EPISODIC REPRODUCTION IN TWO FIRE-PRONE PALMS,SERENOA REPENSANDSABAL ETONIA(PALMAE)

Abstract

This study examined how fire events affected the flowering of two native palms in a fire-prone environment. By examining how flowering varied across vegetative associations, I determined whether plant size or mass influenced flowering, whether canopy openness or increased soil fertility following fire enhanced flowering, and whether potential flowering stimuli interacted. Individuals of the widespread Serenoa repens and narrow endemic Sabal etonia were monitored (for a total of 9900 plant–year records) for growth performance and reproduction in flatwoods, scrubby flatwoods, scrub, and sandhill that were affected by single or multiple fires. In addition, clipping, fertilizing, and clipping+fertilizing experiments were conducted in three vegetative associations to simulate the effects of fire in order to ascertain which stimuli and their interactions encouraged flowering episodes. Both species exhibited marked resiliency to fire, rapidly resprouting from extensive underground stores. The frequencies of leaf production and flowering increased dramatically following fire in all vegetative associations compared to preburn periods, but especially in long-unburned (>60 yr) associations with substantial preburn overstory canopies. Strong episodic flowering responses were triggered after each of three repeated burns conducted during an 8-yr period at a previously long-unburned sandhill. Size, and hence estimated mass, were significant predictors of whether a palm would flower and, if so, how much it flowered. The loss of a palm’s crown by fire, or by clipping, stimulated flowering, but this effect was mediated by light availability. Palms under more complete overstory canopies flowered less than those in light gaps or at open-canopied stands. Fertilization of palms, intended to simulate greater postfire nutrient availabilities, did not stimulate flowering. Logistic regression models were developed for each palm species to estimate the probability of flowering in each vegetative association. These models accurately predicted flowering and nonflowering individuals. However, probability-of-flowering models that were generalized across vegetative associations for each species were less accurate than the association-specific models, which suggests the specific nature of flowering responses. These long-lived palms are well adapted to fire but are highly vulnerable to human-caused disturbance because of their very limited ability to recolonize former habitats.