title: The dynamics and drivers of fuel and fire in the Portuguese public forest.
abstract: The assumption that increased wildfire incidence in the Mediterranean Basin during the last decades is an outcome of changes in land use warrants an objective analysis. In this study we examine how annual area burned (BA) in the Portuguese public forest varied in relation to environmental and human-influenced drivers during the 1943-2011 period. Fire behaviour models were used to describe fuel hazard considering biomass removal, cover type changes, area burned, post-disturbance fuel accumulation, forest age-classes distribution and fuel connectivity. Biomass removal decreased rapidly beyond the 1940s, which, along with afforestation, increased fuel hazard until the 1980s; a subsequent decline was caused by increased fire activity. Change point analysis indicates upward shifts in BA in 1952 and in 1973, both corresponding to six-fold increases. Fire weather (expressed by the 90th percentile of the Canadian FWI during summer) increased over the study period, accounting for 18 and 36% of log(BA) variation before 1974 and after 1973, respectively. Regression modelling indicates that BA responds positively to fire weather, fuel hazard and number of fires in descending order of importance; pre-summer and 2-year lagged precipitation respectively decrease and increase BA, but the effects are minor and non-significant when both variables are included in the model. Land use conflicts (expressed through more fires) played a role, but it was afforestation and agricultural abandonment that supported the fire regime shifts, explaining weather-drought as the current major driver of BA as well. We conclude that bottom-up factors, i.e. human-induced changes in landscape flammability and ignition density, can enhance or override the influence of weather-drought on the fire regime in Mediterranean humid regions. A more relevant role of fuel control in fire management policies and practices is warranted by our findings.
authors.affiliation: Centre for the Research and Technology of Agro-Environmental and Biological Sciences, CITAB, University of Trás-os-Montes and Alto Douro, UTAD, Quinta de Prados, 5000-801 Vila Real, Portugal; Departamento de Ciências Florestais e Arquitetura Paisagista, University of Trás-os-Montes and Alto Douro, UTAD, Quinta de Prados, 5000-801 Vila Real, Portugal. Electronic address: pfern@utad.pt.
authors.forename: Paulo M
authors.initials: PM
authors.lastname: Fernandes
authors.affiliation: Centre for the Research and Technology of Agro-Environmental and Biological Sciences, CITAB, University of Trás-os-Montes and Alto Douro, UTAD, Quinta de Prados, 5000-801 Vila Real, Portugal; Departamento de Ciências Florestais e Arquitetura Paisagista, University of Trás-os-Montes and Alto Douro, UTAD, Quinta de Prados, 5000-801 Vila Real, Portugal.
authors.forename: Carlos
authors.initials: C
authors.lastname: Loureiro
authors.affiliation: ICAAM - Instituto de Ciências Agrárias e Ambientais Mediterrânicas, Departamento de Paisagem, Ambiente e Ordenamento, Universidade de Évora, Núcleo da Mitra, Apt. 94, 7002-554 Évora, Portugal.
authors.forename: Nuno
authors.initials: N
authors.lastname: Guiomar
authors.affiliation: WSL Swiss Federal Institute for Forest, Snow and Landscape Research, Research Group Insubric Ecosystems, Via Belsoggiorno 22, CH-6500 Bellinzona-Ravecchia, Switzerland.
authors.forename: Gianni B
authors.initials: GB
authors.lastname: Pezzatti
authors.affiliation: Centro de Estudos Transdisciplinares para o Desenvolvimento (CETRAD), Universidade de Trás-os-Montes e Alto Douro, Apt. 1013, 5000-801, Portugal.
authors.forename: Filipa T
authors.initials: FT
authors.lastname: Manso
authors.affiliation: Departamento de Ciências Florestais e Arquitetura Paisagista, University of Trás-os-Montes and Alto Douro, UTAD, Quinta de Prados, 5000-801 Vila Real, Portugal.
authors.forename: Luís
authors.initials: L
authors.lastname: Lopes
mesh_terms: D018533:Biomass; D057231:Climate Change; D055864:Droughts; D004784:Environmental Monitoring / Q000379:methods; D005390:Fires; D065928:Forests; D006801:Humans; D019083:Mediterranean Region; D008962:Models, Theoretical; D014887:Weather
keywords: Fire management; Fire modelling; Fire regime; Fuel hazard; Global change; Mediterranean Basin