Do cone age and heating mode determine the opening of serotinous cones during wildfires? A new bench scale approach applied to Pinus halepensis Mill.

Serotiny is a well-known fire adaptive trait in some species, as the Mediterranean conifer Pinus halepensis. However, information about cone opening mechanisms during wildfires and consequences on post fire dispersal is scarce. In addition, standardized methods allowing a realistic simulation of heating modes at bench-scale are not available. In this study, we address for the first time the interacting effects of radiation, convection and direct flame on the opening and seed release of serotinous cones, following a novel repeatable methodology. Using a Mass Loss Calorimeter (MLC) device and a wide range of heat exposures (between 5 and 75 kW m-2) with or without ignition, we intended to simulate realistic cone heating during surface and crown fires in laboratory conditions. Additionally, we included the effect of contrasting serotinous cone ages interacting with heating mode and considering the random individual variation. The proposed methodology has shown a high potential to simulate the complex process of crown fires in relation to cone opening under controlled conditions, detecting a threshold of heat exposure (25-30 kW m-2) for cone opening. We confirmed that heating mode had a highly significant effect in cone opening, interacting with cone age, while cone age effect on its own was marginal. Particularly, ignition significantly increased the efficacy of cone opening and seed release. Moreover, young and old cones behave differently in seed release, both in surface and crown fire simulations. Implementing and adjusting this methodology in other species will allow more realistic and reliable quantitative comparisons than previously attained.

Effectiveness of mechanical thinning and prescribed burning on fire behavior in Pinus nigra forests in NE Spain.

Fuel treatments can mitigate present and future impacts of climate change by reducing fire intensity and severity. In recent years, Pinus nigra forests in the Mediterranean basin have been dramatically affected by the new risk of highly intense and extreme fires and its distribution area has been reduced. New tools are necessary for assessing the management of these forests so they can adapt to the challenges to come. Our main goal was to evaluate the effects of different fuel treatments on Mediterranean Pinus nigra forests. We assessed the forest response, in terms of forest structure and fire behavior, to different intensities of low thinning treatments followed by different slash prescriptions (resulting in: light thinning and lop and scatter; light thinning and burn; heavy thinning and lop and scatter; heavy thinning and burn; and, untreated control). Treatments that used fire to decrease the resulting slash were the most effective for reducing active crown fires decreasing the rate of spread and flame length more than 89%. Low thinning had an effect on torching potential, but there was no difference between intensities of thinning. Only an outcoming crown fire could spread actively if it was sustained by a high-enough constant wind speed and enough surface fuel load. Overall, treatments reduce fire intensity and treated areas have a more homogenous fire behavior response than untreated areas. This provides opportunities to extinguish the fire and reduce the probability of trees dying from the fire. It would be helpful to include ecological principles and fire behavior criteria in silvicultural treatment guidelines in order to perform more efficient management techniques in the future.