Does Fine Fuel Accumulate Over Time in Fire-Free Areas of the Guinea Savanna?

Abstract

Following fires, fine fuel accumulation (standing grass and fallen leaves from grasses and trees) is generally considered a factor that may enhance the likelihood of subsequent fire. However, the influence of the duration of fire exclusion on fine fuel accumulation remains uncertain. In protected areas of the Guinea savanna, woody encroachment (WE) is increasingly occurring. In certain years, WE prevents fire from penetrating the encroached zones, it is therefore necessary to study fine fuel dynamics. This study investigated fuel accumulation in unburnt plots over ten successive years. It was conducted at three distinct sites, each including two plots: a plot subjected to annual prescribed burning in mid-dry season (BU) and an unburnt plot (UNB). Overall, grass biomass which is the main component of fuel, did not vary significantly between the two fire treatments after 10 years. A significantly greater litter biomass was observed in UNB plots. This litter followed a biennial cycle in UNB plots: it increased for two successive years due to the falling of standing grass, then decreased in the third year before beginning a new phase of accumulation. Total fine fuel load did not differ significantly between the two fire treatments after 10 years (1.00 ± 0.09 vs. 1.18 ± 0.12 kg m⁻² for BU and UNB, respectively). The decrease in grass density over the years, combined with a likely high rate of litter decomposition and termite activity, maintained the total fine fuel load of UNB plots at a relatively stable level. Our study highlights that the total fine fuel load does not accumulate continuously in unburnt sites.