and formation of the washed-in zone, resulting in decreased IR and increased runoff amount and transport of detached particles (Agassi et al., 1981, Agassi et al., 1994, Ben-Hur et al., 1998, Kazman et al., 1983, Shainberg and Letey, 1984, Wakindiki and Ben-Hur, 2002). Fire and high temperatures, however, can also affect the physical and chemical properties of the soil and the physicochemical properties of its solution (e.g., Badía and Martí, 2003, Certini, 2005, DeBano et al., 1998, Gimeno-García et al., 2000, Giovannini and Lucchesi, 1997, Giovannini et al., 1988, Giovannini et al., 1990, González-Pérez et al., 2004, Mataix-Solera et al., 2011, Neary et al., 1999). Gimeno-García et al. (2000) and González-Pérez et al. (2004) found that severe fire decreases organic matter content in the soil. Arocena and Opio (2003), Giovannini et al. (1988) and Ulery and Graham (1993) found textural changes in soils after heating them to > 200 °C. Hernández et al. (1997), Iglesias et al. (1997), Kutiel and Inbar (1993), Kutiel and Naveh (1987), Kutiel et al. (1995), Pardini et al. (2004) and Terefe et al. (2008) found that soil heating significantly alters the physicochemical properties of the topsoil solution, changing the ion composition and concentration.

Exposing the soil to wetting–drying cycles can significantly change the concentration and composition of ions in the soil solution which, in turn, can affect seal formation, soil hydraulic properties, and soil loss under consecutive rainstorms (e.g., Ben-Hur et al., 1985b, Ben-Hur et al., 1989, Hardy et al., 1983, Levy et al., 1986, Morin and Benyamini, 1977). Rajaram and Erbach (1998) showed that exposing a clay loam soil to wetting–drying cycles result in an increase in aggregate cohesion and size, but its stability decreased with an increase in drying stress. Wagner et al. (2007) found that wetting–drying cycles initiate aggregate evolution irrespective of soil clay content, although high clay content yielded more stable aggregates. All of these findings suggest that interactions between forest fire, soil heating, and wetting–drying cycles can affect the soil structure and seal, runoff, and soil loss under consecutive rainstorms. These interactions, however, have been little studied or documented.

Wildfires differ in terms of intensity and severity, and therefore their impact on soil properties, runoff and erosion can be diverse (Keeley, 2009). Even within a specific wildfire, local variations in lithology, topography, plant composition, fuel-load distribution, and microclimatic conditions in the forest can result in a heterogeneous spatial distribution of fire intensity and severity (Kutiel et al., 1995, Lavee et al., 1995, Shakesby, 2011). Therefore, in a forest exposed to fire, this spatial distribution can lead to several effects on the underlying soil, such as: soil barely affected by the fire, soil exposed to direct fire, and soil exposed to the heat of the fire only, with no direct flame contact. The objective of the present work was to study the effects of different fire and heating conditions on the physical, chemical, and physicochemical properties of soil, and their impact on IR, surface runoff and soil loss under consecutive rainstorms. We focused on Pale rendzina, a very common soil in forests of the Eastern Mediterranean region.

Section snippets

Experimental site, soil sampling, and tested treatments

The studied area was a planted forest located near the city of Safed in northern Israel (32°58′39″N, 35°30′22″E). The forest stand is a combination of Aleppo pine (Pinus halepensis) and Turkish pine (Pinus brutia) with a mixture of old (> 60 yr) and young trees. The average altitude of the forest is 840 m above sea level with a typical Mediterranean climate: average annual temperature and precipitation are 22 °C and 600 mm, respectively. The soil in the forest is a sandy clay loam, Pale rendzina (

Results and discussion

The physical and chemical characteristics of the unburned soil, soil exposed to direct fire, heated soil, and their respective water extracts are presented in Table 1. The fire treatments were found to differentially alter the soils' characteristics. Heating the soil to 300 °C significantly decreased its organic matter content compared to the unburned soil (Table 1), as a result of its combustion by the high temperature during the heating process. Similar results were found by Giovannini et al.,

Summary and conclusions

  • The various fire treatments changed the physical and chemical properties of the studied soils. Heating the soil to 300 °C combusted the organic matter and significantly decreased its content in the soil. Moreover, the contents of clay and sand decreased and that of silt increased. These changes in mechanical composition were attributed mainly to: (i) dehydration of 2:1 clay minerals leading to strong interactions among the clay particles, which formed silt-sized particles and less clay-sized

Acknowledgments

This project was funded by Xunta de Galicia Project 07MRU007103PR and the Smaller–Winnikow Fellowship Fund for Environmental Research.

References (99)

  • M. Inbar et al.

    Runoff and erosion processes after a forest fire in Mount Carmel, a Mediterranean area

    Geomorphology

    (1998)
  • P. Kutiel et al.

    Fire impacts on soil nutrients and soil erosion in a Mediterranean pine forest plantation

    Catena

    (1993)
  • P. Kutiel et al.

    The effect of fire-induced surface heterogeneity on rainfall-runoff-erosion relationships in an eastern Mediterranean ecosystem, Israel

    Catena

    (1995)
  • H. Lavee et al.

