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Dynamics of topsoil carbon stocks after prescribed burning for pasture restoration in shrublands of the Central Pyrenees (NE-Spain)
Abstract
Prescribed burning has been recently readopted as a management practice in the Central Pyrenees (NE-Spain) to stop shrub encroachment processes and recover pasturelands. The immediate effects of prescribed burning on soil C stocks and related biological properties and their evolution in the short- to mid-term after burning were assessed. The study was conducted during three autumnal prescribed burnings in the Central Pyrenees in the municipalities of Buisán, Asín de Broto and Yebra de Basa. At each site, the topsoil Ah horizon was sampled at soil depths of 0-1, 1-2 and 2-3 cm immediately before and immediately after burning. Additionally, seasonal samplings were conducted every 6 months up to one year in the case of the Asín and Yebra sites and up to 24 months at the Buisán site. The total soil organic C stock (SOCS) total N stock (NS), microbial biomass C (MBC), soil basal respiration (SR) and β-D-glucosidase activity were analyzed. The maximum temperatures recorded at the soil surface were 438 ºC (Buisán), 768 ºC (Asín) and 595 ºC (Yebra). At the Buisán site, burning significantly decreased the SOCS (-52 %), NS (-44 %), MBC (-57 %), SR (-72 %) and glucosidase activity (-66 %) at 0-1 cm depth, whereas fire had no direct effects on soil at the Asín and Yebra sites. The contrasting effects of burning on soil that were observed among sites were found to be related to differences in fire residence time. The prescribed fire at the Buisán site was on a plain slope under slow winds (<8 km h-1) at a burning rate of 0.64 ha h-1, which produced greater impacts on the soil properties than the burnings at the Asín and Yebra sites, where fire spread rapidly (2.72 and 1.43 ha h-1, respectively). At the Buisán site, the SOCS and NS recovered to the unburned values 24 months after burning. One year after burning, the SOCS at Asín were 60 % higher than those of the unburned soils at 0-1 cm depth. At all sites a decreasing trend in soil biological activity in the short- and mid-term was observed. From the results it can be concluded that: 1) the direct effects of burning on soil are highly dependent on the environmental conditions, 2) in the mid-term, the reduction in soil biological activity and the incorporation of ashes and charred plant remains led to an increase in the SOCS of the burned soils.
... The total nitrogen (TN) content was measured using a CHN Leco 628 elemental analyzer and used to express the C/N ratio (g of SOC per g of TN). The microbial biomass carbon (MBC) was estimated using the fumigationextraction method [26], using an extraction factor of 0.38 [27], and was expressed in g of MBC per kg of dry soil. The labile or dissolved organic carbon (DOC), expressed as a fraction of SOC (g of DOC per 100 g of SOC), was obtained from the K 2 SO 4 soluble organic carbon prior to fumigation. ...
... Moreover, in prescribed burnings and wildfires, post-fire increases in N content have been reported due to N-rich ash being incorporated into the soil. Girona-García et al. [27] explained that, when ash is not incorporated into the soil, no significant increases in N stocks can be detected after prescribed burnings. Knicker et al. [36] explains that, as in the present study, soils subjected to moderate heating do not usually experience major C/N differences compared to the unburned soils because the formation of significant amounts of recalcitrant N forms requires high temperatures. ...
... When the temperatures reached were high, the PB produced a partial sterilization of the soil immediately post-fire [38,39]. On the other hand, at lower temperatures, other works reported no changes in this parameter [17,27]. the previously discussed results for DOC and ROC. ...
Fire causes changes in many soil attributes, depending on multiple factors which are difficult to control in the field, such as maximum temperature, heat residence time, charred material incorporation, etc. The objective of this study is to evaluate the effect of a gradient of fire intensities on soils at the cm scale. Undisturbed topsoil monoliths were sampled under scrubs in the subalpine stage in the Southern Pyrenees (NE Spain). They were burned, under controlled conditions in a combustion tunnel, to obtain four charring intensities (CIs), combining two temperatures (50 and 80 °C) and two residence times (12 and 24 min) reached at 1 cm depth from the soil. Unburned soil samples were used as a control. All soils were sampled, cm by cm, up to 3 cm deep. The following soil properties were measured: soil respiration (basal, bSR and normalized, nSR), β-D-glucosidase (GLU), microbial biomass carbon (MBC), glomalin-related soil proteins (GRSPs), soil organic carbon (SOC), labile carbon (DOC), recalcitrant organic carbon (ROC), total nitrogen (TN), soil pH, electrical conductivity (EC) and soil water repellency (SWR). Even at low intensities, GLU, SOC and total GRSP were significantly reduced and, conversely, SWR was enhanced. At the higher CIs, additional soil properties were significantly reduced (MBC and C/N) or increased (DOC, ROC, nSR, easily extractable GRSP). This study demonstrates that there is a differential degree of thermal sensitivity in the measured biochemical soil properties. Furthermore, these properties are more affected at 0–1 cm than at 1–2 and 2–3 cm soil thicknesses.
... The impacts of prescribed burns on soils are spatially variable due to the high heterogeneity of the environmental conditions (Hubbert et al., 2006;Girona-García et al., 2019). Although prescribed burns imply the application of low-intensity fire (Fernandes et al., 2013), different intensities and severities have been reported (Alcañiz et al., 2018). ...
... Although prescribed burns imply the application of low-intensity fire (Fernandes et al., 2013), different intensities and severities have been reported (Alcañiz et al., 2018). Therefore, their effects on soil properties can be very variable depending on the fire and vegetation type, the previous soil conditions, and their correct execution (Scharenbroch et al., 2012;Badía et al., 2017;Alcañiz et al., 2018;Girona-García et al., 2019). Additionally, the sampling method is another factor that can also influence the variations of soil fire impacts, such as the time elapsed after the fire, the mixture of charred O and Ah horizons, and even the depth of soil sampling with a dilution effect (Armas-Herrera et al., 2016;Lucas-Borja et al., 2019;Pereira et al., 2023). ...
... These discrepancies are likely due to the different soil burn severity (SBS). Likewise, soil moisture behavior can vary according to the soil moisture conditions and the prescribed burn type (Girona-García et al., 2019). Even depending on the previous soil moisture conditions, this property can protect the soil against the effects of fire (Badía et al., 2017). ...
Prescribed burn is a tool that must imply low soil burn severity (SBS) levels; however, a wide range of soil impacts have been demonstrated because of the influence of very variable factors. The effects on biological, physical, and chemical soil properties are well reported in numerous studies; nonetheless, there are still questions about the effect of prescribed burns on soils at the micro-scale. As a result, an analysis of the link between micromorphological features and SBS does not currently exist. Thus, the main aim of the present study is to perform a micro-scale evaluation for complementing the SBS visual examination after prescribed burning in a managed pine forest in western Mexico. Morphometry and micromorphology analyses of mineral soil revealed that at low SBS levels, only the soil structure in the first centimeter is affected by prescribed burns. While at high SBS, the prescribed burn affected the first 2 cm, showing soil structure disturbance, ash filling porous, and soil aggregates getting reddish. Therefore, immediate actions have to be made by land managers after applying prescribed burns before the first rain to prevent post-fire surface soil erosion, particularly in bare soil patches where the burned aggregates are more susceptible to rain splash and runoff.
... But, even so, the most sensitive properties, like the microorganisms or the organic matter (Santín and Doerr, 2016), could be severely affected , especially under dense shrubs. In fact, some studies performed in controlled burned areas with E. horridum show immediate and short-to mid-term effects on topsoil organic matter and microbial activity (Armas-Herrera et al., 2018;Girona-García et al., 2019, 2018a In this sense, in the controlled burning of a calcareous forest topsoil, the activity of soil enzymes responsible for participating in the C-cycle (β-D-glucosidase) and certain fractions of soil organic matter have been shown to be particularly sensitive to heat (Pereira et al., 2023). Concretely, β-D-glucosidase (GLU) is considered a soil quality indicator and is directly related to the quantity and quality of soil organic matter (Turner et al., 2002). ...
... Each of the four points were randomly selected with a five-meter separation from each other. Samples from B0 treatment were taken beside the UB ones, a few minutes after the PB was performed, following a similar design to Girona-García et al. (2019). ...
... In each plot, 4 soil replicates (n) for 3 soil depths (0-1, 1-2 and 2-3 cm) have been sampled. Microbial biomass carbon (MBC), expressed as g MBC per kg soil, was determined by the fumigation-extraction method (Vance et al., 1987), using an extraction factor of K ec = 0.38 (Girona-García et al., 2019); this method consists of soil fumigation with chloroform followed by an extraction with 0.5 M K 2 SO 4 (1:5 w/v). Soil respiration or CO 2 efflux was measured in an incubation assay of soil samples under optimal temperature (25°C) and moisture (50 % water-holding capacity) conditions. ...
Since the last half of the 20th Century, scrubs have been invading subclimatic grasslands in the montane and subalpine stages of Spain due to the decrease of the grazing activity. This shrub encroachment reduces biodiversity and the ecopastoral value of the region and leads to the accumulation of woody fuel, which represents a high fire risk. To control the encroachment, prescribed burnings are performed but their effects on soils over the years are still undetermined. This study aims to research about the long-term effects of a prescribed burn of Echinospartum horridum (Vahl) Roth. on topsoil organic matter and biological activity. Soil sampling was carried out in Tella-Sin (Central Pyrenees, Aragón, Spain) and four treatments were selected: unburned (UB), immediately burned (B0), burned 6 years before (B6, mid-term) and burned 10 years before (B10, long-term). Among the obtained results, an immediately after burning decrease on β-D-glucosidase activity (GLU) was found, which did not recover over time. Other properties did not have an immediate reduction but did so over time: total soil organic carbon (SOC), labile carbon (DOC), total nitrogen (TN), basal soil respiration (bSR). And others were not affected at all: microbial biomass carbon (MBC), and the microbial metabolic quotient (qCO2). Moreover, the normalized soil respiration (nSR) increased with the time, which implies an acceleration of the potential mineralization of soil organic carbon. In short, although the elimination of the dense shrubs by fire has not entailed major immediate soil modifications, which would be typical of a low severity prescribed burn, several mid- and long-term effects in the C cycle have been observed. Future studies will have to discern what is the main cause of these modifications (soil microbial composition, edaphoclimatic changes, lack of soil cover and soil loss, soil fertility, etc.).
... But, even so, the most sensitive properties, like the microorganisms or the organic matter (Santín and Doerr, 2016), could be severely affected , especially under dense shrubs. In fact, some studies performed in controlled burned areas with E. horridum show immediate and short-to mid-term effects on topsoil organic matter and microbial activity (Armas-Herrera et al., 2018;Girona-García et al., 2019, 2018a In this sense, in the controlled burning of a calcareous forest topsoil, the activity of soil enzymes responsible for participating in the C-cycle (β-D-glucosidase) and certain fractions of soil organic matter have been shown to be particularly sensitive to heat (Pereira et al., 2023). Concretely, β-D-glucosidase (GLU) is considered a soil quality indicator and is directly related to the quantity and quality of soil organic matter (Turner et al., 2002). ...
... Each of the four points were randomly selected with a five-meter separation from each other. Samples from B0 treatment were taken beside the UB ones, a few minutes after the PB was performed, following a similar design to Girona-García et al. (2019). ...
... In each plot, 4 soil replicates (n) for 3 soil depths (0-1, 1-2 and 2-3 cm) have been sampled. Microbial biomass carbon (MBC), expressed as g MBC per kg soil, was determined by the fumigation-extraction method (Vance et al., 1987), using an extraction factor of K ec = 0.38 (Girona-García et al., 2019); this method consists of soil fumigation with chloroform followed by an extraction with 0.5 M K 2 SO 4 (1:5 w/v). Soil respiration or CO 2 efflux was measured in an incubation assay of soil samples under optimal temperature (25°C) and moisture (50 % water-holding capacity) conditions. ...
... Soil properties and processes are often negatively affected by wildfires or prescribed fires both directly through heating and indirectly through burning and destruction of plant communities in grassland/ rangeland ecosystems (Harris et al., 2007;Snyman, 2015b;Girona-García et al., 2019). The immediate and direct effects of fire are usually short-term and are restricted to the first few centimeters of the topsoil (Snyman, 2015b;Pereira et al., 2018;Girona-García et al., 2019). ...
... Soil properties and processes are often negatively affected by wildfires or prescribed fires both directly through heating and indirectly through burning and destruction of plant communities in grassland/ rangeland ecosystems (Harris et al., 2007;Snyman, 2015b;Girona-García et al., 2019). The immediate and direct effects of fire are usually short-term and are restricted to the first few centimeters of the topsoil (Snyman, 2015b;Pereira et al., 2018;Girona-García et al., 2019). The indirect influence of fire in rangelands is the partial or total loss of plant and litter biomass, as well as changes in plant community composition Abbreviations: SOM, soil organic matter; C, carbon; N, nitrogen; EC, electrical conductivity; BD, bulk density; CCE, calcium carbonate equivalent; OC, organic carbon; TN, total nitrogen; POC, particulate organic carbon; AK, available potassium; AP, available phosphorus; MR, microbial respiration; MBC, microbial biomass carbon; AA, arginine ammonification; CAT, catalase activity; URE, urease activity; ACP, acid phosphomonoesterase activity; ALP, alkaline phosphomonoesterase activity; INV, invertase activity; FR, fungal respiration; BR, bacterial respiration; L-SQI, linear soil quality index; NL-SQI, nonlinear soil quality index. ...
