Burnt Soil Research Articles

Environmental Impact of Bush Burning on the Physico-Chemistry of Mangrove Soil at Eagle Island, Niger Delta, Nigeria

Wetland soils derive their chemical composition from the sedimentary rock underneath. Among the metals produced are trace and nutrient elements which facilitate plant growth. Bush burning near mangrove forest is a common practice that has not been given much attention despite its negative impact on the environment. We thus hypothesize that the application of fire on wetland soil will negatively impact the soil chemistry. We collected soil samples from burnt and unburnt soilsat different distances from the point of burning to compare the concentration of nutrient elements (Calcium (Ca2+), iron (Fe), Magnesium (Mg), Nitrate (NO3-), Phosphate (PO43-) and Potassium (K). The result revealed that there was significant difference between metals (P 0.05). Iron had the highest overall concentration in burnt (10743.75 ± 1508.39 mg/kg) and unburnt (8854.02 ± 1734.86 mg/kg) soils. In contrast, there was no significant difference in the concentration of metals in burnt and unburnt soils (P = 0.07). The order of metal concentration in the burnt soil is Fe > Mg > PO43- > Ca2+> K > NO3- while the order of metal concentration in the unburnt soil is . There was also no correlation between distance and soil metal concentration (r = -0.05; P > 0.05). The result showed that burning does not negatively impact the wetland soil, rather it causes an increase in soil metal concentration probably due to the addition of ash from the burning process, which fertilizes the soil.

Potassium Buffering Potential in Some Burne Soils of North Iraq

This research was conducted to study potassium buffering potential behavior in some burned soils of Baweza – Mosul and Zawita- Dohuk , in north of Iraq. Potassium forms and the buffering potential phenomenon were studied by using thermodynamic parameters according to quantity- intensity ratio (Q/I) at 298 oK) The main results could be summarized as follows A great affection for the firing processto cause a high potassium availability and lost by leaching. The ARKe value ranged widely from 0.02 to 0.08 (mol L-1)1/2, the potassium labile pool (LK) rangedfrom 7.951 to 27.919 cmolc kg-1, the potential buffering capacity (PBCK) ranged between 285.47 and 369.48 cmolc kg-1 (mol L-1)-1/2, the free energy of exchange (-G) were range between 3291.8 and 4819.8 kJ mole-1 and the Gapon selectivity coefficient (kG) values fluctuated within the range 8.44 to 12.88 (L mol-1) 1/2.PF values were 0.018 to 0.025 .

Adoption of sustainable agricultural practices during the pandemic: the case of Ecuadorian family farming systems

PurposeThe objective of this study was to examine the impact of the pandemic on sustainable agricultural practices (SAP) adoption such as: organic fertilizers, minimal use of tillage, crop rotation, soil burning and crop association in the frame of family farming systems in Ecuador.Design/methodology/approachThe present research employed probit models' estimation with pooled data from 2018 to 2020. The study combined three sources of information with The Survey on Surface and Agricultural Continuous Production, as the main. This study also proposed the analysis of six regions: Coast, Coast Mountains, Northern Highlands, Central Highlands, Southern Highlands and the Amazon.FindingsThe authors see a lower adoption in the year 2020, where the pandemic was one of the causes. The only exception was the use of organic fertilizer. The adoption of these sustainable practices differed across the six regions. The findings also reveal that the employment generated by agricultural enterprises had a negative influence on the adoption of three sustainable practices, and that for the remaining practices the effect was positive.Research limitations/implicationsThe data set lacks information on the acceptance and the application of the practices promoted by agricultural technical assistance, which could provide insights into the effectiveness of the learning process. The limited observation period does not allow for investigating long-term effects on sustainable practices adoption.Originality/valueThis study helps to understand the implications of the COVID-19 pandemic in the adoption of SAP. Additionally, this research can help with the scalability of the practices starting from the regions that are most likely to adopt each of them.

