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 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

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

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

Burn Severity and Post-Fire Land Surface Albedo Relationship in Mediterranean Forest Ecosystems

P. 1-11Our study explores the relationship between land surface albedo (LSA) changes and burn severity, checking whether the LSA is an indicator of burn severity, in a large forest fire (117.75 km2, Spain). The LSA was obtained from Landsat data. In particular, we used an immediately-after-fire scene, a year-after-fire scene and a pre-fire one. The burn severity (three levels) was assessed in 111 field plots by using the Composite Burn Index (CBI). The potentiality of remotely sensed LSA as an indicator for the burn severity was tested by a one-way analysis of variance, correlation analysis and regression models. Specifically, we considered the total shortwave, visible, and near-infrared LSA. Immediately after the fire, we observed a decrease in the LSA for all burn severity levels (up to 0.631). A small increase in the LSA was found (up to 0.0292) a year after the fire. The maximum adjusted coe cient of determination (R2 adj) of the linear regression model between the immediately post-fire LSA image and the CBI values was approximately 67%. Fisher’s least significance di erence test showed that two burn severity levels could be discriminated by the immediately post-fire LSA image. Our results demonstrate that the magnitude of the changes in the LSA is related to the burn severity with a statistical significance, suggesting the potentiality of immediately-after-fire remotely sensed LSA for estimating the burn severity as an alternative to other satellite-based methods. However, the persistency of these changes in time should be evaluated in future research.S

Plant and vegetation functional responses to cumulative high nitrogen deposition in rear-edge heathlands

P. 980-990Elevated atmospheric nitrogen (N) deposition is a major driver of change, altering the structure/functioning of nutrient-poor Calluna vulgaris-heathlands over Europe. These effects amply proven for north-western/central heathlands may, however, vary across the ecosystem's distribution, especially at the range limits, as heathlands are highly vulnerable to land-use changes combined with present climate change. This is an often overlooked and greatly understudied aspect of the ecology of heathlands facing global change. We investigated the effects of five N-fertilisation treatments simulating a range of N deposition rates (0, 10, 20, and 50 kg N ha−1 yr−1 for 1 year; and 56 kg N ha−1 yr−1 for 9 years) on the Calluna-plants, the plant functional groups, species composition and richness of two life-cycle stages (building/young- and mature-phase) of Calluna-heathlands at their rear-edge limit. Our findings revealed a dose-related response of the shoot length and number of flowers of young and mature Calluna-plants to the addition of N, adhering to the findings from other heathland locations. However, cumulative high-N loading reduced the annual growth and flowering of young plants, showing early signs of N saturation. The different plant functional groups showed contrasting responses to the cumulative addition of N: annual/perennial forbs and annual graminoids increased with quite low values; perennial graminoids were rather abundant in young heathlands but only slightly augmented in mature ones; while bryophytes and lichens strongly declined at the two heathland life-cycle stages. Meanwhile there were no significant N-driven changes in plant species composition and richness. Our results demonstrated that Calluna-heathlands at their low-latitude distribution limit are moderately resistant to cumulative high-N loading. As north-western/central European heathlands under high-N inputs broadly experienced the loss of plant diversity and pronounced changes in plant species dominance, rear-edge locations may be of critical importance to unravel the mechanisms of heathland resilience to future global change.S

The role of fire frequency and severity on the regeneration of Mediterranean serotinous pines under different environmental conditions

P. 59-68Fire frequency and burn severity may increase in pine forests in the Mediterranean Basin under the warmer and drier climate projected for this region. Our study aims to evaluate the role of fire frequency and burn severity in the post-fire recruitment and development of Mediterranean serotinous pines under different environmental conditions. Two pine forests representing contrasting climatic conditions and soil types that support serotinous pines in the Iberian Peninsula and affected by large wildfires in summer 2012, were selected. In these two study sites, we determined the number of wildfires between 1978 and 2012 and the burn severity of the last fire (2012 at both sites) through the dNBR spectral index. Three and four years after the wildfires, we sampled the density, cover and height of pine seedlings and the cover of woody understory species in 1296 1 m2 plots. The results indicated that the density and cover of pine seedlings was low after two fires combined with high severities, as well as after three fires, regardless of burn severity. Seedling recruitment after three fires was particularly threatened in the most arid study site (0.01 seedlings m−2), resulting in low seedling cover (0.01%). Seedling height decreased with fire frequency in both study sites, and with burn severity owing to fire-induced shifts in soil fertility and microclimatic conditions. There was a significant negative effect of the cover of woody understory species on the recruitment and cover of pine seedlings. Our results suggest that the effects of increasing fire frequency and severity on pine regeneration may be aggravated under arid conditions. Additionally, this study encourages forest managers to avoid the occurrence of frequent crown fires in order to prevent the loss of serotinous pine forest, and provides useful information to predict the scenarios in which post-fire restoration actions would be helpful.S

