Influence of seasonal weather variations on fuel status for some shrubs typical of Mediterranean Basin

Flammability of living vegetation is influenced by several factors including structural properties, commonly referred to as fuel type and chemical properties and moisture content commonly referred to as fuel status. The moisture content of living plant is a critical parameter in fire ignition because it affects flammability. Depending on the moisture content, living vegetation may act as a heat source or a heat sink, either contributing to the energy of fire or retarding fire propagation and intensity. Variations of plant water content are related either to ecophysiology of each species or to seasonal weather variations and fluctuations in soil water availability. Mediterranean shrub species are an important component of the understory vegetation that constitutes the surface fuels primarily responsible for the ignition and the spread of wildland fires in Mediterranean forests. In Mediterranean areas, where climate is characterized by variable winter precipitation and prolonged summer drought, vegetation has flammable structure and chemistry that allow live fuels to propagate wildfire. Moreover, a decrease in vegetation moisture, due to a seasonal decrease of soil water availability, can determine severe fire danger when combined with high meteorological risk (i.e. strong summer wind). Consequently, the knowledge of seasonal variation of flammability and moisture content of vegetation could contribute to identify critical periods of high fire risk in Mediterranean maquis ecosystems. The main objective of this work was to describe the seasonal pattern of live fine fuel moisture content (FMC) and ignitability values for some Mediterranean shrubs, and evaluate the influence of weather seasonality, typical of Mediterranean climate, on the variation of these variables. The study was carried out in a natural reserve area, located in North Western Sardinia (Italy), covered by maquis and gariga. FMC and ignitability of terminal portion of twigs (live fine fuel) were determined periodically during the year on shrubs species. Ignitability (time to ignition) was determined by laboratory test. The phenological phases of each species was also observed during sampling period. During the whole period of experimentation, moisture soil content and meteorological variables were recorded. In this paper, seasonal variations of FMC value are reported and differences between species are showed. In addition, relationships between seasonal variations of FMC and meteorological conditions were analyzed and the influence of FMC variations on ignitability was verified for each species.