The impact of wildfire on stream fishes in an Atlantic-Mediterranean climate: evidence from an 18-year chronosequence

Abstract

-The predicted increase in wildfires associated with climate change poses a risk to freshwater biodiversity that may be exacerbated by river regulation. We studied the effects of wildfire and river management on the fish assemblages of Atlantic-Mediterranean streams in northern Portugal. Employing a chronosquence survey covering an 18-year gradient of impact-recovery from major fire events (ca. 100% catchment burnt), we assessed the ecological response with respect to time since wildfire, interpreting fish assemblages in the context of species traits and characteristics of the river habitat. Non-burnt sites (N = 18; surveyed 4 years previously) were compared to burnt sites (N = 14), two of which were part of the non-burnt set, thus providing a Before-After Impact comparison (BAI; N = 2). Across burnt sites richness and abundance were not related to time since wildfire. BAI revealed a contrast in the response of different species that corresponded to descriptive evidence from the chronosequence of burnt sites. As resource specialists, Salmo trutta were negatively impacted by wildfire; Iberian endemic cyprinids, characterized by generalist traits, demonstrated resistance. Habitat structure was a key determinant of wildfire-impact, increasing with channel slope and the degree of channelization. The low abundance of migratory taxa (S. trutta and Anguilla anguilla) at burnt sites suggested the importance of fish mobility to post-fire recovery. These data demonstrate that trait profiles and habitat descriptions provide pragmatic information for the management of rivers in fire-susceptible regions and suggest that the rehabilitation of these upland stream habitats might enhance ecological resistance and resilience to catchment wildfire. Key-words:wildfire / fishes / species traits / Mediterranean streams / river habitat / conservation management Résumé -L'impact des incendies sur les poissons des cours d'eau en climat atlantique-méditerranéen : étude d'une chronoséquence de 18 ans. L'augmentation prévue des incendies associés au changement climatique pose un risque pour la biodiversité d'eau douce, qui peut être aggravé par la régulation de la rivière. Nous avons étudié les effets des feux et de la gestion de la rivière sur les peuplements de poissons de cours d'eau dans le nord du Portugal. Étudiant la chronoséquence d'un suivi couvrant une durée de 18 ans d'impact-récupération d'incendies majeurs (environ 100 % du bassin versant brûlé), nous avons évalué la réponse écologique temporelle à un incendie, en analysant les assemblages de poissons dans le contexte des traits d'espèces et des caractéristiques de l'habitat de la rivière. Les sites non brûlés (N = 18 ; suivis 4 ans auparavant) ont été comparés à des sites brûlés (N = 14), dont deux faisaient partie de l'ensemble non brûlé, offrant ainsi une comparaison avant-après l'impact (BAI ; N = 2). Parmi les sites brûlés la richesse et l'abondance ne sont pas liées au temps depuis l'incendie. BAI a révélé un contraste dans la réponse des différentes espèces qui...

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