Thesis Title

Biology of the Rare Woodland Perennial Trillium Pusillum Micheaux (Liliaceae) in Southwest Missouri

Date of Graduation

Spring 2003

Degree

Master of Science in Biology

Department

Biology

Committee Chair

Alexander Wait

Subject Categories

Biology

Abstract

Trillium pusillum is a perennial, woodland spring ephemeral that is being considered for listing as an endangered species. To support future efforts to preserve this species, basic ecological data were established for three populations in Missouri. I examined the stage structure of each population-Barker, Heckmaster, and Hoover Woods-and measured light levels, vegetation cover and diversity, soil characteristics, seed dispersal, and flower-visitation rates at each site. Populations at Baker and Heckmaster were large (approximately 6500 and 14,900 total stems, respectively) with stable stage structures. The population at Hoover Woods, where the exotic Euonymus fortunei dominated the herbaceous layer, was small (90 total stems) with an uneven and unstable stage structure. Soil pHs were 6.1 at Baker, 5.9 at Heckmaster and 6.5 at Hoover Woods. Mean leaf area index (LAI), a measure of light penetration through the canopy where the higher the LAI the shadier the understory, was 0.69 in April and 6.49 in June at Baker, 0.94 in April and 6.11 in June at Heckmaster and 1.39 in April and 8.18 in June at Hoover Woods. The presence of the exotic E. fortunei resulted in highter percent of herbaceous cober at Hoover Woods in April and May (55% and 81%, respectively) than at Baker (25% in April and 40% in May) or Heckmaster (28% in April and 29% in May). Dominant tree species at Baker and Heckmaster were oak (Quercus velutina) and hickory (Carya texana and C. cordiformis, respectively) vs. hickory (Carya spp.) and walnut (Juglans nigra) at Hoover Woods. Sequential and total pollinator visits were lower at Hoover Woods, suggesting that T. pusillum on that site may be pollinator limited. Seeds were dispersed at all sites by ants, ecxept at Hoover Woods where 30% of the seeds were dispersed by harvestment (Opilionids), resulting in the loss of some of the benefits associated with dispersal by ants. These data suggest that invasion by exotics, a higher soil pH, a shift in dominance of tree canopy species to one with allelopathic properties (J. nigra), low light levels, possible pollinator limitation, and seed dispersal by harvestment may be associated with the low population and unstable stage distribution at Hoover Woods.

Copyright

© Cynthia S Andre

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