Short-term effects of nitrogen deposition on soil microbial biomass in Calluna heathlands NW Spain: critical loads

[EN] We evaluate the short-term effects of different N deposition loads on nutrient dynamic of soil microbial biomass in Cantabrian heathlands. A surplus of 10 kg N ha-1 yr-1 above N background deposition was required to increase soil microbial biomass N content in old Calluna heathlands, while a surplus of 20 kg N ha-1 yr-1 was required in young ones. The increase of atmospheric N deposition showed no change in soil microbial biomass C content. This caused a decrease in C:N ratio with the highest N deposition loads, being linked to a bacterial biomass dominance against fungal dominanceS

Soil-plant relationship in Calluna heathlands after experimental burning and nitrogen fertilization, studies from NW Spain

[EN] We studied changes in the relationship between soil nutrient content and plant species richness in Calluna heathlands after seven years of experimental burning (B) and nitrogen fertilization (NF). Our results indicate that both the treatments (B, NF, B+NF) and modification of several soil characteristics (total N, available Na, and C:N ratio) reflected in a significant increase in plant species richnessS

Disruption of trophic interactions involving the heather beetle by atmospheric nitrogen deposition

P. 436-445Elevated nitrogen (N) deposition impacts the structure and functioning of heathland ecosystems across Europe. Calluna plants under high N-inputs are very sensitive to secondary stress factors, including defoliation attacks by the heather beetle. These attacks result in serious damage or death of Calluna, its rapid replacement by grasses, and the subsequent loss of heathland. We know very little about the mechanisms that control the populations and trigger outbreaks of the heather beetle, impeding proper management measures to mitigate the damage. We investigated the effects of N deposition on the relationships between the heather beetle, its host plant, and two arthropod predators at building (rejuvenated through fire) and mature heathlands. The study combines field manipulation experiments simulating a range of N deposition rates (0, 1, 2, 5 g N m−2 year−1 for 2 years, and 5.6 g N m−2 year−1 for 10 years), and food-choice laboratory experiments testing the preferences of adults and larvae of the heather beetle for N-treated Calluna plants, and the preferences of predators for larvae grown on plants with different N-content. The larvae of the heather beetle achieved the highest abundances after the long-term (10-year) addition of N at mature Calluna plots in the field. Contrary to the adults, the larvae foraged preferentially on the most N-rich Calluna shoots under laboratory conditions. Predators showed no aggregative numerical responses to the accumulation of heather beetle larvae at high N-input experimental plots. During the feeding trials, predators consumed a small number of larvae, both in total and per individual, and systematically avoided eating the larvae reared on high-N Calluna shoots. Our study showed that the most severe defoliation damage by the heather beetle is inflicted at the larval stage under prolonged availability of high-N inputs, and that arthropod predators might not act as effective regulators of the beetle's populations.S

The Effects of Fire Severity on Vegetation Structural Complexity Assessed Using SAR Data Are Modulated by Plant Community Types in Mediterranean Fire-Prone Ecosystems

This article belongs to the Special Issue The Use of Remote Sensing Technology for Forest Fire[EN] Vegetation structural complexity (VSC) plays an essential role in the functioning and the stability of fire-prone Mediterranean ecosystems. However, we currently lack knowledge about the effects of increasing fire severity on the VSC spatial variability, as modulated by the plant community type in complex post-fire landscapes. Accordingly, this study explored, for the first time, the effect of fire severity on the VSC of different Mediterranean plant communities one year after fire by leveraging field inventory and Sentinel-1 C-band synthetic aperture radar (SAR) data. The field-evaluated VSC retrieved in post-fire scenarios from Sentinel-1 γ0 VV and VH backscatter data featured high fit ( R2 = 0.878) and low predictive error (RMSE = 0.112). Wall-to-wall VSC estimates showed that plant community types strongly modulated the VSC response to increasing fire severity, with this response strongly linked to the regenerative strategies of the dominant species in the community. Moderate and high fire severities had a strong impact, one year after fire, on the VSC of broom shrublands and Scots pine forests, dominated by facultative and obligate seeder species, respectively. In contrast, the fire-induced impacts on VSC were not significantly different between low and moderate fire-severity scenarios in communities dominated by resprouter species, i.e., heathlands and Pyrenean oak forestsSIThis study was financially supported by the Spanish Ministry of Science and Innovation in the framework of the LANDSUSFIRE project (PID2022-139156OB-C21) within the National Program for the Promotion of Scientific-Technical Research (2021–2023), and with Next-Generation Funds of the European Union (EU) in the framework of the FIREMAP project (TED2021-130925B-I00); by the Regional Government of Castile and León in the framework of the IA-FIREXTCyL project (LE081P23); and by National Funds from FCT—Portuguese Foundation for Science and Technology, under the project UIDB/04033/2020. José Manuel Fernández-Guisuraga was supported by a Ramón Areces Foundation postdoctoral fellowshi

