Introduction / Background / JustificationThe tropical and subtropical live oaks (Quercus section Virentes) span Central America as far south as Guanacaste Costa Rica, the Caribbean (Cuba), and the coastal regions of Mexico and the southeastern US as far north as Virginia. They consistently occur in lowland and maritime forests with well-drained soils. They have the highest density wood of any oaks, can withstand hurricanes and contribute important ecosystem services. Objective(s)/Hypothesis(es)In this study, we review the phylogeography and evolutionary history of the lineage, the functional ecology and adaptive differentiation of populations within and among of the seven Virentes species and discuss the prospects and challenges for conservation.MethodsPopulations of all seven Virentes species were sampled to determine population genetic structure, evolutionary relationships, divergence times, and effective population sizes. Leaf morphology, cold and freezing tolerance and drought tolerance were evaluated within and among populations and species in common garden experiments. ResultsPopulation-level differentiation in freezing and drought stress are associated with differential performance and survival. Quercus sagraena in Cuba, Quercus brandegeii in Southern Baja California, Mexico, and Quercus minima in the southeastern US have low effective population sizes and very limited climatic ranges and/or specific fire regimes, making them susceptible to extinction. Moreover, the Costa Rican population of the broadly distributed Quercus oleoides may be a cryptic species and is highly threatened by increasing drought due to climate change. Quercus fusiformis in Texas is threatened by the oak wilt fungus (Bretziella fagacearum), Quercus virginiana has been overharvested, and Quercus geminata has declined due to removal of the maritime forest.Implications/ConclusionsThe tropical and subtropical live oaks (Quercus section Virentes) contain three species that face extinction risk. All species within the lineage face risks due to changing climate, fire suppression, invasive pathogens, overharvesting, and land-use change. Thus, long term persistence of this unique lineage of coveted lowland oak species will require concerted management efforts.
Quercus section Virentes, effective population size, tree threats, adaptive differentiation