Effects of wildfire and post-fire salvage logging on rainsplash erosion in a semi-arid pine forest of Central Eastern Spain

Rainsplash erosion on forested hillslopes can be increased by both wildfires and post-fire salvage logging, especially under semi-arid Mediterranean conditions. However, few studies have compared rainsplash erosion among forest sites impacted by logging to other forest areas. To fill this gap, this study has evaluated surface runoff and soil erosion in a burnt and logged (manually or mechanically) pine forest of Central-Eastern Spain under simulated rainfall and compared it to unlogged and unburnt plots. Compared to the unburnt plots, surface runoff significantly increased (over 150%) in logged areas, with a peak of 220% on the areas directly subjected to logging machinery. Peak runoff was substantially increased by fire (+130%) and less by logging (+8. Soil loss due to rainsplash erosion was about 235% (manual logging) to 750% (mechanical logging) higher compared to the unburnt plots. Wildfire exerted a much higher soil disturbance compared to salvage logging, with a soil hydrological response that can be up to an order of magnitude higher. The increased runoff and erosion rates in response to wildfire and logging were ascribed to soil compaction, which increased on average 60% on logged plots as well as to the removal of vegetation cover (−80%), whereas soil roughness played a minor role. From these results, we suggest using lightweight machinery in burnt soils, to reduce surface runoff and erosion. The possibility of building contour felled log debris using the burnt wood may also be considered, in order to retain the eroded sediments.

The impact of agricultural intensification on carbon dioxide emissions and energy consumption: A comparative study of developing and developed nations

Energy consumption has become a necessity in today’s world, and economies in developing nations cannot thrive without it. Countries with less developed economies face the same challenges of achieving sustained economic growth as those with more advanced economies. Herein, we examine the environmental Kuznets curve (EKC) hypothesis by looking at the interplay between GDP growth, energy use, agricultural output, and the effects of carbon dioxide (CO2) emissions. From 1991 to 2016, we used panel and quantile regression analyses to compare emissions in nine developing countries with those in 13 developed countries. There is the beginning of a reverse U-shaped relationship between agricultural energy use and greenhouse gas emissions. As a result, the verified EKC hypothesis paves the way for a watershed moment in the progress of industrialized nations’ economies. The estimated results of agriculture have a favorable impact on CO2 emissions by 15.16 percent but a negative influence of 2.92 percent on CO2 emissions from using liquid fuels, leading to more severe environmental deterioration. Additionally, in developing countries, feed cropping, deforestation, biomass burning, and deep soil and cropping all have detrimental consequences on the ecosystem. There is a negative correlation between CO2 emissions and economic growth in developing countries and their energy consumption. Although the EKC hypothesis for CO2 emissions was rejected at lower quantiles, it was validated for Qatar, Canada, China, and other high-emitting economies according to the empirical estimation of quantile regression. The findings of this study have important policy implications for reducing carbon dioxide emissions, suggesting that policymakers account for the stage of economic growth currently being experienced when formulating measures to cut energy use and protect the environment. Possible solutions to mitigate environmental degradation include enactment of policies to reduce energy consumption.

Relevance of UAV and sentinel-2 data fusion for estimating topsoil organic carbon after forest fire

The evaluation at detailed spatial scale of soil status after severe fires may provide useful information on the recovery of burned forest ecosystems. Here, we aimed to assess the potential of combining multispectral imagery at different spectral and spatial resolutions to estimate soil indicators of burn severity. The study was conducted in a burned area located at the northwest of the Iberian Peninsula (Spain). One month after fire, we measured soil burn severity in the field using an adapted protocol of the Composite Burn Index (CBI). Then, we performed soil sampling to analyze three soil properties potentially indicatives of fire-induced changes: mean weight diameter (MWD), soil moisture content (SMC) and soil organic carbon (SOC). Additionally, we collected post-fire imagery from the Sentinel-2A MSI satellite sensor (10–20 m of spatial resolution), as well as from a Parrot Sequoia camera on board an unmanned aerial vehicle (UAV; 0.50 m of spatial resolution). A Gram-Schmidt (GS) image sharpening technique was used to increase the spatial resolution of Sentinel-2 bands and to fuse these data with UAV information. The performance of soil parameters as indicators of soil burn severity was determined trough a machine learning decision tree, and the relationship between soil indicators and reflectance values (UAV, Sentinel-2 and fused UAV-Sentinel-2 images) was analyzed by means of support vector machine (SVM) regression models. All the considered soil parameters decreased their value with burn severity, but soil moisture content, and, to a lesser extent, soil organic carbon discriminated at best among soil burn severity classes (accuracy = 91.18 %; Kappa = 0.82). The performance of reflectance values derived from the fused UAV-Sentinel-2 image to monitor the effects of wildfire on soil characteristics was outstanding, particularly for the case of soil organic carbon content (R2 = 0.52; RPD = 1.47). This study highlights the advantages of combining satellite and UAV images to produce spatially and spectrally enhanced images, which may be relevant for estimating main impacts on soil properties in burned forest areas where emergency actions need to be applied.

