Changes in soil properties after prescribed burning for pasture restoration in shrublands of the Central Pyrenees (NE-Spain)

Los pastos seminaturales del Pirineo requieren la intervención humana para su conservación y, tradicionalmente, se han mantenido gracias a la presión ganadera y a la eliminación recurrente del matorral. Sin embargo, como consecuencia del éxodo rural y el consiguiente descenso en la carga ganadera, junto a la prohibición del uso del fuego desde finales del s. XX, las zonas de pastos del Pirineo Central han sufrido procesos de matorralización por especies leñosas como el erizón (Echinospartum horridum). Desde la última década, se vienen realizando esfuerzos para revertir la matorralización y así reducir las cargas de combustible y recuperar pastizales. Las quemas prescritas, definidas como el uso preciso y planificado del fuego para conseguir unos objetivos de gestión predeterminados, suponen una herramienta apta para la eliminación de matorrales y representan una práctica de menor riesgo que las quemas agrícolas tradicionales no controladas. Sin embargo, el fuego puede modificar la mayoría de propiedades físicas, químicas y biológicas del suelo. Por ello, las quemas prescritas se realizan bajo unas condiciones ambientales favorables para reducir su severidad. No obstante, los efectos que dichas prácticas tienen sobre el suelo en ambientes húmedos de montaña son todavía inciertos.El objetivo general de la presente tesis es analizar los efectos que las quemas prescritas de Echinospartum horridum para la recuperación de pastos de puerto tienen sobre las propiedades físicas, químicas y biológicas del suelo a corto y medio plazo en el Pirineo Central (NE de España).En el capítulo 4 se estudió el efecto de las quemas prescritas sobre la agregación, la repelencia al agua y el carbono orgánico en diferentes profundidades y tamaño de agregados del suelo. Las muestras de suelo se tomaron en un área sujeta a una quema prescrita otoñal de baja intensidad a 0-1, 1-2, 2-3 y 3-5 cm de profundidad justo antes de la quema, y seis y doce meses después. Las muestras obtenidas se separaron como: 1) fracción entera de suelo (En el capítulo 5, se analizó el efecto que las quemas prescritas pueden tener sobre propiedades químicas del suelo como el SOC, N total, pH, conductividad eléctrica, contenido en cationes solubles e intercambiables (Ca2+, Mg2+ and K+), capacidad de intercambio catiónico, formas inorgánicas del N (N-NH4+ y N-NO3-) y P asimilable. En cada zona, se muestreó el suelo a 0-1, 1-2 y 2-3 cm de profundidad inmediatamente antes (U), inmediatamente después (B0) y 1 año tras la quema (B12), eliminando previamente restos de hojarasca y/o cenizas. Los resultados indican que en B0, la quema redujo significativamente el contenido en SOC y N total, así como el Ca2+ y Mg2+ intercambiable a 0-1 cm de profundidad, mientras que el resto de propiedades estudiadas no mostraron cambios significativos. Sin embargo, en B12 se detectó un descenso generalizado en el contenido de nutrientes del suelo, probablemente relacionado con procesos de lavado y/o erosión.En los capítulos 6 y 7, se estudió el efecto inmediato de las quemas prescritas sobre los stocks de carbono del suelo y propiedades biológicas relacionadas, así como su evolución a corto y medio plazo. El trabajo se realizó en tres zonas sujetas a quemas prescritas en otoño en el Pirineo Central en los municipios de Buisán, Asín de Broto y Yebra de Basa. En cada zona, se muestreó el horizonte Ah a 0-1, 1-2 y 2-3 cm de profundidad inmediatamente antes y después de cada quema. Además, se realizaron muestreos semestrales hasta un año en el caso de Asín y Yebra y hasta dos años en el caso de Buisán. Se determinaron los stocks de carbono orgánico (SOCS) y nitrógeno total (NS), el carbono de la biomasa microbiana (MBC), la respiración basal (SR) y la actividad β-D-glucosidasa del suelo. Las temperaturas máximas registradas en la superficie del suelo entre los horizontes O y Ah fueron de 438 ºC (Buisán), 768 ºC (Asín) y 595 ºC (Yebra). En Buisán, la quema redujo significativamente los SOCS (-52 %), NS (-44 %), MBC (-57 %), SR (-72 %) y la actividad β-D-glucosidasa (-66 %) en la profundidad de 0-1 cm mientras que no se observaron efectos directos del fuego en las quemas de Asín y Yebra. Las diferencias observadas para las tres zonas se relacionaron con el contrastado tiempo de residencia del fuego. Así, la quema de Buisán se realizó en un área prácticamente llana con viento suave (<br /

Influence of topography on sediment dynamics and soil chemical properties in a Mediterranean forest historically affected by wildfires: NE Iberian Peninsula

Wildfires are a major concern in Mediterranean areas and play an important role in the pedogenic process, as they usually increase soil credibility due to the destruction of vegetation cover and soil structure. On top of these factors, slope and aspect also determine the degree of retention and availability of water and nutrients in soils after fire, which in turn influence the recovery of vegetation and its protective effect against erosion. This work aims to describe the effects of slope and aspect on soil development in an area historically affected by wildfires. The study area is located in Ódena (NE Iberian Peninsula) in a Mediterranean forest. Four representative soil profiles were sampled from a south-facing steep slope, north-facing steep slope, south-facing gentle slope and north-facing gentle slope. In each profile 11 samples were sampled. The amount of soil organic matter (SOM), inorganic C (IC) and total N (TN) as well as cation availability, pH, and electrical conductivity (EC) were determined for all the horizons of each profile. Results showed that IC, TN, C/N ratio, pH, EC and K were mainly affected by aspect, whereas organic matter, C/N ratio, pH, EC, Ca and Mg were especially influenced by slope. Slope determined the amount and availability of SOM and nutrients, which highlights the need to prioritise the management of areas susceptible to erosion in order to ensure soil and ecosystem functionality

