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Effects of prescribed burning for pasture reclamation on soil chemical properties in subalpine shrublands of the Central Pyrenees (NE-Spain)
Abstract
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.
... Los suelos constituyen un recurso indispensable para la vida, siendo primordiales para nuestra sobrevivencia (CRUZ et al., 2004;GARCÍA;RAMÍREZ;SÁNCHEZ, 2012). Sin embargo, este recurso ha estado sujeto a fuertes presiones generadas por diversas actividades, entre las que destacan los incendios forestales. ...
... Los suelos constituyen un recurso indispensable para la vida, siendo primordiales para nuestra sobrevivencia (CRUZ et al., 2004;GARCÍA;RAMÍREZ;SÁNCHEZ, 2012). Sin embargo, este recurso ha estado sujeto a fuertes presiones generadas por diversas actividades, entre las que destacan los incendios forestales. ...
... Los suelos constituyen un recurso indispensable para la vida, siendo primordiales para nuestra sobrevivencia (CRUZ et al., 2004;GARCÍA;RAMÍREZ;SÁNCHEZ, 2012). Sin embargo, este recurso ha estado sujeto a fuertes presiones generadas por diversas actividades, entre las que destacan los incendios forestales. ...
El objetivo fue evaluar el efecto del fuego sobre las propiedades físicas de un suelo afectado por un incendio forestal en el cerro “Corumo”, Sierra de San Luís, Estado Falcón-Venezuela, siendo esta un área estratégica para la protección del ambiente y del Sistema Hidrológico “El Falconiano”. Fueron delimitadas tres áreas: a) Plantación Afectada por el incendio forestal (PA), b) Plantación no Afectada por el incendio forestal (PNA) y c) Bosque Natural (BN). En cada área se seleccionó una parcela de 0,1 hectáreas donde se realizó el muestreo de suelos de manera aleatoria, se tomaron muestras disturbadas y no disturbadas para determinar textura, estabilidad de los agregados, densidad aparente (Da) y humedad gravimétrica (H), también se evaluó la infiltración en campo. Los resultados indican que textura y humedad del suelo no fueron afectadas por el incendio forestal, pero la estabilidad de los agregados de suelo se redujo. La densidad aparente disminuyó y la velocidad de infiltración incrementó en el suelo afectado, indicando que estas propiedades fueron favorecidas por el fuego en suelos degradados por sobrepastoreo. El impacto del fuego sobre las propiedades físicas del suelo a corto plazo puede ir en dos direcciones, afectando negativamente algunas propiedades y mejorando otras.
... Otherwise, EC shows a significant correlation with the main exchangeable cations (Ca 2+ and Mg 2+ ) and organic matter. Many authors have also found that pH and EC sometimes are not affected the same way after a fire (Girona-García et al., 2018c;Granged et al., 2011;Mills and Fey, 2004), while others like Muñoz-Rojas et al. (2016) have found, in fact, a high correlation between them. The decrease in EC and the main exchangeable cations over time is not surprising in an environment with about 1700 mm/yr of MAP (Úbeda et al., 2005;Ulery et al., 1993) and with a recovering vegetation Table 4 Evolution of properties (0-1, 1-2 and 2-3 cm depth) for unburned and burned soils (at 0, 6 and 10 years after burning): pH, Electrical conductivity (EC) and Exchangeable cations (Ca 2+ , Mg 2+ , K + ). ...
... that absorbs essential nutrients (Alcañiz et al., 2016). The incorporation of basic ash, rich in soluble ions and salts (Muñoz-Rojas et al., 2016), into the soil is likely to happen and causes these parameters to increase in the short term (Alcañiz et al., 2018;Gil et al., 2010), sometimes right after the PB (Francos et al., 2019;Girona-García et al., 2018c;Granged et al., 2011) and sometimes within the next few years (Alcañiz et al., 2016;Fontúrbel et al., 2016;Girona-García et al., 2018c). Those effects are expected to disappear in the mid-and long-term. ...
... that absorbs essential nutrients (Alcañiz et al., 2016). The incorporation of basic ash, rich in soluble ions and salts (Muñoz-Rojas et al., 2016), into the soil is likely to happen and causes these parameters to increase in the short term (Alcañiz et al., 2018;Gil et al., 2010), sometimes right after the PB (Francos et al., 2019;Girona-García et al., 2018c;Granged et al., 2011) and sometimes within the next few years (Alcañiz et al., 2016;Fontúrbel et al., 2016;Girona-García et al., 2018c). Those effects are expected to disappear in the mid-and long-term. ...
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.).
... Otherwise, EC shows a significant correlation with the main exchangeable cations (Ca 2+ and Mg 2+ ) and organic matter. Many authors have also found that pH and EC sometimes are not affected the same way after a fire (Girona-García et al., 2018c;Granged et al., 2011;Mills and Fey, 2004), while others like Muñoz-Rojas et al. (2016) have found, in fact, a high correlation between them. The decrease in EC and the main exchangeable cations over time is not surprising in an environment with about 1700 mm/yr of MAP (Úbeda et al., 2005;Ulery et al., 1993) and with a recovering vegetation Table 4 Evolution of properties (0-1, 1-2 and 2-3 cm depth) for unburned and burned soils (at 0, 6 and 10 years after burning): pH, Electrical conductivity (EC) and Exchangeable cations (Ca 2+ , Mg 2+ , K + ). ...
... that absorbs essential nutrients (Alcañiz et al., 2016). The incorporation of basic ash, rich in soluble ions and salts (Muñoz-Rojas et al., 2016), into the soil is likely to happen and causes these parameters to increase in the short term (Alcañiz et al., 2018;Gil et al., 2010), sometimes right after the PB (Francos et al., 2019;Girona-García et al., 2018c;Granged et al., 2011) and sometimes within the next few years (Alcañiz et al., 2016;Fontúrbel et al., 2016;Girona-García et al., 2018c). Those effects are expected to disappear in the mid-and long-term. ...
... that absorbs essential nutrients (Alcañiz et al., 2016). The incorporation of basic ash, rich in soluble ions and salts (Muñoz-Rojas et al., 2016), into the soil is likely to happen and causes these parameters to increase in the short term (Alcañiz et al., 2018;Gil et al., 2010), sometimes right after the PB (Francos et al., 2019;Girona-García et al., 2018c;Granged et al., 2011) and sometimes within the next few years (Alcañiz et al., 2016;Fontúrbel et al., 2016;Girona-García et al., 2018c). Those effects are expected to disappear in the mid-and long-term. ...
