Effect of fire regime on the grass community of the humid savanna of Lamto, Ivory Coast

Abstract

This study assesses the impact of four fire treatments applied yearly over 3 y, i.e. early fire, mid-season fire, late fire and no fire treatments, on the grass communities of Lamto savanna, Ivory Coast. We describe communities of perennial tussock grasses on three replicated 5 × 5-m or 10 × 5-m plots of each fire treatment. Tussock density did not vary with fire treatment. The relative abundance of grass species, the circumference of grass tussocks and the probability of having a tussock with a central die-back, varied with fire treatment. Mid-season fire had the highest proportion of tussocks with a central die-back while the late fire had the smallest tussocks. Tussock density, circumference, relative abundance and probability of having a central die-back varied with species. Andropogon canaliculatus and Hyparrhenia diplandra were the most abundant of the nine grass species. They had the largest tussocks and the highest proportion of tussock with a central die-back. Loudetia simplex was the third most abundant species but was very rare in no fire plots. The distribution of tussock circumferences was right skewed and dominated by small tussocks. The proportion of the tussocks with a central die-back strongly increased with circumference, which could lead to tussock fragmentation. Taken together, this study suggests that fire regimes impact grass demography and that this impact depends on grass species and tussock size.

Effect of fire regimes on the demographic parameters of the perennial tussock grasses of a humid savanna

“…On the contrary, A. ascinodis had a higher overall probability to grow than other species and this probability was high whatever the tussock size. This is consistent with the observed differences in tussock size between species (Koffi et al., ). Schizachyrium platyphyllum generally formed small tussocks with few thin and short tillers (personal observation).…”

“…bipennatum produced more seeds per tussock than the other species and their number of seeds increased quicker with circumference. As seen above, these two species are among the ones with the lowest probability of fragmentation and the smallest tussocks (Koffi et al., ). This suggests that small‐size species reproduce less by fragmentation but more by seeds, which probably explains why these two species invest more in seed production in relation to their size.…”

“…The difference of mortality observed between species confirms that species differ by the effect of tussock size on demographic parameters. The studied grass species can be sorted in three distinct groups according to their tussock circumference i.e., large, medium and small size species (Koffi et al., ). In this context, the high mortality of Sch.…”

“…Andropogon canaliculatus was the species that formed the largest tussocks while A. ascinodis possessed medium size tussocks. These two species were opposed to A. schirensis and L. simplex that had small tussocks and H. diplandra that formed large tussocks (Koffi et al., ) but with fewer large tillers (personal observation). This supports the assumption that tussock fragmentation is influenced by the size and the number of tillers per tussock.…”

“…This is consistent with the fact that Sch. platyphyllum and H. smithiana had on the average small tussocks (Koffi et al., ): higher rates of retrogression tend to lead to small tussocks. As for the effect of tussock size on growth, this could be explained by the lower capacity of resource accumulation of the smaller tussocks.…”