A burning issue: Fire overrides grazing as a disturbance driver for South African grassland bird and arthropod assemblage structure and diversity

In this study, we investigated the responses of two faunal groups, birds and arthropods, to varying degrees of disturbance caused by fire and grazing in South Africa, eight study sites of varying fire frequency and stocking density were studied over two summer seasons (October–March). Bird assemblages reflected habitat disturbance in a diversity of ways, driven by factors ranging from direct disturbance to changes in habitat structure and functioning, and shifts in food availability. Similarly, arthropod diversity and abundance changed seasonally in response to management practices. Fire frequency drives faunal assemblage structure and abundance and, in most cases, overrides the effects of grazing at all taxonomic levels. In particular, fire frequency strongly influenced grassland-breeding birds because farms are burnt in the territory-forming stage of the breeding cycle. Insectivores and nectarivores were disproportionately impacted by intensive commercial management. Of particular concern in this system is the yellow-breasted pipit (Anthus chloris), which is regionally and globally Vulnerable because of habitat loss. This species is sensitive to any form of habitat disturbance, highlighting the need for conservation attention in these grasslands. Of the ten arthropod orders present in the study area, only Orthoptera responded positively to burning. However, orthopterans made up on average 78% of arthropod biomass in moist highland grasslands, resulting in high grasshopper biomass on annually burnt farms: this high biomass in turn supports an abundance of insectivores. This reinforces the importance of process-oriented data where a measure of performance, such as reproductive success, is considered in assessing ecosystem condition.