Long-term Studies of Annual Variation in Growth and Reproduction of the Understory Fern Steiropteris deltoidea in a Hurricane-prone Rainforest in Puerto Rico

Abstract. Two long-term studies were conducted in a rainforest in Puerto Rico that included measurements of leaf and plant functional traits of the common fern species Steiropteris deltoidea. A Fern Demography study (1993-2009) compared annual variation and effects of a category 3 hurricane (Georges, 1998) on fertile and sterile leaf traits. A second long-term study (2003-2019), the Canopy Trimming Experiment, evaluated annual variation in growth and reproduction of S. deltoidea in response to two experimentally simulated and one category 4 hurricane (Maria, 2017). In the Fern Demography study, differences between fertile and sterile leaf production rates and plant leaf count of S. deltoidea were significant while leaf lengths and lifespans did not differ between leaf types. Fertile (but not sterile) leaf production increased three-fold after Hurricane Georges but declined 10-fold by the end of the study. Leaf lifespans of cohorts emerging before and in the three years after Hurricane Georges were significantly shortened by tree and debris fall. Elevated production of fertile leaves and increased plant leaf counts followed the two simulated hurricanes of the Canopy Trimming experiment and two natural hurricanes. Steiropteris deltoidea exhibits a level of interannual flexibility in some growth and reproductive traits in response to a changed understory environment that suggests it may be a good indicator species for evaluating microhabitat hurricane effects. Although S. deltoidea exhibited resilience, predicted increases in frequency and magnitude of hurricanes in response to climate change may test the limits of life history strategies of rainforest understory ferns.