... [C] y nutrimentos (Han et al., 2008;Piñeiro et al., 2009;Pringle et al., 2014;Koci et al., 2020), en la fertilidad del suelo (Lin et al., 2010) y el efecto del pastoreo continuo sobre las propiedades del suelo (Yong-Zhong et al., 2005;Jeddi and Chiaeb, 2010). La quema de vegetación determina ciertos cambios en las propiedades físicas, químicas y biológicas del suelo (López-Hernández et al., 2008;Larroulet et al., 2016;García-Girona et al., 2018a;García-Girona et al., 2018b), por ejemplo, la inestabilidad de la MO en la superficie del suelo (Armas-Herrera et al., 2016), el contenido de MO (Fynn et al., 2003) y los niveles de nutrientes (Hernández-Valencia y López-Hernández, 2002). El uso de herbicidas altera el carbono orgánico (CO), los nutrientes y plantas por uso de glifosato (Nivelle et al., 2017;Rodríguez et al., 2018). ...
... La quema en pastizales es común alrededor del mundo, se ha usado principalmente para controlar arbustos invasivos o vegetación leñosa, eliminar material seco, estimular el crecimiento de arvenses (López-Hernández et al., 2008;Larroulet et al., 2016;Girona-García et al., 2018a, Girona-García et al., 2018b. Sin embargo, esta práctica puede degradar los suelos y ecosistemas. ...
... Por su parte Larroulet et al. (2016) indicaron que el pH se mantiene sin cambios mientras la temperatura del fuego o severidad de la quema no rebase los 540 ºC. Girona- García et al., 2018b). Otra vía para la disminución de P disponible y otros nutrientes es la volatilización o lixiviación en el corto plazo (1 año) (Girona- García et al., 2018a). ...
Livestock in the tropical regions of Mexico is carried out extensively and its practices contribute to the deterioration of the soil. The relationship of cattle management practices with the physical-chemical and biological properties of the soil was studied in agroecosystems of the Sotavento region, Veracruz. The effect of extensive livestock management on the soil was evaluated, in different grazing environments; A management index was developed on a scale from 0 (worst practices) to 100 (best practices) and 30 sites with different vegetation cover were evaluated (monoculture of grasses=MonGra, biodiverse grasslands=PasBio and secondary vegetation=VegSec). Changes in soil properties in MonGra and VegSec after implementing Voisin rational grazing (PRV) as an improvement tool were evaluated and contrasted with extensive grazing. The management index did not differ between environments (p>0.05) and generally ranged from 30 to 50; the best performing practices were tillage and chapeos, while fertilization and grazing had low performance. The implementation of the PRV caused some changes in the physical and chemical properties of the soil (p<0.05), at the end of 14 months, mainly improvements (p<0.05) in apparent density [DA], organic matter [OM] and organic carbon [ CO] at the end of the study. There were also effects of nested management in grazing environments (p<0.05), PRV improved DA only in VegSec and P available in all environments except extensive VegSec, OM and CO improved only in extensive MonGra. The PRV also improved the abundance and richness of soil macrofauna morphospecies (p<0.05). It is concluded that extensive management practices negatively influence the nutrient content of the soil in all grazing environments and PRV regenerates some soil properties in the short term, however, long-term evaluations are required to observe significant changes in soil quality indicators.
... Prescribed fire is commonly used to induce pinyon and juniper mortality on tree-encroached sagebrush steppe sites (McIver and Brunson, 2014;Miller et al., 2014), but can have both positive and negative short-term ecosystem impacts (Pierson et al., 2013(Pierson et al., , 2014(Pierson et al., , 2015Williams et al., 2014a;2016a;2018). Fire has profound effects on soil nutritional status (Caon et al., 2014;Girona-García et al., 2018;Guinto et al., 2001;Kennard and Gholz, 2001;Mataix-Solera and Doerr, 2004;Rau et al., 2007) and physical properties (e.g., Chief et al., 2012;Debano et al., 1970;Granged et al., 2011b;Morris and Moses, 1987;Prosser and Williams, 1998;Stavi et al., 2017). ...
... Prescribed fire is commonly used to induce pinyon and juniper mortality on tree-encroached sagebrush steppe sites (McIver and Brunson, 2014;Miller et al., 2014), but can have both positive and negative short-term ecosystem impacts (Pierson et al., 2013(Pierson et al., , 2014(Pierson et al., , 2015Williams et al., 2014a;2016a;2018). Fire has profound effects on soil nutritional status (Caon et al., 2014;Girona-García et al., 2018;Guinto et al., 2001;Kennard and Gholz, 2001;Mataix-Solera and Doerr, 2004;Rau et al., 2007) and physical properties (e.g., Chief et al., 2012;Debano et al., 1970;Granged et al., 2011b;Morris and Moses, 1987;Prosser and Williams, 1998;Stavi et al., 2017). Soil water repellency is one of the most commonly researched fire-induced alterations to soil physical properties (e.g., Alcañiz et al., 2018;Granged et al., 2011a;Kennard and Gholz, 2001;Pierson et al., 2008;Scharenbroch et al., 2012). ...
