Sutomo. 2018. Species composition and role of exotic invasive pioneers in vegetation establishment on Mount Merapi Volcanic Deposits in Java, Indonesia. Trop Drylands 2: 59-64. The volcanic deposits found in Mt Merapi are relatively new in terms of years since last known eruption. The objective of this study was to make use of the chronosequence method to describe changes in the species composition patterns in vegetation establishment, and to conduct observations on whether pioneer species, especially exotic and perhaps also invasive species, are decreasing or increasing species diversity in the succession. Results showed that the younger deposits were dominated by Athyrium macrocarpum, Polygonum chinense, Paspalum conjugatum and Cyperus flavidus. The older deposits were dominated by Anaphalis javanica, Imperata cylindrica, Polytrias amaura and Eupatorium riparium. Invasive (native and exotic) pioneer species such as Imperata cylindrica, Anaphalis javanica, Calliandra callothyrsus, Polyosma ilicifolia, and Eupatorium riparium showed positive correlation with species diversity. It is important to understand the role of non-native, invasive alien species in the recovery process. Early recovery generally depends on these species to boost the succession, but in the longer term invasive species may affect the successional trajectory.