Continuous Monitoring of Vegetation and Soil Recovery After Eucalyptus grandis Removal in Dense Trees and Shrubs Areas

Abstract

Invasion by invasive alien plants is a global challenge and South Africa has invested billions of Rands to manage invaders through the Working for Water programme. However, regular monitoring after alien plant clearing is hardly done, yet it forms the basis for assessing clearing programme effectiveness, particularly ecosystem recovery trajectories. I monitored both vegetation and soil recovery 6 years after Eucalyptus grandis clearing by Working for Water at Zvakanaka Farm in Limpopo Province of South Africa. Vegetation diversity and soil physical properties were surveyed in 2019 and re-surveyed in 2022 on fell-and-removal and fell-and-stackburn cleared treatments and compared to the nearby uninvaded treatment. Results show a significant increase in species richness in 2022 compared to 2019 in the fell-and-removal treatment. Cover of both native trees and shrubs as well as forbs was significantly higher in 2022 compared to 2019 in the fell-and-removal treatment compared to the fell-and-stackburn treatment. Most secondary invaders such as Acacia mearnsii, E. cloeziana, Lantana camara and Rubus rigidus that frequently occurred in 2019 showed decreased occurrence in 2022 on both cleared treatments. Between the two sampling years, soil compaction improved on the fell-and-removal treatment only, whereas hydraulic conductivity increased significantly in 2022 compared to 2019 in both the fell-and-removal and fell-and-stackburn treatments. Soils that were strongly and severely repellent in 2019 in the fell-and-stackburn treatment were becoming slightly repellent in 2022. These results show varied vegetation and soil improvements between 2019 and 2022 in both the fell-and-removal and fell-and-stackburn cleared treatments an indication that recovery is moving towards a positive vegetation and soil recovery trajectory in the direction of the uninvaded treatment. Recommendations for successful passive restoration such as secondary invasion follow-up clearing are discussed.