Burning causes long-term changes in soil organic matter content of a South African grassland

  • Published source details Fynn R.W.S., Haynes R.J. & O'Connor T.G. (2003) Burning causes long-term changes in soil organic matter content of a South African grassland. Soil Biology & Biochemistry, 35, 677-687.


In African savannas and grasslands, fire is frequently used by livestock farmers and wildlife managers to control bush and to remove dead and dying vegetation of low forage quality. In this study, the effects of burning native ‘southern tall grassveld’ grassland (an open savanna of Acacia sieberiana) on soil organic matter content was investigated in a 50 year field experiment burning trial at Ukulinga, a research farm near the city of Pietermaritzburg (29°24′E, 30°24′S), Kwa-Zulu Natal, South Africa.

The experiment was established in 1950. Treatments (three replicates each) were applied to plots (18.3 x 13.7 m separated by 4.5 m, in a randomized block, comprising: annual burning in winter (first week of August) or spring (i.e. after first rains of at least 12.5 mm in 24 h), biennial and triennial burning in winter, spring or autumn (April), plus no burn (control) and annual mowing.

Soil samples were collected in July 2000 in 2 cm layers down to 10 cm depth. These were analysed for carbon (C) and nitrogen (N). Plant litter and root biomass was also assessed.

Significant decreases in organic C only occurred in the 0-2 cm layer under annual and biennial winter burning and biennial and triennial autumn burning. Spring burning had less affect, attributable to much litter decomposing and/or being incorporated by soil invertebrates, prior to burns. Total N content was decreased substantially to 6 cm depth by all burn treatments (thus the C:N ration widened). Burning also resulted in increased microbial biomass C and root density in the 4-10 cm layer (attributed to decreased litter input but increased root turnover in the soil). Although organic C and total N content decreased with increasing depth, potentially mineralizable N increased (in both unburnt and burnt plots) indicating a shortage of N in these native grasslands.
Note: If using or referring to this published study, please read and quote the original paper, this can be viewed at:

Output references
What Works 2021 cover

What Works in Conservation

What Works in Conservation provides expert assessments of the effectiveness of actions, based on summarised evidence, in synopses. Subjects covered so far include amphibians, birds, mammals, forests, peatland and control of freshwater invasive species. More are in progress.

More about What Works in Conservation

Download free PDF or purchase
The Conservation Evidence Journal

The Conservation Evidence Journal

An online, free to publish in, open-access journal publishing results from research and projects that test the effectiveness of conservation actions.

Read the latest volume: Volume 20

Go to the CE Journal

Discover more on our blog

Our blog contains the latest news and updates from the Conservation Evidence team, the Conservation Evidence Journal, and our global partners in evidence-based conservation.

Who uses Conservation Evidence?

Meet some of the evidence champions

Endangered Landscape Programme Red List Champion - Arc Kent Wildlife Trust The Rufford Foundation Save the Frogs - Ghana Bern wood Supporting Conservation Leaders National Biodiversity Network Sustainability Dashboard Frog Life The international journey of Conservation - Oryx British trust for ornithology Cool Farm Alliance UNEP AWFA Bat Conservation InternationalPeople trust for endangered speciesVincet Wildlife Trust