Bush Encroachment

Back to Conserving Terrestrial Ecosystems

At Malilangwe, several wildlife species – including black-backed jackal, kori bustard, reedbuck, grass owl and secretary bird – depend on open grasslands for feeding, breeding and shelter. These important habitats are increasingly threatened by bush encroachment, the gradual invasion of grasslands by woody shrubs and trees.

Between 1963 and 1991, woody plant cover in Malilangwe’s grasslands increased by 36%. This change was driven by a combination of factors, including prolonged droughts, heavy cattle grazing prior to the reserve’s establishment, and the suppression of natural fires. Together, these conditions reduced grass cover and allowed woody plants to expand into areas that were once open grassland.

An additional factor may be the rise in atmospheric carbon dioxide levels since the 1960s. Higher carbon dioxide concentrations tend to favour woody plants over grasses, and some shrub species are now growing up to three times faster than they did historically. This phenomenon has contributed to widespread bush encroachment across much of southern Africa over the past six decades.

The Role of Fire

Fire-based management was reintroduced to Malilangwe in 1994 and has played an important role in controlling the establishment of new shrub seedlings. However, fire alone is not sufficient to reverse advanced bush encroachment. While burning removes the above-ground parts of mature shrubs, many species quickly regenerate by producing new shoots from their root systems, a process known as coppicing.

Mechanical Clearing and Habitat Restoration

In heavily encroached areas, mechanical clearing has become a necessary management tool. Malilangwe uses skid-steer loaders fitted with specialized clearing heads to uproot shallow-rooted woody shrubs. The removed vegetation is then processed into mulch using industrial grinders.

This mulch is applied to degraded and eroded sites to improve soil conditions and encourage the re-establishment of grasses. A formal study is planned to evaluate the effectiveness of this approach, but early observations indicate that it has considerable potential to accelerate grassland recovery.

After several years of successful implementation, mechanical clearing efforts are now being expanded into the northern parts of the reserve, particularly in areas with sandy loam soils. These soils, combined with relatively high rainfall, produce an exceptional grass response following shrub removal. By restoring these areas to grass-dominated ecosystems, Malilangwe aims to maximize forage production and strengthen the resilience of its landscapes as part of a long-term strategy to adapt to climate change.

A Surgical Approach

We vary our management techniques across the reserve according to grazing pressure and fuel availability. In areas within approximately 3 km of permanent water sources, grazing intensity is so high that insufficient grass fuel remains to carry effective burns. In these locations, mechanical clearing is the only practical method for reducing woody plant cover. Further from water, where grass fuel loads remain adequate, prescribed burning continues to be an effective and cost-efficient tool for preventing shrub encroachment and maintaining open grassland habitats.

By combining fire, mechanical clearing and habitat restoration, Malilangwe is working to preserve its grasslands and the diverse wildlife species that depend on them.