Fire does not transform shrublands of Echinospartum horridum (Vahl) Rothm. into grasslands in the Pyrenees: Development of community structure and nutritive value after single prescribed burns

Prescribed fire has been extensively used in recent years to control woody encroachment into mountain and other grassland–dominated landscapes. In the Aragon Pyrenees, prescribed burns have been mainly used to remove the native thorny shrub Echinospartum horridum (Vahl) Rothm., whose populations are spreading to the detriment of grasslands. To study the effectiveness of the burning of E. horridum to preserve grasslands for livestock grazing, the vegetation of six sites burned 0.5, 2, 3, 6, 15 and 35 years ago was sampled and compared with that of nearby unburned shrubland (control) and grassland (reference). In addition, the nutritional quality of E. horridum was examined and compared to that of the reference grassland to evaluate to what extent shrub growth can be controlled by herbivores after burning. Initial shrub cover recovered as early as 15 years after fire, with E. horridum being dominant. Plant diversity was greatest at intermediate number of years after fire. Initial floristic composition and life–form spectrum were restored 15–35 years after burning. Echinospartum horridum exhibited early lignification that restricts its availability as a palatable forage for the first two years after burning and makes it unlikely to be consumed thereafter, highlighting the difficulty in controlling the expansion of this species by livestock herbivory. The analysis of the nutrient levels suggested an increased shortage of limiting elements, such as phosphorus or sulfur, in the mid–term after burning due to substantial nutrient losses and exports during and after the burn. Our results question the suitability and sustainability of a single prescribed burn as management tool alone to control the expansion of E. horridum and call for caution in its application for fighting shrub encroachment in the Central Pyrenees

Changes in Topsoil Properties after Centennial Scots Pine Afforestation in a European Beech Forest (NE Spain)

In this work, we studied the effects of centenary Scots pine (Pinus sylvestris L.) afforestation on topsoil properties conducted in a deforested area that was previously occupied by a natural European beech (Fagus sylvatica L.) forest. Organic layers and topsoil Ah mineral horizons (0–10 cm) were sampled in the Scots pine and European beech forests of Moncayo Natural Park (north-eastern Spain). The physical (stoniness, aggregate stability, and water repellency persistence and intensity), chemical (total organic C, total N, C/N, pH, and exchangeable Ca2+, Mg2+, Na+, K+, Al3+, and Fe3+), and physicochemical (cation exchange capacity) properties of soil were analyzed. Total organic C and N were also obtained for litter samples. The studied topsoils shared a series of common properties, such as a high stoniness and aggregate stability, very low base content, high cation exchange capacity, and extreme acidity. Soils that developed under the pinewood showed a higher soil water repellency intensity. However, K+ content was significantly higher in the beechwood soil. In both forest types, total organic C and N were similar in topsoil and litter (Hemimoder type), although C and N were pooled in different O-layers. Results indicate that pine afforestation in a deforested area was an adequate measure for soil protection since it did not show significant differences in the long term (ca. 100 years) compared to the nearby natural beech stands

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

Pyrogenic organic matter from palaeo-fires during the Holocene: A case study in a sequence of buried soils at the Central Ebro Basin (NE Spain)

We studied the fire record and its environmental consequences during the Holocene in the Central Ebro Basin. This region is very sensitive to environmental changes due to its semiarid conditions, lithological features and a continuous human presence during the past 6000 years. The study area is a 6 m buried sequence of polycyclic soils developed approximately 9500 years ago that is exceptionally well preserved and encompasses four sedimentary units. The content and size distribution of macroscopic charcoal fragments were determined throughout the soil sequence and the analysis of the composition of charcoal, litter and sediments via analytical pyrolysis (Py-GC/MS). The high amount of charcoal fragments recovered in most horizons highlights the fire frequencies since the beginning of the Neolithic, most of which were probably of anthropogenic origin. In some soil horizons where charcoal was not found, we detected a distribution pattern of lipid compounds that could be related to biomass burning. On the other hand, the low number of pyrolysates in the charcoal could be attributed to high-intensity fires. No clear pattern was found in the composition of pyrolysates related to the age of sediments or vegetation type. The most ancient soil (Unit 1) was the richest in charcoal content and contains a higher proportion of larger fragments (>4 mm), which is consistent with the burning of a relatively dense vegetation cover. This buried soil has been preserved in situ, probably due to the accumulation of sedimentary materials because of a high-intensity fire. In addition, the pyrogenic C in this soil has some plant markers that could indicate a low degree of transformation. In Units 2–4, both the amount of charcoals and the proportions of macrofragments >4 mm are lower than those in Unit 1, which coincides with a more open forest and the presence of shrubs and herbs. The preservation of this site is key to continuing with studies that contribute to a better assessment of the consequences of future disturbances, such as landscape transformation and climate change

