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En los últimos años, los incendios forestales se han convertido en un grave riesgo para la conservación de los ecosistemas debido a las modificaciones en el régimen de los mismos, que están condicionadas por el cambio climático y el cambio en los usos del suelo. En el contexto de cambio global actual, el fuego en la cuenca mediterránea -y en particular en la Península Ibérica- se ha convertido no sólo en una perturbación necesaria y beneficiosa para la dinámica natural de los ecosistemas, sino también en un grave riesgo ecológico, social y económico (World Wide Fund for Nature, 2019). La tendencia observada en las últimas décadas es la disminución del número de incendios forestales a nivel mundial, aunque, debido al patrón de aumento de la frecuencia e intensidad de las sequías a lo largo de toda la cuenca mediterránea (Tramblay et al., 2020), se espera que la recurrencia, severidad, extensión y área de influencia de los incendios forestales aumente en los próximos años (Ruffault et al., 2020). Para poder gestionar correctamente los incendios forestales y afrontar estos eventos como herramientas de modelización del paisaje y obtención de energía (Naveh, 1994; Doerr y Santín, 2016) se debe tener en cuenta uno de los principales factores que determinan el régimen del fuego, la recurrencia, entendida como el número de incendios acaecidos en una zona determinada durante un período de tiempo dado (Johnson, 1992; Pausas et al., 2008; Santana, 2019).

The main objective of this study was to analyse the effect of recurrence and burn severity on ecosystem multifunctionality in Pinus pinaster forests. We selected a large wildfire that occurred in the Sierra del Teleno in 2012 (NW Spain), where we differentiated two recurrences and two burn severity situations. As a result, four scenarios were identified: low recurrence plus low severity, low recurrence plus high severity, high recurrence plus low severity, high recurrence plus high severity. In each one, a number of 1 m x 1 m plots proportional to the burned area were established. Three years after the wildfire we evaluated in each plot: (1) percentage of covered soil, (2) total percentage cover of herbaceous species, (3) percentage cover of each woody species, (4) total plant species richness. Also, a composite soil sample was collected from each plot. Chemical (total organic carbon, total nitrogen and available phosphorus) and microbiological (microbial biomass carbon) properties were analysed in each soil sample. The following variables were used as indicators of ecosystem functions: percentage of covered soil, total cover of herbaceous species, Pinus pinaster cover, total plant richness, total organic carbon, total soil nitrogen, available phosphorus and microbial biomass carbon. Another indicator of ecosystem functions was calculated: floral colours of shrub species diversity using the Shannon index. The values of each ecosystem function indicator were standardized. The indicators/functions of regulating ecosystem services were: Climate regulation (indicator: total % of organic soil carbon) and Erosion protection (indicator: covered soil %). The functions/ indicators of supporting ecosystem services were: soil fertility (indicator: total nitrogen and available phosphorous) and soil quality (indicator: microbial biomass C). The indicators/functions of cultural ecosystem services were: species diversity (indicator: plant species richness) and aesthetic value (indicator: the Shannon index of floral colours). The functions/indicators of provisioning ecosystem services were: grass for livestock (indicator: % cover of herbaceous species) and timber production (indicator: % cover of Pinus pinaster). The results indicated that all scenarios apart from low recurrence plus low severity negatively affected the multifunctionality of the ecosystems.

P. 1057–1069 Two drivers of global change that affect ecosystem function include wildland fire regimes characterised by frequent, severe fires and increased atmospheric nitrogen (N) deposition. However, their combined effect on the post-fire recovery of Mediterranean forests is still little known. We assessed the interactive effects of two fire severities and N addition on the rate and timing of seed germination of three woody species with different post-fire regeneration strategies in fire-prone forests: Pinus pinaster, an obligate-seeder species, and two facultative-seeder species, Pterospartum tridentatum (high-resprouting and low-seeding ability) and Halimium lasianthum (low-resprouting and high-seeding ability). Seeds were subjected to six combinations of temperature [control (no heat treatment), 60 °C (moderate fire severity) and 120 °C (high fire severity) for 5 min] and N fertilisation (without N and with addition of 4.17 g Nm−2 of solid granules of ammonium nitrate, equivalent to three times the current estimate of airborne N deposition in the study area) under laboratory conditions. We found that N fertilisation had a significant, negative effect on the rate of seed germination of the three species under study. Additionally, we detected no differences in P. pinaster germination among thermal treatments; while both P. tridentatum and H. lasianthum had significantly higher germination rates when submitted to high fire-severity conditions. Moreover, the average time of seed germination increased with N fertilisation for P. pinaster but increased after the thermal treatments for H. lasianthum. These results suggest that increased N availability under intense wildfire regimes may hinder post-fire seed germination, regardless of the species’ regeneration strategy, in fire-prone pine forests. SI

