Researchers Reveal How Loss of South African Grasslands to Shrubs Could Affect the Soil and Atmosphere

Ecosystems in today's world are responding to a wide variety of environmental changes. What happens when these changes interact? That was the topic of a recent paper published by Dr. David Ward and international colleagues and graduate students in the journal Scientific Reports.

Although climate change is often viewed as the overriding global challenge, grasslands around the world are actually often directly threatened by a simple neighboring plant. Like a neighbor who gradually shifts their garden further and further onto your lawn, woody shrubs have been gradually moving into grasslands and displacing native grass species.

In their new paper, Dr. Ward and colleagues asked whether this encroachment of woody shrubs into grasslands in South Africa would increase or decrease the amount of carbon stored in the soil under the plants. Answering this question will help us understand whether or not grasslands of the future will become carbon dioxide sources, contributing to the increased carbon dioxide in the atmosphere and global greenhouse effect. This study revealed an important explanation to a puzzling observation – if the goal is to store carbon in grassland soil, shrub encroachment may be harmful in one place, but helpful in another place. The researchers dug down a meter into the Earth to measure carbon stored with and without the encroaching shrubs. Their findings indicate that, in these dry regions of the world, rainfall is the switch that controls the effects of shrub encroachment. They found that encroachment in higher rainfall areas decreases carbon stored in the soil. However, encroachment in lower rainfall areas increases carbon stored in the soil.

Identifying rainfall as a control over the different effects that shrubs can have on grasslands means that we may be able to predict the effects of shrub encroachment on climate change as we continue to learn about these important ecosystems.

Contact Dr. David Ward (, Art & Margaret Herrick Endowed Professor of Plant Biology, Department of Biological Sciences, for more information.

Full Research Article: Mureva, A., D. Ward, T. Pillay, P. Chivenge, M. Cramer. 2018. Soil Organic Carbon Increases in Semi-Arid Regions while it Decreases in Humid Regions Due to Woody-Plant Encroachment of Grasslands in South Africa. Scientific Reports 8:15506.

POSTED: Friday, October 26, 2018 - 2:34pm
UPDATED: Wednesday, February 13, 2019 - 7:02am
Chris Blackwood and David Ward