... and structure (Teague et al., 2008;Vermeire et al., 2014;Snyman, 2015a;Clark et al., 2018). In grassland and shrubland ecosystems, fire reduces soil organic matter (SOM) pools and substrate availability for the microbial community by decreasing carbon (C) inputs into the soil (Rice and Owensby, 2001;Fynn et al., 2003;Fultz et al., 2016;San Emeterio et al., 2016;Girona-García et al., 2019). Several studies have demonstrated a significant influence of fire on numerous soil properties, with burnt grassland and pasture soils frequently having less C, nitrogen (N), moisture, aggregate stability, and consequently the conditions are worse for the microbial life (Liu et al., 2000;Fynn et al., 2003;Snyman, 2003;Mills and Fey, 2004;Fultz et al., 2016;Alcañiz et al., 2018). ...
Recovery of soil quality after wildfire is essential for soil functioning such as nutrient cycling, resistance to biochemical degradation and sustainable plant growth. Post-fire soil quality is crucial for the maintenance of ecosystem sustainability. The objective of this study was to develop a soil quality index (SQI) for assessing post-fire soil quality in upland rangeland ecosystems of a semi-arid region in Central Iran. Soil samples were collected from burnt and unburnt plots at six rangeland sites two years after a wildfire event and analyzed for 22 soil properties. The soil microbial and biochemical properties indicated a greater magnitude of post-fire changes than soil chemical properties. The contribution of microbial respiration to soil quality, obtained using factor analysis, was the highest (36%) followed by particulate organic carbon (22%), microbial biomass carbon (15%), available phosphorus (15%) and alkaline phosphomonoesterase activity (12%). This indicates that microbial properties, labile carbon and phosphorus availability are the most important soil quality indicators to detect the wildfire effects in the study rangelands. The SQI value was, on average, 28% lower in burnt rangelands (0.39–0.55) than unburnt rangelands (0.56–0.75); indicating disturbance by wildfire would be accompanied by the loss of soil functioning. This illustrates that fire decreased soil quality, which did not recover two years after fire, probably due to the high grazing pressure and climatic conditions (i.e., longer drought periods and water limitation). Apparently, a longer period of time would be required for the complete recovery of soil quality in these semi-arid rangelands. In this study, we demonstrate that an integrated SQI would be more useful to assess post-fire soil functions than single soil properties in fire-affected rangelands of semi-arid climates.
... They even consider that this prescribed burning may have decreased the sand-sized particles of the soil, despite the inertia of the texture against heat (Badía and Martí, 2003;. These results contrast with those obtained with more recent prescribed burning of erizón, where more cases without effects than with effects have been detected and, generally, limited to the upper cm and reversible over time (Armas-Herrera et al., 2018;Girona-García et al., 2019). In many cases, it is difficult to find changes on soil properties after prescribed fires because of the limited heat transfer to the soil (Alcañiz et al., 2018). ...
... Among the few changes detected after the prescribed burning , it is worth noting the WR decrease in the burned topsoil (0-1 cm), where WR practically disappears (WDPT decreased significantly from 1335 s in unburned soil to 7 s in 1-yr burned soil). This change was not detected immediately after the fire at the Yebra de Basa site, as other soil properties related as SOC did (Girona-García et al., 2019). Instead, in a nearby prescribed burn of the same shrubs (at the experimental site of Buisán) we found the opposite effects , which were attributed to the longest duration of burning. ...
... We interpret that, although the low-intensity fast-moving prescribed burn didn't cause immediate damages (Girona-García et al., 2019), the temporary loss of a protective soil cover (vegetation, litter, ash) lead to the mobilization of soil particles, mainly fine sand, by the successive raindrop impact (the MAP is about 1000 mm/year in Yebra de Basa site). This process (splash effect) would include two steps: Science of the Total Environment xxx (xxxx) xxx-xxx Fig. 6. ...
The dense thicket Echinospartum horridum (Vahl, Rothm) is expanded in secondary pastures of the Central Pyrenees (NE-Spain). The control of this grassland encroachment is attempted through prescribed burnings, trying to minimize its direct effects on the soil. But the structural changes on the new soil surface, burned and bare, are unknown in the medium-term. To check it, soil aggregate stability (SAS), mean weight diameter of the aggregates (MWD), water repellency (WR), unsaturated hydraulic conductivity (k), and soil organic carbon (SOC) were measured in the surface (at 0–1, 1–2, 2–3, and 3–5 cm) in both unburned and 1-yr burned soils, after verifying that it suffered no direct damage. We also used the digital images of thin sections, obtained from undisturbed and oriented topsoil samples, to detect potential changes in soil microstructure.
No significant changes were found in SAS, MWD and SOC for any thickness of soil studied. But the WR, which was high before and just after burning, decreased significantly in the upper soil cm after 1-yr burning. WR decrease coincides with the 6-fold increase of the unsaturated hydraulic conductivity (k) and the presence of cappings on the burned topsoil. Cappings are coatings poor in organic matter and composed by fine sand-sized particles of angular quartz, mixed with charcoal, covering irregularly the original topsoil. The formation of cappings seems to derive from the impact of raindrops on the bare soil surface, hence its irregular spatial distribution. Summarizing, removing bushes by means of a low-intensity fast-moving prescribed burning caused the formation of discontinuous cappings without worsening significantly the rest of the measured properties.
... The magnitude and duration of soil heating determine the depth and duration of heat penetration, and therefore the extent of secondary effects caused by a fire (Girona-García et al. 2019;Brady et al. 2022). In a modeling context, the depth and duration of heating depend on the soil properties, the thermal boundary conditions at the soil surface and the initial distribution of soil moisture (Badía et al. 2017). ...
... Higher temperatures (>400°C) near the soil surface could also cause water-repellent layers to disappear (Robichaud and Hungerford 2000;Badía et al. 2017). Additionally, accurate modeling of soil moisture near the surface is informative because the near-surface soil contains seed sources and hosts high microbial activity (Girona-García et al. 2019) that is important for long-term soil health. ...
Background Wildfires, prescribed fires and slash-pile burns are disturbances that occur in many terrestrial ecosystems. Such fires produce variable surface heat fluxes causing a spectrum of effects on soil, such as seed mortality, nutrient loss, changes in microbial activity and water repellency. Accurately modeling soil heating is vital to predicting these second-order fire effects. The process-based Massman HMV (Heat–Moisture–Vapor) model incorporates soil water evaporation, heat transport and water vapor movement, and captures the observed rapid evaporation of soil moisture. Aims Improve the Massman HMV model and compare it with Campbell soil heating model using four independent soil temperature datasets collected during burning. Methods The models were evaluated using similar BFD curves against observed temperature and soil moisture using standard statistical methods. Key results Results suggest reasonable agreement between the Massman HMV model and field soil temperature data under various burn scenarios and it was consistently more accurate than the Campbell model. Conclusions The Massman HMV model improved soil heating predictions and provided soil moisture predictions. Implications The Massman HMV model was incorporated in the First Order Fire Effects Model (FOFEM ver. 6.7) with a user-friendly interface that allows managers to assess the heating impacts of fire on soil temperature and moisture.
... To limit the impact of wildfires, post-fire management techniques can be applied in fire-prone forests to restore the pre-fire functionality (Girona-García et al. 2019). These techniques can be implemented on burned hillslopes-for example, mulching, barriers, salvage logging-and/or in channels draining burned catchments through the construction of small check dams (Lucas-Borja 2021). ...
... The effects of wildfire and post-fire management on the main components of the burned forests have been widely explored, including in Mediterranean areas (Caon et al. 2014;Moody et al. 2013;Shakesby 2011;Shakesby and Doerr 2006;Stavi 2019;Wagenbrenner et al. 2021;Zavala et al. 2014). In general, these post-fire management techniques can achieve the planned objectives, as has been generally acknowledged (Girona-García et al. 2019;Vieira et al. 2018a). However, the response of the forest ecosystem is site-specific and depends on several environmental factors, such as post-fire weather, timely application of post-fire measures, and vegetal species (Lucas-Borja, Jing, et al. 2022;Vieira et al. 2018b). ...
Fungi are involved in several biotic processes in soil. Many studies have investigated the impacts of wildfire on fungal communities but few have explored their diversity after post-fire management. This study seeks to fill this gap by evaluating the species richness, diversity and evenness of fungi, and many soil properties in a severely burned forest in Central-Eastern Spain ten years after installing log erosion barriers (LEBs) as post-fire management treatment. When compared to the unburned soils, all diversity indices of fungal communities - especially species richness and abundance, +39%, - significantly increased in burned and untreated sites. This was mainly due to the long time elapsed from wildfire and post-fire treatment and the high cover of dead wood, which supported soil humidity for fungi development. Compared to burned areas, LEBs further increased the fungal biodiversity, +43% in species richness and +22% in abundance. This increased biodiversity was supported by a higher content of organic matter, nutrients and some enzymes. Therefore, LEBs used in post-fire management can be suitable for the increased development of some fungi species, and their diversity, in semi-arid forests affected by severe wildfires.
Keywords: high-severity fire; soil biological processes; species richness; diversity; evenness; fungal communities; post-fire management.
... These methods include the use of prescribed burning, shrub clearing and mechanical shredding (Montiel and Kraus 2010;Cadenas et al. 2024). Prescribed burning has been increasingly used (Fernandes et al. 2013) to prevent fire hazards in these mature shrubland ecosystems, breakdown shrub encroachment processes and to create grazing resources (Girona-García et al. 2019;Cadenas et al. 2024). This technique and its effectiveness and benefits for the conservation and sustainability of ecosystems have been questioned, as it has shown positive and/or negative, and unchanged effects on C cycling and storage (Fernandes et al. 2013;San Emeterio et al. 2016;Alcañiz et al. 2016;Girona-García et al. 2019;Cadenas et al. 2024). ...
... Prescribed burning has been increasingly used (Fernandes et al. 2013) to prevent fire hazards in these mature shrubland ecosystems, breakdown shrub encroachment processes and to create grazing resources (Girona-García et al. 2019;Cadenas et al. 2024). This technique and its effectiveness and benefits for the conservation and sustainability of ecosystems have been questioned, as it has shown positive and/or negative, and unchanged effects on C cycling and storage (Fernandes et al. 2013;San Emeterio et al. 2016;Alcañiz et al. 2016;Girona-García et al. 2019;Cadenas et al. 2024). ...
Understanding the effects of prescribed burning management practices in combination with anthropogenic nitrogen (N) deposition on soil carbon (C) storage capacity is of crucial importance in Mediterranean mountain shrublands. To address this issue, an experiment was conducted to assess the effects of prescribed burning (Burn, B / No Burn, NB), N additions (0, 15, and 50 kg N·ha⁻¹·year⁻¹, N0, N15, N50) and their interactive effects on various soil parameters in a shrubland located in the mountain range of Madrid over 2-year period. The results of the study confirmed that both low-intensity prescribed burning and short-term N additions did not alter the C stocks in the soil and floor shrubs. Furthermore, the combination of these two factors did not lead to an increase in soil C accumulation. However, the prescribed fire treatment caused divergent responses in soil parameters and fluxes. Specifically, it caused transient changes including decreased soil respiration (Rs), alterations in the soil microbial community, increased soil water content, temperature, and soil pH, and changes in NH4, NH3, and available P. Moreover, the cumulative amount of N added gradually depressed Rs, and microbial biomass. Additionally, the interaction between prescribed burning and N fertilisation did not modify the effects associated with fire. The findings indicate that prescribed burning, as implemented in the experiment, can be effectively employed in Mediterranean shrublands, as it did not significantly affect soil C storage under both current and future N deposition scenarios.
... erosion) compared with reference conditions (e.g. unburned plots) across a range of studies, and to test the variable's statistical significance (Girona-García et al., 2019;Gurevitch et al., 2018). For example, Girona-García et al. ...
... Second, soil heating due to fire with moderate severity consumes organic matter and mineral bindings , thus resulting in a reduction in soil aggregate stability (Fernández et al., 2010;Larsen & MacDonald, 2007;Parson et al., 2010) and critical shear stress. Third, the induced SWR and soil crusting, synergistically with the breakdown of soil aggregates, decrease the infiltration capacity of burned soils (Girona-García et al., 2019;Silva et al., 2019). ...
Prescribed fires are one of the most effective tools to reduce the risk of wildfires but this treatment may negatively affect the hydrological and erosive response of soil, with noticeable increases in surface runoff and soil erosion. Many studies have been published on this matter but there is no consensus in the literature on the magnitude and duration of these effects since the relevant hydrological conditions are site-specific. Moreover, the relationship between post-fire hydrology and its main environmental drivers has been little explored. This study has carried out a bibliographic review and a meta-analysis of the changes resulting from prescribed fire applications (water infiltration, soil water repellency (SWR), surface runoff and soil erosion) using a database of 85 case studies from 41 academic papers that have been published over the last 23 years. The effects of annual precipitation, soil slope, burn severity, fire application season, post-fire ground cover, and vegetation type on those changes have also been statistically explored. The bibliographic review has revealed that previous case studies have not been equally distributed across the globe but concentrated in only a few countries, mainly the USA and Spain. The meta-analysis has revealed that: (i) water infiltration generally decreases and soil water repellency appears with noticeable increases in surface runoff and soil erosion immediately after the prescribed fire, while the pre-fire values progressively recover over time; (ii) the window of disturbance in burned soils may last a few months (with some exceptions); (iii) annual precipitation and soil slope significantly influence water infiltration and surface runoff, but not soil erosion, in both the short-term and medium-term; (iv) moderate-to-high levels of soil burn severity severely enhance surface runoff and soil erosion, and noticeably reduce water infiltration in the short-term; (v) the level of ground cover burning is important for reducing the runoff rates, but it plays a minor role in water infiltration and soil erosion rates; (vi) the prescribed fire applied in spring results in lower increases in short-term runoff and erosion, while fire applications in summer and in shrublands produce the highest increases in soil loss.