Woody species encroachment into herbaceous and shrub-dominated vegetations is a concern in many rangeland ecosystems of the world. Arrival of woody species into affected rangelands leads to changes in the spatial structure of vegetation and alterations of biophysical processes. In the western USA, encroachment of pinyon (Pinus spp.) and juniper (Juniperus spp.) tree species into sagebrush steppes poses a threat to the proper ecohydrological functioning of these ecosystems. Prescribed fire has been proposed and used as one rangeland improvement practice to restore sagebrush steppe from pinyon-juniper encroachment. Short-term effects of burning on the ecohydrologic response of these systems have been well documented and often include a period of increased hydrologic and erosion vulnerability immediately after burning. Long-term ecohydrologic response of sagebrush steppe ecosystems to fire is poorly understood due to lack of cross-scale studies on treated sites. The aim of this study is to evaluate long-term vegetation, hydrologic, and erosion responses at two pinyon-juniper-encroached sagebrush sites 9 years after prescribed fire was applied as a restoration treatment. Thirty-six rainfall simulation experiments on 6 m × 2 m plots were conducted for 45 min under two conditions: a dry run (70 mm h⁻¹; dry antecedent soils) and a wet run (111 mm h⁻¹; wet antecedent soils). Runoff and erosion responses were compared between burned and unburned plots. Overall, increases in herbaceous cover in the shrub-interspace areas (intercanopy area between trees) at both sites 9 years post-burn resulted in runoff- and erosion-reduction benefits, especially under the wet runs. While the initially more degraded site characterized by 80% bare ground pre-burn, registered a higher overall increase (40% increase) in canopy cover, greater post-fire reductions in runoff and erosion were observed at the less degraded site (57% bare ground pre-burn). Runoff and erosion for the wet runs decreased respectively by 6.5-fold and 76-fold at the latter site on the burned plots relative to control plots, whereas these decreases were more muted at the more degraded site (2.5 and 3-fold respectively). Significant fragmentation of flow paths observed at the more-degraded site 9 years post-fire, suggests a decreased hydrologic connectivity as a mechanism of runoff and erosion reduction during post-fire recovery.
... However, a significant increase in soil electric conductivity (EC) from 0 to 1 cm could be observed between the most intense burns (HS, HL) and the control (UB), and between HL and LS (Figure 5b). The increase in EC could have been caused by the partial combustion of SOM at the shallowest soil depth, as well as the combustion fine roots, that liberates soluble nutrients into the soil [54]. Badía et al. [13], did not find significant changes in pH after high intensity burning applied directly to the mineral Ah horizon; unlike in the present study, their soils were highly calcareous, with an important buffer capacity. ...
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.
... However, there is evidence that even the improvement caused by burnings on soil attributes and nutrient availabilities occurs only in short periods after burning (Dick et al., 2008). Girona-García et al. (2018) studied subalpine vegetation that includes grasses. In twelve months ofter burning, they detected a decrease on topsoil nutrient availability. ...
Objective: We evaluate the effects of phosphate fertilization on the leaf blade productivity of unburned Brachiaria brizantha, cv. Marandu, as well its chemical-bromatological composition compared to the pasture burning in the southwestern Amazon. Theoretical Framework: Brazilian Amazon has one of the highest proportion of planted pastures in Brazil and the Brachiaria brizantha is the most used species. The burning is an important factor that lead to the gradual degradation of pastures. These circumstances generate pastures with low capability of providing feed for cattle farming. The improvement caused by burnings occurs only in short periods after burning. Some alternative sources with a low content of soluble P, in turn, increases biomass productivity and the nutritional value of cultivated species. Method: A field experiment was carried out in a completely randomized blocks design. The treatments consisted of unburned pasture treated with 0, 25, 100 and 200 kg ha-1 of P compared to the pasture burning. After applying the treatments, the pasture was desiccated in order to homogenize the plant emergence and growth after the period without rain from July to September. Results and Discussion: The dose of 100 kg ha-1 of P for unburned pasture promoted better productivity and mineral nutrient concentrations, and leaf quality for animal consumption was improved. Values of acid detergent fiber, neutral detergent fiber, lignin and crude protein indicate an adequate bromatological composition of leaf for animal consumption at 56 days of growth. Research Implications: The practical and theoretical implications of this research are discussed, providing insights into how the results can be applied or influence practices in the field of pasture management without fire using. These implications could encompass on how to apply and how much of an alternative phosphate must be applied to the soil to supply phosphorus for B. brizantha instead of using fire in the pasture management. Originality/Value: This study contributes to the literature by highlighting the superiority of phosphorus application from alternative source allied to N and K fertilization compared to the pasture burning practice in the Southwestern Amazon. This innovative approach can be used as a base for new researches and applied in the level of cattle farmers.
... In this ecosystem, total soil C content was unaltered but directly related to MBN and PGD. Controlled burns in shrub-encroached Pyrenean grasslands have shown varying eects on soil C stocks: no eect, immediate post-re decline, and mid-term increase due to ash and charred plant material incorporation into the soil Girona-García et al., 2018, 2019. Burn intensity likely infuences SOC variability by limiting C availability or microbes in specic soil spots. ...
... The burning of pasture is applied globally, particularly in countries such as South Africa, Zambia and Australia, and in North and South America [107]. This method, however, has effects on the environment such as the decrease in soil nutrients leading to leaching and/or erosion [109]. Animal nutrition also plays a part in controlling ticks, as nutrition mediates host resistance to ticks [110]. ...
Ticks are amongst the important ectoparasites where livestock are concerned, as they adversely affect the animals through bloodsucking. In tropical and subtropical countries, they transmit pathogens such as babesiosis, theileriosis, ehrlichiosis, and anaplasmosis in cattle, causing a reduction in production rate and significant concomitant economic losses. Ticks affect 80% of the cattle population across the world, with an estimated economic loss of USD 20–30 billion per year. In South Africa, economic losses in the livestock industry caused by ticks and tick-borne diseases are estimated to exceed USD 33 million per year (ZAR 500 million). There are seven major genera of ixodid ticks in Southern Africa (i.e., Amblyomma, Dermacentor, Haemaphysalis, Hyalomma, Ixodes and Rhipicephalus). The environment in which a tick lives is made up of all the various biological and abiotic factors that are either necessary or unnecessary for its life. The areas where various ticks have been found have been documented in many publications. Using these data, maps of possible species’ habitats can be made. Historical records on tick distribution may be incorrect due to identification mistakes or a change in the tick’s name. All the sources used to generate the maps for this review were unpublished and came from a wide range of sources. To identify tick species and the accompanying microbial ecosystems, researchers are increasingly adopting tick identification methods including 16S and 18S rDNA gene sequencing. Indeed, little is known about the genetic alterations that give important traits, including the predilection for tick hosts, transmission, and acaricide resistance. Opportunities for exploring these changes in tick populations and subpopulations are provided by advancements in omics technologies. The literature on the variety of ixodid ticks, their direct and indirect effects, and control methods in South Africa is compiled in this review.
