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Fire regimes in mountain landscapes of southern Europe have been shifting from their baselines due to rural abandonment and fire exclusion policies. Understanding the effects of fire on biodiversity is paramount to implement adequate management. Herein, we evaluated the relative role of burn severity and heterogeneity on bird abundance in an abandoned mountain range located in the biogeographic transition between the Eurosiberian and Mediterranean region (the Natural Park 'Baixa Limia-Serra do Xurés'). We surveyed the bird community in 206 census plots distributed across the Natural Park, both inside and outside areas affected by wildfires over the last 11 years (from 2010 to 2020). We used satellite images of Sentinel 2 and Landsat missions to quantify the burn severity and heterogeneity of each fire within each surveyed plot. We also accounted for the past land use (forestry or agropastoral use) by using a land cover information for year 2010 derived from satellite image classification. We recorded 1735 contacts from 28 bird species. Our models, fitted by using GLMs with Poisson error distribution (pseudo-R2-average of 0.22 ± 0.13), showed that up to 71% of the modeled species were linearly correlated with at least one attribute of the fire regime. The spatiotemporal variation in burnt area and severity were relevant factors for explaining the local abundance of our target species (39% of the species; Akaike weights >0.75). We also found a quadratic effect of at least one fire regime attribute on bird abundance for 60% of the modeled species. The past land use, and its legacy after 10 years, was critical to understand the role of fire (Akaike weights >0.75). Our findings confirm the importance of incorporating remotely sensed indicators of burn severity into the toolkit of decision makers to accurately anticipate the response of birds to fire management.

Fire regimes in mountain landscapes of southern Europe have been shifting from their baselines due to rural abandonment and fire exclusion policies. Understanding the effects of fire on biodiversity is paramount to implement adequate management. Herein, we evaluated the relative role of burn severity and heterogeneity on bird abundance in an abandoned mountain range located in the biogeographic transition between the Eurosiberian and Mediterranean region (the Natural Park ‘Baixa Limia–Serra do Xurés’). We surveyed the bird community in 206 census plots distributed across the Natural Park, both inside and outside areas affected by wildfires over the last 11 years (from 2010 to 2020). We used satellite images of Sentinel 2 and Landsat missions to quantify the burn severity and heterogeneity of each fire within each surveyed plot. We also accounted for the past land use (forestry or agropastoral use) by using a land cover information for year 2010 derived from satellite image classification. We recorded 1735 contacts from 28 bird species. Our models, fitted by using GLMs with Poisson error distribution (pseudo-R2-average of 0.22 ± 0.13), showed that up to 71% of the modeled species were linearly correlated with at least one attribute of the fire regime. The spatiotemporal variation in burnt area and severity were relevant factors for explaining the local abundance of our target species (39% of the species; Akaike weights >0.75). We also found a quadratic effect of at least one fire regime attribute on bird abundance for 60% of the modeled species. The past land use, and its legacy after 10 years, was critical to understand the role of fire (Akaike weights >0.75). Our findings confirm the importance of incorporating remotely sensed indicators of burn severity into the toolkit of decision makers to accurately anticipate the response of birds to fire management.

[Background]: ‘Megafire’ is an emerging concept commonly used to describe fires that are extreme in terms of size, behaviour, and/or impacts, but the term’s meaning remains ambiguous. [Approach]: We sought to resolve ambiguity surrounding the meaning of ‘megafire’ by conducting a structured review of the use and definition of the term in several languages in the peer-reviewed scientific literature. We collated definitions and descriptions of megafire and identified criteria frequently invoked to define megafire. We recorded the size and location of megafires and mapped them to reveal global variation in the size of fires described as megafires. [Results]: We identified 109 studies that define the term ‘megafire’ or identify a megafire, with the term first appearing in the peer-reviewed literature in 2005. Seventy-one (~65%) of these studies attempted to describe or define the term. There was considerable variability in the criteria used to define megafire, although definitions of megafire based on fire size were most common. Megafire size thresholds varied geographically from > 100–100,000 ha, with fires > 10,000 ha the most common size threshold (41%, 18/44 studies). Definitions of megafire were most common from studies led by authors from North America (52%, 37/71). We recorded 137 instances from 84 studies where fires were reported as megafires, the vast majority (94%, 129/137) of which exceed 10,000 ha in size. Megafires occurred in a range of biomes, but were most frequently described in forested biomes (112/137, 82%), and usually described single ignition fires (59% 81/137). [Conclusion]: As Earth’s climate and ecosystems change, it is important that scientists can communicate trends in the occurrence of larger and more extreme fires with clarity. To overcome ambiguity, we suggest a definition of megafire as fires > 10,000 ha arising from single or multiple related ignition events. We introduce two additional terms – gigafire (> 100,000 ha) and terafire (> 1,0