The following practical recommendations arise from this study: (i) research should be better distributed across all environmental contexts on a global scale; (ii) post-fire management actions should be immediately implemented after the prescribed fire application; (iii) prescribed fire should be carried out in spring and the soil burn severity should be kept low during burning; (iv) the monitoring studies should be prolonged at least for some years (more than two or three) after prescribed fire; (iv) the catchment-scale investigations, although more difficult and expensive, should be encouraged (avoiding, however, areas to sparsely burnt in the context of the whole catchment); (v) the monitored variables should also include the most important physical, chemical and biological properties of soil, the cover and structure of regenerating vegetation, as well as the water quality parameters; (vi) the effects of repeated applications of prescribed fire should be experimentally assessed; (vii) guidelines for standardized and appropriate measurements and analytical methods in experimental activities should be set up. These indications support the use of land managers in the monitoring of the hydrological impacts of the prescribed fire and in the choice of sites where post-fire management actions must be implemented. The last recommendation of this study is the creation of an experimental database supporting the bibliographic review and the meta-analysis, which is made available to other researchers and land managers, to create a public, easily-accessible and comprehensive tool for future research needs and professional use.
Keywords: water infiltration; soil water repellency; surface runoff; soil erosion; annual precipitation; soil slope; soil burn severity; burn season; post-fire ground cover; vegetation type
... Global warming is expected to speed up the reduction of SOM, with the concomitant release of more CO 2 into the atmosphere and the further alteration of climate [84]. In this context, the climate-increased frequency of wildfires is also able to promote soil degradation and desertification through SOM oxidation, a phenomenon, however, highly dependent upon temperature and fire residence time [85]. As a further testament of the intricate relationships between climate and soil quality, the Intergovernmental Panel on Climate Change (IPCC) provides its own precise definition of land degradation: "a negative shift in land condition due to direct or indirect human-induced activities resulting in a long-term reduction or loss of biological productivity, ecological integrity, or human value" [86]. ...
... Our results suggest that prescribed burning in larch forests reduces combustible loads and fire risks without reducing the potential for soil carbon sequestration, which is beneficial for forest health and combustible management [12,41,54,55]. When measuring the impacts of prescribed burning on forests for more rational forest management, it is important to look at changes in community structure and biodiversity, changes in soil structure and erosion resistance [56], and changes in the probability of a regional forest burn [57], in addition to soil carbon pools. ...
The mechanism through which fine root biomass affects soil carbon accumulation after prescribed burning remains unclear. In this study, the biomass of fine roots in different life forms (larch, shrub, and grass) and the total soil carbon (STC) were determined after prescribed burning. Relative to a control, the total soil carbon increased one week after the fire (11.70 mg·g⁻¹; 28.1%) and decreased after 8 months (7.33 mg·g⁻¹; 16.7%), returning to control levels 10 months post-fire. There was a reduction in the larch fine root biomass (FRB) (0.20–0.48 t·ha⁻¹; 35.3%–46.1%; these ranges represent the significant variation interval of fine root biomass after the fire across different time periods, compared to the control) but an increase in the shrub FRB (0.06–0.14 t·ha⁻¹; 101.6%–158.4%) and herb FRB (0.06–0.13 t·ha⁻¹; 591%–3200%) during the vegetation recovery process after the fire. The complementary growth of different plant life forms contributed to the changes in FRB. This also caused changes in the different life forms of FRBs’ effects on STC. Prescribed burning increased the contribution of FRB to STC. The compensatory growth of fine roots from different life forms drives the stabilization of the soil carbon pool after prescribed burning. Prescribed burning reduced the litter fuel and changed the FRB of different life forms, but it did not affect the long-term accumulation of STC.
... Prescribed burning in forest is defined as a method for fire use, to achieve precisely and clearly defined goals (Girona-García et al., 2019): it is used to decrease wildfire risk and change ecological processes (Matosziuk et al., 2019). Generally, prescribed burning was a less pronounced compared to wildfires, as they apply to appropriate weather conditions and reach lower intensities and severities (Fonseca et al., 2022). ...
Dissolved organic carbon (DOC) is an important function of soil organic carbon and sensitive to environmental disturbance. Few studies have explored the variations in soil DOC dynamics and effects on soil physicochemical properties following prescribed burnings. In this study, Pinus koraiensis plantation forests in Northeast China were selected and subjected to prescribed burning in early November 2018. Soil DOC and different soil physicochemical and biological properties in the 0-10 cm and 10-20 cm soil layers were sampled six times within two years after a prescribed burning. In this study, some soil physicochemical (SOC, TN, and ST) and microbial biomass properties (MBC) recovered within two years after a prescribed burning. Compared to the unburned control stands, the post-fire soil DOC concentrations in the upper and lower soil layers increased by 16% and 12%, respectively. Soil DOC concentrations varied with sampling time, and peaked one year after the prescribed burning. Our results showed that soil chemical properties (NH4+-N and pH) rather than biological properties (microbial biomass) were the main driving factors for changes in post-fire soil DOC concentrations. Current study provides an important reference for post-fire and seasonal soil C cycling in plantation forests of Northeast China.
... This is consistent with the study of Santorufo et al. (2021), who found a similar result in Mediterranean Andosol properties 2 years after fire. Moreover, the OM level was not recovered even 10 years after a wildfire in the semi-arid Zagros woodlands (Sadeghifar et al., 2020) and 6 years after a fire in the Mediterranean shrubland (Girona-García et al., 2019). In another study, the total carbon and nitrogen levels in a pine plantation (Pinus halepensis Miller) in Catalonia, Spain, could not be restored to the initial levels 9 years after the prescribed fire (Alcañiz et al., 2016), most likely because the recovery of SOC, STN, and soil nutrients (available P, K, Ca, and Mg) starts with vegetation restoration, especially grass species. ...
The hill tribes in Thailand traditionally depend on rotational shifting cultivation (RSC). However, insufficient understanding remains on post-fire soil properties and soil erodibility (k-values) with fallow years. To address this gap, the levels of soil organic carbon (SOC), soil total nitrogen (STN), soil nutrients, and soil erodibility after fire in RSC were investigated. Topsoil (0–10 cm) samples from sites with 4 (RSC-4Y), 5 (RSC-5Y), and 7 (RSC-7Y) fallow years in Chiang Mai Province, northern Thailand, were taken at four time points: before burning, 5 min after burning, 9 months after burning, and 2 years after burning. Soil pH, electrical conductivity, and soil nutrient (available P, K, and Ca) levels were increased after burning and remained higher than the pre-burning levels for at least 2 years. The SOC stock decreased after burning in all fallow fields. At 2 years after burning, the SOC stock in RSC-4Y was higher than before burning, whereas in RSC-5Y and RSC-7Y, the levels had not reached the pre-fire levels. The STN stocks of all studied fields significantly decreased after burning and had not reached the pre-burning levels after 2 years. After burning, the topsoil of RSC-4Y was most susceptible to erosion. However, only in RSC-4Y, the k-value was unchanged at 2 years after burning. Three different approaches are recommended for post-fire land management: 1) farmers should not cut and remove the weeds and grasses at the soil surface, 2) burning should be performed around late winter or early summer (November–February) to inhibit complete combustion, and 3) contour-felled log erosion barriers should be made by using the trunks remaining after the fire to trap the sediment and slow down surface runoff.
... To find out, a study has been conducted to determine the short (B0), medium (5 years, B5) and long-term (9 years, B9) evolution of prescribed fires effects on topsoil properties, especially biological ones, in a location of Central Pyrenees. Soil was sampled up to 3 cm, based on Girona et al. (2019). Microbial carbon (Cmic), soil respiration (SR) and enzymatic β-glucosidase activity (β-G) were analyzed. ...
... The burned area was identified by visual survey in those sites more recently burned, and with the help of the local Nature Protection officers (APN by their Spanish acronym) in those sites burned longer ago. According to the EPRIF, these sites had not burned in the preceding decades, at least for the last 50 yr, and the canopy closure and coverage of E. horridum before burning was equal or close to 100% in all cases, which is in agreement with our own observation of the burns in 2015 and 2016 (Armas-Herrera et al., 2018;Girona-García et al., 2019). ...
Prescribed fire has been extensively used in recent years to control woody encroachment into mountain and other grassland–dominated landscapes. In the Aragon Pyrenees, prescribed burns have been mainly used to remove the native thorny shrub Echinospartum horridum (Vahl) Rothm., whose populations are spreading to the detriment of grasslands. To study the effectiveness of the burning of E. horridum to preserve grasslands for livestock grazing, the vegetation of six sites burned 0.5, 2, 3, 6, 15 and 35 years ago was sampled and compared with that of nearby unburned shrubland (control) and grassland (reference). In addition, the nutritional quality of E. horridum was examined and compared to that of the reference grassland to evaluate to what extent shrub growth can be controlled by herbivores after burning. Initial shrub cover recovered as early as 15 years after fire, with E. horridum being dominant. Plant diversity was greatest at intermediate number of years after fire. Initial floristic composition and life–form spectrum were restored 15–35 years after burning. Echinospartum horridum exhibited early lignification that restricts its availability as a palatable forage for the first two years after burning and makes it unlikely to be consumed thereafter, highlighting the difficulty in controlling the expansion of this species by livestock herbivory. The analysis of the nutrient levels suggested an increased shortage of limiting elements, such as phosphorus or sulfur, in the mid–term after burning due to substantial nutrient losses and exports during and after the burn. Our results question the suitability and sustainability of a single prescribed burn as management tool alone to control the expansion of E. horridum and call for caution in its application for fighting shrub encroachment in the Central Pyrenees.
... Long periods of grazing and cattle trampling have direct effects on soil structure by increasing soil compaction [86], thereby degrading the soil physical quality over time. Furthermore, the burning of pastures, a management practice commonly used to improve pasture soil quality [87] with short-term benefits [88], reduces the soil organic matter, soil biodiversity, nutrient content, soil moisture and aggregate stability [89][90][91][92], thus accelerating the soil degradation. ...
Successional processes in abandoned pastures in the Amazon region have been well-documented for the floristic component; however, soil succession has been poorly studied. This study assessed the physical, chemical and biological responses of soils in the Amazon region during the natural succession process in two main landscapes of the Colombian Amazon. Soil data on soil physico–chemical (bulk density, macroaggregates, pH and minerals) and biological (soil macrofauna) composition were evaluated along chronosequence with four successional stages: (i) degraded pastures, (ii) young (10–20-year-old), (iii) middle-age (25–40-year-old) and (iv) mature forests, in two different landscapes (hill and mountain). Individual soil variables and a synthetic indicator of soil quality (GISQ) were evaluated as tools for natural succession monitoring. The results corroborated the negative impact that cattle ranching has on Amazon soils. After 10 years of natural succession, the physico–chemical and biological soil components were widely restored. Less soil compaction and organic carbon occurred in older successional stages. Soil macrofauna richness and density increased along the chronosequence, with an evident association between the macrofauna composition and the macroaggregates in the soil. None of the individual soil properties or the GISQ indicator discriminated among natural succession stages; therefore, new soil quality indicators should be developed to monitor soil quality restoration in natural successions.
... Some authors report unaltered pH values and ephemeral variations in electrical conductivity (Badía et al. 2017;Alcañiz et al. 2020), while, one year after the prescribed fire, other research shows marked decreases in nitrogen (Blankenship and Arthur 1999;Muqaddas et al. 2015) as well as the recovery to pre-fire contents of magnesium and calcium (Alcañiz et al. 2020). It has been found that the recovery of pre-fire soil properties may take place over short (Zhao et al. 2015) or long (Alcañiz et al. 2016) time spans, depending on fire temperature and residence time, topography of the burned area, rainfall, and degree of vegetation regeneration Girona-García et al. 2019). Therefore, further research is needed to better understand the effects of prescribed fires in environments with contrasting characteristics (Hubbert et al. 2006;Hueso-González et al. 2018). ...
Prescribed fire, although having low intensity and being able to reduce the risk, of wildfire may modify soil properties in the short term, with possible increases in runoff and erosion risk. Soil mulching with vegetation residues is one of the most common post-fire management strategies. Residues of fern, which is abundant on the Mediterranean forest floor, may be used to replace straw for mulching fire-affected areas. However, the effects of prescribed fires are not completely understood, and there is no data regarding the use of fern to protect soil after fire in the literature. To fill this gap, selected soil chemical parameters were analysed, on a comparative basis, in three Mediterranean forests (pine, oak and chestnut) in Calabria (Southern Italy). These parameters were measured immediately and one year after fire in unburned, burned and not treated, and burned and mulched soils. Changes in soil chemical properties among the different treatments were significant, and the effects of the prescribed fire and mulching were dependent on the time elapsed from their application and forest species. In general, mulching was not effective in limiting the changes in the monitored soil properties compared to the pre-fire values. Each forest species showed different temporal trends in changes of soil properties.
... Wildfires are often associated with rapid losses of SOM, driven by thermal decomposition (Shakesby et al., 2015). However, prescribed burning, with lower fire temperatures than wildfires, used to control biomass loads in forest, shrublands and grassland can lead to increases in SOM, due to temporary soil enrichment with ash and charred material and a reduction in soil biological activity, depending on fire temperature and residence time (Girona-García et al., 2019). ...