... Different prescribed fire studies carried out in Spain, using thermocouples to measure soil temperatures at different depths, showed that the maximum temperature reached ranged from 300°C at the soil surface to lower than 125°C and 30 min duration at 2 cm depth (Fontúrbel et al., 2012;Armas-Herrera et al., 2016;Girona-García et al., 2018). However, soil heating laboratory studies conducted to simulate the effects of fire on microorganisms under field are often performed with 0-5 cm depth mineral layer at high temperatures (range 150-500°C) during a large period of time (0.5 to 4 h) (Díaz-Raviña et al., 1992;Serrasolsas and Khanna, 1995;Bárcenas-Moreno et al., 2011;Barreiro et al., 2020). ...
The effect of fire severity and recurrence on the recovery of enzymatic activities (β-glucosidase, urease, acid phosphatase) and bacterial activity was monitored. Unburned and burned soil samples from soil affected by a high severity wildfire and by a low severity experimental fire were subjected in laboratory to a temperature gradient to simulate different fire severities. These samples were subjected to a second laboratory heat treatment to simulate the effect of recurrence. Soil temperature was measured and used to calculate the degree hours reached by the soil. The results showed: a) a strong effect of repeated soil heating at different temperatures on soil microbial activity; b) a different sensitivity of enzymatic activities and bacterial activity to fire, c) the magnitude of changes in these biochemical properties was related to the extent of heat supplied to samples and the previous fire/heat history, and d) degree hours are adequate to quantify the severity of heat treatments and to examine their effects on soil microbial activity. The relationships between degree hours and the different biochemical properties analyzed clearly demonstrate that the usefulness of these biochemical properties to detect the soil microbial community response to the heat stress followed the order: urease activity > acid phosphatase activity > β-glucosidase activity ≫ bacterial activity.
... When extensive grazing delays the recovery and expansion of the gorse in grasslands, a low recurrence of burns is needed to control the resprout, allowing a sustainable burning regime (Gómez et al., 2019). Frequent burns can produce undesirable changes in soil functioning and nutrient pools (Girona-García et al., 2018;Godwin et al., 2017;San Emeterio et al., 2016), and also have negative impacts on plant communities. The activity of herbivores (selective defoliation, dung deposition and gap generation) increases environmental heterogeneity and creates new opportunities for plant species as a result of changes in their competitive hierarchies (Adler et al., 2001;Gaujour et al., 2012;Piqueray et al., 2015). ...
Over millennia, the combination of controlled burnings and extensive grazing has maintained mosaic landscapes and preserved mountain grasslands in southern Europe. In the last century, deep socio-economic changes have led to an abandonment of traditional uses, to a general decline of the domestic herbivory and to a misuse of burning practices. This study aims to quantify how the decoupling of burning and grazing regimes affects in the long-term the structure, diversity and dynamics of high-mountain, shrub-encroached grasslands. In spring 2012, four treatments (burned-grazed, burned-ungrazed, unburned-grazed and unburned-ungrazed) were set up at three sites in the Special Area of Conservation Roncesvalles-Selva de Irati, in southwest Pyrenees. During seven years, we monitored floristic composition and the height of the native tall-grass Brachypodium rupestre in four plots at each site. In the burned plots, we surveyed the resprout of the dominant shrub Ulex gallii and the dynamics of recovering of the herbaceous vegetation. Plant communities evolved differently in grazed and ungrazed plots. Extensive grazing, despite being lower than in previous decades, maintained plant diversity and limited shrub encroachment. The total absence of grazing fostered the encroachment of U. gallii at two sites and the expansion of B. rupestre at the other site. When B. rupestre cover was greater than 60%, the encroachment of U. gallii was reduced. This research highlights the competition that occurs between shrubs and tall-grasses in the absence of grazing, and the modulating effect exerted by the burnings and the site-specific features. Understanding local plant dynamics is the first step to design the most appropriate practices that help to preserve diversity at the landscape and the community level in high-mountain grasslands of south Europe.
... 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.
... It is noteworthy that the differences observed in our study compared to the results obtained after other prescribed burnings can be related to many variability-inducing factors, such as 1) the intensity, duration and distribution of fire (Granged et al., 2011); 2) moisture and amount of fuel loads (Neary et al., 1999); 3) weather conditions (Fernandes et al., 2013); 4) soil water content (Massman, 2012); 5) the sampled soil thickness (Badía-Villas et al., 2014) and 6) whether the ashes were completely removed prior to sampling (Girona-García et al., 2018b). ...
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.
... In total we received 12 contributions from the Mediter- ranean, Temperate, South America, Siberian, Iceland and Asia moun tainous environments. The contributions were focused in several im- pacts of climate and human activities on soil and sediment processes such as long-term effects of wildfire ( Francos et al., 2018-in this is- sue), prescribed fires (Girona- Garcia et al., 2018-in this issue), land abandonment and woody encroachment (Nadal-Romero et al., 2018b-in this issue), agriculture and livestock (Avellaneda-Torres et al., 2018-in this issue), restoration with forest residues (Hueso- -in this issue), impact of check dams on mountain torrents channel geometry ( Zema et al., 2018-in this is- sue), river suspended sediment ( Rodríguez-Blanco et al., 2019-in this issue), forest throughfall and soil properties impact on water con- tent ( Molina et al., 2019-in this issue), slope and rock glaciers dy- namic ( Serrano et al., 2019-in this issue; Tanarro et al., 2019-in this issue), soil and geomorphological processes associated with glacial periglacial processes (Oliva and Ruiz-Fernandez, 2018-in this issue) and soil and vegetation development in glaciated landscapes ( Lizaga et al., 2019-in this issue). ...
Plant litter decomposition is driven by soil biota and biophysiochemical conditions as well as substrate quality.
