Short Term Soil and Vegetation Recovery After Acacia Mearnsii Removal in Vhembe Biosphere Reserve, South Africa

Abstract

Short term monitoring of soil and vegetation recovery following alien plant removal is required to reveal how ecological restoration is progressing. This study examined the recovery of soil physical properties and vegetation following Acacia mearnsii removal at Zvakanaka farm in Limpopo Province, South Africa. Soil and vegetation measurements were conducted in paired cleared, invaded and natural sites on 10 x 10 m plots. Results of the study show significantly (P < 0.001) higher soil moisture content in invaded and natural compared to cleared sites. Soil penetration was significantly (P < 0.001) higher in cleared than invaded and natural sites. Both infiltration rate and hydraulic conductivity showed no significant (P > 0.05) difference between the three sites. Strongly repellent soils were recorded in cleared sites only. Results showed a significant (P < 0.05) increase in measured diversity indices (species richness, Shannon-Wiener, Simpson's and evenness index) in cleared and natural than in invaded sites. However, most secondary woody invasive alien plants were recorded in cleared sites. The study concludes that A. mearnsii clearing triggers varying changes in soil physical properties. Although native plants are present in cleared sites, recovery may be hampered by the growth of secondary woody invasive alien plants.

Black (Acacia mearnsii) and silver wattle (Acacia dealbata) invasive tree species impact on soil physicochemical properties in South Africa: A systematic literature review

“…The gravimetric water content was generally higher on invaded and low on cleared soils relative to the uninvaded, while both cumulative infiltration and saturated hydraulic conductivity were low on invaded and higher in cleared soils compared to the control ( Table 2 ). The increase in moisture content on invaded soils is due to the availability of acacia trees that avoid direct sun heating, hence less evaporation [ 11 ]. The moisture content in cleared areas is expected to decrease as the soil is bare.…”

“…The cost of clearing invasive species is estimated at about R6.5 billion annually [ 10 ]. These plants outcompete native vegetation, resulting in biodiversity loss and environmental deterioration [ 11 ]. They exacerbate water scarcity difficulties, increase the likelihood and intensity of wildfires, and place economic constraints on agricultural and water management [ 12 ].…”

“…A study by Naudé [ 30 ] reported significantly higher bulk density in Acacia mearnsii under invaded compared to uninvaded soils. In siltstone soil in Limpopo, Acacia mearnsii cleared soils had significantly lower gravimetric water content compared to invaded and uninvaded sites under siltstone [ 11 ]. Similarly, results observed by Ndou and Ruwanza [ 24 ] under sandy soils in the Eastern Cape Province had a significant difference in gravimetric water content between Acacia mearnsii cleared and uninvaded.…”

Soil health indicators for monitoring forest ecological restoration: a critical review

“…All articles reported significant differences against the reference in the short term. Water content decreases in soils where exotic species are removed or have reduced vegetation cover and only showed recovery after the tree establishment (e.g., Ruwanza & Tshililo 2019). Therefore, it is advisable to space out the evaluations of this indicator and consider it for medium to long‐term evaluations.…”