Soil fire severity is more relevant than fire frequency in explaining soil, carbon and nitrogen losses and vegetation recovery after wildfire in NW Spain

NW Spain is one of the regions of Europe most affected by rural fires and where there is a particularly high risk of increased soil erosion after fire. An increase in fire frequency is expected to enhance soil erosion and the associated carbon and nitrogen losses, impairing vegetation recovery and compromising ecosystem resilience.In this study, the influence of recurrent fires on soil erosion, carbon and nitrogen loss as well as on vegetation recovery was assessed in four shrubland areas dominated by Erica australis L. Pterospartum tridentatum (L.) Willk. And Ulex gallii Planch, burned in October 2017. Two of the areas were burned twice, between 2010 and 2017, and the other two areas were burned once, in 2017. Soil burn severity was moderate to high in all experimental sites. Soil erosion along with vegetation cover and diversity were monitored during the two years after fire, on 24 plots of 80 m2.In the first year after fire, the mean sediment yield was 24.1 Mg ha−1 in the areas burned twice and 17.4 Mg ha−1 in the areas burned once. Fire frequency did not significantly influenced soil loss unlike the carbon and nitrogen concentrations in eroded sediments. Sediment losses as well as carbon and nitrogen losses were significantly associated with soil burn severity.Vegetation recovery was not affected by fire frequency in the shrublands, which were dominated by resprouters. No alteration in species composition was observed, indicating the high degree of resilience of the communities.In summary, recurrent fires occurring within an interval of 10 years seemed to have little effect on sediment yield and vegetation recovery. The significant influence of soil burn severity on sediment yield and vegetation recovery highlighted the importance of considering this factor in fire prevention plans for fire-prone areas.

Debris flow occurrence under changing climate and wildfire regimes: A southern California perspective

In southern California, wildfire incidents are increasing in frequency and magnitude. There is a great deal of research predicting the impact of climate change on large scale fire regimes. These impacts, now the new normal, include increases in future fire incidents and burn severities. Yet predictive studies on how ecosystems respond to changing fire regimes are lacking. Identifying trends in post-fire erosion patterns, such as post-fire debris flows, is critical for increasing human resiliency and adaptation to changing weather patterns and eventual long-term climate change. The relative historical abundance of post-fire debris flows in southern California presents this concern: will worsening wildfire regimes result in more post-fire debris flows? Our research addresses this concern by utilizing a descriptive approach to analyze post-fire debris flows in southern California from 2001 to 2018 to elucidate possible trends. We found that 84 % of debris flows originate from watersheds with soils burnt at moderate soil burn severity. We found that debris flow occurrence is more reliant on the percent coverage of a soil burn severity classification than its areal extent. Further, larger fires also tended to produce more debris flows and most (73 %) debris flow watersheds occurred in predominantly bedrock areas. Our research suggests that the number of post-fire runoff-generated debris flows in the region will increase if fires continue to increase in size, occur on slopes of at least 20°, burn south-facing watersheds with bedrock of igneous or sedimentary origin to at least a moderate severity, and peak rainfall intensity return intervals do not change. These findings highlight the interconnectivity between natural erosive processes, wildfires, humans, and climate change.

