Fire spread control for management purpose: Fuel moisture critical threshold in annually burned dry savanna of west Africa

Fire serves as management tool in protected areas in savanna ecosystems, particularly for biodiversity conservation and tourism purposes. However, selecting the appropriate burning periods that align with management objectives remains a major challenge for managers. For fire spreading, taking into account soil and fuel moisture levels, which vary throughout the season, is essential. This study aimed to identify the moisture content controlling fire spread and to determine its critical threshold. Through monthly experimental burnings on 90 plots in Comoé National Park’s savanna ecosystems, we measured soil and fuel moisture contents throughout a complete dry season spanning from October 2023 to March 2024. The results showed that soil moisture (p ˂ 0.001) and fuel moisture (p ˂ 0.001) decreased as the season progressed. Regarding fire spread, the rate of spread increased when soil moisture (p ˂ 0.001) and fuel moisture (p ˂ 0.001) decreased. On the other hand, the distance traveled by flames that was indicating continuous fire spread, was exclusively influenced by fuel moisture content (p ˂ 0.001). Fire spreading risk mapping revealed the fuel moisture critical threshold of 30.35 ± 2.35% from December. Above this threshold, fuel moisture limits fire spread by its dominant influence. But below it, the probability of continuous fire spread was high and almost certain, because fuel moisture ceases to be a limiting factor. This quantitative threshold provides park managers with an objective tool for timing prescribed burns according to specific fire management objectives.