Growth and reproduction of Scirpus americanus following fire and lesser snow geese herbivory on the upper Texas Gulf coast

Abstract

SciMus americanus is a perennial, rhizomatous herb which occurs in coastal marshes along both Atlantic and Pacific coasts. S-. americanus is an important food source for lesser snow geese ( Chen aerulescens caeruiescens) (LSG) along the Texas and Louisiana Gulf coasts. Fire is used in the management of S-. ameficanus stands. This study was designed to evaluate the influence of fire and LSG herbivory on growth, development, and reproduction of SciEpus americanus. The study was conducted along the upper Texas Gulf coast on the San Bernard National Wildlife Refuge approximately II 0 km southwest of Houston, Texas. Foliar cover, canopy height, and stem density were measured for two years following a management bum and subsequent LSG herbivory. Seed numbers per stem and per @ were determined. Germination of field collected seeds was ascertained. Number of seeds nf2 of soil was used to estimate the seed bank of S. americanus. All in situ observations were considered relative to areas subjected to fire and/or LSG herbivore. Development of shoots, tillers, and rhizomes of experimentally grown S. americanus plants was also evaluated. Areas used by LSG had decreased foliar cover, height, and stem densities. Effects were still significant after one year. Fire positively affected regeneration, but burned areas were no longer different from controls after one year. Seed production per stem increased due to disturbance. Disturbed plants also produced more germinable seeds. Cold stratification significantly increased germination. Disturbed areas had larger Sciipus americanus seed banks during the first year. Plants grown in vitu attained heights, stem densities, and below-ground development comparable to plants naturally re-established in situ following fire or LSG herbivory. Results suggest recovery of Scirpus americanus stands following fire and LSG herbivory can approach pre-disturbance levels within a year. S. americanus may respond to cataclysmic disturbance events by allocating large amounts of energy to sexual reproduction. Re-establishment of S.. americanus from seed may produce stands usable by geese after one growing season; however, though large-scale seeding of S. americanus for LSG management purposes may be feasible, further research is needed, since seedlings have not been observed in natural stands.