    Effect of surface roughness on runoff and erosion in a Mediterranean ecosystem: the role of fire

    Geomorphology

    (1995)
  • B. Ludwig et al.

    Modelling cation composition of soil extracts under ashbeds following an intense slashfire in a eucalypt forest

    For. Ecol. Manage.

    (1998)
  • J. Mataix-Solera et al.

    Can terra rossa become water repellent by burning? A laboratory approach

    Geoderma

    (2008)
  • J. Mataix-Solera et al.

    Fire effects on soil aggregation: A review

    Earth Sci. Rev.

    (2011)
  • J. Mataix-Solera et al.

    Soil properties as key factors controlling water repellency in fire-affected areas: evidences from burned sites in Spain and Israel

    Catena

    (2013)
  • A.G. Mayor et al.

    Post-fire hydrological and erosional responses of a Mediterranean landscape: seven years of catchment-scale dynamics

    Catena

    (2007)
  • J. Morin et al.

    The effect of raindrop impact on the dynamics of soil surface crusting and water movement in the profile

    J. Hydrol.

    (1981)
  • D.G. Neary et al.

    Fire effects on belowground sustainability: a review and synthesis

    For. Ecol. Manage.

    (1999)
  • G. Pardini et al.

    Relative influence of wildfire on soil properties and erosion processes in different Mediterranean environments in NE Spain

    Sci. Total Environ.

    (2004)
  • G. Rajaram et al.

    Drying stress effect on mechanical behaviour of a clay-loam soil

    Soil Tillage Res.

    (1998)
  • P. Robichaud

    Fire effects on infiltration rates after prescribed fire in Northern Rocky Mountain forests, USA

    J. Hydrol.

    (2000)
  • R.A. Shakesby

    Post-wildfire soil erosion in the Mediterranean: review and future research directions

    Earth Sci. Rev.

    (2011)
  • R.A. Shakesby et al.

    Wildfire as a hydrological and geomorphological agent

    Earth Sci. Rev.

    (2006)
  • R.A. Shakesby et al.

    The erosional impact of soil hydrophobicity: current problems and future research directions

    J. Hydrol.

    (2000)
  • B. Soto et al.

    Effects of burning on nutrient balance in an area of gorse (Ulex europaeus L.) scrub

    Sci. Total Environ.

    (1997)
  • T. Terefe et al.

    Influence of heating on various properties of six Mediterranean soils. A laboratory study

    Geoderma

    (2008)
  • S.W. Woods et al.

    The effects of soil texture and ash thickness on the post-fire hydrological response from ash-covered soils

    J. Hydrol.

    (2010)
  • M. Agassi et al.

    Effect of electrolyte concentration and soil sodicity on infiltration rate and crust formation

    Soil Sci. Soc. Am. J.

    (1981)
  • M. Agassi et al.

    Effect of drop energy and soil and water chemistry on infiltration and erosion

    Water Resour. Res.

    (1994)
  • L.E. Allison

    Organic carbon

  • L.E. Allison et al.

    Carbonate

  • S. Assouline

    Rainfall-induced soil surface sealing: a critical review of observations, conceptual models, and solutions

    Vadose Zone J.

    (2004)
  • D. Badía et al.

    Plant ash and heat intensity effects on chemical and physical properties of two contrasting soils

    Arid Land Res. Manage.

    (2003)
  • L.D. Baver et al.

    Soil Physics

    (1972)
  • J. Benavides-Solorio et al.

    Post-fire runoff and erosion from simulated rainfall on small plots, Colorado Front Range

    Hydrol. Process.

    (2001)
  • J.D. Benavides-Solorio et al.

    Measurement and prediction of post-fire erosion at the hillslope scale, Colorado Front Range

    Int. J. Wildland Fire

    (2005)
  • M. Ben-Hur

    Seal formation effects on soil infiltration and runoff in arid and semiarid regions under rainfall and sprinkler irrigation conditions

  • M. Ben-Hur et al.

    Effect of soil texture and CaCO3 content on water infiltration in crusted soil as related to water salinity

    Irrig. Sci.

    (1985)
  • M. Ben-Hur et al.

    Effect of water quality and drying on soil crust properties

    Soil Sci. Soc. Am. J.

    (1985)
  • M. Ben-Hur et al.

    Cotton canopy and drying effects on runoff during irrigation with moving sprinkler systems

    Agron. J.

    (1989)
  • M. Ben-Hur et al.

    Compaction, aging, and raindrop-impact effects on hydraulic properties of saline and sodic vertisols

    Soil Sci. Soc. Am. J.

    (1998)
  • M. Ben-Hur et al.

    Soil structure changes: aggregate size and soil texture effects on hydraulic conductivity under different saline and sodic conditions

    Aust. J. Soil Res.

    (2009)
  • M. Ben-Hur et al.

    Overland flow, soil erosion and stream water quality in forest under different perturbations and climate conditions

  • G. Certini

    Effects of fire on properties of forest soils: a review

    Oecologia

    (2005)
  • H.D. Chapman

    Cation-exchange capacity

  • Y. Chen et al.

    Scanning electron microscope observations on soil crusts and their formation

    Soil Sci.

    (1980)
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