Causes of a seedling recruitment advantage for an encroaching oak over a historically dominant oak in a fire-restored open oak woodland

ABSTR A C T The lack of natural oak regeneration within forests is one of the most pressing conservation issues facing oakdominated ecosystems in eastern North America. Although the restoration of suitable fire regimes appears to favor oaks over fire -sensitive mesophytes in many cases, differences in the effects of fire restoration on different species of oak have not received nearly as much attention. In particular, greater sapling recruitment of historically lowland Quercus alba compared to that of the historically upland and dominant Quercus stellata in response to fire restoration appears to be related to differences in seedling establishment, but the causes of these differences are not clear. In this study, we investigated species differences in acorn viability and rate of removal by predators, as well as differences in oak seedling emergence, survival, and vigor over two growing seasons (fall 2020 to fall 2022) in a restored oak woodland in northern Mississippi (USA). The proportion of viable acorns was greater for Q. alba than for Q. stellata, especially in 2020. Both species had similar acorn predation/removal rates in the winter of 2021. Seedling survival and vigor were greater in Q. alba than in Q. stellata, although these differences were more pronounced in patches dominated by the invasive Microstegium vimineum. Seedling emergence, survival, and vigor for both oak species were significantly lower in patches dominated by M. vimineum than in those dominated by native species. Neighboring vegetation and litter removal significantly increased seedling survival in both species. The positive effect of neighbor/litter removal on seedling survival was no greater in patches dominated by M. vimineum than in those dominated by native species, a result consistent with the existence of legacy effects of M. vimineum. Altogether, our findings suggest greater acorn viability combined with higher seedling survival and vigor in Q. alba than in Q. stellata may contribute to the lower regeneration rates of the historically dominant Q. stellata compared to encroaching Q. alba in firemaintained woodlands. Negative effects of an invasive grass, M. vimineum, may further complicate restoration efforts.