Summary 1 Dicranopteris linearis (Gleicheniaceae) a native fern common throughout the Old World tropics and Polynesia forms dense thickets > 3 m deep over large areas of open-canopy oligotrophic wet Hawaiian rainforests. Our objectives were to identify leaf- and whole plant-level traits that are key to its success and to determine its community- and ecosystem-level consequences in primary successional sites. 2 Along an elevational gradient from 90 to 1660 m mean maximum net assimilation rates of Dicranopteris ranged from 2.9 to 5.0 µmolm-2 s- 1 compared with 3.6- 9.5 µmolm-2 s- 1 in the codominant tree Metrosideros polymorpha. Gas-exchange characteristics did not explain Dicranopteris\ success nor its trends in production. 3 However indeterminate clonal growth form shallow rhizomes marcescent leaves with low decomposability and a mat-forming capacity enabled Dicranopteris to colonize sites and to maintain dominance via high effective leaf area despite its low biomass. Phosphorus use efficiency which reached 24kgg-1 was exceptionally high allowing colonization of phosphorus-poor sites. 4 Dicranopteris contributed up to 74% of above-ground net primary productivity in a site where it contained only 14% of live biomass. It accounted for up to 57% and 47% of total nitrogen and phosphorus uptake by plants respectively where it contained only 24% and 30% of plant nitrogen and phosphorus. Dicranopteris leaves are short-lived and slow to decompose; thus fixed carbon is transferred quickly to soil detrital pools where it contributes to aggrading soil organic matter pools and may exacerbate oligotrophic conditions thereby strongly influencing soil genesis and ecosystem development. 5 The fern therefore influences forest-floor light regimes and directs later community development. An exclusion experiment demonstrated that Dicranopteris competed with Metrosideros but lack of revegetation in 40% of the exclusion area after 39 months showed that Dicranopteris also colonized microenvironments unavailable to its endemic codominants. Dicranopteris may play an important role in resisting invasions of exotic species into Hawaiian rainforests.