Impact of a native invasive weed (Microstegium ciliatum) on regeneration of a tropical forest

Abstract

Infestations of invasive plants can hinder forest regeneration in biodiversity hotspots in tropical Asia. Microstegium ciliatum is a native grass in parts of tropical and subtropical Asia. To assess impacts of Microstegium on secondary forest succession in its native range, a field experiment was undertaken in abandoned agricultural settlements in Cuc Phuong National Park, Vietnam from 2016 to 2018. Plots were established across 6 sites under low, medium and high tree canopy levels. In manipulated plots, M. ciliatum was killed with a grass-specific herbicide and invading vines were cut in a subset of plots; control plots were untreated. The results show that in its native range Microstegium can be invasive with impacts on forest restoration. Application of herbicide reduced the cover of M. ciliatum from 85 to 3% and increased the diversity and number of tree seedlings within the 2 years of the experiment. There was no difference in tree seedling abundance between the herbicide and herbicide + vine cutting treatments, but the number of tree seedling species was significantly higher in the latter in the 2nd year after treatments were applied under the medium canopy. The overstory influenced forest regeneration in the manipulated plots as there was a greater number of tree seedlings and species in plots under medium and high-density canopies. The results suggest that management of the native invasive grass under tree canopies will facilitate forest restoration after disturbance from agriculture and lead to the early recruitment of mid and late successional forest species.