Investigating effects of Black wattle (Acacia mearnsii) invasion on selected soil chemical properties in the Afromontane ecosystem of the Vumba uplands in Zimbabwe

Black wattle ( Acacia mearnsii ) encroachment into native habitats can modify soil properties, which in turn affects general ecosystem functioning. This study determined pH, moisture content, phosphorus, nitrogen, carbon, total dissolved solids (TDS), and soil electrical conductivity (EC) between areas invaded by Acacia mearnsii and native vegetation in the Vumba area. It was hypothesized that soils in invaded sites would exhibit significantly higher concentrations of soil organic carbon and total nitrogen, but significantly lower pH levels and lower moisture content, compared to adjacent non-invaded sites. Soil samples were collected in May 2025 from a depth of 30 cm using an auger, utilizing equal sampling across set 25 m × 25 m plots within two distinct strata: Invaded habitats and native plant habitats. Laboratory analyses were performed to determine the selected soil chemical properties, and a paired t-test was conducted using Minitab 17 statistical software. Acacia mearnsii invasion significantly altered soil chemical properties, with substantial differences observed between invaded and uninvaded sites. Significant variations were recorded for soil pH ( p < 0.01), nitrogen ( p < 0.001), carbon ( p < 0.006), EC ( p < 0.001), TDS ( p < 0.001), and moisture content ( p < 0.001); for all significant variables: ( N = 20, df = 19). Conversely, phosphorus levels remained largely unaffected and showed no significant difference between the sampled sites ( N = 20, df = 19, p = 0.165). Consequently, the initial hypothesis was accepted, as the data confirmed significant alterations in soil nutrients, acidity, and moisture levels following invasion. These findings highlight the disruptive impact of the species on soil chemistry, suggesting that invasive species management programs must be implemented to curtail further invasion in Vumba uplands.