Soil, a non-renewable resource, sustains life on Earth by supporting around 95% of global food production and providing ecosystem services such as biomass production, filtration of contaminants and transfer of mass and energy between spheres. Unsustainable management practices and climate change are threatening the natural capital of soils, particularly in the Mediterranean region, where increasing population, rapid land-use changes, associated socio-economic activities and climate change are imposing high pressures on the region's shallow soils. Despite evidence of high soil susceptibility to degradation and desertification, the true extent of soil degradation in the region is unknown. This paper reviews and summarises the scientific literature and relevant official reports, with the aim to advance this knowledge by synthesizing, mapping, and identifying gaps regarding the status, causes, and consequences of soil degradation processes in the European Mediterranean region. This is needed as scientific underpinning of efforts to counteract soil degradation in the region. Three main degradation categories are then considered: physical (soil sealing, compaction, erosion), chemical (soil organic matter, contamination, salinisation), and biological. We find some degradation processes to be relatively well-documented (e.g. soil erosion), while others, such as loss of biodiversity, remain poorly addressed, with limited data availability. We suggest establishment of a continuous, harmonised soil monitoring system at national and regional scale in the Mediterranean region to provide comparable datasets and chart the spatial extent and temporal changes in soil degradation, and corresponding economic implications. This is critical to support decision-making and fulfilment of related sustainable development goals.
... Fire also has immediate effects on soil chemical properties such as pH, electrical conductivity (EC) and nutrient content (Fernández-García et al. 2019a), that can last several years and even decades depending on fire severity (Francos et al. 2018a). The study of fire impacts on soils is usually focused on the uppermost soil layers, as in most cases, direct fire-induced changes can only be detected in the first 5 cm of soil (Girona-García et al. 2019;Fernández-García et al. 2020a). However, the effect of forest fires on soil throughout history can also be analysed in deeper layers of the soil profile because the uppermost layers can be detached from a specific site and then, transported and buried in another. ...
Wildfires are a major concern in Mediterranean areas and play an important role in the pedogenic process, as they usually increase soil credibility due to the destruction of vegetation cover and soil structure. On top of these factors, slope and aspect also determine the degree of retention and availability of water and nutrients in soils after fire, which in turn influence the recovery of vegetation and its protective effect against erosion. This work aims to describe the effects of slope and aspect on soil development in an area historically affected by wildfires. The study area is located in Ódena (NE Iberian Peninsula) in a Mediterranean forest. Four representative soil profiles were sampled from a south-facing steep slope, north-facing steep slope, south-facing gentle slope and north-facing gentle slope. In each profile 11 samples were sampled. The amount of soil organic matter (SOM), inorganic C (IC) and total N (TN) as well as cation availability, pH, and electrical conductivity (EC) were determined for all the horizons of each profile. Results showed that IC, TN, C/N ratio, pH, EC and K were mainly affected by aspect, whereas organic matter, C/N ratio, pH, EC, Ca and Mg were especially influenced by slope. Slope determined the amount and availability of SOM and nutrients, which highlights the need to prioritise the management of areas susceptible to erosion in order to ensure soil and ecosystem functionality.
... Several studies have highlighted the impacts of fire on soil characteristics. The immediate and direct effects of fire are usually short-term and are restricted to the first few centimeters of the topsoil [7]. The indirect influence of fire in rangelands is the partial or total loss of plant and litter biomass, as well as changes in plant community composition and structure [8]. ...
Mediterranean regions are the most impacted by fire in Europe. The effects of fire on soil greatly vary according to several factors such as vegetation cover type, but they are scarcely studied. Therefore, this research aimed at evaluating the combined impacts of fire and vegetation on single soil characteristics and on the overall soil quality and functionality through two soil quality indices, simple additive (SQI) and a weighted function (SQIFUNCT). In order to reach the aims, burnt and unburnt soils were collected under different vegetation cover types (herbs and shrubs, black locust, pine and holm oak) within the Vesuvius National Park. The soils were analyzed for the main abiotic (water and organic matter content, total C, N, Ca, K, Cu and Pb concentrations, C/N ratio) and biotic (microbial and fungal biomasses, basal respiration, β-glucosidase activity) characteristics. On the basis of the investigated soil characteristics, several soil functions (water retention, nutrient supply, contamination content, microorganism habitat and activities), and the soil quality indices were calculated. The results showed that the impact of fire on soil quality and functionality was mediated by the vegetation cover type. In fact, fire occurrence led to a decrease in water and C/N ratio under herbs, a decrease in C concentration under holm oak and a decrease in Cu and Pb concentrations under pine. Although the soil characteristics showed significant changes according to vegetation cover types and fire occurrence, both the additive and weighted function soil quality indices did not significantly vary according to both fire occurrence and the vegetation cover type. Among the different vegetation cover types, pine was the most impacted one.
... Several recent studies have investigated the impact of prescribed pastoral fires on high-mountain soils in the southern Pyrenees and have focused on microbiological and biochemical properties (Armas-Herrera et al., 2018;Girona-García et al., 2018a, 2019Múgica et al., 2018), bioavailable nutrients (Girona-García et al., 2018c;Múgica et al., 2018), and total C and nitrogen (N) reservoirs in the whole topsoil layer (Nuche et al., 2018;Girona-García et al., 2019) and in different aggregate-size classes (Girona-García et al., 2018b). However, little is known about the effects of high-mountain pastoral burns on the composition and nutrient concentration of organic matter in the high-mountain soils. ...
High-mountain soils are rich in partially decomposed organic matter, which is highly sensitive to mineralization and fire. Prescribed burning is performed in the Pyrenees to keep subalpine grasslands open for grazing. The compositions of the ash, litter and duff layers, and the particulate organic matter (POM) of the topsoil in the 0–1, 1–2, 2–3, and 3–5 cm depths were analyzed in relation to the nutrient availability after the prescribed burning of a stand encroached by erizón (Echinospartum horridum). The concentrations of C, N, P, and S and organic components (nonstructural, hemicellulose, cellulose, and lignin-type) were determined before the prescribed burn and 0, 6, 12, 18, and 24 months after the prescribed burn. The fire consumed the aboveground biomass, the litter and part of the duff layer, and the most thermostable (i.e., lignin-type) components and the least volatile elements (P, S) were selectively preserved in the resulting ash. Prescribed burning caused significant losses of organic-C and N only in the 0–1 cm depth (–72% and –68%, respectively). The organic-C loss was mostly (82%) from the POM, whereas the N loss was from more similar proportions of the POM (57%) and the nonparticulate organic matter (NPOM) (43%). However, few changes were observed in the composition of the organic matter, which pointed to a largely uneven combustion that resulted in a substantial part of the organic matter remaining largely untouched by the fire. After 6 months, the duff layer was depleted in hemicellulose by 32% compared to immediately after the burn, and fragmentation of the POM into the NPOM was observed. During the second spring, N- and P-rich charred POM were incorporated into the top 1 cm, while C-rich charcoal particles underwent fragmentation and vertical transport into the deeper soil. The preburn ecosytem was limited by P, and likely also by S. The plant available N showed transient increases of 1.5–2.1 times the immediate postburn levels for nitrate-N at 12 months after burning, and of up to 10–20 times for ammonium-N at 18 months. In contrast, the concentrations of plant-available P and S gradually declined to 1.8–3.3 and 1.8–4.0 times, respectively, lower at 24 months after the burn. Results indicated that fire-induced increases in the nutrient availability can be short-lived in high-mountain habitats, but steadier and likely more persistent nutrient inputs can derive from the gradual breakdown of charred organic matter.
... this C-debt may take longer to be repaid (Peterson and Reich, 2001;Wardle et al., 2003). However, in agreement with our results, recovery of SOC following frequent fire has been observed in other studies (Coetsee et al., 2010;Girona-García et al., 2019) and may be explained by the presence of early successional or surviving native grasses with large root systems that offset initial soil C loss (Brockway and Lewis, 1997;Cleary et al., 2010;Rasse et al., 2005). Indeed, despite an increased cover of exotic annual grasses in our burned sites, these sites also retained a significant presence of perennial native bunchgrasses, including Poa secunda J. Presl and the deep-rooted species Leymus cinereus (Scribn. ...
Increased fire frequency in semi-arid ecosystems can alter biochemical soil properties and soil processes that underpin ecosystem structure and functioning, thus threatening native plant communities and the species that rely on them. However, there is much uncertainty about the magnitude of change as soils are exposed to more fires, because soil recovery and changes in fire severity following a first fire mediate the impact of successive fires on soil properties. With this study we aim to evaluate how increased fire frequency affects soil biochemical properties (i.e. soil pH, soil organic matter (SOM), soil organic carbon (SOC), soil structure and mineral N) and processes (i.e. microbial and enzymatic activity) in a sagebrush-steppe ecosystem located in the Columbia Plateau Ecoregion, Washington, USA. During 2016, we collected soils from once (2012), twice (2003 and 2012), and thrice (2003, 2007, and 2012) burned areas, enabling us to test the hypothesis that increasing fire frequency will exacerbate the impact of fire on soil properties and processes. Our study yielded three main results: (1) fire reduced the total soil C concentration and soil C in aggregates relative to unburned soil, but only when soil was exposed to fire once (i.e. the most recent fire), (2) compared to the unburned soils, SOM contents, enzyme activity and microbial CO2 respiration were suppressed in the once and thrice burned soils, but not in the twice burned soils, and (3) fire increased NO3⁻-N contents across the once and twice burned sites, and reduced enzyme activity associated with N cycling in the thrice burned sites. Taken together, our findings suggest that a one-time fire in this shrub dominated semi-arid ecosystem significantly changes soil biochemical attributes and microbially driven processes. With sufficient time between fires, these structural and functional properties can partially recover, and this may persist even after a second fire, but recovery is limited when a third fire creates an additional disturbance at a shorter time interval. Furthermore, while soil C pools and microbial decomposition processes were able to recover with sufficient time, greater soil resource availability prevailed in soil across all fire frequencies, indicating that fire is likely to promote invasion and reduce ecosystem stability, even when other soil properties recover.
... As emissões provenientes das queimas, além de alterar a umidade do solo, em função das mudanças na taxa de infiltração e na taxa de transpiração, podem alterar, por consequência o estoque de água no solo(REDIN, et al., 2011). Os efeitos diretos das queimadas no solo são altamente dependentes das condições ambientais, a médio prazo, a redução da atividade biológica do solo e a incorporação de cinzas e restos de plantas carbonizadas levaram a um aumento no carbono orgânico do solo, nos solos queimados(GIRONA-GARCIA et al., 2019). Nos seres humanos, estudos epidemiológicos mostram que a exposição a poluentes gasosos e material particulado está associada a maior incidência de sintomas das vias aéreas inferiores, como tosse, dispneia e sibilância, especialmente em crianças(ARBEX et al., 2014).A Figura 3 apresenta os dados sobre a quantidade de área em hectares autorizadas para a queima controlada por município na série temporal estudada.figura ...
... As emissões provenientes das queimas, além de alterar a umidade do solo, em função das mudanças na taxa de infiltração e na taxa de transpiração, podem alterar, por consequência o estoque de água no solo(REDIN, et al., 2011). Os efeitos diretos das queimadas no solo são altamente dependentes das condições ambientais, a médio prazo, a redução da atividade biológica do solo e a incorporação de cinzas e restos de plantas carbonizadas levaram a um aumento no carbono orgânico do solo, nos solos queimados(GIRONA-GARCIA et al., 2019). Nos seres humanos, estudos epidemiológicos mostram que a exposição a poluentes gasosos e material particulado está associada a maior incidência de sintomas das vias aéreas inferiores, como tosse, dispneia e sibilância, especialmente em crianças(ARBEX et al., 2014).A Figura 3 apresenta os dados sobre a quantidade de área em hectares autorizadas para a queima controlada por município na série temporal estudada.figura ...
Soils constitute the major reservoir of mercury (Hg) in terrestrial ecosystems, whose stability may be threatened by wildfires. This research attempts to look at the effect of prescribed fire on the presence of Hg in a shrubland ecosystem from NE Portugal, delving into its relationship with soil aggregate size and the molecular composition of soil organic matter (SOM). During the prescribed fire, on average 347 mg Hg ha−1 were lost from the burnt aboveground biomass of shrubs and 263 mg Hg ha−1 from the combustion of the soil organic horizon. Overall, Hg concentration and pools in the mineral soil did not show significant changes due to burning, which highlights their role as long-term Hg reservoirs. The higher Hg concentrations found in smaller aggregates (<0.2 mm) compared to coarser ones (0.5–2 mm) are favored by the higher degree of organic matter decomposition (low C/N ratio), rather than by greater total organic C contents. The Hg-enriched finest fraction of soil (<0.2 mm) could be more prone to be mobilized by erosion, whose potential arrival to water bodies increases the environmental concern for the Hg present in fire-affected soils. The SOM quality (molecular composition) and the main organic families, analyzed by Fourier-transform infrared spectroscopy in combination with multivariate statistical analysis, significantly conditioned the retention/emission of Hg in the uppermost soil layers. Thus, before the fire, Hg was strongly linked to lipid and protein fractions, while Hg appeared to be linked to aromatic-like compounds in fire-affected SOM.