Macroscale effects of the Monument Fire on suitable habitat of the Trinity bristle snail in the Greater Trinity Basin, Klamath Bioregion, northern California

I evaluated the impact and extent of the Monument Fire on the geographic range and suitable macrohabitat of the Trinity bristle snail (Monadenia setosa), a California endemic with limited distribution in northern California. Total area burned by the fire was ~87,984 ha or 46.0% of the species range (n = 191,156 ha). Total area of suitable macrohabitat for the species is ~107,913 ha of which 44.5% (n = 47,962 ha) was encompassed by the fire. Results show that the total area of forest cover-type vegetation and individual forest stand attributes impacted by the fire was not significantly different from areas within the species range not burned by the fire. There was no significant proportional differences in the six sequential categories of suitable macrohabitat burned by the fire (i.e., Low, Low-moderate, Moderate, Moderate-high, High, Critical suitability). The percentage of Moderate and Moderate-high suitable macrohabitat burned was only somewhat greater than predicted by the pre-fire species habitat suitability model (HSM). Many individual watersheds were encompassed by the fire and the resulting mosaic of burned watersheds was highly variable. Application of the Soil Burn Severity (SBS) map identified 8,293 ha (17.3%) of Unburned or very low burned soil, 24,191 ha (50.5%) of Low burned soil, 13,998 ha (29.2.1%) of Moderately burned soil, and 1,460 ha (3.0%) of Highly burned soil within the boundaries of the Monument Fire. When applied to categories of suitable macrohabitat, I calculated that 31,096 ha (100%) of Low to Low-moderate and 13,998 ha (96.1%) of Moderate to Moderate-high suitable macrohabitat were burned. High and Critical areas of macrohabitat suitability were much less impacted by high SBS (n = 1,461 ha [58.0%] because these regions were small in size, highly fragmented, widely dispersed across the landscape, and separated by major topographic and riverine discontinuities.

Variability of soil properties with fire severity in pine forests and reforested areas under Mediterranean conditions

Abstract It is well known how fires affect the properties of forest soils depending on its severity. A better understanding of the magnitude of these impacts is essential to setup effective management actions after fire against the losses of soil and biodiversity. However, physical, chemical and biological processes in burnt soils are complex, resulting in a diversity of fire-induced changes, as acknowledged in many literature studies. Moreover, these changes may be even variable between natural forests and reforested areas. This study explores the changes in the most important soil properties with fire severity, from low to high. The main chemical parameters of soils were measured after field sampling in different pine forests (burnt natural stands, reforested areas as well as unburnt sites) of Castilla La Mancha (Central Eastern Spain). In comparison to the unburnt soils, the investigation has shown in the burnt areas: (i) no evident changes in soil pH at all fire severities, except in natural stands burnt at a very high severity (showing an increase of about 10%); (ii) increases in the organic carbon content (by about 70%) of soils burnt at a moderate fire severity under both forest ecosystems, and in reforested areas at very high fire severities (+95%); (iii) small differences in the nitrogen content of soil, except for a significant increase measured in soils burnt at an moderate fire severity under both the natural pine stand and reforested area (about +300%); (iv) a limited variability of the phosphorous content in the soil, with only an increase in soils under natural pine stands burnt at moderate fire severity (by 250%); (v) increases in magnesium and potassium contents in soils burnt at the highest fire severities for both land conditions, and decreases in calcium content in reforested areas burnt at the highest severity. Due to some negative impacts (increase in pH and decrease in organic carbon), the implementation of post-fire management actions at natural pine stands burnt at the highest fire severity should be a priority over reforested areas. Overall, this study did not show a straightforward pattern between soil properties, fire severity and land condition. This means that other parameters (for instance, the hydrological properties of soils) that were not explored in this investigation could have played an important role, and therefore must be taken into consideration when defining post-fire management actions.

Heat–induced changes in soil properties: fires as cause for remobilization of chemical elements

Abstract Exposure of soil constituents to elevated temperatures during wildfire can significantly affect their properties and consequently, increase the mobility of the bound contaminants. To estimate the potential of wildfires to influence metal remobilization from the burned soil due to the changes in cation exchange capacity (CEC) after organic matter combustion and mineral alteration and degradation, changes in soil properties after exposure to different temperatures was investigated. This was accomplished through analysis of geochemical, mineralogical and surface physicochemical properties of a soil sample exposed to different temperatures in a laboratory. Heating the soil sample at 200 °C, 500 °C and 850 °C resulted in an increase in pH (from 5.9 to 12.3), decrease in cation exchange capacity (from 47.2 to 7.3 cmol+kg−1) and changes in the specific surface area (observed only at 500 °C), that are associated with structural modifications of clay minerals and ferromagnetic minerals. Extraction analysis showed the increase in the concentration of almost all analysed elements (Al, Cd, Co, Cr, Fe, Mn and Zn) in soil eluates. The observed increase, following high– temperature heating (500 °C and 850 °C), was as much as 15 times higher (e.g., Al), compared to the native soil sample (25 °C). This strongly indicates that wildfire can act as a trigger for remobilization of heavy metals.

