A LIFE HISTORY APPROACH TO THE STUDY OF PLANT SPECIES RARITY: Gentianopsis crinita IN NEW YORK STATE
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Robertson, Heather Jane
Gentianopsis crinita (Froel.) Ma, (fringed gentian), is a rare biennial plant, native to eastern North America. Generalizations about the life history characteristics of biennials, and the habitats where these plants occur, provided a framework for examining the critical factors affecting the rarity of Gentianopsis crinita in New York State. The relative significance of these factors was assessed by comparing Gentianopsis crinita's responses to those of Daucus carota L. (wild carrot), a common biennial that occurs in the same localities as Gentianopsis crinita. The principal study sites were two old fields near Ithaca in Tompkins County, and a landslide at Letchworth State Park in Livingston County. In one old field, seeds were sown in experimental treatments that represented successional habitats ranging from bare ground to scrub more than 3 m tall. Survival and reproduction of both species were enhanced where interspecific competition was reduced by ground disturbance and clipping of vegetation, but both species also persisted among tall herbs and low woody shrubs less than 1 m high. Neither species survived in tall scrub. Experiments indicated that Gentianopsis crinita may lack a persistent buried seed bank, and according to previous studies, so does Daucus carota. Flowering individuals of Gentianopsis crinita had a higher seed output on average than Daucus carota despite greater losses to herbivores. Although Gentianopsis crinita performed at least as well as Daucus carota in all these ways, observations and experiments revealed that the distribution and abundance of Gentianopsis crinita were more limited by its narrower tolerance of edaphic conditions. In contrast to Daucus carota, survival and growth required relatively high soil moisture levels and circumneutral to alkaline soils. The results also demonstrated that the optimal ecological conditions for Gentianopsis crinita, where survival, growth and reproductive output are greatest, can shift spatially over time, because patches of more fertile soils sometimes have inadequate moisture. Recommended conservation action includes permanent prevention of scrub encroachment on preserves and the selection of preserves containing refuge areas that are wet enough to maintain populations even in dry years.
Cook, Robert; Marks, Peter; Smith, Charlie
Ph. D., Plant Ecology
Doctor of Philosophy