Effect of Fuel Management and Forest Composition on Fire Behavior ^†

In Southern Europe, Portugal has registered the largest number of wildfires and the second largest burned area [1]. Fuel Breaks are one of the ways of prevention and containment of wildfires present in legislation (Decree-Law nº 82/2021). However, the measures and standards that regulate Fuel Breaks lack scientific validation to assess their effectiveness.

This study aims to evaluate the effect of fuel management of Fuel Breaks and the effect of forest type on surface fire behavior. Thirty pairs of Managed Areas vs. Non-Managed Areas were sampled. These were distributed throughout the Central Region of Portugal, in ten eucalyptus stands, ten maritime pine stands, and ten mixed stands of eucalyptus and other species. Field data, including the loads and structure of fuels, fuel moisture and micrometeorological information, were collected and used to develop fuel models and perform surface fire behavior simulations in Behave Plus 6 Beta. The results show that only one third of the statistical tests showed significant differences (

Table 1. Descriptive statistics and Wilcoxon test for fire behavior in managed vs. unmanaged areas of Eucalyptus, Maritime Pine and Mixed Stands.

Fire Behavior
Eucalyptus	Managed			Not Managed			Wilcoxon
	Average	Standard Deviation	Standard Error	Average	Standard Deviation	Standard Error	V	p-Value
Fire Rate of Spread (m/min)	1.89	1.56	0.49	2.9	3.22	1.02	13.5	0.31
Fire Heat per Unit Area (kJ/m²)	6618.4	2849.68	901.15	18,158.4	9813	3103.14	0	<0.01
Fireline Intensity (kW/m)	645.64	951.44	300.87	2370.27	3682.62	1164.55	7	0.04
Flame Length (m)	1.26	0.82	0.26	2.20	1.61	0.51	7	0.04
Mixed stands	Managed			Not managed			Wilcoxon
	Average	Standard Deviation	Standard Error	Average	Standard Deviation	Standard Error	V	p-value
Fire Rate of Spread (m/min)	6.12	5.17	1.63	2.67	1.80	0.57	45	0.08
Fire Heat per Unit Area (kJ/m²)	16,234.00	6300.49	1992.39	20,491.9	5216.33	1649.55	8	0.04
Fireline Intensity (kW/m)	2954.67	2942.50	930.50	1620.83	1230.34	389.07	40	0.23
Flame Length (m)	2.67	1.47	0.47	2.16	0.82	0.26	41	0.19
Maritime pine	Managed			Not managed			Wilcoxon
	Average	Standard Deviation	Standard Error	Average	Standard Deviation	Standard Error	V	p-value
Fire Rate of Spread (m/min)	1.89	1.23	0.39	1.62	1.50	0.48	27	0.64
Fire Heat per Unit Area (kJ/m²)	14,708.3	12,647.43	3999.47	17,901.0	10,262.42	3245.26	20	0.49
Fireline Intensity (kW/m)	882.31	1071.74	338.92	962.47	998.34	315.70	25	0.85
Flame Length (m)	1.47	0.94	0.30	1.59	0.88	0.28	26	0.92

) in surface fire behavior between Managed and Unmanaged areas.

Likewise, only one statistical test (out of 12) showed significant differences in fire behavior between the three types of stands. Our results show that the reduction in fuel load and depth in Managed areas was annulated by the more severe meteorological conditions (stronger wind speed and lower moisture) observed in these areas. However, it should be taken into consideration that this study only assessed surface fire. Despite these results, Fuel Breaks are an important instrument of prevention and containment of wildfires; they allow better access to means of combat and decrease the likelihood of ignition from, for example, roads and power transmission lines. On the other hand, different results would probably be obtained by including crown fire simulations and more severe weather scenarios.

Author Contributions

Conceptualization, M.P., A.O. and J.S.; methodology, M.P., A.O. and J.S.; software, M.P. and A.O.; validation, M.P. and A.O.; formal analysis, M.P., A.O., J.S. and P.F.; investigation, M.P., A.O. and J.S.; resources, J.S.; data curation, M.P., A.O. and J.S.; writing—original draft preparation, M.P. and A.O.; writing—review and editing, J.S. and P.F.; visualization, M.P., A.O., J.S. and P.F.; supervision, J.S.; project administration, J.S.; funding acquisition, J.S. All authors have read and agreed to the published version of the manuscript.