Growth and Fertilization Responses of Hawaiian Tree Ferns

Abstract

Responses of a tree fern (Cibotium glaucum) to nutrient additions were examined in two rain forest sites in Hawaii Volcanoes National Park, Hawaii. In the younger forest (ca 200 yr old), separate additions of nitrogen and of phosphorus (but not additions of all other macro- and micronutrients) increased fern stem height growth. Nitrogen but not phosphorus increased leaf production, but fertilization had no effect on maximum leaf longevity (39 mo). In the older forest (> 1000 yr old), nitrogen additions did not alter fern growth parameters; fern stem height growth and leaf production were greater in unfertilized plots of the > 1000 yr old forest than in unfertilized plots in the younger forest; and leaf longevity (maximum of 34 mo) was shorter. Leaf production (February-April) and leaf mortality (August-November) were highly seasonal, with mortality occurring several months after expansion of new leaves. The asynchronous leaf recruitment and mortality resulted in cyclic monthly variability in leaves per fern. Our data support other studies suggesting that more rapid leaf turnover occurs in nutrient-rich sites, and that nitrogen appears to be the nutrient most limiting to growth in the early stages of primary succession.