Dynamics of topsoil carbon stocks after prescribed burning for pasture restoration in shrublands of the Central Pyrenees (NE-Spain)

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 °C (Buisán), 768 °C (Asín) and 595 °C (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.publishe

Modelling the Probability of Growth and Aflatoxin B1 Production of Aspergillus Flavus under Changing Temperature Conditions in Pistachio Nuts

Proceedings of the 9th International Conference on Predictive Modelling in FoodThe aim of this work was to use probability models for the prediction of growth and aflatoxin production by Aspergillus flavus as a strategy to mitigate the aflatoxin presence in pistachio nuts during postharvest. Logistic models, with temperature and time as explanatory variables, were fitted to the probability of growth and aflatoxin B1 (AFB1) production under constant temperature levels, afterwards they were used to predict probabilities under non-isothermal scenarios. The models obtained showed levels of concordance from 80 to 100% in most of the cases. Moreover, the presence of AFB1 in pistachio nuts could be correctly predicted through AFB1 models developed in agar medium or through growth models in pistachio nuts. These findings can support decision making, at transport and storage level, and could be used by producers and processors to predict the time for AFB1 production by A. flavus in pistachio nuts in postharvest

Effect of a long-term afforestation of pine in a beech domain in NE-Spain revealed by analytical pyrolysis (Py-GC/MS).

Poster presentado en lal EGU General Assembly 2015, held 12-17 April, 2015 in Vienna, Austria. id.12736The replacement of native beech forests (Fagus sylvatica) by Scots pine (Pinus sylvestris) afforestation may exert changes in soil properties, particularly in soil organic matter (SOM) [1]. It is known that the products generated by Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) pyrolysis of organic matter are related to their origin [2 and references therein]. Therefore this technique can be used to investigate said changes. In this work, Py-GC/MS is used to study changes in SOM quality surrogated to the effect of the centennial replacement of beech by Scots pine. The soils studied were two acid soil profiles developed on quartzites under a humid climate at an altitude of 1400-1500 masl from Moncayo (Iberian range, NE-Spain). For each soil profile three organic layers (litter: OL, fragmented litter OF and humified litter OH) and the mineral soil horizons (Ah, E, Bhs and C) were sampled. After 100 years since the pine afforestation, differences in the relative abundance of lipids released by pyrolysis were observed in the O-layers ranging from 3.82-7.20% in pine soils and 0.98-1.25% in beech soils. No differences were observed in mineral horizons with depth except for the C horizons where beech lipid content was much higher (21.25%) than in that under pine (1.07%). Both pine and beech soils show similar nitrogen compounds relative contents along the soil profile, increasing from OL to Ah (3.49-9.11% and 2.75-11.73% in beech and pine respectively) with a conspicuous reduction in the E horizon. It is remarkable the absence of nitrogen compounds in beech Bhs and C horizons. The relative content of aromatic compounds in O-layers show opposite trends for beech and pine; an enrichment in aromatic compounds is observed in beech OL layer (12.39%) decreasing to 4.11% in OH layer in contrast, whereas for pine O-layers the aromatic compounds relative abundance was higher in the OH (5.83%) than in the OL layer (2.8%). Mineral Ah and E horizons show similar values in both beech (18.30-10.09%) and pine (15.81-10.01%) soils; nevertheless the relative abundance of aromatic compounds content is higher in beech mineral horizons Bhs (41.96%) and C (30.91%) than in those under pine (11.43% and 13.04% for Bhs and C respectively). Polycyclic aromatic hydrocarbons (PAHs) were only observed in the mineral soil horizons showing similar relative abundances ranging from 0.61-6.63% in beech and 0.96-3.05% in pine soils. The highest PAHs relative abundance was found in the Bhs horizon under beech. This may indicate the occurrence of fire events in the area and its translocation and accumulation by leaching from top soil in the spodic horizon. Differences in the relative abundances of lignin derived pyrolysis products (Methoxyphenols) were mainly observed in the O-layers whereas the relative abundances were similar for the mineral horizons that ranged from 1.49-4.31% in beech and 1.42-4.67% in pine. Lignin relative abundance is much higher in OH beech layer (31.88%) than in pine OH layer (14.99%) whereas similar relative contents were found in OL and OF layers ranging from 26.21-27-12% and 20.22-25.92% in beech and pine respectively. In the soil developed under beech the polysaccharide derived moieties show a relative content increase along the profile from a 9.86% in OL layer to a 29.86% in E horizon followed by a remarkable decrease in the Bhs (4.86%) and C (11.22%). Besides, the polysaccharide relative abundance in the soil under pine show a similar trend ranging from 12-23% to 30.65% but the decrease in Bhs and C horizons was found less marked (26.83% and 24.12% respectively).This study is part of the results of the FUEGOSOL (CGL2013-43440-R) and GEOFIRE Projects (CGL2012-38655-C04-01) funded by the Spanish Ministry for Economy and Competitiveness. N.T Jiménez-Morillo is funded by a FPI research grant (BES-2013-062573).Peer Reviewe