Effects of Neltuma juliflora (Sw.) DC. Invasion on Soil Health: A Case Study of Areas Bordering the Nyumba Ya Mungu Reservoir, Northern Tanzania

Abstract

African drylands face growing pressures from land use change, climate change and non-native plant invasions. Invasive tree species can alter soil functioning by modifying physical, chemical and biological indicators of soil health, but quantitative evidence of these impacts remains limited. This study assessed the effects of Neltuma juliflora (formerly Prosopis juliflora) invasion on physical, chemical and biological indicators of soil health in the drylands of northern Tanzania. To compare soil health indicators, 50 paired invaded–uninvaded (20 × 20 m) plots were surveyed and data analysed using generalized linear mixed models. Response variables included soil organic carbon, carbon dioxide efflux, bulk density, soil pH, total nitrogen, available phosphorus, the C:N ratio, soil moisture and soil temperature, with invasion status (1 = invaded, 0 = uninvaded) as the predictor variable. Results showed that N. juliflora invasion was associated with significant (p < 0.001) increases in soil organic carbon and total nitrogen, suggesting enhanced soil nutrient status. Soil organic carbon increased from 0.30% to 0.75% and total nitrogen from 0.04% to 0.09%. Carbon dioxide efflux increased from 5.53 to 12.34 g m⁻² day⁻¹, suggesting soil carbon loss through soil respiration, while bulk density increased from 1.54 to 1.62 g cm⁻³, and soil pH from 6.8 to 7.4, reflecting deterioration of physical soil condition through compaction and alkalinization, respectively. However, available phosphorus, soil moisture, soil temperature and the C:N ratio did not differ significantly (p > 0.05) between invaded and uninvaded areas. These findings highlight that N. juliflora invasion creates an ecological trade-off, improving some soil health indicators while leaving others unchanged or negatively affected. The impacts of N. juliflora invasion are therefore multifaceted and require balanced consideration in dryland ecosystem management.