Prescribed burns can affect the abundance and diversity of soil arthropods and the biophysiochemical conditions
in terrestrial ecosystems. In this study, we examined the effects of a prescribed burn on soil arthropods and litter
chemistry in decomposing litter during a total of 469-days field incubation using litter from two grasses, Dichanthium annulatum and Megathyrsus maximus, in a subtropical moist pastureland of Puerto Rico. We found the prescribed burn substantially elevated ultraviolet (UV) radiation and soil temperature; and significantly
decreased the diversity of litter total arthropods, especially predators and Mesostigmata mites, during the initial 5 months after the burn. However, the prescribed burn had no effect on either the biophysical environment nor on arthropod abundance and diversity during the subsequent incubation period of >5 months after the burn. Furthermore, the prescribed burn substantially increased the immobilization of iron (Fe) and Manganese (Mn), and decreased sulfur (S) concentration in the decomposing litter. Prescribed burn had no interactions with substrate quality for percent mass remaining (PMR) and elemental release or accumulation. Low substrate quality D. annulatum litter with a carbon to phosphorus (C/P) ratio of 614 was associated with higher microbivore diversity and higher predator density than higher substrate quality M. maximus litter with a C/P ratio of
266 during the entire incubation period. Lower initial concentration of litter P, magnesium (Mg) and calcium (Ca) in D. annulatum resulted in higher immobilization of these elements in decomposing litter than in M. maximus. Our study suggest that prescribed burn can impose short-term changes in biophysiochemical conditions and the diversity of arthropods in litter decomposition during the initial recovery period of about 5 months after a burn, thus highlighting a high resilience of the grassland ecosystem to fire disturbance, and that it can bring lasting changes in the cycling of Fe, Mn, and S in subtropical moist pastureland that can alter ecosystem productivity.
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.
Soils are among the most valuable non-renewable resources on the Earth. They support natural vegetation and human agro-ecosystems, represent the largest terrestrial organic carbon stock, and act as stores and filters for water. Mankind has impacted on soils from its early days in many different ways, with burning being the first human perturbation at landscape scales. Fire has long been used as a tool to fertilize soils and control plant growth, but it can also substantially change vegetation, enhance soil erosion and even cause desertification of previously productive areas. Indeed fire is now regarded by some as the seventh soil-forming factor. Here we explore the effects of fire on soils as influenced by human interference. Human-induced fires have shaped our landscape for thousands of years and they are currently the most common fires in many parts of the world. We first give an overview of fire effect on soils and then focus specifically on (i) how traditional land-use practices involving fire, such as slash-and-burn or vegetation clearing, have affected and still are affecting soils; (ii) the effects of more modern uses of fire, such as fuel reduction or ecological burns, on soils; and (iii) the ongoing and potential future effects on soils of the complex interactions between human-induced land cover changes, climate warming and fire dynamics.
This article is part of the themed issue ‘The interaction of fire and mankind’.
This state-of-knowledge review about the effects of fire on soils and water can assist land and fire managers with information on the physical, chemical, and biological effects of fire needed to successfully conduct ecosystem management, and effectively inform others about the role and impacts of wildland fire. Chapter topics include the soil resource, soil physical properties and fire, soil chemistry effects, soil biology responses, the hydrologic cycle and water resources, water quality, aquatic biology, fire effects on wetland and riparian systems, fire effects models, and watershed rehabilitation.
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.
Soil organic carbon and nutrient content are analysed at topsoil cm-scale in a Rendzic Phaeozem from an Aleppo pine forest in semiarid Central Ebro Basin (NE-Spain). Soil depth affected by a severe wildfire is studied immediately after burning and a year later, trying to differentiate the heat shock and the ash/charcoal deposition effects. One week after the wildfire, soil organic carbon content (SOC) on burned topsoil decreases significantly at 0–1 cm soil depth. Wildfire degrades polysaccharides and proteins and eliminates, or at least reduces, biogenic compound markers, derived from lignin and lipids, but only above 2 cm soil depth. A characteristic cracking in the alkane series, as well as the presence of pyrogenic polycyclic aromatic hydrocarbons are also observed in the burned 1st cm topsoil. Below 2 cm the fire has little or no effect in soil organic matter molecular assemblage. Calcium, magnesium, potassium, ammonium, nitrate and phosphorous increased significantly a week after the fire, in the first cm soil depth. These modifications detected immediately after the fire (SOC decrease and nutrient increase) are related to the heat released during the severe wildfire. One year after the wildfire, SOC in the 1st cm of burned topsoil regain the same level to that observed in unburned sites, which could be a consequence of burned residues and black ash incorporation and even new inputs on soil surface derived from the reblooming processes, which starts after the fire. With the exception of nitrates whose concentration is higher in burned plots than the control ones within 0–3 cm of soil depth studied, nutrient concentration relatively decreased one year after the wildfire. Despite this decrease, fire effect (memory) still remains at the 1st cm topsoil, with many nutrients having comparatively high concentration in the burned soils under semiarid climate.
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.
The effects of burning no nitrogen (N) losses and transformations in red pine ( Pinus resinosa Ait.), eastern hemlock [ Tsuga canadensis (L.) Carr.], and Douglas‐fir ( Pseulotsuga menziesii )/western larch ( Larix occidentalis Nutt.) forest floor were investigated. Organic horizon samples were burned at 400°C for 30 min in a top‐heating oven to simulate field conditions. Measurements taken immediately after burning showed total and available N losses from the O 1 horizons but gains in total and available N in underlying layers. After burning, the litter was incubated for 5 weeks and analyzed for ammonium and nitrate concentrations and changes in acidity. Each forest floor type displayed varying patterns of ammonification, nitrification and immobilization of N. The N changes appeared related to the differing initial N contents of the organic material.
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.
Prescribed fire is a common site preparation practice in forest management in southern China. However, the effect of fire on soil properties and N transformations is still poorly understood in this region. In this study, soil properties and N transformations in burned and unburned site of two vegetation types (Eucalyptus plantation and shrubland) were compared in rainy and dry seasons after 2 years' prescribed fire. Soil pH and soil NH4-N were all higher in the burned site compared to the unburned control. Furthermore, burned sites had 30-40 % lower of soil total phosphorus than conspecific unburned sites. There was no difference in soil organic matter, total N, soil exchangeable cations, available P or NO3-N. Nitrogen mineralization rate of 0-5 cm soil in the unburned site ranged from 8.24 to 11.6 mg N kg(-1) soil month(-1) in the rainy season, compared to a lower level of 4.82-5.25 mg N kg(-1) soil month(-1) in the burned sites. In contrast, 0-5 cm layer nitrification rate was overall 2.47 mg N kg(-1) soil month(-1) in the rainy season, and was not significantly affected by burning. The reduced understory vegetation coverage after burning may be responsible for the higher soil NH4-N in the burned site. This study highlights that a better understanding the effect of prescribed burning on soil nutrients cycling would provide a critical foundation for management decision and be beneficial to afforestation in southern China.
