Background
The study of wildfire interactions (i.e., spread limitation and reburns) is gaining traction as a means of describing the self-limiting process of fire spread in the landscape and has important management implications but has scarcely been attempted in Europe. We examined to what extent previously burned areas restricted the development of individual large wildfires (> 500 ha) in mainland Portugal.
Results
For the 1984–2021 period, we (1) modeled the proportion of large wildfire perimeters coinciding with transitions to shorter time since fire (TSF), i.e., locations where fire spread ceased upon encountering assumedly less flammable fuels, and (2) characterized the prevalence of different TSF in the composition of the area burned by large wildfires in relation to available TSF. Only 4% of the large wildfires did not comprise edges intersecting past wildfires. Low TSF (especially up to 8 years) resulted in large-wildfire perimeter limitation at TSF transitions. This effect was further enhanced by high historical burn probability and proximity to roadways and watercourses. Perimeter limitation did also increase under high (but not very high or extreme) fire danger, benefiting from maximum seasonal firefighting preparedness. TSF prevalence in the composition of large-wildfire area was extremely variable and thus an overall weak pattern emerged, with minimum and maximum prevalence respectively at TSF < 2 years and TSF ≥ 6 years.
Conclusions
Large wildfire limitation in Portugal is hampered by fast fuel build-up after fire, indicating a short-lived fire-hazard reduction effect under the prevailing Mediterranean humid climate of the study region. Nonetheless, such effect should be considered when planning fuel-reduction treatments and can be used opportunistically during large-wildfire suppression operations.This study was carried out in the framework of Forest Research Centre (CEF), Lisbon, Portugal (UIDB/00239/2020), and Centre for the Research and Technology of Agro-environmental and Biological Sciences (CITAB), Vila Real, Portugal (UIDB/04033/2020), funded by Portuguese National Funds through FCT—Foundation for Science and Technology. The first author received support from FCT through Ph.D. Grant PD/BD/142961/2018, funded by the Ministry of Science, Technology and Higher Education, and by the European Social Fund – Operational Program Human Capital within the 2014–2020 EU Strategic Framework and also through doctoral program SUSFOR (PD/00157/2012). JMCP participation was partially supported by research project FIRE-MODSAT II (PTDC/ASP- SIL/28771/2017). NG was funded by the European Union through the European Regional Development Fund in the framework of the Interreg V-A Spain-Portugal program (POCTEP) under the CILIFO (Ref. 0753_CILIFO_5_E) and FIREPOCTEP (Ref. 0756_FIREPOCTEP_6_E) projects and by National Funds through FCT under the Project UIDB/05183/2020