Interactions between large high-severity fires and salvage logging on a short return interval reduce the regrowth of fire-prone serotinous forests

P. 54-63New fire disturbance regimes under accelerating global environmental change can have unprecedented consequences for ecosystem resilience, lessening ecosystem natural regeneration. In the Mediterranean Basin, fire-dependent obligate seeder forests that are prone to increasingly frequent stand-replacing fires and then salvaged logged repeatedly can be vulnerable to additional disturbances for decades. In this study, we investigated, for the first time, the cumulative and interactive effects of two large high-severity fires at a short (<15-year) return interval and the subsequent burned timber harvesting with biomass removal on the post-disturbance recovery of such forests. We further assessed the type and amount of the material legacies (deadwood) that persisted through the different post-disturbance successional trajectories, as well as the influence of these legacies on forest regeneration. The early recovery of the studied forests after two consecutive large fires and post-fire logging was, in the first place, driven by fire repetition, which led to reduced seedling recruitment and enhanced regrowth of resprouter shrubs. Despite no interactive effects between fire and logging were detected after a single large fire event, two repeated fires followed by salvage harvesting had a greater negative impact than two fires alone (synergistic effects) on seedling establishment; while a lower positive impact (subadditive effects) on the recovery of resprouter shrubs. There was also an interaction modification effect in which fire repetition worsened the per-unit impact of salvage logging on forest regeneration. Nonetheless, the residual legacies, i.e., fine and coarse woody debris (unburned needles, downed branches, pieces of deadwood, and burned pine cones) that remained after the manual harvesting of the burned trees, aided seedling re-establishment and hindered the regrowth of the shrubby understorey. These findings indicate that high-intensity salvage logging after two large high-severity fires at a short return interval is inadvisable in fire-prone serotinous pine forests, unless it explicitly retains the key material legacies that help tree natural regeneration and enhance ecosystem resilience to the next disturbance.S

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

ALOS-2 L-band SAR backscatter data improves the estimation and temporal transferability of wildfire effects on soil properties under different post-fire vegetation responses

Remote sensing techniques are of particular interest for monitoring wildfire effects on soil properties, which may be highly context-dependent in large and heterogeneous burned landscapes. Despite the physical sense of synthetic aperture radar (SAR) backscatter data for characterizing soil spatial variability in burned areas, this approach remains completely unexplored. This study aimed to evaluate the performance of SAR backscatter data in C-band (Sentinel-1) and L-band (ALOS-2) for monitoring fire effects on soil organic carbon and nutrients (total nitrogen and available phosphorous) at short term in a heterogeneous Mediterranean landscape mosaic made of shrublands and forests that was affected by a large wildfire. The ability of SAR backscatter coefficients and several band transformations of both sensors for retrieving soil properties measured in the field in immediate post-fire situation (one month after fire) was tested through a model averaging approach. The temporal transferability of SAR-based models from one month to one year after wildfire was also evaluated, which allowed to assess short-term changes in soil properties at large scale as a function of pre-fire plant community type. The retrieval of soil properties in immediate post-fire conditions featured a higher overall fit and predictive capacity from ALOS-2 L-band SAR backscatter data than from Sentinel-1 C-band SAR data, with the absence of noticeable under and overestimation effects. The transferability of the ALOS-2 based model to one year after wildfire exhibited similar performance to that of the model calibration scenario (immediate post-fire conditions). Soil organic carbon and available phosphorous content was significantly higher one year after wildfire than immediately after the fire disturbance. Conversely, the short-term change in soil total nitrogen was ecosystem-dependent. Our results support the applicability of L-band SAR backscatter data for monitoring short-term variability of fire effects on soil properties, reducing data gathering costs within large and heterogeneous burned landscapesS