Woody-plant encroachment in a South African savanna. Photograph by C.S. Harker.

By Joseph Douglas Mandla White, Nicola Stevens, Jolene Fisher, Sally Archibald, and Chevonne Reynolds.

Read the full article here.

Across the world’s grasslands and savannas, human-driven changes have benefited trees and shrubs at the expense of grasses. This process is known as “woody-plant encroachment” and it is changing the composition, structure and function of these formerly open ecosystems. One of the functions of open rangeland ecosystems is the suite of valuable ecosystem services they provide to people. Services include direct provision of raw products, such as grass forage, water, and wood. Loss of grasses and an increase in woody plants change the availability of these provisioning ecosystem services. Though the responses to encroachment will vary across different ecosystem types, broadly, the provision of water and grass forage will suffer, while the provision of wood will be boosted.

Using two national scale datasets on 1) woody-plant encroachment and 2) household use of natural resources in South Africa, we asked who and where is most impacted by the increases in woody plants. We found that low-income municipalities with the greatest use of natural resources (such as grass forage, water collection and wood for building, cooking, or heating) are strongly correlated with the highest rates of encroachment. In addition, we found that average rates of natural resource use are consistent across grass forage, water collection and wood use. This means that low-income municipalities will experience simultaneous costs and benefits to increased woody cover.

Based on previous evidence, we suggest that the combined costs of decreased grass forage and water supply, will outweigh the benefits of increased wood supply. We then identified the municipalities with the lowest incomes, highest rates of encroachment and greatest costs to natural resources. These municipalities have the highest risk and vulnerability of ecosystem changes and most require restoration interventions.

We suggest that the recognition of woody-plant encroachment as a major form of land degradation and identification of the people most at risk to environmental change is crucial to determining appropriate, targeted restoration actions. These steps and can help guide policy for both local governments and larger international efforts, such as the UN Decade of Ecological Restoration.