Demography of Cyathea hornei (Cyatheaceae), a Tropical Tree-Fern in Fiji

Abstract

A population of the tree-fern Cyathea hornei (Cyatheaceae) was studied in the tropical forest environ- ment of Viti Levu, Fiji. Plants monitored over a 2.5 year period indicated that leaf production is greatest in the hot, wet season and that leaf longevity is 1.1-1.6 years. Plants vary in the rates of leaf production (3-9 year^-1) and stem growth (1.5-40 cm year^-1). From the spacing of leaf scars on the stems and observed growth rates it is possible to estimate the growth history and age of plants. The age class structure of the populations is consistent with a 2% annual mortality, and the largest plants observed (550 cm stem length) have an age of 80-105 years. Reproduction commences in plants of about 150 cm stem length, and each fertile plant produces 4 x 10⁷ 2 2 x 10⁷ s.d. spores year -^-1. Annual net production varies greatly, up to 760 g year-^-1, and in typical fertile plants is allocated as follows: roots 15%; stems 23%; leaves 58%; and sori 4%.