Rapid detection of polycyclic aliphatic hydrocarbons in complex organic matrices using Analytical Pyrolysis (Py-GC/MS)

Póster P37 presentado en las 13 Jornadas de Análisis Instrumental, celebradas del 14-16 de noviembre 2011, en Barcelona, España.-- [email protected] pyrolisis (Py-GC/MS) is a fast and reproducible technique widely used in the structural characterization of organic matrices. Usual analytical methods for the study of polycyclic aliphatic hydrocarbons (PAHs) involve more or less complex and time-consuming sample preparation and extraction steeps, often with the use of high quantities of organic solvents. In order to illustrate the potential of the technique for a rapid qualitative assessment of PAHs, Py-GC/MS is used here giving results of PAHs assemblages directly detected in a number of extremely complex organic matrices. Homogenised samples (1-5 mg) are placed in a double-shot pyrolyzer (Frontier Laboratories, model 2020i) attached to an Agilent 6890N GC-MS. The initial temperature was 100°C that was increased at 20°C min-1 to a final pyrolysis temperature of 500°C for 1 min. The GC instrument was equipped with a DB5MS (J&W Scientific; 30 m × 250 µm × 0.25 µm film thickness) column; oven temperature programme was: 50°C (1 min) to 100°C at 30°C min-1, then to 300°C at 20°C min-1 (held 10 min). The carrier gas was He at a controlled flow of 1 ml min-1. The detector was an Agilent 5973 mass selective detector and mass spectra were acquired with 70 eV ionizing energy. Compound assignment was achieved via extracting ion chromatograms (XIC) for selected ions, low resolution mass spectra and comparison with published and stored (NIST and Wiley libraries).Peer Reviewe

Variaciones en profundidad de las propiedades de un suelo yesoso forestal bajo quema controlada

[EN]: Changes produced by fire on soils depends on several factors (vegetation, soil type, temperature, etc.). Here we study the influence of fire on a gypsiferous forest soil located northwest of the city of Zaragoza. Six blocks of undisturbed soil were collected and burned under laboratory conditions reaching 272.9 ± 21.7 oC at 1cm depth. The fire caused significant differences (p <0.05) in all studied parameters from the O horizon and in the first centimeter of the Ah horizon. No significant differences (p <0.05) for any parameters below this depth were observed. The O horizon, strongly hydrophobic, became hydrophilic after burning. Burning induced a loss of 3.14 Mg organic carbon/ha, less than half of the values reported for other soils with mollic horizon (8.3 Mg/ha). In our soil, the loss is due to a 53.8% in the O horizon by 35.8% in the first centimeter of the Ah, and only 10.4% is lost deeper. [ES]: Los cambios producidos por el fuego en el suelo dependen de varios factores (vegetación, tipo de suelo, temperatura, etc.). En este caso se estudia la influencia del fuego en un suelo yesoso forestal al noroeste de la ciudad de Zaragoza. Para ello se tomaron seis bloques de suelo inalterado que se quemaron en laboratorio hasta una temperatura, a 1cm de profundidad, de 272.9 ± 21.7 oC. El fuego produjo diferencias significativas (p<0.05) en todos los parámetros estudiados en el horizonte O y en el primer centímetro del horizonte Ah. No encontrándose diferencias significativas (p<0.05) para ningún parámetro por debajo de esta profundidad. El horizonte O, fuertemente hidrofóbico, tras la quema se convierte en hidrofílico. La quema supone una pérdida de 3.14 Mg de carbono orgánico/ha, menos de la mitad de los valores dados para otros suelos con horizonte móllico (8.3 Mg/ha). En nuestro suelo, la pérdida se debe en un 53.8% al horizonte O, en un 35.8% en el primer centímetro del Ah, y solo el 10.4% se pierde a mayor profundidad.Este trabajo forma parte del Proyecto de Investigación en materia de medio ambiente y sostenibilidad financiado por DGA-La Caixa. Convocatoria 2011, Ref. GA-LC-055/2011.Peer Reviewe

Changes in soil organic matter composition after Scots pine afforestation in a native European beech forest revealed by analytical pyrolysis (Py-GC/MS)

