Leaf Phenology and Trunk Growth of the Deciduous Tree Fern Alsophila firma (Baker) D. S. Conant in a Lower Montane Mexican Forest

Abstract

Tree ferns are often regarded as evergreen, non-seasonal, slow-growing plants of tropical forests. However, several species possess seasonal leaf phenology patterns and seasonal differences in growth rates. To investigate the environmental triggers which influence leaf phenology and to measure trunk growth rates, we studied a population of Alsophila firma at Las Cañadas, Huatusco, State of Veracruz, Mexico. We measured leaf traits monthly for 26 mo and trunk height at the beginning and end of the study. Alsophila firma showed a unique seasonal pattern of leaf phenology, shedding its leaf pinnules when they are yellow or still green during the wet season, and 50–70% of plants stay leafless for at least 1 mo, after which strongly asynchronous leaf flush occurs. This phenological pattern may be of advantage to evade higher herbivore pressure of the wet season and to benefit from higher light levels in the understory during the dry season when a proportion of canopy trees are leafless. The trunks had a mean height of 2.46 ± 0.16 m, a mean leaf number of 5.2 ± 0.27 (n = 169), and 25% of the plants were fertile. Mean annual trunk growth was 17.1 ± 0.85 cm. Based on this trunk growth rate, the tallest tree ferns (>10 m) are at least 60 yr old.