THE ECOLOGY OF THE CLIMBING FERN DICRANOPTERIS-LINEARIS ON WINDWARD MAUNA-LOA, HAWAII

1 Dicranopteris linearis (Gleicheniaceae), a native fern common throug hout the Old World tropics and Polynesia, forms dense thickets > 3m de ep over large areas of open-canopy, oligotrophic, wet Hawaiian rainfor ests. Our objectives were to identify leaf- and whole plant-level trai ts that are key to its success and to determine its community- and eco system-level consequences in primary successional sites. 2 Along an el evational gradient from 90 to 1660 m, mean maximum net assimilation ra tes of Dicranopteris ranged from 2.9 to 5.0 mu mol m(-2) s(-1), compar ed with 3.6-9.5 mu mol m(-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, clon al growth form, shallow rhizomes, marcescent leaves with low decomposa bility, and a mat-forming capacity enabled Dicranopteris to colonize s ites and to maintain dominance via high effective leaf area, despite i ts low biomass. Phosphorus use efficiency, which reached 24 kg g(-1), was exceptionally high, allowing colonization of phosphorus-poor sites . 4 Dicranopteris contributed up to 74% of above-ground net primary pr oductivity in a site where it contained only 14% of live biomass. It a ccounted 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 slo w to decompose; thus, fixed carbon is transferred quickly to soil detr ital pools where it contributes to aggrading soil organic matter pools and may exacerbate oligotrophic conditions, thereby strongly influenc ing soil genesis and ecosystem development. 5 The fern therefore influ ences forest-floor light regimes and directs later community developme nt. An exclusion experiment demonstrated that Dicranopteris competed w ith Metrosideros, but lack of revegetation in 30% of the exclusion are a after 39 months showed that Dicranopteris also colonized microenviro nments unavailable to its endemic codominants. Dicranopteris is may pl ay an important role in resisting invasions of exotic species into Haw aiian rainforests.