Changes in rainfall distribution promote woody foliage production in the Sahel

Martin Brandt,Christin Abel,Jean-Pierre Wigneron,Compton J Tucker,Yves Auda,Laurent Kergoat,Rasmus Fensholt,Pierre Hiernaux,Stefanie M Herrmann,Abdoul Aziz Diouf,Kjeld Rasmussen,Wenmin Zhang,Cheikh Mbow

doi:10.1038/s42003-019-0383-9

Abstract

Dryland ecosystems comprise a balance between woody and herbaceous vegetation. Climate change impacts rainfall timing, which may alter the respective contributions of woody and herbaceous plants on the total vegetation production. Here, we apply 30 years of field-measured woody foliage and herbaceous mass from Senegal and document a faster increase in woody foliage mass (+17 kg ha−1 yr−1) as compared to herbaceous mass (+3 kg ha−1 yr−1). Annual rainfall trends were partitioned into core wet-season rains (+0.7 mm yr-1), supporting a weak but periodic (5-year cycles) increase in herbaceous mass, and early/late rains (+2.1 mm yr−1), explaining the strongly increased woody foliage mass. Satellite observations confirm these findings for the majority of the Sahel, with total herbaceous/woody foliage mass increases by 6%/20%. We conclude that the rainfall recovery in the Sahel does not benefit herbaceous vegetation to the same extent as woody vegetation, presumably favoured by increased early/late rains.

Highlights

Dryland ecosystems comprise a balance between woody and herbaceous vegetation
We first compared a variety of different Earth observation datasets against field observations on green vegetation mass, consisting of annually collected (1987–2016) above-ground herbaceous mass (AGH) and woody plant foliage mass (WPF) from nine field sites (Fig. 1, Supplementary Fig. 1)
The concept of separating herbaceous and woody components using satellite data is based on the contrasting phenology of woody and herbaceous vegetation, with annual herbaceous plants wilting towards the end of the wet season while woody plants keep their green foliage during a fraction of the dry season[24,25,26,27]

Summary

Introduction

Dryland ecosystems comprise a balance between woody and herbaceous vegetation. Climate change impacts rainfall timing, which may alter the respective contributions of woody and herbaceous plants on the total vegetation production. Annual rainfall trends were partitioned into core wet-season rains (+0.7 mm yr-1), supporting a weak but periodic (5-year cycles) increase in herbaceous mass, and early/late rains (+2.1 mm yr−1), explaining the strongly increased woody foliage mass Satellite observations confirm these findings for the majority of the Sahel, with total herbaceous/woody foliage mass increases by 6%/20%. While Earth observation data have been used extensively to document the spatial and temporal dynamics of vegetation production since the early 1980s2,8, satellite observed vegetation dynamics in drylands have rarely been separated into their herbaceous and woody components and validated against field observations[9,10]. The limited availability of continuous long-term field observations of vegetation growth and the failure of satellite systems to readily distinguish between woody and herbaceous vegetation components impedes analysing the link between the dynamics in woody/herbaceous plants and the temporal changes in seasonal rainfall distributions. Strong relationships between field and satellite data justify extrapolation of findings from the field plots to larger areas

Objectives

Methods

Results

Conclusion