Demography of the dominant perennial grass species of a humid African savanna
Résumé
Perennial grasses are the main source of fuel during fires in savannas. The demography of these grasses likely varies between species although they have the same general architecture and coexist in savannas. However, very few studies compare their demography. Similarly, their demography likely varies between years because of the variability in weather condition and fire intensity. We described and compared the demography and life-cycle of the four dominant perennial grass species (Andropogon canaliculatus, Andropogon schirensis, Hyparrhenia diplandra and Loudetia simplex) of the Lamto savanna (Ivory Coast) and assessed the influence of their demographic features (stasis, fecundity, growth, fragmentation and retrogression) on this demography. Grass species were monitored over three consecutive years (2015-2016, 2016-2017 and 2017-2018) on three 5 m × 10 m plots. We used a size-classified matrix model with 5 circumference classes (3-10 cm, 10-20 cm, 20-35 cm, 35-50 cm and >50 cm). Results showed differences in the age-based parameters, asymptotic growth rates (λs) and elasticities of the λs of the grass species. The population of A. canaliculatus, A. schirensis and H. diplandra were slowly declining while L. simplex was significantly declining. There were noticeable year-to-year variations in the demography of these four species. The most important demographic parameter influencing λs was the stasis in all species, while retrogression and fragmentation contributed to a relative homogeneity of ages between size-classes 2 to 5. This study provides new insights about the demography of Guinean savanna grasses that could be used to describe the mechanisms of their coexistence, and inform fire management policies.
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