Mulching with forest residues has proved to be highly effective in reducing post‐fire soil losses at the plot scale. However, its effectiveness has not been quantified at the application rates that are typically used in operational post‐fire land management (2–3 Mg ha‐1 using straw), as well as at scales larger than 100 m2. The present study compared post‐fire erosion rates for six convergent hillslopes or swales of 500 to 800 m2, three of which were left untreated while the other three were mulched immediately after the fire with shredded eucalypt bark at a rate of 2.4 Mg ha‐1. Erosion rates were monitored at irregular intervals during the first three post‐fire years, whilst ground cover was assessed yearly. Selected topsoil properties (0–2 cm) such as organic matter content and aggregate stability were determined at a single occasion – two years after the wildfire, for three micro‐environments separately: bare soil, and under mulch/litter and vegetation. Soil losses on the untreated swales decreased with post‐fire year from 2.2 to 0.4 and 0.11 Mg ha‐1 yr‐1 (respectively for the first, second and third post‐fire years), while the mulched swales produced 84%, 77% and 38% less soil losses than the untreated swales. Soil losses also depended on slope aspect, with the north‐facing swales producing less erosion than the west‐facing ones. This could be linked to their significant differences in bare soil, vegetation and stone cover, or a combination thereof. The type of micro‐environment also played a significant role in topsoil properties (stone content, bulk density, resistance to penetration/shear stress, porosity and organic matter content). The present results add to the increasing evidence that forest residues should be duly considered for operational post‐fire land management. Forest residues were highly effective in reducing erosion from swales at application rates as low as the typical 2 Mg ha‐1 of post‐fire straw mulch. © 2019 John Wiley & Sons, Ltd. Burnt swales of 600 m2 were mulched with eucalypt shredded barks at a rate of 2.4 Mg ha−1 and erosion rates monitored over three years. Mulching reduced erosion from 84 to 77 and 36%, respectively for the first, second and third years and organic matter losses decreased significantly due to forest residue. Forest residue mulching should beduly contemplated as an operational measure in post‐fire emergency stabilization programs and plans.
Mountain grasslands are generally rich in soil organic C, but the typical high spatial variability of mountain environments, together with the different management systems, makes their soil C content particularly variable. Socio-economic changes of the past decades have caused a progressive abandonment of the traditional use for grazing of some areas, while grazing pressure at easily accessible grasslands have increased. Here, we analyse the effect of these land-use changes on the factors regulating the soil C accumulation and stocks. Overgrazing generally leads to a reduction above- and below-ground litter inputs and a decrease in soil C stocks, affecting some soil physicochemical and biological properties. Additionally, the labile C inputs coming from animal faeces may accelerate the mineralisation of organic matter. Grazing abandonment causes a reduction of aboveground productivity, but the lack of consumption causes a short-term accumulation of organic matter. Its effect on belowground biomass and productivity is less clear. At longer term, grazing abandonment causes a change in the plant community composition, having the shrub encroachment the strongest effect on C storage. The low biochemical quality of shrub litter delays its decomposition and allows higher organic matter accumulation in the topsoil. But the effect of shrub proliferation at the deeper soil is less clear. The low root turnover of shrubs compared to grasses may reduce the C inputs to the soil. But, at the same time, the reduction of the root exudates may also reduce the microbial activity and the organic matter mineralisation.
Wildfires are a global problem that can require the application of fire-fighting chemicals for combating them. These compounds can have negative effects on forest ecosystems; however, there are few studies about their influence on the soil microbial community. The aim of this work is to analyse under field conditions the impact of a prescribed fire and the addition at normal field doses of three different fire-fighting chemicals (foaming agent, ammonium polyphosphate, Firesorb) on different soil properties, 10 years after the fire and retardant addition. The study was performed in a Humic Cambisol under scrubland located in Galicia (NW Spain). Several physical, physicochemical, chemical (water holding capacity, pH, electric conductivity, total C and N, hydro-soluble C and carbohydrates), biochemical and microbiological [biomass C, enzyme activities, respiration, bacterial growth, fungal biomass and growth, biomass and community composition by the phospholipid fatty acid (PLFA) pattern] properties were analysed in the 0–2- and 2–5-cm soil layers. A marked effect of soil depth and no effects of prescribed fire on most analysed properties were observed, suggesting that soil chemical quality was recovered after 10 years, although changes in microbial community composition were still detected 10 years after the prescribed fire and the retardant addition. The PLFA pattern combined with principal component analysis allows us to differentiate the microbial communities according to both soil depth and soil treatment. The ammonium polyphosphate was the fire-fighting chemical with the strongest effects on the composition of soil microbial communities, which is in accordance with marked changes observed in vegetation.
Aims Soil water repellency (SWR) in Mediterranean sub-humid environments is poorly studied in soils derived
from basic bedrock. This study addressed this gap by comparing SWR in soil samples collected before/after a prescribed burning in a Mediterranean shrubland overlaying limestone.
Methods Sampling was performed on two adjacent slopes (NE/SW) underneath Quercus coccifera, Pistacia lentiscus, Arbutus unedo shrubs, and on bare inter-patches, at two depths (0–2 and 2–5 cm). Samples were sieved at <0.25, 0.25–1, 1–2 and <2 mm and SWR was assessed through the Water Drop Penetration Time (WDPT) in each fraction. Samples were analysed for pH, AS, CaCO3 and SOM.
Results SWR was present before fire, mainly in the <0.25 and 0.25–1 mm fractions at 0–2 cm, which could be explained by SOM (amount and chemical composition). Persistence varied between the two slopes (NE > SW) and the four patches (Arbutus unedo > Pistacia lentiscus ≈ Quercus coccifera > Bare). The low-severity fire lightly increased SWR but did not affect the above-mentioned prefire differences.
Conclusions The wax and resins from different shrub species have implications for SWR persistence on the finer soil fractions. Prescribed fire increased the severity of SWR at surface but also its frequency at the subsurface layer.
In this study, we analyzed the effect of topography, particularly slope, on the expansion rates and population dynamics of Echinospartum horridum at small spatial and temporal scales in the grassland communities of Ordesa-Monte Perdido National Park (OMPNP) (NE Spain). E. horridum is a thorny cushion dwarf, endemic of Spain and south of France, forming dense mono-specific large patches difficult to be penetrated by other plants and large herbivores once it is established. Between 2005 and 2007, we collected demographic parameters from 300 marked plant; of E. horridum that were distributed in the center and the edge of four patches. At the patch edge, two of the four patches had a high slope (>= 10 degrees) and two had a low slope (< 10 degrees), whereas at the patch centers the slope was high (18 degrees-30 degrees). To calculate invasion speed, we use aerial photographs from 1981 and 2003. Plants in the center of patches had lower growth rates, fewer flowers, and higher crown death rates than did le plants at edge of patches. Slope influenced significantly invasion rates: the speed of expansion was lowest on gentle slopes, probably because of competition with grass. The speed of diffusion from 1981 to 2003 varied from 2.09 m yr(-1) on the steep slopes to 1.93 m yr(-1) on the shallow slope. Plant dynamics at patch edges suggest that colonization by E. horridum will continue in the grasslands of the OMPNP.
Land abandonment exacerbated by climate change has led to increased woody plant encroachment of mountain grasslands in many regions of the world. The present study assessed woody plant encroachment below 2100 m a.s.l. (the potential tree line) in the Central Pyrenees of Spain and the association of this encroachment with changes in land use. Remote sensing data from Landsat-5 Thematic Mapper (TM) from the mid-1980s and mid-2000s were analyzed by supervised classification for identification of land cover types. The transition matrix indicated that shrublands were the most dynamic plant communities. Consequently, 21% of cultivated areas, 19% of dense grasslands, and 24% of sparse grasslands became shrublands during the period analyzed, and 35% of shrublands became forest. Generalized Additive Mixed Models (GAMM) was used to identify biophysical and anthropogenic factors that were significantly correlated with woody plant encroachment of dense and sparse grasslands. Distance to the nearest woody plant habitat (shrub or forest) was the most strongly correlated factor with woody plant encroachment of both types of grasslands. This factor explained 69% and 71% of the variance in models of dense and sparse grasslands, respectively. Besides this factor, anthropogenic factors had larger effects on woody plant encroachment of dense grasslands, regions that were more productive and accessible. However, biophysical and especially topographic factors had slightly greater effects on woody plant encroachment of sparse grasslands, regions that were less productive and accessible. The changes in land cover that we observed indicated that land cover has become more homogeneous. There have been reductions in the variety, functions, and services of the plant communities, particularly in areas below the potential tree line that are vulnerable to the development of woody plant habitats.
Ecuadorian páramo grasslands have become the focus of Payment for Ecosystem Services programs that have promoted land-use changes such as afforestation and reduction of burning, grazing of cattle or sheep, and agricultural expansion. However, limited information exists on the relationships between land use in páramos and the production of ecosystem services, including the direction and magnitude of changes in carbon storage. In an evaluation of eight sites representing incentivized land uses, we found significant differences in both soil carbon and aboveground carbon. The results support previous findings on the effects of pine plantations and suggest that limiting burning may be effective at enhancing carbon storage. They also indicate that, in highly productive grasslands such as the páramo, both belowground and aboveground C storage can be high, even when compared to some types of afforestation, providing support for greater attention to the role of grassland conservation in climate mitigation strategies.
Following wildfires in the United States, the U.S. Department of Agriculture and U.S. Department of the Interior mobilize Burned Area Emergency Response (BAER) teams to assess immediate post-fire watershed conditions. BAER teams must determine threats from flooding, soil erosion, and instability. Developing a postfire soil burn severity map is an important first step in the rapid assessment process. It enables BAER teams to prioritize field reviews and locate burned areas that may pose a risk to critical values within or downstream of the burned area. By helping to identify indicators of soil conditions that differentiate soil burn severity classes, this field guide will help BAER teams to consistently interpret, field validate, and map soil burn severity.
This study examines the effects of a prescribed fire, conducted in grassland in order to maintain a fire break, on soil quality (pH and nutrients) in the Prades Mountains in the Mediterranean climate of north-east Spain. Soil at a 4 × 18 m study plot, located in an abandoned agricultural terrace on calcareous bedrock at 760 m above sea level, was sampled at 0–5 cm depth at 42 sampling points before, immediately after and one year after the burn and analysed for pH and carbon, nitrogen, potassium and phosphorous content. Fire intensity was low and surface soil temperatures did not exceed 200°C. All parameters examined showed a significant increase immediately after the fire. One year later, pH and total carbon had returned to pre-fire levels, and nitrogen and phosphorous were above, whereas potassium levels had decreased to below pre-fire levels. Overall, the prescribed fire did not appear to adversely affect soil. However, using prescribed burning on an annual basis as a tool to maintain an effective fire break may not allow enough time for the soils to fully recover.
Although studies have addressed the influence of fire on soil biochemical processes, there have been no reports on how prescribed fire followed by wildfire influences microbial activity and nutrient cycling. Over a 21-mo period we monitored changes in soil nitrogen (N) and carbon (C) of a ponderosa pine (Pinus ponderosa P.&C. Lawson) and Douglas-fir [Pseudotsuga menziesii var. glauca (Beissn.) Franco] forest (both O horizon and 0-10 cm of mineral soil) that had been exposed either to prescribed fire (PB), wildfire (WF), prescribed fire three months prior to wildfire (PBWF), or no fire as an unburned control. Total N, potentially mineralizable N (PMN), NH4/+-N and NO3/--N concentrations in surface (0-10 cm) mineral soils were significantly increased immediately after WF. Soils exposed to prescribed fire prior to wildfire also had elevated concentrations of total N, PMN and NH4/+-N, but were significantly lower than in WF alone. Potentially mineralizable N was significantly reduced on all fire-exposed sites from 9 mo to the end of the study period. Although mineral soil NO3/--N concentrations in fire-exposed soils were similar to the unburned control 12 mo after fire, resin sorbed NO3/--N was 88 μg capsule-1 in WF soils vs. 24 μg capsule-1 in PBWF soils, and 1.3μ g capsule-1 in the unburned control. Microbial biomass in the WF mineral soils was as low as 52 μg g-1 21 mo after fire while microbial biomass in PBWF soils remained above 100 μg g-1 throughout the study. It appears that prescribed fire prior to wildfire may attenuate the effects of wildfire on soil and may have predisposed the microbial community to the effects of heating.
The extent of the soil organic carbon pool doubles that present in the atmosphere and is about two to three times greater than that accumulated in living organisms in all Earth's terrestrial ecosystems. In such a scenario, one of the several ecological and environmental impacts of fires is that biomass burning is a significant source of greenhouse gases responsible for global warming. Nevertheless, the oxidation of biomass is usually incomplete and a range of pyrolysis compounds and particulate organic matter (OM) in aerosols are produced simultaneously to the thermal modification of pre-existing C forms in soil. These changes lead to the evolution of the OM to ''pyromorphic humus'', composed by rearranged macromolecular substances of weak colloidal properties and an enhanced resistance against chemical and biological degradation. Hence the occurrence of fires in both undisturbed and agricultural ecosystems may produce long-lasting effects on soils' OM composition and dynamics. Due to the large extent of the C pool in soils, small deviations in the different C forms may also have a significant effect in the global C balance and consequently on climate change. This paper reviews the effect of forest fires on the quantity and quality of soils' OM. It is focused mainly on the most stable pool of soil C; i.e., that having a large residence time, composed of free lipids, colloidal fractions, including humic acids (HA) and fulvic acids (FA), and other resilient forms. The main transformations exerted by fire on soil humus include the accumulation of new particulate C forms highly resistant to oxidation and biological degradation including the so- called ''black carbon'' (BC). Controversial environmental implications of such processes, specifically in the stabilisation of C in soil and their bearing on the global C cycle are discussed. D 2004 Elsevier Ltd. All rights reserved.
