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Livestock management promotes bush encroachment in savanna systems by altering plant-herbivore feedback

Citation

Koch, Franziska; Tietjen, Britta; Tielbörger, Katja; Allhoff, Korinna (2022), Livestock management promotes bush encroachment in savanna systems by altering plant-herbivore feedback, Dryad, Dataset, https://doi.org/10.5061/dryad.44j0zpchr

Abstract

This repository contains all code to reproduce the analysis in Koch et al. 2022 "Livestock management promotes bush encroachment in savanna systems by altering plant-herbivore feedback".

We use a set of coupled differential equations to describe competition between shrubs and grasses, as well as plant biomass consumption via grazing and browsing. Grazers were assumed to receive a certain level of care from farmers, so that grazer densities emerge dynamically from the combined effect of vegetation abundance and farmer
support. Our main goal was to understand how critical transitions from grass-dominated to shrub-dominated system states were affected by the dynamic role of grazing.

Our results show that bistability emerges for intermediate levels of farmer support due to positive feedback that arises from competition between shrubs and grasses and from herbivory. We furthermore demonstrate that disturbances, such as drought events, trigger abrupt transitions from the grass dominated to the shrub dominated state and that the system becomes more susceptible to disturbances with increasing farmer support.

Methods

We used numerical simulations to analyse system dynamics under different livestock management and disturbance regimes. Then, we quantified all self-reinforcing and self-dampening feedback loops to determine their relative importance in shaping system (in)stability. The whole analysis was performed in python. For details, see the Methods section of the corresponding paper.

Funding

Bundesministerium für Bildung und Forschung, Award: 01LC1821B