In boreal forests of eastern Canada, wildfire has gradually been replaced by clearcut harvesting as the most extensive form
of disturbance. Such a shift in disturbance may influence the chemical properties of the forest floor and its capacity to
cycle and supply nutrients, with possible implications for forest productivity. We compared the effects of stem-only harvesting
(SOH), whole-tree harvesting (WTH) and wildfire on the chemical composition of forest floor organic matter and nutrient availability
for plants, 15–20years after disturbance in boreal coniferous stands in Quebec (Canada). The forest floor on plots of wildfire
origin was significantly enriched in aromatic forms of C with low solubility, whereas the forest floor from SOH and WTH plots
was enriched with more soluble and labile C compounds. The forest floor of wildfire plots was also characterized by higher
N concentration, but its high C:N and high concentration of 15N suggest that its N content could be recalcitrant and have a slow turnover rate. Total and exchangeable K were associated
with easily degradable organic structures, whereas total and exchangeable Ca and Mg were positively correlated with the more
recalcitrant forms of C. We suggest that the bulk of Ca and Mg cycling in the soil–plant system is inherited from the influx
of exchangeable cations in the forest floor following disturbance. The buildup of Ca and Mg exchangeable reserves should be
greater with wildfire than with harvesting, due to the sudden pulse of cation-rich ash and to the deposition of charred materials
with high exchange capacity. This raises uncertainties about the long-term availability of Ca and Mg for plant uptake on harvested
sites. In contrast, K availability should not be compromised by either harvesting or wildfire since it could be recycled rapidly
through vegetation, litter and labile organic compounds.
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.
The aim of this paper is to identify the habitat types listed in the Habitats Directive Annex I that require low-intensity
agricultural management for their existence. We assessed the link between the Annex I habitat types and agricultural practices
in order to identify habitat types that depend on the continuation of agricultural practices or whose existence is prolonged
or spatially enlarged via blocking or reducing the secondary succession by agricultural activities. 63 habitat types that
depend on or which can profit from agricultural activities—mainly grazing and mowing—were identified. They are classified
into 2 groups: (1) habitats fully dependent on the continuation of agricultural management; (2) habitats partly dependent
on the continuation of agricultural management. This paper also briefly discusses habitat types for which either doubts remain
on their dependence on agricultural management, or the relation to extensive farming practices exists only in part of their
area of distribution in Europe or under certain site conditions, respectively. Assessments of the conservation status of habitats
of European Importance by 25 EU Member States in 2007 showed that habitats identified by us as depending on agricultural practices
had a worse status than non-agricultural habitats.
KeywordsAgricultural management–Favourable conservation status–Grazing–Habitats Directive–High Nature Value Farmland–Mowing–Natura 2000–Ostermann list
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.
This study examines the direct impact of a moderate/high-severity prescribed fire on phosphorous (P) stocks and partitioning in oligotrophic soils of a dry eucalypt forest within Sydney's water supply catchments, Australia. We also quantify and characterize the P present in the ash produced in this fire, and explore its relationships with the maximum temperatures recorded in the litter layer during the burn.
In these oligotrophic soils, P concentrations were already relatively low before the fire (< 130 mg kg− 1, mainly in organic forms). The fire consumed the entire litter layer and the thin Oa soil horizon, creating 6.3 ± 3.1 t ha− 1 of ash, and resulted into direct net P losses of ~ 7 kg ha− 1. The P lost was mostly organic and there was a moderate net gain of inorganic and non-reactive P forms. Importantly, only a small proportion of the post-fire P was bioavailable (equivalent to ~ 3% of the total P lost during fire). Higher total P concentrations in ash corresponded with higher maximum temperatures (> 650 °C) recorded in the burning litter layer, but effects of fire temperature on ash P partitioning were not significant.
Fire not only transformed P chemically, but also physically. Our results show that, immediately after fire, up to 2 kg ha− 1 of P was present in the ash layer and, therefore, highly erodible and susceptible to be transported off-site by wind- and water erosion. Even if most of this P was, initially, of low bioavailability, its transfer to depositional environments with different geochemical conditions (e.g. anoxic sediments in water reservoirs) can alter its geochemical forms and availability. Further investigation of potential P transformations off-site is therefore essential, particularly given that SE-Australian water supply catchments are subject to recurrent perturbation by prescribed fire and wildfires. The latter have already resulted in major algal blooms in water supply reservoirs.
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.
Wildfires affect ecosystems depending on the fire regime. Long-term studies are needed to understand the ecological role played by fire, especially as regards its impact on soils. The aim of this study is to monitor the long-term effects (18years) of a wildfire on soil properties in two areas affected by low and high fire severity regimes. The properties studied were total nitrogen (TN), total carbon (TC), C/N ratio, soil organic matter (SOM) and extractable calcium (Ca), magnesium (Mg), sodium (Na) and potassium (K). The study was carried out in three phases: short- (immediately after the wildfire), medium- (seven years after the wildfire) and long-term (18years after the wildfire). The results showed that in both fire regimes TN decreased with time, TC and SOM were significantly lower in the burned plots than they were in the control in the medium- and long-terms. C/N ratio was significantly lower at short-term in low wildfire severity area. Extractable Ca and Mg were significantly higher in control plot than in the burned plots in the medium-term. In the long-term, extractable Ca and Mg were significantly lower in the area exposed to a high severity burning. No differences were identified in the case of extractable Na between plots on any of the sampling dates, while extractable K was significantly higher in the plot exposed to low wildfire than it was in the control. Some restoration measures may be required after the wildfire, especially in areas affected by high severity burning, to avoid the long-term impacts on the essential soil nutrients of TC, SOM, extractable Ca and Mg. This long-term nutrient depletion is attributable to vegetation removal, erosion, leaching and post-fire vegetation consumption. Soils clearly need more time to recover from wildfire disturbance, especially in areas affected by high severity fire regimes.