Projections of future wildfire regimes forecast an increased frequency of large high-severity fires that create very harsh environmental conditions and constitute a challenge to post-fire ecosystem regeneration. Under these new circumstances, better knowledge of the plant interaction mechanisms underlying post-fire seedling establishment success would aid restoration management to achieve the intended targets. We evaluated the combined effect of recurrent large stand-replacing fires and conventional post-fire restoration activities (salvage logging after a single large fire, and direct seeding and linear subsoiling plus seedling planting after two subsequent large fires) on tree seedling recruitment and performance (development, annual growth, and biomass) in the early stages of succession in fire-prone maritime pine ( Pinus pinaster Ait.) ecosystems. We quantified plant facilitative/competitive interactions between naturally recruited pine seedlings, neighbouring seedlings and potential nurse shrubs with different post-fire regeneration strategies (obligate seeders vs resprouters), by computing the relative interaction index (RII). The results evidenced that fire recurrence altered plant species composition and conditioned initial pine seedling recruitment and establishment, prevailing over the expected negative impact of salvage logging and positive impact of seeding. Seedling recruitment was sufficient to ensure natural tree regeneration after a single fire event and undermined by repeated fires. Both delaying burned timber removal during salvage logging operations and retaining immature dead trees without commercial value onsite in subsoiled stands enhanced seedling recruitment via facilitative interactions. Higher seedling growth and height under shrubs than in open ground resulted in lower aerial and root biomass, indicating elongation in response to shade, and net competition for resources. Inter-specific competition between naturally regenerated seedlings and shrubs was aggravated by intra-specific competition with neighbouring seedlings and by mechanical site preparation in subsoiled stands. All in all, post-burn increased soil fertility most likely counterbalanced the environmental stress created by fire, shifting the net outcome of plant interactions from positive (facilitation) to negative (competition). We recommend alternative post-fire management actions that decrease plant competition and take advantage of facilitation by residual burned wood, to ultimately accelerate ecosystem recovery after large stand-replacing fires.

This research aimed to estimate the splash erosion and its evolution during the first months in specific land uses after a forest fire. The study area was located in Congosto (North-West Spain), in the margins of Spanish drylands, after a wildfire occurred in May 2012, which burned 15.56 ha of scrubland and Pinus reforestation. Two different burned land uses were selected and compared to control areas: i) burned pine forest; and, scrublands. Rainfall intensity and the number, sizes and speed of raindrops were measured by an optical disdrometer and soil loss by funnels. Moreover, infiltration, soil moisture content, aggregate stability, water repellence, pH and organic matter were also measured. Results showed that the highest soil losses occurred in the burned areas, especially in the scrubland plots. The most influential factors were the presence of bare soil and the low vegetation recovery rate. Changes in soil properties did not significantly influence splash erosion, although an increase in the presence of smaller classes of aggregates could promote erosion in the scrubland. We conclude that the vegetation ecosystem restoration is the key issue to be considered after a wildfire, especially, in those types of land uses which are severely affected by the fire in the margins of drylands.

Producción Científica, We analysed the relationship between burn severity indicators, from remote sensing and field observations, and soil properties after a wildfire in a fire-prone Mediterranean ecosystem. Our study area was a large wildfire in a Pinus pinaster forest. Burn severity from remote sensing was identified by studying immediate post-fire Land Surface Temperature (LST). We also evaluated burn severity in the field applying the Composite Burn Index (CBI) in a total of 84 plots (30 m diameter). In each plot we evaluated litter consumption, ash colour and char depth as visual indicators. We collected soil samples and pH, soil organic carbon, dry aggregate size distribution (MWD), aggregate stability and water repellency were analysed. A controlled heating of soil was also carried out in the laboratory, with soil from the control plots, to compare with the changes produced in soils affected by different severity levels in the field. Our results shown that changes in soil properties affected by wildfire were only observed in soil aggregation in the high severity situation. The laboratory-controlled heating showed that temperatures of about 300 ◦C result in a significant reduction in soil organic carbon and MWD. Furthermore, soil organic carbon showed a significant decrease when LST values increased. Char depth was the best visual indicator to show changes in soil properties (mainly physical properties) in large fires that occur in Mediterranean pine forests. We conclude that CBI and post-fire LST can be considered good indicators of soil burn severity since both indicate the impact of fire on soil properties., Ministerio de Economía y Competitividad y el Fondo Europeo de Desarrollo Regional (FEDER), en el marco del proyecto GESFIRE (AGL2013-48189-C2-1-R), Junta de Castilla y León en el marco del proyecto SEFIRECYL (LE001P17)