Is fire really the answer to bush encroachment?

A 10-year study conducted in Kruger National Park by scientists from South African National Parks, Stellenbosch University and Harvard University has shown that high-density fires do not have a long-term effect on the scourge of bush encroachment.

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An experiment on the use of high-intensity fires to control bush encroachment in South Africa’s Kruger National Park (KNP) has revealed that these fires did not result in a meaningful long-term reversal of the problem.

In mid-February 2023, the results of this largescale, decade-long investigation were published in the Journal of Applied Ecology in an article titled ‘High-intensity fires may have limited medium-term effectiveness for reversing woody plant encroachment in an African savanna’.

Prof Brian van Wilgen, emeritus professor of invasion biology at Stellenbosch University (SU) and one of the co-authors of the article, says most studies that advocate the use of high-intensity fires in the fight against bush encroachment are based on short-term observations. “I think [ours] is the first study to assess the effectiveness of this management practice over a decade,” he adds.

CAUSES ARE UNCLEAR

Bush or woody encroachment, a natural process involving the increase in density of smaller trees and shrubs, is taking place in savannahs around the world.

This is concerning, since increased woody cover results in less grass being available for animals to graze or use as a habitat.

Although the true causes are complex and not that clear, it is generally accepted that a reduction in the frequency and intensity of fires, coupled with an increase in atmospheric carbon dioxide (CO2), may be to blame.

In 2010 and again in 2013, adjacent sites in the southern parts of the KNP, covering thousands of hectares, were burnt using low-, medium- and high-intensity fires.