Forest productivity is limited by soil P availability in several forest ecosystems worldwide. Most of the soil available P is probably produced by the mineralization of organic forms of P when these forms dominate in the soil. Severe wildfires lead to loss of soil organic compounds and therefore represent a strong risk of loss of soil P. The objective of the present study was to examine how the temperature reaching during burning affects the P fractions in organic horizons and soil. For this purpose, we conducted experimental burns of intact soil monoliths with their organic horizons. We then used Hedley chemical sequential fractionation and 31P MNR spectroscopy to determine the effects of temperature during burning on soil P fractions. In the unburned organic horizons, the organic P represented 70% of the total P and it was completely mineralized when the temperatures reached above 500 °C. Similarly, in the unburned mineral soil, organic P forms represented 76% of the total P and the organic P was reduced by around 50% in the moderate soil burn severity (SBS) levels. In the highest SBS, the concentration of inorganic P (Pi) with a fast turnover rate (representing available P) was three times higher and the concentration of Pi with a slow turnover rate (representing the sum of inorganic fractions bound to Al and Ca) was eight times higher than in the unburned soil. By contrast, the organic P fractions decreased with the temperature reached during the fire, with 200 °C considered a threshold for the total thermal mineralization of organic P, mainly the labile organic fraction. These findings suggest that high temperatures lead to release of Pi, most of which is precipitated by P forms such as Pi with a slow turnover rate. It appears that the high burn severity associated with temperatures higher than 200 °C strongly disrupts soil P dynamics, increasing the occlusion capacity and decreasing the bioavailability.
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.
Prescribed fires are a common management practice in the Mediterranean region and can be an alternative to reduce the quantity of fuel and hence decrease the wildfire risk. This research focused in effects of a prescribed fire, which was applied in Montesinho Natural Park (PNM), in soil properties and on soil erosion processes. Chemical soil properties were assessed before, two, six and thirty-six months after the fire. Despite low fire intensity, soil chemical changes were observed. Thirty-six months after the fire it turned out that the soil organic matter, pH values and electrical conductivity were similar to those seen before the fire. However, the same was not verified with the values of the exchangeable bases, extractable potassium and phosphorus and exchangeable acidity that differ from the observed ones before the fire. Runoff and soil loss were monitored in a set of 4 m² paired plots installed in the study area, during 14 months after the fire and summed annual losses equivalent to 10.3 mm runoff and 1.3 Mg ha− 1 soil loss. Although corresponding to a short monitoring period, these results may add to a better knowledge of the potential susceptibility of burnt shrublands to soil degradation and their natural recovery rates.
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.
Soil heating is a key factor in changing the biological and physicochemical properties of soil. Extensive
experiments have been conducted to identify the heating effects on soil properties. However, selecting
temperature and time of exposure are critical in laboratory experiments. Herein, a realistic soil-heating
gradient was applied to detect soil nutrient changes. This realistic soil-heating gradient is adequate to
linearly change most of the soil chemical properties (~70% of the nutrient evaluated). Overall, peak
temperature is more important in inducing chemical changes in the soil than time of exposure is.
Furthermore, nutrient release is closely connected to the gradient temperature and groups of nutrients
are either released or depleted at certain heating temperatures. Soil organic matter (SOM) begins to be
depleted at a low temperature of 250°C. In addition, its reduction affects, to the same extent, the cation
exchange capacity. Overall, the moderate temperature of 350°C results in optimum improvement of soil
nutrients.
During natural and prescribed fires, combustion of heavy surface fuel loads can expose underlying soil to high temperatures causing thermal alteration of soil minerals and other changes in soil properties. We studied the effect of fire on soil cation exchange capacity (CEC) by comparing severely burned soils to nearby unburned soils at five forest and woodland sites in California, USA. Combusted logs and heavy fuel produced reddened zones of thermally altered soil underlain by blackened zones where heat exposure was lower. The cation exchange capacities of the reddened soils were 57 to 82% lower than the unburned soil while the blackened soils had 31 to 53% less CEC than unburned soil. The reddened soil experienced the highest burning temperatures resulting in the loss of organic carbon (OC), the conversion of goethite to maghemite or hematite, the destruction of kaolin, and dehydroxylation and permanent collapse of vermiculite and chlorite. Overall, most of the CEC loss was due to thermal destruction of soil organic matter (SOM), but this CEC will be restored in the post-fire ecosystem succession as biomass re-accumulates and rebuilds soil humus. The loss of CEC due to mineral alteration is longer lasting, though limited in spatial extent.
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.
Before and after a prescribed burning, the upper 2.5 cm of soil in patches of forage, nonforage, and shrub vegetation were sampled. Then, bulk density, gravimetric moisture, pH in water, available phosphorus, exchangeable cations, cationic exchange capacity, total nitrogen, total, particulate, and mineral organic carbon contents were determined. Maximum temperature ranges reached over the ground during burning were measured and the highest values were registered in shrubs. Results showed that total, particulate, and mineral organic carbon and total nitrogen contents and percent base saturation increased in all soils after burning, without detecting differential effects between vegetation patches. After burning, available phosphorus content increased both for forage and shrub patches. A Na+ content decrease was observed for all soils in the different patches while Mg2+ content increased. No changes in the other analyzed variables were observed. Prescribed burning, as studied in the present work, might improve the Caldenal soils’ chemical fertility, mainly due to an increase in labile organic matter and some nutrients essential for plant growth.
Intense rainfall events after severe wildfires can have an impact on soil properties, above all in the Mediterranean environment. This study seeks to examine the immediate impact and the effect after a year of an intense rainfall event on a Mediterranean forest affected by a high severity wildfire. The work analyses the following soil properties: soil aggregate stability, total nitrogen, total carbon, organic and inorganic carbon, the C/N ratio, carbonates, pH, electrical conductivity, extractable calcium, magnesium, sodium, potassium, available phosphorous and the sodium and potassium adsorption ratio (SPAR). We sampled soils in the burned area before, immediately after and one year after the rainfall event. The results showed that the intense rainfall event did not have an immediate impact on soil aggregate stability, but a significant difference was recorded one year after. The intense precipitation did not result in any significant changes in soil total nitrogen, total carbon, inorganic carbon, the C/N ratio and carbonates during the study period. Differences were only registered in soil organic carbon. The soil organic carbon content was significantly higher after the rainfall than in the other sampling dates. The rainfall event did increase soil pH, electrical conductivity, major cations, available phosphorous and the SPAR. One year after the fire, a significant decrease in soil aggregate stability was observed that can be attributed to high SPAR levels and human intervention, while the reduction in extractable elements can be attributed to soil leaching and vegetation consumption. Overall, the intense rainfall event, other post-fire rainfall events and human intervention did not have a detrimental impact on soil properties in all probability owing to the flat plot topography.
