Impacts of exotic weed invasion on surface runoff and sediment yield in Eucalyptus plantations on slopes in Central Yunnan, SW China

Limited research on the hydrological impacts of invasive weeds hampers sustainable forest management and ecosystem restoration in biological invasive scenarios. This study assumed that alien weed invasion could affect surface runoff and sediment formation, with the extent of invasion determining its impact on soil and water conservation. To test this hypothesis, three Eucalyptus benthamii Maiden & Cambage plantations in Central Yunnan, Southwest China, infested with Agerina adenophora (Spreng.) R. M. King & H. Rob., were selected as the experimental sites. Runoff and sediment were monitored on slopes with varying invasion levels—severe invasion (SI), light invasion (LI), no invasion (NI) with litter coverage, and bare surface (BS)—over a year. The results showed that the cumulative runoff on the NI slopes (1.24 mm) and SI slopes (2.65 mm) was significantly lower (p < 0.05) than that on the LI slopes (15.40 mm) and BS slopes (13.10 mm); similarly, the cumulative sediment on the NI slopes (3.3 × 10−3 Mg/ha) and SI slopes (2.4 × 10−3 Mg/ha) was significantly lower (p < 0.05) than that on the LI slopes (0.11 Mg/ha) and BS slopes (0.14 × 10−3 Mg/ha). Therefore, in areas of light invasion, weed-invaded slope forests are prone to serious soil and water loss, emphasizing the need for prevention; however, in severely degraded forests, maintaining heavily invasive weed populations is beneficial for soil and water conservation. This study provides a scientific foundation for ecologically restoring degraded forests impacted by exotic weed invasion.