The Shang dynasty remains at the Guoyuanzui site in Lutai Mountain, Huangpi District, Wuhan

Abstract The Hubei Provincial Institute of Cultural Relics and Archaeology et al. excavated at the Guoyuanzui site in Lutai Mountain, Huangpi District, Wuhan, Hubei from 2019 to 2020, and discovered a series of Shang dynasty remains, including residential and bronze casting areas. Features related to bronze casting include architectural structures, ash ditches, ash pits, red burnt soil pits, furnaces, round-shaped burnt ground surfaces, clay mold pits, and backfill pits. Unearthed artifacts range from bronzes, casting-related artifacts, pottery artifacts, and stone objects. Most of the Shang dynasty casting remains found at Guoyuanzui are of the same period as those of the Huayuanzhuang phase in Huanbei Shang City through Yinxu Phase I. The Guoyuanzui site is another Shang dynasty core settlement in the middle of the Yangtze River after Panlongcheng. The excavation at Guoyuanzui is significant for the discussion of the Shang dynasty’s strategic management of South China, and thus is of immense value in revealing the civilizational developmental trajectory in the middle reach of the Yangtze River.

The Excavation of a Neolithic site at Jingtoushan in Yuyao, Zhejiang

Abstract The Zhejiang Provincial Institute of Cultural Relics and Archaeology and other authorities excavated the Jingtoushan site from 2019 to 2020, revealing various features such as ash pits, storage pits, red burnt soils, shell middens, and the loci of tool manufacture. Unearthed artifacts are made of pottery, stone, bone and antler, mussel, wood, and textile. In addition, a large number of faunal, floral, and minerals are also collected. The Jingtoushan site, dating between 8300 and 7800 BP, is the only prehistoric shell midden site discovered thus far in Zhejiang. It also has the oldest and deepest shell midden deposits along the coastal areas of China.

Energy dispersive X-ray fluorescence analysis to estimate the maximum temperature reached in burned soils from an Amazonian region.

Determining the maximum temperature reached in soil during burning is important when evaluating fire intensity. Forest conversion is an ongoing process in the Amazon ecosystem. It is of utmost importance to predict fire effects on soil properties and avoid damaging environmental systems. Spectroscopic methods combined with multivariate statistics may provide chemical and mineralogical information from soil. This study aims at predicting the maximum temperature reached in Oxisols from an Amazonian region in Brazil. Slash-and-burn and pasture samples collected after fire events and unburned forest soil samples submitted to heating (250-800°C) were investigated. Energy-dispersive X-ray fluorescence (EDXRF) was used to acquire chemical data. The experimental procedure is rapid and requires minimal sample preparation and no hazardous chemical reagents. The EDXRF data, combined with partial least squares regression, were applied in controlled-heated samples from five different sites of forest, pasture, and slash-and-burn areas. Estimated temperatures for burned samples ranged from 317 to 609°C. Considering the instrumental advantages and the achieved results, the use of EDXRF combined with multivariate analysis is a feasible alternative technology to evaluate fire effects in soil.

Multivariate Analysis with XRD Data as a Fingerprinting Technique to Study Burned Soils

Fire is a natural process with recognized recurrence. However, ongoing climate change and human activities are causing some disturbances in their natural regimes in most ecosystems. It is important to improve the methodologies used to evaluate the fire-induced changes in soils. This study aims at investigating the potential of the X-ray diffraction (XRD) technique to be used as a fingerprinting technique for burned soils. Multivariate analysis was employed to analyze the XRD data. Hierarchical Cluster Analysis (HCA) and local Partial Least Squares (PLS-2) models were performed. The soil samples are classified as Ferralsols and were collected from an Amazon region, Brazil, from forests, pastures and a slash-and-burn area. The studied temperatures ranged between 25 and 800 °C. Major differences were found for gibbsite, goethite and kaolinite contents due to dehydration. PLS-2 analysis presented better results than HCA as it provided information concerning the two features of the investigated soils, the collection site and the temperature. Therefore, it was possible to characterize soils from different sites and soils heated at different temperatures by using XRD data with multivariate analysis. Such methodology provided important information that may be used in areas with these environmental and soil conditions.

