To explore the possible relationship between diseased trees and wildfires, we assessed the flammability of canker-resistant and susceptible common cypress clones that were artificially infected with Seiridium cardinale compared to healthy trees. This study explored the effect of terpenoids produced by the host plant in response to infection and the presence of dead plant portions on flammability. Terpenoids were extracted and quantified in foliage and bark samples by gas chromatography–mass spectrometry (GC–MS). A Mass Loss Calorimeter was used to determine the main flammability descriptors. The concentration of terpenoids in bark and leaf samples and the flammability parameters were compared using a generalized linear mixed models (GLMM) model. A partial least square (PLS) model was generated to predict flammability based on the content of terpenoid, clone response to bark canker and the disease status of the plants. The total terpenoid content drastically increased in the bark of both cypress clones after infection, with a greater (7-fold) increase observed in the resistant clone. On the contrary, levels of terpenoids in leaves did not alter after infection. The GLMM model showed that after infection, plants of the susceptible clone appeared to be much more flammable in comparison to those of resistant clones, showing higher ignitability, combustibility, sustainability and consumability. This was mainly due to the presence of dried crown parts in the susceptible clone. The resistant clone showed a slightly higher ignitability after infection, while the other flammability parameters did not change. The PLS model (R²Y = 56%) supported these findings, indicating that dead crown parts and fuel moisture content accounted for most of the variation in flammability parameters and greatly prevailed on terpenoid accumulation after infection. The results of this study suggest that a disease can increase the flammability of trees. The deployment of canker-resistant cypress clones can reduce the flammability of cypress plantations in Mediterranean areas affected by bark canker. Epidemiological data of diseased tree distribution can be an important factor in the prediction of fire risk.

Little is known about the interactions between the variables involved in the post-fire response of Mediterranean pine species to prescribed burning (PB). Thus, it is essential to develop an empirical model in order to assess the influence of tree and stand attributes, burn season, and fire severity on the probability of stem cambium damage occurring. Prescribed burnings were conducted in different seasons and areas covering a wide climatic and ecological range. Potential explanatory variables were measured. A random effects hurdle model framework was used to evaluate the temperature duration above 60 °C as a proxy for stem cambium damage at tree scale. The results showed significant differences in cambium damage between the PB seasons. Pinus nigra was more resistant than other pine species. Bark thickness was critical for protecting cambium. Volume of crown scorch, percentage of stem scorch, and maximum outer bark temperature were directly related to temperature duration above 60 °C in the cambium. Prescribed burning conducted under tree canopy in Mediterranean pine species generally results in a low level of cambium damage. Empirical models could help managers to predict the effects of PB and thus select the most suitable prescriptions.

We investigated the influence of fire severity, logging of burnt wood, local ecological factors and their interaction on the natural regeneration, survival and growth of maritime pine (Pinus pinaster Ait.), following a fire that took place in 2005. During the period 2006–2020, a sample of 1900 seedlings were monitored, in which three post-fire treatments were applied: (1) Early logging (before seedling emergence); (2) Delayed logging (after emergence); and (3) No management. Multivariate semi-parametric and non-parametric techniques were used to model seedling survival, estimated density and growth of natural pine regeneration. Seedling survival was 31% with a mean density of more than 2000 seedlings/ha at the end of the study period. Logging before seedling emergence was positively related with pine survival and density. Delayed logging resulted in the lowest seedling density and regeneration. Fire severity had a negative influence on regeneration density. The findings indicate that site conditions and fire severity have a stronger influence on natural regeneration of maritime pine than subsequent post-fire management treatments. In order to ensure the presence of maritime pine in pure or mixed stands, silvicultural work is required to control competition from other species and reduce the risk of new wildfires.

Aim of study: To assess the effect of prescribed underburning (PB) and tapping on resin yields in maritime pine stands. We hypothesized that PB reduces fire hazard, generates stress at the cambium level and potentially increases the number of resin canals and resin yield after tapping. Area of study: Northern Plateau of the Iberian Peninsula, central-eastern Spain. Material and methods: Six 50 m x 50 m plots were established in a Pinus pinaster Ait. stand, three of which were burned and tapped in 2018 and three controls plots (tapped only). Resin yield was monitored in 90 trees over four years (2018-2021). A Generalised Linear Mixed Model (GLMM) for repeated measures was used to analyse resin production. Average resin yield per tree was predicted by Treatment as a fixed between-subject factor (two levels: Tapping only vs PB+Tapping) and years as within-subject factor (four levels: 2018, 2019, 2020, 2021). Plot and tree were considered random factors. Main results: The GLMM revealed the significant effect of time (years after tapping), plot and tree. However, the potential effect of meteorology (time), site (plot) and the interaction between fire and individual trees (stress that potentially increases number of resin canals) did not generally have any effect on resin yield at stand level. The resin yield was maintained in burned and tapped plots relative to the tapped only control stand. Research highlights: Prescribed underburning before tapping in order to reduce fire hazard is compatible with tapping P. pinaster stands but does not increase the resin yield.

Conocer el impacto de alternativas de gestión de la madera quemada sobre la regeneración post-incendio y los combustibles forestales asociados a lo largo del tiempo es fundamental para determinar el riesgo de recurrencia y severidad potencial del fuego. Este estudio analizó los efectos a medio plazo de la gestión post-incendio de la madera quemada en masas de Pinus pinaster tras el incendio de El Rodenal (Guadalajara, 2005), que afectó más de 12.000 ha incluyendo pinares jóvenes y maduros. A partir de la caracterización de los combustibles existentes 8 y 16 años después del fuego (2013 y 2021), se analizó la evolución del riesgo de incendio a escala de paisaje comparando la corta y saca de la madera quemada (escenario real) frente a no intervención (escenario ficticio). Se generó cartografía de modelos de combustible post-incendio a partir de la primera y segunda cobertura LiDAR-PNOA, asociando los parámetros de cargas y alturas en función de datos de parcelas de seguimiento de la regeneración. Con las cartografías obtenidas se realizaron simulaciones del comportamiento del fuego bajo distintos escenarios de riesgo meteorológico (moderado, alto y extremo). Los resultados a escala de paisaje mostraron que la saca de madera redujo la carga de combustible grueso, pero favoreció la regeneración de herbáceas y matorral, aumentando la continuidad del combustible y el riesgo de mayor velocidad de propagación. Por el contrario, la no intervención favoreció árboles muertos en pie, retrasando la regeneración, pero acumulando gran cantidad de combustible muerto que aumentó la intensidad y severidad potencial del fuego. En ambos casos, la evolución de la vegetación tras incendio mostró un aumento de la carga de combustible y su riesgo asociado. Este estudio destaca la necesidad de realizar una gestión preventiva tras el fuego a medio plazo, para reducir la recurrencia de incendios severos y evitar daños irreversibles en ecosistemas previamente quemados.