Abstract
Wildfires are currently considered the major threat to forests in Mediterranean countries. It has been implied that a large percentage of arson-caused fires in Spain are connected with the extensive reforestation programs implemented between 1940 and 1970. However, no consistent studies have been conducted to study the relationships between arson-caused fires and stand origin. Therefore, the goal of this study was to analyze occurrences and model the influence of forest stand origin (artificial or not) on the development of wildfires in peninsular Spain. Twenty-one neural network models were trained to estimate fire incidence through fire type (surface or crown fire), burned area and total treed burned area, based on stand age (years), canopy cover (%), natural age class (from seedling to mature stages) and fuel type classification. Models were built for reforested stands and natural stands of Pinus pinaster Ait., the Mediterranean pines Pinus sylvestris L., Pinus nigra Arn., Pinus halepensis Mill. and Eucalyptus sp. L’Hér., or groups of these species, and the resulting models were compared. Reforested stands presented higher fire incidence than natural stands mainly for productive species like Pinus pinaster Ait. According to the fire type models, thickets had a large influence in the development of crown fires in reforested stands in a general model for all species, the model with the Mediterranean group of pines, and the Pinus pinaster Ait. model. Vertical continuity influenced crown fire propagation in natural Mediterranean pines and in Eucalyptus stands. Presence of shrubs, grasslands and wood slash was related to surface fires in models for both reforested and natural stands. The results suggested that stand origin was influential on fire incidence, at least with regard to fire type and commercial species in the northwestern region of Spain.
Highlights
During the last decades, more than 95% of the wildfires occurred in Spain and in other SouthernEuropean Mediterranean countries were of anthropogenic origin, and over 55% of them were classified as arson-caused fires [1,2]
It is remarkable that the ignition rate of P. pinaster is much higher in reforestation polygons (RF) stands than in nonreforested areas (NRF) stands, in a contrary pattern to the other Pinus species, with higher rates in natural stands
Though some authors stated in previous work that wildfires in South Europe have affected mainly conifers reforested in the 1940’s and 1950’s (P. pinaster, P. halepensis, and Eucalyptus sp. stands) [11,12,13,14,15], and others [6,7,8] indicated reforestations as a major factor of occurrence of arson wildfires in Spain, we found this only true for a few of the most productive and fast-growing species
Summary
More than 95% of the wildfires occurred in Spain and in other SouthernEuropean Mediterranean countries were of anthropogenic origin, and over 55% of them were classified as arson-caused fires [1,2]. Simon et al [4], Alvarez et al [5] and Fuentes-Santos et al [6] have cited resentment against reforestations as a motivation for arson-caused fires. Forests 2019, 10, 229 in the fire reports a code for “Arson fires motivated by resentment against reforestations” [1]. In the past, these arson-caused fires would have been triggered by the discontent of many rural communities for the shifting of their productive and rangelands into forest [7] and towards the wood rights’. Other motivations have risen over time; forcing land use changes is a potentially relevant, but difficult to prove, motivation in Southern European countries that depend on the tertiary sector [9]
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