While the existence of a latitudinal gradient in plant defenses is often taken for granted, the results of the few intraspecific tests that have been performed have been equivocal. We used a dominant and foundation North American tree species, white oak (Quercus alba), to test if traits varied along a latitudinal gradient or if they were arrayed in a geographic mosaic. Condensed and hydrolyzable tannins in white oak leaves play roles as defenses against natural enemies, in nutrient cycling and leaf decomposition, and are associated with community structure of folivores. White oak saplings were grown from seed in a common garden in Kingston, Rhode Island, U.S.A. using acorns from eleven different sites in the eastern United States ranging from Massachusetts to Florida. We sampled leaves from 97 white oak saplings in June 2009, and assayed the leaves for condensed tannins, hydrolyzable tannins, and total phenolics.

Results/Conclusions

No apparent latitudinal trends emerged from these data, although the means differed significantly among the sites of seed origin (p < 0.001 for all three measures) and varied over a wide range for all three chemical traits measured (ca. two-fold for hydrolyzable tannins and total phenolics, and over three-fold for condensed tannins). These data are consistent with these traits being distributed in a geographic mosaic, and further work in this system will investigate the distributions of other traits important for plant defense, ecosystem function and herbivore community structure.