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.
Fire transforms fuels (i.e. biomass, necromass, soil organic matter) into materials with different chemical and physical properties. One of these materials is ash, which is the particulate residue remaining or deposited on the ground that consists of mineral materials and charred organic components. The quantity and characteristics of ash produced during a wildland fire depend mainly on (1) the total burned fuel (i.e. fuel load), (2) fuel type and (3) its combustion completeness. For a given fuel load and type, a higher combustion completeness will reduce the ash organic carbon content, increasing the relative mineral content, and hence reducing total mass of ash produced. The homogeneity and thickness of the ash layer can vary substantially in space and time and reported average thicknesses range from close to 0 to 50 mm. Ash is a highly mobile material that, after its deposition, may be incorporated into the soil profile, redistributed or removed from a burned site within days or weeks by wind and water erosion to surface depressions, footslopes, streams, lakes, reservoirs and, potentially, into marine deposits.
Steam distillation methods of determining ammonium, nitrate, and nitrite in the presence of alkali-labile organic nitrogen compounds are described. They involve the use of magnesium oxide for distillation of ammonium, ball-milled Devarda alloy for reduction of nitrate and nitrite to ammonium, and sulfamic acid for destruction of nitrite. The methods are rapid, accurate, and precise, and they permit nitrogen isotope-ratio analysis of ammonium, nitrate, and nitrite in tracer studies using 15N-enriched compounds. They give quantitative recovery of ammonium, nitrate and nitrite added to soil and plant extracts, and appear suitable for analysis of biological materials.
The effects of fire in the landscape are commonly assessed through the evaluation of ash properties. Among other properties, colour is one of the methods more frequently used. However, little is known about the effect of fire severity on ash chemical and extractable elements. Ash is an important source of nutrients in terms of landscape recovery after fire. In this study we analysed the effects of fire severity (estimated using ash colour) on ash chemical properties, CaCO3, pH, Total Carbon (TC), Total Nitrogen (TN), C/N ratio and some ash water-extractable elements, such as Calcium (Ca), Magnesium (Mg), Sodium (Na), Potassium (K), Total Phosphorous (TP), Total Sulphur (TS) and Silica (Si) collected in Portugal (N = 102) after three wildfires that occurred in the same ecosystem, composed mainly of maritime pine, Pinus pinaster, and cork oak, Quercus suber. The results showed significant statistical differences among ash colour at a p < 0.05 for ash water-extractable K and Si, at a p < 0.01 for ash water-extractable Ca, Mg, Na and TS, and the major differences were observed (at a p < 0.001) for ash CaCO3, pH, TC, TN, C/N ratio and water-extractable TP. Ash CaCO3, pH and water-extractable TS increased with fire severity and ash TC, TN, C/N ratio and water-extractable TP showed a decrease. In the remaining elements, no trend is identified. Major concentrations of ash TC, TN, C/N ratio and water-extractable Ca, Mg and K were identified in very dark brown and black ash. CaCO3, pH and water-extractable TS were identified in higher quantities in light grey ash. These findings show that fire severity is an important determinant of the type and amount of water-extractable nutrients present in ash that later can be incorporated into the soil and become available for plant growth.
The relationship between water soluble and exchangeable cations (Ca, Mg, Na, and K) was investigated for surface horizons of 195 soils including many taxonomic categories and a wide range in physical and chemical properties from around the world. This will provide information on exchangeable soil cation solubility for use in estimating plant uptake and leaching potential. Amounts of water soluble and exchangeable cations were not consistently related (r2 of 0.50, 0.08, 0.77, and 0.49 for Ca, Mg, Na, and K). High correlations were biased by high water soluble and exchangeable cation levels of a few soils that had 3.8- and 2.5-fold greater mean than median values. The ratio of exchangeable to water soluble cations was closely related to cation saturation (r2 of 0.87, 0.95, 0.95, and 0.93 for Ca, Mg, Na, and K, respectively). As the degree of saturation of the exchange complex by a certain cation increased, solubility increased. A change in saturation had less effect on K than on Na, Mg, and Ca solubility. Only exchangeable soil cations (NH4OAc extractable) are routinely measured and reported in soil survey reports, thus, water soluble levels may be determined from cation saturation. This will allow estimation of the amounts of cation that can potentially move in solution through the soil or be taken up by plants. Use of cation saturation, in addition to exchangeable content, will better characterize soil cation availability by representing quantity, intensity, and buffer factors.
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 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.
Anthropogenic burning in dry dipterocarp forests has become a common practice throughout Thailand. It is feared, that too frequent fires may result in a loss of soil fertility and thus ecosystem productivity. The aim of this study was to quantify aboveground nutrient pools in fine fuels and nutrient losses during prescribed fires applied to plots of different fire frequency histories in the Huay Kha Khaeng Wildlife Sanctuary, Thailand. Fire frequency was determined from satellite images and ranged from frequent, infrequent, rare and unburned with fire occurrences of 7, 2, 1 and 0 out of the past 10 years, respectively. Element losses were calculated as the difference between nutrient pools in the fuel before burning and the post-burning residues comprising ash, charcoal, and unburned matter, which were recovered quantitatively using aluminium trays. The percent nutrient loss was highest at sites that had undergone frequent burning in the past and was lowest at infrequently burned sites. When viewed over a ten-year period, nutrient losses from a fire regime with one fire per decade had much lower losses than the more frequent fire occurrences. Frequent fires in these forests promoted a grassy understorey, and there appeared to be a positive feedback of fire frequency on nutrient losses, because the fine fuel consumption through fire was higher in the grassy understorey than in previously less frequently burned understoreys. A comparison between estimates of ecosystem nutrient inputs and fire-related losses of N, P, Ca, and K associated with burning regimes representing 7, 3, and 1 fire per decade showed that the frequent recurrence of fire will lead to a long-term depletion of P, Ca, and K, and probably also N. Owing to the relatively low fine fuel accumulation following fire, which reached a maximum of ca. 12 t ha− 1 after ca. 10 years, prescribed fires can be carried out at longer intervals such as once per decade in a safe manner to conserve nutrients on site.
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.