Demography and Production of Leptopteris wilkesiana (Osmundaceae), a Tropical Tree-Fern From Fiji

Abstract

The demography of Leptopteris wilkesiana (Osmundaceae) was studied in an area of undisturbed primary forest near Suva, Viti Levu, Fiji. The tree-fern has a single growth flush of 3-9 new leaves each wet season, and this is apparent as a distinct annual band of stipe scars on the trunk. Trunk ages ranged up to 133 years and trunk height growth averages 1.6 cm year^-1. Leaf longevity is normally 2-2½ years. There was a 1% probability that a trunk would fall over, or be knocked over, each year; most trunks produced new roots at the lowest part of the fallen stem and continued growing. Sporangia production commenced in plants 30-45 cm tall and increased with leaf size and the number of leaves. Spore pro- duction ranged up to 17 x 10⁶ spores year^-1 on a large plant, and 3 x 10⁸ spores year^-1 for a population of 100 plants, while recruitment of sporophytes was estimated at 1 year^-1. Annual net production ranged up to 38 g oven-dry tissues on a large plant of which 55% was leaf production and 8% sporangia production.