The footprint of large wildfires on the multifunctionality of fire-prone pine ecosystems is driven by the interaction of fire regime attributes

[EN], Background Mediterranean ecosystems dominated by Pinus pinaster Ait. (maritime pine) are subject to a shift from fuel-limited to drought-driven fire regimes, characterized by an increasing wildfire extent, recurrence, and severity. Previous studies have not addressed the interacting effects of fire recurrence and severity on the ecosystem multifunctionality (EMF) of maritime pine forests, although complex relationships between such fire regime attributes are expected. Here, we evaluated the medium-term effects of fire recurrence and severity on the EMF response of unmanaged, native pine ecosystems dominated by Pinus pinaster in the western Mediterranean Basin. We considered four key ecosystem functions computed from functional indicators (carbon regulation, decomposition, soil fertility, and plant production), which were pooled into an EMF construct. The fire regime effects on the trade-offs and synergies between the considered ecosystem functions were also analyzed. Results Multiple ecosystem functions responded differentially to fire recurrence and severity. Fire recurrence had a strong effect on soil fertility, decomposition, and plant production functions. No significant effects of fire severity on any of the individual functions were detected. However, both fire regime attributes interacted to determine soil fertility and decomposition functions, suggesting that their performance is only impaired by fire severity when fire recurrence is low. The differing responses to the fire regime attributes among ecosystem functions fostered a significant EMF response to fire severity and its interaction with fire recurrence, indicating that the effect of fire severity on EMF was stronger under low fire recurrence scenarios, even when relationships between individual functions and fire severity were weak. Fire recurrence caused significant trade-offs between functions to emerge. However, these trade-offs were not strong enough to differ significantly from the intrinsic trade-offs (i.e., regardless of the fire regime) of maritime pine ecosystems. Conclusions Our results indicated the need to use an integrative approach to assess the response of ecosystem functioning to the fire regime in maritime pine ecosystems. Adaptive management responses are necessary towards the minimization of repeated burnings and the reduction of the fuel load in unmanaged maritime pine stands of the western Mediterranean Basin with similar characteristics to those analyzed in this study.[ES], Antecedentes Los ecosistemas mediterráneos dominados por pino marítimo (Pinus pinaster Ait.) están sujetos a cambios en regímenes de fuego limitados por el combustible hacia regímenes conducidos por la sequía, y caracterizados por un incremento en la extensión, recurrencia y severidad de los incendios. Estudios previos no han abordado los efectos interactivos de la recurrencia y severidad del fuego en la multifuncionalidad de los ecosistemas (EMF) en bosques de pino marítimo, aunque cabe esperar relaciones complejas entre estos atributos del regimen de fuego. En este trabajo, evaluamos los efectos a medio plazo de la recurrencia y severidad en la respuesta de la multifuncionalidad de los ecosistemas (EMF) de bosques nativos dominados por pino marítimo no gestionados en la cuenca Mediterránea occidental. Consideramos cuatro funciones clave calculadas a partir de indicadores funcionales (regulación del carbono, descomposición, fertilidad del suelo, y producción egetal) los cuales fueron agrupados en un constructo EMF. Los efectos del régimen de fuego sobre las sinergias y contrapartidas entre las funciones ecosistémicas también fueron analizados. Resultados Múltiples funciones ecosistémicas respondieron diferencialmente a la recurrencia y severidad. La recurrencia del fuego tuvo un efecto muy fuerte en la fertilidad del suelo, en la descomposición y en las funciones de producción. Ningún efecto significativo de la severidad del fuego fue detectado en ninguna de las funciones individuales. Sin embargo, los atributos de ambos regímenes de fuego interactuaron para determinar las funciones de fertilidad y descomposición, sugiriendo que su rendimiento es afectado por la severidad solo cuando la recurrencia del fuego es baja. Las diferentes respuestas a los atributos de los regímenes de fuego entre las funciones ecosistémicas promueven una respuesta significativa de la EMF a la severidad del fuego y su interacción con la recurrencia, indicando que el efecto de la severidad sobre la EMF fue más fuerte bajo escenarios de baja recurrencia, aun cuando las relaciones entre funciones individuales y la severidad fueran débiles. La recurrencia del fuego causó la aparición de ontrapartidas significativas entre funciones. Obviamente, estas contrapartidas no fueron lo suficientemente fuertes para diferir significativamente de aquellas intrínsecas (i.e., independientemente del régimen de fuego) en los ecosistemas de pino marítimo. Conclusiones Nuestros resultados indican la necesidad de usar una aproximación integrada para determinar la respuesta del funcionamiento al régimen de fuego en ecosistemas de pino marítimo. Respuestas de manejo adaptativo son necesarias para la minimización de quemas repetidas y la reducción de la carga de combustible en rodales de pino marítimo no gestionados en la cuenca Mediterránea, con características similares a aquellos analizados en este estudio.SIAEIBritish Ecological SocietyPortuguese Foundation for Science and Technolog