[Resumo] Os rápidos cambios ambientais que se están a producir a nivel global afectan de forma directa á distribución e abundancia das especies. Isto converte á conservación nun dos principais obxectivos da ecoloxía moderna. Detectar a tempo estes cambios é fundamental á hora de establecer medidas efectivas de conservación. A teledetección representa unha ferramenta imprescindible, pero aínda pouco desenvolta, para o estudo a diferentes escalas espaciais e temporais, do hábitat reprodutor de especies ameazadas. Neste traballo modelizamos o hábitat reprodutor da píllara das dunas (Charadrius alexandrinus), a cal presenta tendencias poboacionais que indican un forte declive a curto prazo en España. A partir do arquivo histórico da misión Landsat, obtivéronse índices espectrais de vexetación e contido en auga que permitiron caracterizar anualmente cada praia de posible nidificación. Estas variables foron incluídas como preditores nun modelo lineal xeneralizado mixto, co obxectivo de explicar a variación especiotemporal no número de parellas da píllara das dunas en Galicia nun período de 22 anos (1999-2020). Os resultados confirman que as variables preditoras obtidas por teledetección, que caracterizan a vexetación, o contido en auga ou a reflectividade do solo, presentan unha alta capacidade explicativa da variación no número de parellas nidificantes de píllara das dunas na costa galega (R2 marxinal = 0,5; R2 condicional = 0,757). Das 11 variables non correlacionadas incluídas no modelo, 7 resultaron significativas, 4 fan referencia ao contido en auga (MSAVI_mean, NDWI_min, MNDWI_range e NDWI2_sd) e as 3 restantes están relacionadas co estado da vexetación e a diferenciación entre esta e o solo nu (MSAVI_mean, EVI_max e EVI2_max). Este traballo confirma a utilidade e o potencial da teledetección para modelizar as variacións espaciotemporais en parámetros chave da nidificación da píllara das dunas na costa de Galicia., [Resumen] Los rápidos cambios ambientales que se están produciendo a nivel global afectan de forma directa a la distribución y la abundancia de las especies. Esto convierte a la conservación en uno de los principales objetivos de la ecología moderna. Detectar a tiempo estos cambios es fundamental a la hora de establecer medidas eficaces para la conservación. La teledetección representa una herramienta imprescindible pero todavía poco desarrollada, para el estudio a diferentes escalas espaciales y temporales, del hábitat reproductor de especies ameazadas. En este trabajo modelizamos el hábitat reproductor del chorlitejo patinegro (Charadrius alexandrinus), el cual presenta tendencias poblacionales que indican un fuerte declive a corto plazo en España. A partir del archivo histórico de Landsat, se obtuvieron índices espectrales de vegetación y contenido en agua que permitieron caracterizar anualmente cada playa de posible nidificación. Estas variables fueron incluidas como predictores en un modelo lineal generalizado mixto, con el objetivo de explicar la variación espaciotemporal en el número de parejas de chorlitejo patinegro en Galicia en un período de 22 años (1999-2020). Los resultados confirman que las variables predictoras obtenidas por teledetección, que caracterizan la vegetación, el contenido en agua o la reflectividad del suelo, presentan una alta capacidad explicativa de la variación en el número de parejas de chorlitejo patinegro en la costa gallega (R2 marginal = 0,5; R2 condicional = 0,757). De las 11 variables no correlacionadas incluidas en el modelo, 7 resultaron significativas, 4 hacen referencia al contenido en agua (MSAVI_mean, NDWI_min, MNDWI_range e NDWI2_sd) y las 3 restantes están relacionadas con el estado de la vegetación y la diferenciación entre esta y el suelo desnudo (MSAVI_mean, EVI_max e EVI2_max). Este trabajo confirma la utilidad y el potencial de la teledetección para modelizar las variaciones espaciotemporales en parámetros clave de, [Abstract] The rapid environmental changes taking place globally directly affect the distribution and abundance of species. This makes conservation one of the main objectives of modern ecology. Detecting these changes on time is essential when establishing effective measures for conservation. Remote sensing represents an essential but still underdeveloped tool for the study at different spatial and temporal scales of the reproductive habitat of threatened species. In this study we model the breeding habitat of the Kentish Plover (Charadrius alexandrinus), which shows population trends that indicate a strong short-term decline in Spain. From Landsat historical archive, spectral indices of vegetation and water content were obtained that allowed each beach of posible nesting to be characterized annually. These variables were included as predictors in a generalized linear mixed model, with the aim of explaining spatio-temporal variation in the number of pairs of Kentish Plover in Galicia over a 22 years period (1999-2020). The results confirm that the predictor variables obtained by remote sensing, which caracterize the vegetation, the water content or the soil reflectance, have a hight explanatory capacity of the variation in the number of pairs of Kentish Plover on the Galician coast (marginal R2 = 0.5; conditional R2 = 0.757). Of the 11 uncorrelated variables included in the model, 7 resulted singnificant, 4 of them refer to the water content (MSAVI_mean, NDWI_min, MNDWI_range e NDWI2_sd) and the remaining 3 are related to the state of vegetation and the differentiation between it and the bare soil (MSAVI_mean, EVI_max e EVI2_max). This study confirms the usefulness and potential of remote sensing to model spatio-temporal variation in key parameters of Kentish Plover nesting on the Galcian coast.