Soil microbiology is crucial for soil system functioning. Fire can affect soil microbes directly through heating and indirectly by modifying soil properties. Microbes will also be affected by post-fire environmental factors and the reestablishment of vegetation. The most important factor affecting soil microbes seems to be the burn severity, which is controlled by such factors as fire intensity, duration, and soil properties which normally causes a decrease in the numbers of microbes. The temperatures reached in the topsoil are often sufficient to affect soil microorganisms and other soil properties related to the post-fire microbial recolonization. In extreme cases, the topsoil can undergo complete sterilization. Fungi seem to be more sensitive to heating than bacteria and actinomycetes, and a higher impact under wet soil conditions has been reported. In the case of fungi that form arbuscular mycorrhizas, almost all the studies show a negative influence resulting in a reduced number of propagules. An important factor is the presence of fungal resistant structures, such as sclerotia, from which new mycelia originate to colonize new plants. The activity of soil microorganisms also decreases due to changes in the quality of organic matter. In the short-term, mainly due to the increase in soluble carbon and nutrients in affected soils, an increase in heterotrophic bacteria population basal respiration is commonly observed. After depletion of the easily mineralized organic compounds, this initial increase in microbial basal respiration is generally followed by a decrease as the remaining carbon and nitrogen forms are more
After vegetation fires considerable amounts of severely or partly charred necromass (referred to here as char) are incorporated
into the soil, with long-term consequences for soil C and N dynamics and thus N availability for primary production and C
and N transport within the soil column. Considering results reported in the pyrolysis literature in combination with those
obtained from controlled charring of plant material and soil organic matter (SOM), it has become clear that common models
claiming char as a graphite-like material composed mainly of highly condensed polyaromatic clusters may be oversimplified.
Instead, I suggest a concept in which char is a heterogeneous mixture of heat-altered biopolymers with domains of relatively
small polyaromatic clusters, but considerable substitution with N, O and S functional groups. Such a concept allows fast oxidation
facilitating both microbial attack and dissolution. Although, char is commonly believed to degrade more slowly than litter,
over the long term and under oxic conditions, char may degrade to an extent that it becomes indistinguishable from naturally
formed SOM. Oxygen depletion or environments with low microbial activity may be necessary for char to survive without major
chemical alteration and in considerable amounts for millennia or longer.
Soil microbes regulate the transfer of carbon (C) from ecosystems to the atmosphere and in doing so influence feedbacks between
terrestrial ecosystems and global climate change. Fire is one element of global change that may influence soil microbial communities
and, in turn, their contribution to the C dynamics of ecosystems. In order to improve our understanding of how fire influences
belowground communities, we conducted a meta-analysis of 42 published microbial responses to fire. We hypothesized that microbial
biomass as a whole, and fungal biomass specifically, would be altered following fires. Across all studies, fire reduced microbial
abundance by an average of 33.2% and fungal abundance by an average of 47.6%. However, microbial responses to fire differed
significantly among biomes and fire types. For example, microbial biomass declined following fires in boreal and temperate
forests but not following grasslands fires. In addition, wildfires lead to a greater reduction in microbial biomass than prescribed
burns. These differences are likely attributable to differences in fire severity among biomes and fire types. Changes in microbial
abundance were significantly correlated with changes in soil CO2 emissions. Altogether, these results suggest that fires may significantly decrease microbial abundance, with corresponding
consequences for soil CO2 emissions.
KeywordsBiome–Fire–Fire severity–Fungi–Global climate change–Meta-analysis–Microbial biomass–Soil CO2 emissions
Soil microorganisms have numerous functional roles in forest ecosystems, including: serving as sources and sinks of key nutrients and catalysts of nutrient transformations; acting as engineers and maintainers of soil structure; and forming mutualistic relationships with roots that improve plant fitness. Although both prescribed and wildland fires are common in temperate forests of North America, few studies have addressed the long-term influence of such disturbances on the soil microflora in these ecosystems. Fire alters the soil microbial community structure in the short-term primarily through heat-induced microbial mortality. Over the long-term, fire may modify soil communities by altering plant community composition via plant-induced changes in the soil environment. In this review, we summarize and synthesize the various studies that have assessed the effects of fire on forest soil microorganisms, emphasizing the mechanisms by which fire impacts these vital ecosystem engineers. The examples used in this paper are derived primarily from studies of ponderosa pine-dominated forests of the Inland West of the USA; these forests have some of the shortest historical fire-return intervals of any forest type, and thus the evolutionary role of fire in shaping these forests is likely the strongest. We argue that the short-term effects of fire on soil microflora and the processes they catalyze are transient, and suggest that more research be devoted to linking long-term plant community responses with those of the mutually dependent soil microflora.
The abandonment of the traditional pastoral activities in the subalpine grasslands of the Central Pyrenees (NE-Spain) has resulted in shrub encroachment processes that are dominated by species such as the Echinospartum horridum. Therefore, prescribed burning has been recently readopted in this region as a management tool to stop the spread of shrubs and recover grasslands. We aimed to assess the effect that this practice may have on soil chemical properties such as SOC, N, pH, EC, water-extractable and exchangeable cations (Ca2+, Mg2+ and K+), cation exchange capacity, inorganic N forms (N-NH4+ and N-NO3-) and available P. We studied two prescribed burnings conducted at the subalpine level of the Central Pyrenees in the municipalities of Tella-Sin (April 2015) and Buisán (November 2015). At each site, the topsoil was sampled in triplicate at soil depths of 0-1, 1-2 and 2-3 cm immediately before (U), immediately after (B0) and one year after (B12) burning, and litter and/or ashes were removed prior to sampling. The results indicate that in the B0 samples, burning significantly reduced the SOC and N contents as well as the exchangeable Ca2+ and Mg2+ at 0-1 cm, whereas the rest of the studied properties remained virtually unchanged. However, in the B12 samples we detected a decrease of nutrient content that was probably related to leaching and/or erosion processes.
Woody encroachment has been an ongoing process in the subalpine belt of Mediterranean mountains, after land abandonment, the disappearance of the transhumant system and the decrease of the livestock number. The main objectives of this study were: (i) to identify land use/land cover (LULC) changes from 1956 to 2015, and (ii) to investigate the effects of LULC changes in physical and chemical soil properties and soil organic carbon (SOC) and nitrogen (N) stocks. It is hypothesized that woody encroachment in the subalpine belt may lead to significant changes in soil properties, and will generate an increase in the SOC stocks. A land use gradient was identified in the subalpine belt of the Central Spanish Pyrenees: (i) subalpine grasslands, (ii) shrublands, (iii) young forests, and (iv) old forests. Mineral soil samples were collected every 10 cm, down to 40 cm, at three points per each LULC and a total of 48 samples were analyzed. The results showed that (i) woody encroachment has occurred from 1956 to 2015 due to the expansion of coniferous forests and shrublands (at the expense of grasslands), (ii) land cover and soil depth had significant effects on soil properties (except for pH), being larger in the uppermost 0–10 cm depth, (iii) SOC and N contents and stocks were higher in the grassland sites, and (iv) the woody encroachment process initially produced a decrease in the SOC stocks (shrublands), but no differences were observed considering the complete soil profile between grasslands and young and old forests. Further studies, describing SOC stabilization and quantifying above-ground carbon (shrub and tree biomass) are required.
Soil organic matter, aggregation and water repellency are relevant interrelated soil properties that can be af- fected by fire. The aim of this work was to analyse the effects of shrub prescribed burning for pasture reclamation on the soil aggregate stability, organic carbon and water repellency of different soil depths and aggregate sizes in a subalpine environment. Soil samples were collected from an area treated by an autumnal low-intensity pre- scribed fire in the Central Pyrenees (NE-Spain) at 0–1, 1–2, 2–3 and 3–5 cm depths just before and ~1h, 6 months and 12 months after burning. Samples were separated as whole soil (<10mm) and 6 sieve frac- tions,<0.25, 0.25–0.5, 0.5–1, 1–2, 2–4 and 4–10mm. We analysed soil organic C (SOC), aggregate stability (AS) and soil water repellency (SWR). In the unburned samples, SOC and SWR were higher in the<0.25 to 2mm sieve fractions than the 2 to 10mm sieve fractions. Fire severely and significantly decreased the SOC content in the whole soil and the<0.25mmfraction at 0–1cm depth and in the 0.25–0.5mmfraction at 0–2cm depth. SWR was reduced by burning mainly at 0–1cm depth for the whole soil and the<0.25 to 2mm sieve fractions. Nevertheless, the AS of the 0.25–0.5mm aggregates increased after fire, while the rest of the sieve fractions remained virtually unaffected. One year after the prescribed burning, SOC slightly increased and SWR recovered in the fire-affected fractions, while the AS for all aggregate sizes and depths showed a considerable decrease. The results suggest that the direct effects of burning are still present one year after burning, and the post-fire situation may pose an increased risk of soil loss. Furthermore, our results indicate that fine soil fractions are more likely to be affected by fire than coarser soil fractions and highly influence the whole soil behaviour
We determined the short and medium‐term effects of prescribed burns on soil organic matter content and biological activity in grazing areas invaded by the shrub Echinospartum horridum (Vahl) Rothm. in the Pyrenees of Huesca (Spain). Soil samples were collected at 0‐1, 1‐2 and 2‐3 cm depths in triplicate just before the burn, immediately after the burn (T0), and one and five years later (T1, T5). We analysed the contents of total soil organic C (SOC) and N, soil respiration, microbial biomass C, and β‐D‐glucosidase and acid phosphatase activities. Fire provoked an immediate high decrease in the contents of SOC (‐40.2 %) and N (‐26.3 %) in the first 3 cm, which were even lower at T5 (‐50.3 % and ‐46.5 %, respectively). This can be explained as follows: (i) low incorporation of burned organic matter due to removal by wind and runoff; (ii) changes in microclimate increasing soil temperature and enhancing mineralization; and (iii) a stimulating effect on decomposition due to the release of nutrients. Soil biological activity was affected at T0 in the first 3 cm (‐49.3 % glucosidase, ‐48.2 % phosphatase and ‐54.5 % respiration rate). Microbial biomass C content was also affected by fire at T0 (‐32.3 %) but was close to its initial value at T5. The results suggest that these soils are particularly sensitive to fire. Adjusting the frequency and intensity of the burns is necessary to minimize their impact on the soil and to ensure the suitability of this management practice.
Aims
Sub‐alpine grassland ecosystems have some of the highest biodiversity in Europe and constitute high‐value natural resources. These grasslands are under threat because of the abandonment of traditional agro‐pastoral activities and subsequent invasion by woody species. In the Central Pyrenees (Spain) several management techniques have been used to stop expansion of the highly encroaching shrub Echinospartum horridum . However, the ways in which these techniques affect recovery of sub‐alpine grasslands are poorly understood. The final goal of this study is to gain information about the effects of E. horridum management practices and provide recommendations for the local stakeholders.
Methods
This study evaluated the efficacy of controlled fires and mechanical removal of above‐ground vegetation in controlling expansion of E. horridum into sub‐alpine grasslands in the Central Pyrenees. E. horridum demography (germination and survival), soil seed bank and soil properties were recorded in two E. horridum stands where vegetation was previously removed by (1) fire (burning treatment) or (2) mechanical removal (cutting treatment) and (3) an undisturbed E. horridum stand (control).
Results
The burning treatment increased germination and survival of E. horridum seedlings more than the cutting treatment, relative to the control. Therefore, cutting appeared to be a better option for controlling E. horridum . Soil seed density was higher in the management treatments than in the control, but it did not harbour sub‐alpine grasslands species. E. horridum removal favoured recharge of the soil with seeds that arrived by dispersal. The soil seed bank in the burning treatment had higher seed abundance and seed diversity than in the cutting treatment; however, fire promoted a loss of soil nutrients.
Conclusions
The soil seed bank composition (low abundance and diversity of native species) coupled with rapid regeneration rate of E. horridum would prevent recovery of the sub‐alpine grassland based on the soil seed bank alone. Traditional shepherding has been reported to favour seed dispersal, and here we recommend E. horridum removal with cutting treatment as an additional practice for integrated management and recovery of the sub‐alpine grasslands.
Prescribed burning has been readopted in the last decade in the Central Pyrenees to stop the regression of subalpine grasslands in favour of shrublands, dominated among others by Echinospartum horridum (Vahl) Rothm. Nevertheless, the effect of this practice on soil properties is uncertain. The aim of this work was to analyse the effects of these burnings on topsoil organic matter and biological properties. Soil sampling was carried out in an autumnal prescribed fire in Buisán (NE-Spain, November 2015). Topsoil was sampled at 0–1 cm, 1–2 cm and 2–3 cm depth in triplicate just before (U), ~ 1 h (B0), 6 months (B6) and 12 months (B12) after burning. We analysed soil total organic C (TOC), total nitrogen (TN), microbial biomass C (Cmic), soil respiration (SR) and β-D-glucosidase activity. A maximum temperature of 438 °C was recorded at soil surface while at 1 cm depth only 31 °C were reached. Burning significantly decreased TOC (− 52%), TN (− 44%), Cmic (− 57%), SR (− 72%) and β-D-glucosidase (− 66%) at 0–1 cm depth while SR was also reduced (− 45%) at 1–2 cm depth. In B6 and B12, no significant changes in these properties were observed as compared to B0. It can be concluded that the impact of prescribed burning has been significant and sustained over time, although limited to the first two topsoil centimetres.