Changes in a Humic Cambisol heated (100–500 °C) under laboratory conditions: The significance of heating time

P. 237-246La influencia de la temperatura y su duración, que son algunos de los componentes más importantes para determinar los efectos del fuego en suelo propiedades, fueron estudiados en la capa de 0-5 cm de un Humic Cambisol desarrollado durante los conglomerados silíceos y bajo un arbusto de Erica australis. El suelo era arenoso con 8,5 g 100 g-1 de materia orgánica, pH de 4.7 y P disponible aproximadamente 0,16 mg kg-1. El índice de estabilidad en agua (ISA) fue 64.9, que se consideraba bueno. Análisis térmico diferencial (DTA) mostró la presencia de dos picos, uno endotérmico hasta 177 ° C y otra exotérmica entre 229 ° C y 579 ° C. Las muestras se calentaron a 100 ° C, 200 ° C y 500 ° C durante 5, 15, 30 y 60 min después de alcanzar la temperatura seleccionada. Para evitar un gradiente de temperatura en el perfil se utilizó una capa de muestra de 2 cm de profundidad. Calentamiento del suelo a 100 ° C en el cuatro tiempos de calentamiento y 200 ° C durante 5 min no produjo cambios significativos en el pH, materia orgánica, N total, relación C / N, P disponible, cationes extraíbles y WSI. Los suelos calentados a 200 ° C durante 15, 30 y 60 min y 500 ° C durante 5 min, mostró un aumento significativo en P disponible (de 0,9 a un máximo de 17,6 mg kg-1) y cationes divalentes (Ca2 + 4,4 a 46,3 y Mg2 + 1,5 a 8,7 mg kg-1). Para suelos calentados a 500 ° C durante 15, 30 y 60 min, un claro incremento en soluble contenido de Na + (0,5 a 1,8 mg kg-1) y pH (5,5 a 8,1), además de una disminución significativa de la materia orgánica (de 8,7% a 2,4%) se detectó. Como consecuencia de ello se encontró una disminución importante de WSI (del 64,9% al 54,3%)S

Soil-vegetation relationships in Mediterranean forests after fire

P.1-13Background Wildfires are one of the major environmental concerns in Mediterranean ecosystems. Thus, many studies have addressed wildfire impacts on soil and vegetation in Mediterranean forests, but the linkages between these ecosystem compartments after fire are not well understood. The aim of this work is to analyze soil-vegetation relationships in Mediterranean burned forests as well as the consistency of these relationships among forests with different environmental conditions, at different times after fire, and among vegetation with different functional traits. Results Our results indicate that study site conditions play an important role in mediating soil-vegetation relationships. Likewise, we found that the nature of soil-vegetation relationships may vary over time as fire effects are less dominant in both ecosystem compartments. Despite this, we detected several common soil-vegetation relationships among study sites and times after fire. For instance, our results revealed that available P content and stoichiometry (C:P and N:P) were closely linked to vegetation growth, and particularly to the growth of trees. We found that enzymatic activities and microbial biomass were inversely related to vegetation growth rates, whereas the specific activities of soil enzymes were higher in the areas with more vegetation height and cover. Likewise, our results suggest that resprouters may influence soil properties more than seeders, the growth of seeders being more dependent on soil status. Conclusions We provide pioneer insights into how vegetation is influenced by soil, and vice-versa, in Mediterranean burned areas. Our results reflect variability in soil-vegetation relationships among study sites and time after fire, but consistent patterns between soil properties and vegetation were also detected. Our research is highly relevant to advance in forest science and could be useful to achieve efficient post-fire management.S

