Needle senescence affects fire behavior in Aleppo pine (Pinus halepensis Mill.) stands: a simulation study.

The brunt of the fire season in the Western Mediterranean Basin occurs at the beginning of July, when live fuel moisture content is near its maximum. We have tested whether a potential explanation to this conundrum lies in Aleppo pine needle senescence, which typically occurs in the weeks preceding the peak in burned area. Our objective was to simulate the effects of needle senescence on fire behavior.

We simulated the effects of needle senescence on canopy moisture and structure. Fire behavior was simulated across different phenological scenarios and for two highly contrasting Aleppo pine stand structures, a forest and a shrubland. Wildfire behavior simulations were done with BehavePlus6 across a wide range of wind speeds and of dead fine surface fuel moistures.

We have recorded that the transition from surface to passive crown fire occurred at lower wind speeds under simulated needle senescence in the forest and in the shrubland. Transitions to active crown fire only occurred in the shrubland under needle senescence. Maximum fire intensity and severity were always recorded in the needle senescence scenario.

In conclusion, we have shown evidence, for the first time to our knowledge, that Aleppo pine needle senescence may enhance the probability of crown fire development at the onset of the fire season, and it could partly explain the concentration of fire activity in early July in the Western Mediterranean Basin.