Response of an Early Succesional Community in Fiji to Phosphorus Enrichment

Effects of phosphorus enrichment (195 kg P ha-1) on density, cover, and diversity in a one-year-old community at an excavation site in Fiji were assessed after ten and a half weeks by comparing changes in community characteristics in eight 4 m2treated and eight 4 m2untreated plots. Increases in total density, total cover, and total number of species per plot were significantly greater in treated plots. Other diversity measures (total species, Shannon-Wiener index (H'), and Pielou's evenness (J')), however, were very similar in treated and untreated plots before and after treatment. Among major, plant-growth-form groups, only herbaceous kinds (ephemeral forbs, graminoids, cryptogams plus forbs) exhibited significantly greater increases in density or relative cover in treated plots; responses of woody plants (trees, shrubs), vines, and zingibers overlapped statistically. Herbaceous species were probably enhanced most strongly by P enrichment because their shallow, fibrous root systems allow efficient absorbtion of P near the surface, and other groups may be adapted to naturally low levels of available P, most herbs being weedy exotics.