7 páginas.- 5 figuras.-- 1 tabla.- 42 referencias.- Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.scitotenv.2019.07.229The introduction of coniferous species in former deciduous forests may exert changes in soil organic matter, particularly in its molecular composition. In this work, pyrolysis-gas chromatography–mass spectrometry was used to study changes in SOM quality related to the centennial afforestation of Scots pine in an area formerly covered by European beech forest in the NE-flank of the Moncayo Natural Park (NE-Spain). For each soil profile three organic layers (fresh litter, fragmented litter and humified litter) and mineral soil horizons (Ah, E, Bhs and C) were studied. A total of 128 compounds were identified in the pyrograms, and composition differences were detected among the organic and mineral soil layers as well as between soils under beech and pine, for the main compound classes: nitrogen compounds, aromatics, lignin methoxyphenols, polycyclic aromatic hydrocarbons, lipids and polysaccharide-derived moieties. Such chemical differences were found to be derived from the biomass composition of the predominant vegetation type that was incorporated into the soil and from its progression into the soil profile. The analysis of the distribution of alkanes indicated higher SOM stabilization in the native beech forest soil. The signal of beech biomarkers (long chain n-alkanes C31-C33) found in the pine E horizon indicates the permanence of SOM derived from the natural forest ca. 100 years after the afforestation.This study is part of the results of the FUEGONEO (CGL2016-76620-R) and INTERCARBON (CGL2016-78937-R) projects funded by the Spanish “Ministerio de Economía y Competitividad”. Girona-García, A. was funded by an FPI research grant (BES-2014-068072) of the “Ministerio de Economía y Competitividad” (Spanish government). Thanks are due for the financial support to CESAM (UID/AMB/50017 - POCI-01-0145-FEDER-007638), to FCT/MCTES through national funds (PIDDAC), and the co-funding by the FEDER, within the PT2020 Partnership Agreement and Compete 2020. We also thank the Aragonese Agents for Nature Protection (APN) of the Moncayo Natural Park for their collaboration and for issuing the sampling permits.Peer reviewe

Changes in water repellency, aggregation and organic matter of a mollic horizon burned in laboratory: Soil depth affected by fire

High variability in the literature is reported on the soil depth affected by forest fires because many factors are involved. We study the fire-induced changes on properties related to soil erodibility as water repellency (WR), soil aggregate stability (SAS) and organic matter at topsoil centimeter-scale (O horizon, and Ah horizon at 1, 2 and 3. cm depth). In order to achieve this aim, topsoil monoliths (Rendzic Phaeozem) were sampled from an Aleppo pine forest, with no recent history of forest fires and burned in an outdoor combustion tunnel.Fire caused an immediate and significant decrease in WR, total organic carbon (TOC) and pyrolyzed carbon (PyC) in the O horizon. The Ah horizon was also affected by burning but only up to 2. cm soil depth and with a different intensity according to the soil property: TOC was not significantly affected; WR and PyC decreased up to the upper centimeter and SAS up to 2. cm Ah horizon depth. Soil burning involved the loss of 2/3 of the pre-fire TOC of the O horizon and 1/3 of the TOC of the upper centimeter of the Ah horizon. Fire also modified the structural composition of organic matter, an effect that was apparent again only above 2. cm depth. Specifically the relative abundance of typical vegetation markers (terpenes, resinic acids) and lignin markers (methoxyphenols) decreased. Fire fragmented the long-chain molecules of the alkylic series (n-alkanes, alkenes, fatty acids and methylated fatty acids). This observation, together with a conspicuous reduction in the amount of organic molecules with functional groups in the upper centimeters of the soil monoliths, may be related to the fire-induced decreases in WR and SAS. In conclusion, moderate burning of a mollic horizon in the laboratory produced changes in the hydrophobicity, aggregation, and organic matter only up to 2. cm depth.Peer Reviewe

The effect of heat in soil organic matter (SOM). Experience from controlled burning experiments of unaltered soil blocks

3 pages, 1 figure, 8 references.-- Comunicación oral presentada en Session 1. Pyrogenic C: Distribution and stability, en European Science Foundation-Exploratory Workshop, celebrado del 5-7 de noviembre 2013, en Sevilla, España.Wildfire is an important disturbance factor in many ecosystems, especially in the Mediterranean Basin (Keeley et al., 2012). Forest fires exert changes in soil organic matter (SOM) quality and quantity (González‐Pérez et al., 2004) that in turn affect relevant and closely related characteristics like soil runoff and erosion response, due to changes on factors like wettability and aggregation (Certini et al., 2011; Mataix‐Solera et al., 2011). The effects of heat in SOM are highly variable and dependent of many interrelated factors (Badía et al., 2011).Peer reviewe