Phosphate Mining Induced Vegetation Changes on Nauru Island

Postmining succession and pre—mining forest vegetation were studied on the isolated, tropical, central—Pacific, phosphate—rich island of Nauru. An analysis was made of the extent to which natural vegetation has been reestablished on the highly disturbed open—pit phosphate—mined areas that constitute some three—quarters of this 22—km² island. Sixty—four sample quadrats were taken from the successional range of revegetated mined areas and from the unmined plateau forest. Frequency and percent cover were obtained for all species to determine their ability to colonize different microhabitats in the mined area. A complete inventory was also made of all plant species present on Nauru, to identify the pool of potential recolonizers of the mined area. Of the 467 plant species found on Nauru, 47 native and 79 introduced weed species are potential short— and long—term colonizers. We found 50 of these 126 potential colonizers in the 64 sample quadrats. Highly dispersible, exotic weed species predominate in primary succession, but they are rapidly replaced by native plants such as Dodonea viscosa and Ficus prolixa, and by pantropical strand plants such as Scaevola taccada, Morinda citrifolia, Premna obtusifolia, Guettarda speciosa, and Calophyllum inophyllum. These species are scattered and stunted, however, when compared to their growth habitat in the unmined forest. The resultant succession seems to be progressing very slowly in the highly disturbed habitats. Centuries will be needed for the forest to reestablish naturally, even in a modified form, and most likely the forest will be composed primarily of Calophyllum inophyllum and other native coastal strand trees as dominants, with Ficus prolixa on the exposed coral—limestone pinnacles that remain after mining. If, however, the landscape is artificially modified by leveling the pinnacles and filling in the pit bottoms, and if suitable exotics are introduced, the succession could be altered considerably, much to the benefit of postmining generations of Nauruans.