My interests are in plant population genetics, phylogeography, and systematics. All of my projects either involve species exhibiting striking geographic disjunctions or species of conservation concern. I have ongoing projects in three main systems, which I have briefly summarized below.
Phylogeography of eastern North American trees
More than 50 plants share a disjunction between what is today the eastern United States and the Sierra Madre Oriental Mountains of eastern Mexico. Very few animals are known to share this disjunction. Fossil pollen data suggest that the origin of this temperate flora in Mexico can be traced as far back as the Pliocene (~2.5-5.3 million years ago). The time at which the disjunction arose between the US and Mexico, however, remains unclear. I continue to work on several tree species that share this disjunction, integrating molecular approaches, intraspecific divergence time estimation, and ecological niche modeling to obtain a more comprehensive picture of the past. Our understanding of the past ultimately informs our interpretation of the future, such that the data generated in these studies will also be used to predict future species distributions.
Reproductive ecology of American beech in response to beech
American beech ( Fagus grandifolia) is a dominant canopy tree species in forest communities of eastern North America, but persists as a unique forest type in the highest elevations of the Great Smoky Mountains. Beech gaps, as they are commonly known, are islands of primarily single-species stands otherwise surrounded by spruce fir forests. Clonal reproduction has long been considered to be the mechanism sustaining these populations, and we now have preliminary genetic data that support this hypothesis. Now these stands are faced with the potential of a double threat to their existence: 1) beech bark disease and 2) climatic warming. My collaborators and I continue to track recovery of these unique forests in response to the threats using a interdisciplinary approach that includes population genetics, dendrochronology, and field ecology.
Illicium (Illiciaceae): systematics and biogeography of a
basal angiosperm clade
Illicium is a relatively small (~30-40 spp.), monophyletic group of basal angiosperms best known for its distinctive star-shaped woody fruits and aromatic leaves and flowers. Approximately 30-40 species are currently recognized throughout southeast Asia, North America, and the Greater Antilles. By exhibiting numerous well-documented geographic disjunctions, Illicium provides an excellent opportunity for testing biogeographic hypotheses across these regions. Convergent morphologies complicate taxonomic identification, and only limited molecular divergence among species has been recovered so far. While the center of species diversity is in southeast Asia, there are seven species endemic to the New World (U.S.=2; Mexico=1; Hispaniola=2; Cuba=2). Data from chloroplast sequence and nuclear microsatellites will continue to be collected to address questions of taxonomic relatedness, floral evolution, and biogeography in this system.