Investigating the determinants of woody vegetation encroachment in African drylands

Booker Ogutu, Jadu Dash, Kelvin Peh

The African drylands is inhabited by close to 270 million people whose main source of livelihood is subsistence pastoral livestock grazing, which rely on the availability of good quality pasture. Climate change is expected to result in significant changes to the characteristics and function of these drylands. In the 1970s and 1980s, the region was hit by several severe droughts, which led to the hypothesis that desertification was expanding southwards of the Sahara Desert. However, recent studies based on satellite remote sensing data have shown that since the mid-1990s, majority of African drylands (especially in the north) have been experiencing vegetation greening, dominated by encroachment of woody vegetation [1]. This greening has been attributed to several factors including wetter climatic conditions, CO2 fertilization from increased CO2 in the atmosphere, land use/land cover change, changing wildfire regimes etc. [2]. Even though various studies have provided evidence supporting each of the above factors as drivers to greening in the African drylands, what is currently not clear is why the greening in these drylands is dominated by woody encroachment rather than any other vegetation type. This study intends to investigate the key factors and mechanisms that promote the domination of woody vegetation in the greening of the African drylands.



Recent studies have shown that vegetation greening in African drylands tend to be dominated by encroachment of woody vegetation [2]. However, it is currently not clear what factors lead to woody vegetation dominating the vegetation greening in the African drylands. The principle aim of this project is to determine the factors and mechanisms that promote the dominance of woody vegetation encroachment in the greening of the African drylands. Firstly, the study will identify the drylands where woody vegetation is dominant in driving vegetation greening by analyzing various Earth Observation data (e.g., Optical data and SAR data). The study will then evaluate how various abiotic (e.g., precipitation, temperature, wildfire regimes etc.) and biotic factors (vegetation phenology, plant phylogeny, plant traits, adaptation characteristics etc.) contribute to the greening of African drylands. These factors will be combined using multivariate regression techniques and modelling to determine the key factors and mechanisms that enable woody vegetation to dominate vegetation greening in African drylands. The output from this research will shed light into factors determining the dynamics of dryland ecosystems under a changing climate and provide information needed for their effective management.


University of Southampton

The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted at The School of Geography and Environmental Science. Specific training will include:

  • Earth Observation data retrieval, analysis, and interpretation
  • Multivariate statistical modelling


Eligibility & Funding Details: 

Please see for details.

Background Reading: 

[1] Fensholt, R., et al., 2012. Greenness in semi-arid areas across the globe 1981–2007—an Earth observing Satellite based analysis of trends and drivers. Remote Sens. Environ. 121, 144–158.

[2] Brandt, M., et al., (2016) Assessing woody vegetation trends in Sahelian drylands using MODIS based seasonal metrics. Remote Sens. Environ. 183, 215–225.