Soils constitute one of the most valuable resources on earth, especially because soil is renewable on human time scales. During the 20th century, a period marked by a widespread rural exodus and land abandonment, fire suppression policies were adopted facilitating the accumulation of fuel in forested areas, exacerbating the effects of wildfires, leading to severe degradation of soils. Prescribed fires emerged as an option for protecting forests and their soils from wildfires through the reduction of fuels levels. However such fires can serve other objectives, including stimulating the regeneration of a particular plant species, maintaining biological diversity or as a tool for recovering grasslands in encroached lands. This paper reviews studies examining the short- and long- term impacts of prescribed fires on the physical, chemical and biological soil properties; in so doing, it provides a summary of the benefits and drawbacks of this technique, to help determine if prescribed fires can be useful for managing the landscape. From the study conducted, we can affirm that prescribed fires affects soil properties but differ greatly depending on soil initial characteristics, vegetation or type of fire. Also, it is possible to see that soil's physical and biological properties are more strongly affected by prescribed fires than are its chemical properties. Finally, we conclude that prescribed fires clearly constitute a disturbance on the environment (positive, neutral or negative depending on the soil property studied), but most of the studies reviewed report a good recovery and their effects could be less pronounced than those of wildfires because of the limited soil heating and lower fire intensity and severity.
The aim of this work is to investigate the topsoil thickness affected by burning under contrasting soil moisture content (field capacity versus air-dried conditions). A mollic horizon of an Aleppo pine forest was sampled and burned in the laboratory, recording the temperature continuously at the topsoil surface and at soil depths of 1, 2, and 3cm. Changes in soil properties were measured at 0-1, 1-2, 2-3, and 3-4cm. Both the maximum temperature and the charring intensities were significantly lower in wet soils than in air-dried soils up to 3cm in depth. Moreover, soil heating was slower and cooling faster in wet soils as compared to dry soils. Therefore, the heat capacity increase of the soil moistened at field capacity plays a more important role than the thermal conductivity increase on heat transfer on burned soils. Burning did not significantly modify the pH, the carbonate content and the chroma, for either wet or dry soil. Fire caused an immediate and significant decrease in water repellency in the air-dried soil, even at 3cm depth, whereas the wet soil remained hydrophilic throughout its thickness, without being affected by burning. Burning depleted 50% of the soil organic C (OC) content in the air-dried soil and 25% in the wet soil at the upper centimeter, which was blackened. Burning significantly decreased the total N (TN) content only in the dry soil (to one-third of the original value) through the first centimeter of soil depth. Soluble ions, measured by electrical conductivity (EC), increased after burning, although only significantly in the first centimeter of air-dried soils. Below 2cm, burning had no significant effects on the brightness, OC, TN, or EC, for either wet or dry soil.
In Europe, rural depopulation and the abandonment of pastoral practices in mountain areas trigger deep changes in the landscape, which result in the accumulation of lignified fuels and the increased risk of fires, a sensitive issue in southern areas of the continent. From prehistory, a pyric herbivory has been practiced in European mountain regions. Pastoral fires created open communities, amenable to wild and domestic grazing, and herbivores perpetuated them by controlling fuel accumulation. In the last decades, the declining of extensive herbivory has given a prominent role to prescribed fires in order to preserve open communities. As a consequence, a new scenario of increased burning frequency and reduced herbivory emerges, which may affect the soil function in different ways. Our aim was to evaluate the effects of experimental burnings on soil function and nutrients cycling of a mountain gorse (Ulex gallii Planch.) shrubland, with the absence/presence of extensive grazing. We performed traditional “bush-to-bush” burnings in three experimental mountain plots and analysed seasonally along a 2-year period the soil function in relation to C-cycle (dissolved organic C, microbial biomass C and glucosidase activity), N-cycle (inorganic N forms, dissolved organic N, microbial biomass N and urease activity), P-cycle (phosphatase activity) and overall bacterial catabolic activity. Fire effects were time dependent and extensive grazing had a low influence on them. Fire originated a transient pulse of inorganic-N forms in the short term, which disappeared after 1 year, and increased dissolved organic N forms, which attenuated with time. In burned areas, a decrease of total N and microbial biomass N, and a slow-down of N- and P-cycle enzymatic activities were observed in the mid-term coinciding with a decrease of soil moisture. Since a higher burning frequency is a feasible situation that may affect mountain, nutrient-poor soils, the enduring effects of prescribed fires need to be taken into account to establish the optimal date of burning and the adequate recurrence regime that avoid negative impacts on the soil function and minimize the loss of nutrients from the soil reservoir.
Intensive management has been proposed as a method of preserving European heathland ecosystems,
many of which have undergone a process of decline in the last decades. Non-intensive management
techniques such as prescribed burning, shrub clearing and mechanical shredding could also play a role in
heathland preservation and simultaneously be used to reduce fuel accumulation and thus minimize
fire
hazard in
fire prone areas. However, information about the specific effects of these practices on soil
microbiota is particularly scarce. This study examines the effects of the above-mentioned treatments on
microbial properties in the soil organic layer (O horizon) and the upper two cm of mineral soil (as soil
quality indicators) in shrubland ecosystems in NW Spain. The microbial parameters were measured
periodically between spring 2010 (before treatments) and spring 2014 (4 years later). The most
noticeable responses in microbial parameters were observed in the soil organic layer. Prescribed burning
induced more pronounced changes than mechanical shredding and clearing. Although most of the
changes in microbial parameters were ephemeral, some of them lasted three years.
Prescribed burning is the deliberate application of fire under selected conditions to accomplish predetermined
management objectives. It is generally accepted that controlled use of fire has neutral or even positive effects
on soils due to its lower temperature, intensity and severity compared to wildfires. However, very few studies
have examined the effects of prescribed burning of shrub vegetation in humid mountain areas on soil properties. The objective of this work was to determine the immediate effects of prescribed burning on the quality and biochemical stability of soil organic matter (SOM) in areas encroached by shrubs in the Central Pyrenees (NE Spain). Soil samples were sampled in triplicate immediately before and after burning from the Ah horizon at 0–1, 1–2 and 2–3 cm depths. We quantified the variations as a direct result of burning in (1) the SOM content, (2) the content and mineralization rates of labile and recalcitrant C pools as inferred from incubation assays (141 days), and (3) the soil biological activity related to C cycling (microbial biomass C and β-D-glucosidase activity). Nearly all the soil properties studied were significantly affected by fire, varying in terms of extent of the effect and the soil depth affected. The total soil organic C (SOC), C/N ratio, β-D-glucosidase activity, C-CO2 efflux and estimated content of labile SOC decreased significantly up to 3 cmdepth. The total N and microbial biomass C were significantly affected only in the upper cmof the soil (0–1 cm). These results describe a short-term stronger impact of the prescribed fire on topsoil properties than usually reported. However, comparing these findings to other studies should be performed with caution because of the different environments considered in each case, as well as the differing soil thicknesses found in the literature, typically between 5 and 15 cm, which can lead to a dilution effect associated with the actual impacts of fire on soil properties. In this sense, the choice of a suitable soil thickness or sampling just after burning can be relevant factors in the detection of the immediate effects of fire. Shortand medium-term monitoring of the soils is needed to assess the suitability of this practice for pasture maintenance and for adapting the frequency of prescribed fires in order to minimize its impact on soil.
Land abandonment is a global issue with important implications in Mediterranean mountain areas. Abandoned Mediterranean croplands start a process of secondary succession that is initially colonized by grasslands, shrubs and forest. In Mediterranean mountain areas, the process is very slow, so the shrubs remain for decades, preventing livestock from accessing pastureland. Therefore, farmers have to burn or clear the shrubs in order to provide pasture, a practice that has recently been encouraged by several regional governments in Spain. Data from experimental plots of the Aísa Valley Experimental Station in the Spanish Pyrenees allow to evaluate the effects of burning and clearing shrubs on physical and chemical soil properties, runoff production and soil erosion rates. The results suggested that clearing shrubs returned more positive results than burning, as it improved soil quality and slowed soil erosion while producing slightly higher runoff coefficients, which is very important in Mediterranean environments where water is a scarce resource. Clearing shrubs improves soil characteristics by increasing organic matter and CN ratio, which promote the expansion of herbaceous species with a high pastoral value. The results suggested that the policy of clearing shrubs is suitable for managing abandoned lands in Mediterranean mountain areas. Further studies at catchment scale will be needed to confirm the impact of substituting shrubs for meadows and to understand the connectivity of the flows measured from pedon and slope to the watershed scale.
This study examines the effects of a prescribed fire on soil chemical properties in the Montgrí Massif (Girona, Spain). The prescribed forest fire was conducted in 2006 to reduce understory vegetation and so prevent potential severe wildfires. Soil was sampled at a depth of 0–5 cm at 42 sampling points on four separate occasions: prior to the event, immediately after, one year after and nine years after. The parameters studied were pH, electrical conductivity (EC), total carbon (C), total nitrogen (N), available phosphorus (P), potassium (K+), calcium (Ca2 +) and magnesium (Mg2 +). All parameters (except pH) increased significantly immediately after the fire. One year after burning, some chemical parameters – namely, EC, available P and K+ – had returned to their initial, or even lower, values; while others – pH and total C – continued to rise. Total N, Ca2 + and Mg2 + levels had fallen one year after the fire, but levels were still higher than those prior to the event. Nine years after the fire, pH, total C, total N and available P are significantly lower than pre-fire values and nutrients concentrations are now higher than at the outset but without statistical significance. The soil system, therefore, is still far from being recovered nine years later.
Total carbon (C) in soils is the sum of both organic and inorganic C. Organic C is present in the soil organic matter fraction, whereas inorganic C is largely found in carbonate minerals. The wet combustion analysis of soils by chromic acid digestion has long been a standard method for determining total C, giving results in good agreement with dry combustion. Methods for total C are basic for many of the procedures used to determine organic C in soils. In contrast to noncalcareous soils, inorganic C must be removed from calcareous or limed soils before the analysis if wet or dry combustion techniques are used to directly measure the organic C present. The organic matter content of soil may be indirectly estimated through multiplication of the organic C concentration by the ratio of organic matter to organic C commonly found in soils.
Soil enzymes are critical to soil nutrient cycling function but knowledge on the factors that control their response to major disturbances such as wildfires remains very limited. We evaluated the effect of fire-related plant functional traits (resprouting and seeding) on the resistance and resilience to fire of two soil enzyme activities involved in phosphorus and carbon cycling (acid phosphatase and β-glucosidase) in a Mediterranean shrublands in SE Spain. Using experimental fires, we compared four types of shrubland microsites: SS (vegetation patches dominated by seeder species), RR (patches dominated by resprouter species), SR (patches co-dominated by seeder and resprouter species), and IP (shrub interpatches). We assessed pre- and post-fire activities of the target soil enzymes, available P, soil organic C, and plant cover dynamics over three years after the fire. Post-fire regeneration functional groups (resprouter, seeder) modulated both pre- and post-fire activity of acid phosphatase and β-glucosidase, with higher activity in RR and SR patches than in SS patches and IP. However, we found no major differences in enzyme resistance and resilience between microsite types, except for a trend towards less resilience in SS patches. Fire similarly reduced the activity of both enzymes. However, acid phosphatase and β-glucosidase showed contrasting post-fire dynamics. While β-glucosidase proved to be rather resilient to fire, fully recovering three years after fire, acid phosphatase showed no signs of recovery in that period. Overall, the results indicate a positive influence of resprouter species on soil enzyme activity that is very resistant to fire. Long-lasting decrease in acid phosphatase activity probably resulted from the combined effect of P availability and post-fire drought. Our results provide insights on how plant functional traits modulate soil biochemical and microbiological response to fire in Mediterranean fire-prone shrublands.
Heating any soil during a sufficiently intense wildfire or prescribed
burn can alter it irreversibly, causing many significant, long-term
biological, chemical, and hydrological effects. Given the
climate-change-driven increasing probability of wildfires and the
increasing use of prescribed burns by land managers, it is important to
better understand the dynamics of the coupled heat and moisture
transport in soil during these extreme heating events. Furthermore,
improved understanding and modeling of heat and mass transport during
extreme conditions should provide insights into the associated transport
mechanisms under more normal conditions. The present study describes a
numerical model developed to simulate soil heat and moisture transport
during fires where the surface heating often ranges between 10,000 and
100,000 W m-2 for several minutes to several hours.
Basically, the model extends methods commonly used to model coupled heat
flow and moisture evaporation at ambient conditions into regions of
extreme dryness and heat. But it also incorporates some infrequently
used formulations for temperature dependencies of the soil specific
heat, thermal conductivity, and the water retention curve, as well as
advective effects due to the large changes in volume that occur when
liquid water is rapidly volatilized. Model performance is tested against
laboratory measurements of soil temperature and moisture changes at
several depths during controlled heating events. Qualitatively, the
model agrees with the laboratory observations, namely, it simulates an
increase in soil moisture ahead of the drying front (due to the
condensation of evaporated soil water at the front) and a hiatus in the
soil temperature rise during the strongly evaporative stage of the soil
drying. Nevertheless, it is shown that the model is incapable of
producing a physically realistic solution because it does not (and, in
fact, cannot) represent the relationship between soil water potential
and soil moisture at extremely low soil moisture contents (i.e.,
residual or bound water: θ < 0.01 m3
m-3, for example). Diagnosing the model's performance yields
important insights into how to make progress on modeling soil
evaporation and heating under conditions of high temperatures and very
low soil moisture content.
Heating any soil during a sufficiently intense wild fire or prescribed
burn can alter soil irreversibly, resulting in many significant and well
known, long term biological, chemical, and hydrological effects. To
better understand how fire impacts soil, especially considering the
increasing probability of wildfires that is being driven by climate
change and the increasing use of prescribe burns by land managers, it is
important to better understand the dynamics of the coupled heat and
moisture transport in soil during these extreme heating events.