Heat and smoke from wildfires influence water temperature and dissolved oxygen levels in headwater streams

Wildfire has become increasingly common and severe in forested landscapes across the western United States. Stream and air temperatures within these landscapes are influenced not only by direct heating during the fire but by shading from heavy smoke. In addition, dissolved oxygen (DO) can be affected by increased ash inputs from fire or reduced primary production under lower light conditions. Because collecting data as the event occurs is challenging, most research exploring fire effects on streams has focused on responses months to years after the event as opposed to during and immediately after the fire. We sought to understand how physical stream parameters change as wildfire burns near streams, how stream temperature responses vary through a stream reach, how parameters respond to shading from pervasive smoke during and shortly after the fire, and how fire severity correlates with observed changes. In this study, we report measurements of light, air temperature, stream temperature, and DO across eleven 2nd- to 4th-order streams in the western Cascade Mountains of Oregon, USA, 1 wk before, during, and 1 wk after an extensive wildfire in 2020. Burning near streams resulted in a brief increase in daily maximum stream temperature of 4.5°C at the most severely burned site but small increases or decreases at less affected sites. Longitudinal replication revealed that temperature responses can be patchy at relatively small scales (∼50 m). DO daily minima decreased by 1.3 to 16.9% saturation on the day of the fire, with the magnitude of effect corresponding to burn severity. Across all 11 sites, riparian and watershed estimates of Rapid Assessment of Vegetation Condition after Wildfire and soil burn severity were better correlated with stream temperature responses to fire than percentage of watershed burned. Smoke effects were pervasive, both spatially and temporally, resulting in decreased light, stream temperature maxima, and diurnal variation in DO. Our results suggest that acute changes to physical stream parameters caused minimal harm to aquatic biota at our sites, and the effects of smoke on physical stream parameters will likely impose larger immediate effects on headwater streams than heating from the fire itself.

Fire and land use impact soil properties in a Mediterranean dry sclerophyll woodland

Fire directly impacts soil properties responsible for soil function and can result in soil degradation. Across the globe, climate change-induced droughts and elevated temperatures are exacerbating fire regime severity, breadth, and frequency, thus posing a threat to soil function and dependent ecosystem services. In Australia, the 2019–2020 fire season consumed nearly 50% of Kangaroo Island, South Australia, burning both dry sclerophyll woodland and adjacent historically cleared and grazed pastureland. Due to exacerbated fire regime elements, e.g., intensity and area affected, and interactions with historical land use, post-fire recovery of soil function was uncertain. This study assessed the impacts of a) the 2019–2020 fire event in Western River, Kangaroo Island on dry sclerophyll woodland and b) the interaction between this fire event and historical clearing and grazing on post-fire function of the soil. To do so, the following physicochemical and biological soil properties were analysed: labile active carbon, total carbon, total nitrogen, carbon to nitrogen ratio (C/N), pH, electrical conductivity, soil water repellency, aggregate stability, microbial community composition, and microbial diversity. Our results showed that the fire was of high severity, causing a reduction in nutrient content, an extreme rise in pH, and significant modifications to fungal communities in burnt compared to unburnt dry sclerophyll woodland. Furthermore, clearing and grazing raised post-fire soil nutrient levels and soil microbial diversity but reduced soil C/N and the abundance of ectomycorrhizal fungi in burnt pastureland compared to burnt woodland soils. This study highlights the role of management and fire severity in post-fire outcomes and emphasizes the need for comprehensive soil function assessments to evaluate the impacts of disturbance on soil. Taking direct measure of soil properties, as done here, will improve future assessments of fire season impacts and post-fire recovery in fire-prone landscapes.

