It is increasingly clear that large-bodied wildlife play both direct and indirect roles in carbon cycling. However, their influence has not been explicitly incorporated into traditional models of carbon dynamics. It is urgent to fill this gap with research illuminating the roles of large wildlife in carbon cycling, as large wildlife are particularly threatened by the widespread biodiversity loss that characterizes the Anthropocene.
Kenya’s savanna ecosystem, with its relatively intact assemblage of megafauna, provides an ideal framework for questions regarding the role of large wildlife in the carbon cycle. Utilizing a long-term exclosure experiment, we examined carbon turnover, carbon flux, and microbial respiration in the presence and absence of large herbivores. We then paired these findings with data from complementary experimental plots that allowed domestic cattle (while either allowing or excluding large wildlife), thus allowing us to examine potential synergistic or conflicting interactions between native wildlife loss and the encroachment of pastoralism. In each herbivore treatment, we measured carbon turnover rates with a year-long litter decomposition experiment, carbon flux in situ with a closed-chamber system, and microbial respiration rates in lab by incubating sampled soil.
We discovered a significant effect of herbivore presence/absence on carbon dynamics. Carbon turnover measured via litter decomposition by soil fauna over one year was significantly lower in plots without any large herbivores. Soil samples collected from plots with only native herbivores had lower microbial respiration rates and accumulation of carbon dioxide than plots that had cattle and native herbivores, those that only had cattle, and those without any large herbivores. Plots without any large herbivores had higher in situ carbon flux than plots with only native herbivores, and plots with both native herbivores and cattle; flux data indicate that increasing herbivore presence results in successively lower carbon flux.
Our findings demonstrate strong impacts of large herbivores on carbon dynamics in this ecosystem, and highlight the differential effects of wild and domestic herbivores on these dynamics. Cumulatively, these results suggest that models predicting future carbon dynamics need to account for large wild and domestic herbivores. They also underscore the importance of understanding the interactions between native herbivores and managed livestock on savanna ecosystem function. As both wildlife loss and climate change continue in parallel in the Anthropocene, understanding the impacts of large-bodied species (and their loss from ecosystems) on carbon dynamics is of great importance.