Interactions between mediterranean shrub species eight years after experimental fire

p. 235-241Este trabajo es parte de un estudio más amplio en el que se analizaron diferentes combinaciones de especies para la revegetación de forma experimental quemado brezales. En este caso particular, se determinó si había alguna interacción entre la especie dominante, Erica australis, que se recuperaron por rebrote vegetativo, y la Cytisus sp., ocho años después del fuego y siete años después de la siembra. El estudio detallado se realizó sobre cada metro cuadrado de la cubierta y la altura de ambas especies en tres parcelas 160 m2. La cobertura total superó el 100 % en todas las subtramas sembradas con Cytisus, mientras que no alcanzó el 65% en los otros, cuando ambas especies conviven juntos. Hubo una correlación inversa entre las tapas de ambas especies y una correlación positiva entre la altura Erica australis y de la cubierta y la altura de Cytisus No hubo diferencia significativa en Erica cubren en parcelas sembradas con Cytisus y parcelas no sembradas. Podría haber alguna competencia por la luz, pero ambas especies son capaces de coexistir con alta superposición dosel, por lo menos durante algún tiempo. Cytisus se está expandiendo desde la cabeza de serie argumentos secundarios, lo que sugiere que la cubierta densa de Erica australis no impide el establecimiento de CytisusS

Effects of fertilization and cutting on the chemical composition of vegetation and soils of mountain heathlands in Spain

p. 417-424Se estudian los efectos en las propiedades del suelo y en la composición de Calluna vulgaris y Erica tetralix sometidos a fertilización y al corte experimental en tres puertos de montaña en el norte de España. Un total de 90 parcelas 1m2 reciben diferentes combinaciones de corte y el doble a deposición atmosférica de nitrógeno (5,6 gm-2.yr-1) como nitrato de amonio. Una de las especies dominantes ericáceas (Calluna y Erica) se cortaron selectivamente con la mano en la planta y se comparó el contenido de nivel y rodaje nitrógeno en abril de 1998. En cada parcela de se tomó una muestra de suelo al principio y después de 12, 24 y 36 meses de los tratamientos. Las propiedades del suelo como materia orgánica, nitrógeno total, fósforo y pH disponible se determinaron. Hubo una disminución gradual del contenido de fósforo en las tres áreas hasta que dos años después del tratamiento, aunque los valores tienden a recuperarse en dos de las áreas en la tercera años de estudio. Se observó un aumento en el contenido de materia orgánica en todas las áreas. Hay un claro aumento en la planta contenido en N en las parcelas fertilizadas en comparación con las no-fertilizadas y la Calluna siempre tiene un mayor contenido de nitrógeno de Erica. Este aumento es más pronunciado un año después de los tratamientos en una de las zonas y después de dos años en los otros dos áreas. En algunos casos, la eliminación de una especie se ve favorecer aumento de nitrógeno en la otraS

Predicting potential wildfire severity across Southern Europe with global data sources

.The large environmental and socioeconomic impacts of wildfires in Southern Europe require the development of efficient generalizable tools for fire danger analysis and proactive environmental management. With this premise, we aimed to study the influence of different environmental variables on burn severity, as well as to develop accurate and generalizable models to predict burn severity. To address these objectives, we selected 23 wildfires (131,490 ha) across Southern Europe. Using satellite imagery and geospatial data available at the planetary scale, we spatialized burn severity as well as 20 pre-burn environmental variables, which were grouped into climatic, topographic, fuel load-type, fuel load-moisture and fuel continuity predictors. We sampled all variables and divided the data into three independent datasets: a training dataset, used to perform univariant regression models, random forest (RF) models by groups of variables, and RF models including all predictors (full and parsimonious models); a second dataset to analyze interpolation capacity within the training wildfires; and a third dataset to study extrapolation capacity to independent wildfires. Results showed that all environmental variables determined burn severity, which increased towards the mildest climatic conditions, sloping terrain, high fuel loads, and coniferous vegetation. In general, the highest predictive and generalization capacities were found for fuel load proxies obtained though multispectral imagery, both in the individual analysis and by groups of variables. The full and parsimonious models outperformed all, the individual models, models by groups, and formerly developed predictive models of burn severity, as they were able to explain up to 95%, 59% and 25% of variance when applied to the training, interpolation and extrapolation datasets respectively. Our study is a benchmark for progress in the prediction of fire danger, provides operational tools for the identification of areas at risk, and sets the basis for the design of pre-burn management actions.S