The distribution of Bouteloua curtipendula in the eastern United States is generally limited to small and isolated populations on limestone-derived valley soils within the Ridge and Valley Physiographic Province in the Appalachian Mountains. In Pennsylvania, populations are <0.3 ha in extent and at least >16 km apart. Bouteloua curtipendula is found on extremely xeric sites: shallow, rocky, slightly alkaline, clay loams on south-southwest facing slopes. Diaspores of B. curtipendula can only travel at most a few meters on the wind and seeds are destroyed in the rumens of grazing ungulates; therefore, the long-distance dispersal mechanism is primarily by adhesion to animal fur. Two experiments tested the adhesion of B. curtipendula diaspores to eight mammal furs: coyote, red fox, rabbit, white-tailed deer, elk, bison, cattle and horse. A new index, the Dispersal Index (the product of “% diaspores that attached” and “% diaspores that remained after shaking”), was generated to represent the percentage of all diaspores that came into contact with the furs that remained attached. Bison and elk furs scored the highest on the Dispersal Index, suggesting that these two wild ungulates were important for B. curtipendula dispersal. However, both ungulates have been extirpated from most of their presettlement ranges in the Appalachians. According to herbarium records and modern field data, population numbers have declined by 48% during the past century, mostly due to agriculture, development and woody plant invasion due to fire suppression. Due to the absence of long-distance dispersers and the scattered distribution of suitable edaphic conditions, B. curtipendula is “trapped” on small sites that are shrinking due to woody plant invasion.
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Vol. 149 • No. 2