Fire decreases gross mineralization rate but does not alter gross nitrification rate in boreal forest soils

Wildfire has several environmental and ecological effects on soil biogeochemistry, including the nitrogen (N) cycle in forest ecosystems. In this study with 30 days of incubation, we examined the effect of a fire event on changes in soil properties, especially gross N mineralization and nitrification processes in boreal forest soils. We also tested how the addition and removal of fire-derived natural pyrogenic carbon (PyC, 1.5%) affected N transformation processes. After incubation, the concentrations of NH4+-N, NO3−-N, total N, and dissolved organic N were largely enhanced in the burnt soils compared to the unburnt soils. Fire significantly decreased gross N mineralization rates from 6.88 μg N g−1 d−1 to 0.87 μg N g−1 d−1 and NH4+ immobilization rates from 6.04 μg N g−1 d−1 to 0.55 μg N g−1 d−1 but did not significantly affect gross N nitrification rates or NO3− immobilization rates on day 30. The removal from the burnt soil or addition to the unburnt soil of PyC had no significant effect on N transformation. The abundances of nirK, nosZ I, narG, and nifH in the burnt soils were the highest across the different treatments. Our study revealed that fire decreased gross N mineralization processes, which was associated with enhanced abundances of N-cycling genes (nirK, nosZ I and narG) in the boreal forest soils.

Mid-Term Natural Regeneration of Pinus halepensis Mill. after Post-Fire Treatments in South-Eastern Spain

Straw mulching and salvage logging are common management techniques after forest wildfires. However, these post-fire actions may result in an additional disturbance in burned soils, which may hamper the natural regeneration of forest species, especially in Mediterranean areas. The results of the investigations on the impacts of these post-fire management techniques are still insufficient, and especially about post-fire regeneration of Pinus halepensis Mill. This tree species is typical of the western Mediterranean Basin and is hardly threatened by forest wildfires. To fill these literature gaps, this study explores the effects of salvage logging after straw mulching on the regeneration of Pinus halepensis Mill. throughout four years after a wildfire. These effects have been also related to the changes in the main chemical properties of the supporting soils. Compared to the burned but non-treated areas, after four years of fire and post-fire treatments, we found that: (i) mulched and non-logged sites showed a significantly higher number of seedlings (+66%) with larger diameter (+12%) and higher height (+25%); (ii) logging did not significantly increase this number (+74%), but, in mulched and logged sites, the seedlings had significantly lower diameters (−18%) and heights (−9%); (iii) an increase in the seedling number (+29%), and decreases in the plant diameter (−34%) and height (−15%) were observed in the non-mulched and logged areas; (iv) no significant differences in the other morphometric parameters of seedlings were detected among all post-fire treatments; (v) a clear gradient between the organic matter content of soils and the number of plants growing under the four treatments was evident. These results support the task of forest managers in accelerating the recovery of natural vegetation in burned pine forests in the Mediterranean environment.

Experimental assessment of tundra fire impact on element export and storage in permafrost peatlands

Extensive studies have been performed on wildfire impact on terrestrial and aquatic ecosystems in the taiga biome, however consequences of wildfires in the tundra biome remain poorly understood. In such a biome, permafrost peatlands occupy a sizable territory in the Northern Hemisphere and present an extensive and highly vulnerable storage of organic carbon. Here we used an experimental approach to model the impact of ash produced from burning of main tundra organic constituents (i.e., moss, lichen and peat) on surrounding aquatic ecosystems. We studied the chemical composition of aqueous leachates produced during short-term (1 week) interaction of ash with distilled water and organic-rich lake water at 5 gsolid L−1 and 20 °C. The addition of ash enriched the fluid phase in major cations (i.e., Na, Ca, Mg), macro- (i.e., P, K, Si) and micronutrients (i.e., Mn, Fe, Co, Ni, Zn, Mo). This enrichment occurred over <2 days of experiment. Among 3 studied substrates, moss ash released the largest amount of macro- and micro-components into the aqueous solution. To place the obtained results in the environmental context of a peatbog watershed, we assume a fire return interval of 56 years and that the entire 0–10 cm of upper peat is subjected to fire impact. These mass balance calculations demonstrated that maximal possible delivery of elements from ash after soil burning to the hydrological network is negligibly small (<1–2 %) compared to the annual riverine export flux and element storage in thermokarst lakes. As such, even a 5–10 fold increase in tundra wildfire frequency may not sizably modify nutrient and metal fluxes and pools in the surrounding aquatic ecosystems. This result requires revisiting the current paradigm on the importance of wildfire impact on permafrost peatlands and calls a need for experimental work on other ecosystem compartments (litter, shrubs, frozen peat) which are subjected to fire events.