Genetic diversity of red oak (Quercus rubra) populations along an urban to rural gradient

Background/Question/Methods

Global deforestation has led to the clearing of nearly two-thirds of the total forest cover on earth. Fragmented forests are now more common than contiguous expanses of intact forest, and forest fragmentation has been linked to reductions in genetic diversity of surviving populations. Fragmentation is particularly extensive in urban areas, but while some studies have examined effects of urbanization on genetic diversity in animals, little is known about effects on genetic diversity in plant populations. In this study, we used microsatellite analysis to examine genetic diversity in overstory red oak (Quercus rubra) stands in remnant forests along an urban (New York, NY, USA) to rural (Putnam County, NY, USA) gradient in the Greater New York City Metropolitan Area.

Results/Conclusions

We found limited effects of urbanization on genetic diversity, heterozygosity, and gene flow. There were no clear effects of fragment size on genetic diversity. Further, soil characteristics, including soil microbial diversity and function did not show clear relationships with genetic diversity. These patterns suggest genetic diversity may reflect the founder populations prior to forest clearing. As this study focused on adult trees, that existed prior to clearing, different patterns may be observed among trees established following fragmentation; further research is needed to address this issue. Further, biotic and abiotic variables not addressed in our study may play key roles in regulating genetic diversity in forests fragmented by urbanization. As urban populations grow and cities expand into more rural areas, a detailed understanding of the changes in genetic diversity of surviving species, and the environmental variables that govern them, will help indicate changing patterns and process in new urban ecosystems.