Furthermore, improving understanding of heat and mass transport during
such extreme conditions should also provide insights into the associated
transport mechanisms under more normal conditions as well. Here I
describe the development of a new model designed to simulate soil heat
and moisture transport during fires where the surface heating often
ranges between 10,000 and 100,000 Wm-2 for several minutes to
several hours. Model performance is tested against laboratory
measurements of soil temperature and moisture changes at several depths
during controlled heating events created with an extremely intense
radiant heater. The laboratory tests employed well described soils with
well known physical properties. The model, on the other hand, is
somewhat unusual in that it employs formulations for temperature
dependencies of the soil specific heat, thermal conductivity, and the
water retention curve (relation between soil moisture and soil moisture
potential). It also employs a new formulation for the surface
evaporation rate as a component of the upper boundary condition, as well
as the Newton-Raphson method and the generalized Thomas algorithm for
inverting block tri-diagonal matrices to solve for soil temperature and
soil moisture potential. Model results show rapid evaporation rates with
significant vapor transfer not only to the free atmosphere above the
soil, but to lower depths of the soil, where the vapor re-condenses
ahead of the heating front. Consequently the trajectory of the solution
(soil volumetric water content versus soil temperature) is very unusual
and highly nonlinear, which may explain why more traditional methods
(i.e., those based on finite difference or finite element approaches)
tend to show more numerical instabilities than the Newton-Raphson method
when used to model these extreme conditions. But, despite the intuitive
and qualitative appeal of the model's numerical solution, it
underestimates the rate of soil moisture loss observed during the
laboratory trials, although the soil temperatures are reasonably well
simulated.
Wildfire is the major type of disturbance in forest and shrubland ecosystems in Galicia (NW Spain). Soil stabilization and rehabilitation techniques are frequently used to minimize the impact of fire on the ecosystems affected. However, information concerning the specific effects of these post-fire practices on soil microbiota is particularly scarce. In the present study we assessed the effect of an experimental fire of low severity, alone and combined with one of two post-fire stabilization treatments (seeding and mulching), on soil microbial communities in a shrubland area in the region. Measurements of soil microorganism biomass (microbial C determined by both the fumigation-extraction and the substrate induced respiration techniques), activity (respiration, β-glucosidase, urease and phosphatase) and diversity (community level physiological profiles by Biolog Ecoplates) were made at different times (1, 90, 180 and 365 days) after the fire and application of the stabilization treatments, and compared with the same measurements made in the respective unburned control soil. Microbial biomass and activity were generally reduced by fire, whereas the microbial diversity was increased by fire. However, the fire-induced changes in microbial communities were relatively small compared with the marked temporal variations in the microbial parameters analyzed, suggesting that this type of fire does not substantially change the soil functioning. This response can be partly explained by the relatively low temperature that the soil reached during the experimental fire. Mulching and seeding treatments did not have any effect on biomass, activity and diversity of soil microorganisms. The implications of these results for management practices are discussed.
The aim of this study is to determine the short-term effects of fire on nitrogen and phosphorus soil concentration in heathland sites dominated by Calluna vulgaris in the Cantabrian Mountain range (NW Spain). Three C. vulgaris heathlands sites (San Isidro, Riopinos I and Riopinos II) were selected. In June 2005, one plot (20 m × 20 m) per site was subjected to an experimental fire and the other was used as a control. Immediately after the fire, ten ash samples and ten soil samples (at a depth of 5 cm) were collected and thoroughly mixed. Soil moisture, temperature, total N, NH4+, NO3−, total P, available P and pH were determined in each sample. The quantity of ashes deposited was 300 g/m2, with a pH of 9, low N content but higher P concentrations. Significant differences in temperature and soil moisture were detected between the fire-treated and control plots. No significant differences for soil pH, total and available P, total N and NO3− concentration were found between the treatments. However, the concentration of ammoniacal-N indicated a significant increase 11 months post-fire and was produced by the changes in environmental soil conditions after the fire. Our results show that low intensity fires do not modify the concentration of N and P in the soil. However, post-fire conditions favour an increase in ammoniacal-N one year later.
We report here the results of laboratory and computer simulations designed to supply information on soil temperatures under forest and range fires. Measurements of temperature and water content in a soil column that was heated strongly at the surface showed a consistent pattern of warming and drying. In initially wet soil, temperature rose to around 95[degrees]C and remained there until the water content of the soil at that depth dropped below about 0.02 m3 m3. When the soil was initially dry, the temperature increased more rapidly, but even the moisture present in air-dry soil was sufficient to slow the rate of temperature rise when temperatures reached 90[degrees]C. A linked-transport model, which simultaneously computes changes in temperature and water content, simulated the main features of heat and water flow in a soil column heated to high temperature. There were no consistent deviations of measured from modeled temperatures, but the water content simulations consistently showed a greater buildup of moisture ahead of the heating front than did the measurements, and less drying of the soil in the heated layers when the initial soil water content was low. Soils from sand to clay, and with differing mineralogies, water contents, and bulk densities were used to compare measurements and simulations. The model performed well in all cases. Since the temperature simulations are reasonable, the model appears suitable for predicting fire effects in the field.
(C) Williams & Wilkins 1995. All Rights Reserved.
The effects of different fire intensities on physiochemical soil properties have been studied in this research. The experiment was conducted in a eucalyptus forested area near the Namadgi National Park (ACT, Australia), and four fire intensities were achieved by adding different amounts of fuel load: 0 kg m− 2 (control), 2 kg m− 2 (low fire intensity), 4 kg m− 2 (moderate fire intensity) and 8 kg m− 2 (high fire intensity). Soil surface peak temperatures reached at each plot were 14, 142, 317 and 525 °C, respectively. Immediate changes in soil properties under different fuel loads were studied and monitored monthly during a 7-month period.
The first-year effect of two different prescribed burning treatments on throughfall, runoff and soil erosion was evaluated in gorse shrubland (Ulex europaeus L.) in Galicia (NW Spain). The treatments compared were: intense burn, light burn and control (no burn).Accumulated annual throughfall represented between the 81 and 87 per cent of total rainfall in intensely burned and lightly burned areas, respectively, whereas in the unburnt areas it was 60 per cent. No significant differences between burning treatments were found for the annual throughfall. However, runoff was significantly greater in intensely burned plots (1·5-times) than in lightly burned plots. Burning also resulted in a significant increase in runoff (between 2·5 and 1·7-times, respectively) compared with controls. Total soil losses were small in all treatments, but the intense burn caused significantly greater soil erosion (5·8-times) compared with the unburned areas. Soil losses after the light burn did not significantly differ from the control although they were higher (2·3-times). The relationships obtained between erosion and several rainfall parameters were significantly different in burned areas compared to the control. The same response was observed for runoff. Annual erosion losses showed a strong dependence on percentage of bare soil even for small values of this variable. Litter thickness was also a very important variable influencing on erosion rates.This study indicated that by combining ignition techniques and high litter moisture content to maintain the percentage of bare soil below 85 per cent, soil erosion was low. Nevertheless, this result was constrained by the low rainfall that occurred during the study. Copyright © 2005 John Wiley & Sons, Ltd.
The intensity of a fire is an important factor determining the recovery of soil microorganisms after a forest fire, since it can alter the quality and quantity of carbon sources. Recovery of the microbial community was studied in a Mediterranean pine forest soil subjected to different temperatures to simulate the short-term effects of fire intensity on bacterial and fungal growth, estimated using leucine incorporation for bacteria and acetate incorporation into ergosterol for fungi. Soil samples were heated for 15 min at 50, 80, 120, 200, 300, 400 and 500 °C. After inoculation with fresh soil, and adding water to achieve 60% WHC, the soils were incubated at 20 °C for 21 days. Bacterial growth was initially inhibited in the samples heated above 50 °C (totally inhibited ≥ 200 °C), but recovered within days to levels much higher than the control, except for the samples heated at 500 °C, where growth remained low throughout the incubation period due to the destruction of most of the organic matter. After the first week of incubation, the bacterial response decreased to values close to, but still above, that of the control. Samples heated at 200 °C showed the highest cumulative bacterial growth. Fungal growth was initially lower than in the control in all the heated samples (totally inhibited ≥ 200 °C). Fungal growth recovered slowly during incubation in soils heated at ≤ 300 °C, but the cumulative growth in heated soils did not exceed that in the control. No fungal growth was observed in samples heated at the two highest temperatures. Soil respiration was initially totally inhibited in soil heated at ≥ 200 °C, but recovered rapidly in all soils; the highest respiration being observed already 1 day after inoculation. This is the first time both fungal and bacterial growth has been directly estimated in heated soils. High soil pH favouring bacteria can explain these results, but the differences in fungal and bacterial responses suggest a competitive interaction between these groups.
In the Mediterranean region, cycles of controlled burning combined with continuous grazing appear to have been an effective tool for maintaining isolated Calluna vulgaris heathlands in the form in which they occur in many places in the Atlantic region. Changes in land use and management of the mosaic of extensively exploited heathland and associated grassland over recent decades, such as bringing land into cultivation followed by its abandonment and the prohibition of fires has resulted in a process of transformation into new shrub communities with lower biodiversity. In the Mediterranean region, these changes are similar to those described in the Atlantic area, but encroachment occurs faster and could lead ultimately to afforestation by Mediterranean woodland.In a study area of 300 ha of heathland in the Spanish Mediterranean basin (specifically, in the Montseny Natural Park and Biosphere Reserve), comparison of present and former vegetation showed that shrub cover increased from 15% in 1967 to 32% in 2000. Broom (Cytisus scoparius) was the main invasive species in abandoned crop fields, whereas Mediterranean holm oak forest (Quercus ilex) increased by 18%. The surface area of fernlands doubled and C. vulgaris heathlands decreased from 35% to just 9% during the same period. Intermixed grasslands also decreased moderately and progressively from 4% to 3%.It seems probable that cycles of fires are more important in terms of shrub control and biodiversity conservation than continuous grazing alone, even at a high rate of stocking (four small ruminants per hectare per year). This encroachment process throws into relief the role that isolated habitats can play as a monitor of land use changes.
This study assessed the first-year effect of three ecosystem restoration treatments (prescribed fire, mechanical thinning, and their combination) on soil enzyme activity, soil N transformations, and C:N ratios of soil organic matter and mineral soil in eight North American forested ecosystems. The ecosystems we studied were part of the larger Fire and Fire Surrogate (FFS) network, and all had a history of frequent fire that has been altered by almost a century of organized fire suppression. Across all eight sites there were no statistically significant effects of the three manipulative treatments on phosphatase activity or chitinase activity; in contrast, at the network-scale phenol oxidase activity was reduced by fire alone, relative to the control. There was no significant network-scale effect of the three treatments on net N mineralization or net nitrification. Soil C:N ratio increased modestly after mechanical thinning, but not after prescribed fire or the combination of fire and thinning. There was a statistically significant reduction in forest floor C:N ratio as a result of all three treatments. Ordination of the differences between the treated and control areas indicated that fire alone resulted in greater changes in phenol oxidase activity and net nitrification than did the other two treatments. Large-scale restoration treatments such as those utilized in this study produce modest proximate effects on soil microbial activity and N transformations.
The increase in atmospheric concentration of CO2 by 31% since 1750 from fossil fuel combustion and land use change necessitates identification of strategies for mitigating the threat of the attendant global warming. Since the industrial revolution, global emissions of carbon (C) are estimated at 270±30 Pg (Pg=petagram=1015 g=1 billion ton) due to fossil fuel combustion and 136±55 Pg due to land use change and soil cultivation. Emissions due to land use change include those by deforestation, biomass burning, conversion of natural to agricultural ecosystems, drainage of wetlands and soil cultivation. Depletion of soil organic C (SOC) pool have contributed 78±12 Pg of C to the atmosphere. Some cultivated soils have lost one-half to two-thirds of the original SOC pool with a cumulative loss of 30–40 Mg C/ha (Mg=megagram=106 g=1 ton). The depletion of soil C is accentuated by soil degradation and exacerbated by land misuse and soil mismanagement. Thus, adoption of a restorative land use and recommended management practices (RMPs) on agricultural soils can reduce the rate of enrichment of atmospheric CO2 while having positive impacts on food security, agro-industries, water quality and the environment. A considerable part of the depleted SOC pool can be restored through conversion of marginal lands into restorative land uses, adoption of conservation tillage with cover crops and crop residue mulch, nutrient cycling including the use of compost and manure, and other systems of sustainable management of soil and water resources. Measured rates of soil C sequestration through adoption of RMPs range from 50 to 1000 kg/ha/year. The global potential of SOC sequestration through these practices is 0.9±0.3 Pg C/year, which may offset one-fourth to one-third of the annual increase in atmospheric CO2 estimated at 3.3 Pg C/year. The cumulative potential of soil C sequestration over 25–50 years is 30–60 Pg. The soil C sequestration is a truly win–win strategy. It restores degraded soils, enhances biomass production, purifies surface and ground waters, and reduces the rate of enrichment of atmospheric CO2 by offsetting emissions due to fossil fuel.
Restoring the natural fire regime to forested systems that have experienced fire exclusion throughout the past century can be a challenge due to the heavy fuel loading conditions. Fire is being re-introduced to mixed conifer forests in the Sierra Nevada through both early season and late season prescribed burns, even though most fires historically occurred in the late season. We assessed the impact of early and late season prescribed fires on soil biogeochemical and microbiological parameters that are important for ecosystem recovery. We found that the late season burns had more dramatic short-term effects on soil abiotic conditions (temperature, moisture and pH), mineral soil carbon levels, total inorganic nitrogen, and microbial activity than the early season burns, relative to unburned sites, suggesting a higher severity burn. However, the total soil nitrogen pools and fluxes and soil respiration rates were not differentially impacted by burn season. These burn season effects suggest that soil variables may be regulated more strongly by fire severity than by the season in which the prescribed fire is conducted.