Jonathan Sherratt

Title

Inferring the historical origin of vegetation patterns

Abstract

Landscape-scale patterns of vegetation occur worldwide at interfaces between semi-arid and arid climates. They are important as potential indicators of climate change and imminent regime shifts, and arise from positive feedback between vegetation and infiltration of rainwater. On gentle slopes the typical pattern form is bands (stripes), oriented parallel to the contours, and their wavelength is probably the most accessible statistic for vegetation patterns. I will discuss the use of mathematical models to investigate the historical origin of these patterns. I will show that the two alternative possibilities – degradation of uniform vegetation and colonisation of bare ground – can be distinguished by the relationship between pattern wavelength and slope gradient. Specifically, degradation of uniform vegetation generates patterns whose wavelength increases with slope, while colonisation of bare ground gives the opposite trend.  As a case study, I will discuss sub-Saharan Africa (the “Sahel” region), showing that model predictions and historical rainfall data together imply that vegetation patterns originated by the colonisation of bare ground, either during c.1760-1790 or since c.1850.

Short bio 

Jonathan Sherratt was an undergraduate at the University of Cambridge (1985-1988) and did graduate work at the Universities of Washington and Oxford.  His D.Phil. was supervised by J.D. Murray and P.K. Maini.  After a postdoc at Oxford, he was a lecturer and then senior lecturer at the University of Warwick (1995-1997) before moving to a Professorship at Heriot-Watt University.