Mathematical Modelling of Grazing in Drylands

Lead Research Organisation: University of Edinburgh
Department Name: Sch of Mathematics

Abstract

Drylands are areas where the rainfall is so low that it limits vegetation growth. If we exclude deserts, drylands represent about 40% of the Earth land surface. These regions are threatened by desertification i.e. degradation of the land into a state of non-productivity. It is driven by climatic factors as well as human activities. Alongside deforestation and poor agricultural practice, animal husbandry is identified as one of the causes of land degradation. However, there is some controversy around the impact of grazing in arid regions. Livestock have been alternately charged and absolved of being a leading cause of desertification, with some actors even prescribing grazing as a solution to the problem. The general consensus is that overgrazing is a driver of land degradation but the dynamics of grazing systems are still not well understood. Half of the world's livestock is concentrated in arid regions and about 70% of the rural West and East African drylands population rely fully or partially on livestock for survival. Furthermore, "demand for African livestock and livestock products is expected to grow rapidly". Trying to satisfy this increasing demand without adequate policing can lead to irreversible long-term ecological and hence socio-economical prejudice. It is therefore essential to to try to elucidate the processes involved in grazing systems and design optimal grazing strategies. One source of uncertainty when trying to predict the effects of grazers on a system lies in the plants' response to grazing. There is evidence that plants can respond to biomass removal with a modified growth rate. The nature and extent of this response, known as compensatory growth, can determine the tolerance of a vegetated system to grazing. The project aims at informing decisions about the optimal number of grazers a system can sustain, through mathematical modelling. We can refer to this goal as a management approach. In this project we incorporate 3 different plant response scenarios -namely constant growth rate, linearly increasing growth rate and linearly decreasing growth rate- into a preexisting mathematical model for grazing in arid ecosystems. We study the outcome through stability analysis and discuss the ecological interpretation for each of these scenarios.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/S023291/1 01/10/2019 31/03/2028
2279089 Studentship EP/S023291/1 01/09/2019 31/08/2023 Toyo V Vignal