Resilience in Diet-quality Strategies of Mixed Native and Non-native Herbivore Communities in Semi-arid and Sub-humid Savanna Ecosystem

The global climate change processes are expected to impact African savanna ecosystems in their ecological functionality and availability of food resources for herbivores. To understand the feeding responses of large savanna herbivores placed to space-constrained and two environmentally distinct (semi-arid versus sub-humid savanna) conditions, we investigated the diet quality of five species living in a mixed community of species native and non-native for the West African savanna and compared them between the two sites as a proxy for a potential ecosystem shift due to climate change. Grazers and mixed feeders maintained diet quality in most nutrients at similar levels, while browser’s diet had lower nitrogen and fibres, specifically lignin, and more calcium in semi-arid savanna. Our findings suggest that adaptation to different ecosystems with no possibility to leave the area required changes in feeding behaviour across feeding types to maintain diet quality, especially mixed feeders escaped the competition with zebras for grasses in sub-humid savanna by switching to browse. Pure browser experienced reduced diet quality in drier environment and may potentially become susceptible to ecosystem changes. Conservation strategies should facilitate both, animals’ adequate behavioural responses together with nutritional resilience in changing savanna landscapes.

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

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.

Does the Date of Burning Affect Carbon and Nutrient Losses in a Humid Savanna of West Africa?

A significant impact of fires is the transfer to the atmosphere of the elements contained in combusted biomass. This study was carried out in the Guinean savanna of Lamto (Côte d’Ivoire) to evaluate fire-mediated carbon and nutrient losses from biomass according to the date of burning. The fire regimes tested consisted of three different burning dates: early (EF), mid (MF), and late (LF) season fires, on nine 0.5 ha plots. Carbon and five elemental nutrients were assessed in the aboveground biomass prior to burning and in ash and unburnt biomass after fires; losses were assessed by subtraction. The proportion of nutrients transferred to the atmosphere varied from 42 % (K) to 98 % (C). The lowest losses were recorded during the EF and the greatest during the MF and LF. Emission of CO2 was relatively greatest during the EF than during the MF and LF (16, 14 and 13 t ha-1 respectively). The proportion of the fine ash fraction (< 1 mm) was the greatest during MF. The highest concentrations of K, P, Ca and Mg occurred in this fraction, most susceptible to losses due to wind and rainfall. The percentage losses of C, N and K were positively correlated with fire maximal temperatureand flame height, explaining the relatively higher losses during MF. Over the long term, the MF applied annually, would lead to important depletion of soil nutrients, particularly N and P, which contributes to the low availability of nutrients in the soils of Lamto savannas.