Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Effects of herbivore-induced disturbances on above- and belowground community heterogeneity within a semi-arid sodic African savanna

Auteur : Erasmus, Leon Loewan

Université de soutenance : North-West University

Grade : MSc (Environmental Sciences), 2022

Résumé partiel
Large mammalian herbivores (LMH) function as significant drivers of change within consumer-controlled grassy biomes, essentially maintaining Africa’s open ecosystems through numerous top-down and bottom-up feedbacks. These feedbacks fundamentally drive and maintain invaluable ecological processes and cycles, subsequently regulating system structure and functioning. Yet, heterogeneous savanna ecosystems are faced with anthropogenic-induced changes to native LMH communities with which these systems evolved. The most common change to herbivore communities includes the switch towards single-species pastoralism at the expense of a diverse suite of wild African herbivores. Such dramatic changes in native herbivore communities might affect several underlying structural and functional constituents of these herbivore-adapted systems through top-down trophic cascades. Numerous studies have reported on the compartmentalised effects of native LMH on vegetation structure and edaphic properties. Given the link between these structural constituents and associated soil microbes (bacteria and fungi), herbivory is potentially a major driver of belowground microbial community structure and activity, and subsequently, soil function. However, little is known about the long-term impact of herbivory, and particularly the loss thereof, on bacterial and fungal community composition and potential implications for microbially-mediated decomposition. Considering the close association between herbivory and preferentially foraged sodic vegetation, sodic patches are suggested to exhibit changes related to altered herbivory intensity over short time scales. The Nkuhlu research exclosures within the Kruger National Park (KNP), South Africa, provided an ideal setting to explore spatial and temporal heterogeneity patterns within intensively utilised herbivore-driven sodic patches, and how these patterns are affected by changes in native herbivore communities. This study was specifically designed to elucidate the effects of herbivory, or the loss thereof from a herbivore-adapted system, on belowground microbial community structure and associated soil-based decomposition of detrital plant material, and how these potential belowground changes are related to observed changes in vegetation structure and edaphic properties. Sampling was conducted within five sites, each comprising five experimental plots, located across three herbivore treatments of varying intensity within the Nkuhlu exclosures. Successful retrieval of tea bags after the application of the extended, site-specific version of the Tea Bag Index (TBI) highlighted the value of this approach to quantify decomposition in a disturbance-driven savanna ecosystem

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