Forb community responses to an extensive drought in two contrasting land-use types of a semi-arid Lowveld savanna

F Siebert,J Klem,H Van Coller

doi:10.2989/10220119.2020.1726464

F Siebert, J Klem + Show 1 more

Open Access

https://doi.org/10.2989/10220119.2020.1726464

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Abstract

Projected increases in the frequency and severity of drought events are expected to impose changes in the ecology of native forb communities in semi-arid ecosystems. We examined the state of forb communities during, and directly after an extreme drought event across two contrasting land-use types, which included a protected area (high diversity of free roaming wild herbivores) and communal rangeland (long history of intensive cattle grazing) in a semi-arid Lowveld savanna of the Gazankulu area, South Africa. Forb floristic data were collected towards the end of the drought and repeated after the drought release a few months later. Forb community composition was significantly different among land-use types. Community changes were not induced by annual forb emergence alone, but through species-specific dominance shifts, which differed among land-use types. Forb richness, diversity and biomass were equally low at both land-use types and increased significantly after the drought release, although the magnitude of response was much stronger in the protected area, whereas drought contributed to a directional change in the protected area with a complete post-drought turnover in both annual and perennial forb species, much less variability was observed in the communal rangeland, which may suggest long-term effects imposed by land-use history.

Highlights

Ecological research in semi-arid savannas is increasingly focused on quantifying ecosystem responses to global environmental change (Ruppert et al 2015; Bunting et al 2018)
The observed forb community dynamics during, and directly after an extreme drought event emphasised that contrasting land-use types with divergent herbivore assemblages, herbivory pressure and duration of disturbance impacts may reveal both similar and conflicting results
Despite several unexpected response patterns, our results added to our understanding of the combined effects of drought and herbivory on forb communities at two opposite end of land-use type disturbances

Summary

Introduction

Ecological research in semi-arid savannas is increasingly focused on quantifying ecosystem responses to global environmental change (Ruppert et al 2015; Bunting et al 2018). In African savannas, changes in the assembly and density of herbivores, especially increasing livestock densities at the cost of a diverse suite of native herbivores with whom these ecosystems evolved, combined with predictions of future increases in drought events are of particular concern (Ruppert et al 2015; Zerbo et al 2016; Riginos et al 2018) Quantifying such land-use and climate effects on savanna herbaceous vegetation dynamics is essential for the management and conservation of semi-arid ecosystems, because herbaceous plants provide important goods and services to African livelihoods (Martin et al 2016). Forbs are an important source of biodiversity in grasslands and savannas (Uys 2006; Buitenwerf et al 2011; Trollope et al 2014; Scott-Shaw and Morris 2015; Siebert and Scogings 2015) that are functionally diverse, which suggest stronger resilience to environmental disturbances

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