Uneven-aged and even-aged logging alter foliar phenolics of oak trees remaining in forested habitat matrix

Abstract

Despite potential links between logging-induced changes in abiotic factors, variation in plant secondary chemistry, and foliage consumption by herbivores, few studies have investigated the impacts of timber extraction on plant anti-herbivore metabolites. To determine if uneven-aged (UAM, i.e., selective logging) and even-aged (EAM, i.e., clear-cutting) management regimes impacted levels of foliar phenolics in Quercus alba and Q. velutina (white and black oak, respectively), we quantified the levels of condensed tannins (CT) and total phenolics in the leaves of canopy and understory trees located within landscapes undergoing UAM, EAM, or no harvest (NHM) in the southeastern Missouri Ozarks. In the understory, total phenolics were slightly elevated in Q. velutina trees in UAM relative to trees in NHM and EAM sites but lower in Q. alba trees in EAM relative to trees in UAM and NHM sites. Furthermore, treatment effects on understory total phenolic concentrations were greater in older forests. In the canopy, treatments altered plant chemistry only for trees in block 2, where CT concentrations were elevated in trees within UAM and EAM sites relative to NHM for Q. alba, but elevated in UAM and reduced in EAM relative to NHM for Q. velutina. Understory trees of both species had higher levels of both CT and total phenolics when growing on slopes with south- and west-facing aspects than on those with north- and east-facing aspects. Our results indicate that timber harvests, even at low levels of extraction (10% biomass removal), altered concentrations of foliar polyphenolics in Q. alba and Q. velutina but that the effects of logging on phenolics were dependent on blocking factors (forest age and previous management history). In addition, defoliation levels generally were lower where concentrations of phenolics where higher (e.g. in the canopy and on south- and west-facing slopes). In combination with additional studies of the impacts of phenolics on oak herbivores, as well as studies of the impacts of herbivores on oak growth, our results indicate that changes in foliar chemistry due to forest management practices may have large consequences for Ozark forest communities.