Modeling anthropogenic and natural fire ignitions in an inner-alpine valley

Abstract

Abstract. Modelling and assessing the factors that drive forest fire ignitions is critical for fire prevention and sustainable ecosystem management. In southern Europe, the anthropogenic component of wildland fire ignitions is especially relevant. 10In the Alps, however, the role of fire as a component of disturbance regimes in forest and grassland ecosystems is poorly known. The aim of this work is to model the probability of fire ignition for an alpine region in Italy using a regional wildfire archive (1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)) and MaxEnt modeling. We analyzed separately: i) winter forest fires; ii) winter fires on grasslands and fallow land; iii) summer fires. Predictors were related to morphology, climate, and land use; distance from infrastructures, number of farms, and number of grazing animals were used as proxies for the anthropogenic component; collinearity among 15 predictors was reduced by a Principal Component Analysis. 30% of ignitions occurred in agricultural areas, 24% in forests.Ignitions peaked in the late winter-early spring. Negligence from agro-silvicultural activities was the main cause of ignition (64%); lightning accounted for 9% of causes across the study timeframe, but increased from 6% to 10% between the first and second period of analysis. Models for all groups of fire had a high goodness-of-fit (AUC 0.90-0.95). Temperature was proportional to the probability of ignition, and precipitation inverse-proportional. Proximity from infrastructures had an 20 effect only on winter fires, while the density of grazing animals had a remarkably different on summer (positive correlation) and winter (negative) fires. Implications are discussed regarding climate change, fire regime changes, and silvicultural prevention. Such spatially-explicit approach allows to carry out spatially targeted fire management strategies, and may assist in developing better fire management plans. 25

Effects of large herbivores on fire regimes and wildfire mitigation

“…Thirteen studies (see Table S1) found that grazing reduces wildfire frequency. Most other studies found that grazing only reduces wildfire frequency in certain cases, depending on the time of the year, the management associated with grazing (Vacchiano et al, 2018) or the vegetation type (Starns et al, 2019). In some cases, herbivore presence creates the conditions for more frequent but lower intensity fires, therefore reducing the frequency of extreme wildfires.…”

“…In alpine environments, fire ignitions typically peak at the end of winter and beginning of spring when much of the pastoral burning occurs. As this is done prior to livestock introduction, there is a positive correlation between density of animals and fire frequency in the summer, and a negative correlation in winter (Vacchiano et al, 2018). The same occurs in tropical forests and other ecosystems where livestock rearing is a key driver of conversion of forest to grasslands, often by using prescribed fires (Bernardi et al 2019).…”

“…Also, historical evidence of changes in fire frequencies shows that declines in pastoral management and rearing of livestock, especially in mediterranean regions (Kalabokidis et al, 2007;Torres-Manso et al, 2014), increased wildfire frequency. However, in some cases, grazing management practices are associated with increased fire ignitions and frequency (Cano-Crespo et al, 2015;Vacchiano et al, 2018;Zumbrunnen et al, 2012). Thus, the ability of herbivores to reduce fire frequency depended on season, intensity of grazing or landscape type (see Table S1).…”

Blitzschlagbrände und Sommertrockenheit: Gibt es einen Zusammenhang?

“…In den borealen Wäldern Nordeuropas beläuft sich ihr Anteil auf etwa 10% (Schweden: 8%, Granström 1993;Finnland: 13%, Larjavaara et al 2005a). In der Schweiz betrug der Anteil der Blitzschlagbrände in der Periode 2000 bis 2018 im Jahresdurchschnitt 12.3%, im Hochsommer (Juni, Juli und August) aber 30.5% 1 , was durchaus mit an-deren alpinen Gebieten vergleichbar ist (Cesti et al 2005, Müller et al 2013, Vacchiano et al 2018.…”