Grass dynamics along a woody-plant density reduction gradient in a South African savanna

Abstract

Woody plant encroachment threatens ecosystem services and functioning, thereby reducing herbaceous plant population persistence and community stability. We assessed the impact of woody removal intensity (WRI) on the grass ground cover, grass composition, diversity and richness, and rangeland condition in a South African savanna over a period of four growing seasons (2018–2022). Selective tree removal was applied to reduce woody density (4 065 ± 109 plants ha⁻¹) of the control (0% WRI) to 10, 20, 50, 75 and 100% WRIs, with four replicates per WRI. Rangeland condition, measured as the abundance of decreaser grass species, at 50, 75 and 100% was significantly higher than the control (0% WRI), with 50% WRI recording the greatest contribution. However, grass species diversity and evenness were similar across the treatments. In addition, herbaceous cover increased across the woody removal gradient, with the control plots recording the lowest cover. Overall, results showed that moderate removal of trees (i.e. 50%) in rangelands encroached by woody plants has the potential to maximise rangeland condition and can be used as a strategy for the restoration of herbaceous vegetation.

Keywords:

• Marikana Thornveld
• rangeland condition
• vegetation rehabilitation
• woody-plant encroachment
• woody-plant removal