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The evolution of fire-stimulated flowering in the genus Pityopsis (Asteraceae).
Gowe, Amy*,1, Brewer, Steve1, 1 University of Mississippi, University, Mississippi
ABSTRACT- One hypothesized benefit of ecological restoration of fire-dependent ecosystems is increased reproductive success of fire-adapted species. Unequivocal evidence for the existence of fire-adapted species is lacking in many systems however. The genus Pityopsis (Asteraceae) has been hypothesized to contain at least one fire-adapted species, P. graminifolia. This species dramatically increases flowering in response to lightning-season fires. In this study, we documented the occurrence of fire-stimulated flowering in all Pityopsis species and examined relationships between fire-stimulated flowering, historic fire frequency, and the light environment for each species. In addition, we constructed a phylogeny of the genus based on published morphological data and then mapped fire-stimulated flowering on the resulting topology. Floral induction and tree and groundcover canopy coverage within each species′ preferred habitat were quantified for all but one species (P. ruthii, an endangered species) at field sites in Massachusetts, Georgia, Florida, and Mississippi. Photographs and published data were used to infer flowering patterns and the light environment for P. ruthii. Results of our investigations support the following the hypotheses: 1) Fire-stimulated flowering occurred in one subgeneric taxonomic group (sect. Graminifoliae) but not the other (sect. Pityopsis). 2) Fire-stimulated flowering tended to occur in habitats or microsites that contained a dense groundcover canopy during years without fire. 3) Fire-stimulated flowering was more likely to occur in areas of relatively high pre-Colonial fire frequency in the United States. The phylogenetic analysis tentatively suggested that the two sections of Pityopsis were not distinct clades. Furthermore, the character used to distinguish sections in previous taxonomic treatments may, in part, be an artifact of describing a disproportionately large number of non-reproductive plants in years without a lightning-season fire. If our phylogenetic hypothesis is correct, then some species may have gained or lost fire-stimulated flowering during diversification of the group.
Key words: plant competition, fire ecology, pine savannas, coastal dunes