Overstory Thinning Impacts Fruit Production and Handling of the Nonnative Shrub, Rhamnus frangula, in a Young Temperate Forest

Abstract

Forest management has the potential to drive demographic shifts among woody plants in the forest understory, which may impact the success of nonnative species and can determine future trajectories of forest communities. Here, we consider the relationships between nonnative fruiting shrubs, frugivores, and forest management practices in a young mixed mesophilic hardwood forest, exploring how forest management influences both fruit production and bird-mediated fruit handling in nonnative shrubs within the forest understory. Specifically, we measured fruit production in the nonnative shrub, Rhamnus frangula, and handling of artificial fruit mimics within 1 ha forest plots subjected to one of three management treatments: (1) overstory thinning (thinning of the forest canopy trees by 20% using a mix of girdling and selective-felling), (2) overstory thinning coupled with nonnative shrub removal, or (3) unmanaged control. We found forest management to be a driver of both fruit production in Rhamnus frangula and fruit handling by birds in the forest understory, with higher productivity and rates of fruit handling in areas with overstory thinning relative to controls. These shifts in fruit availability and plant-animal interactions have the potential to serve as a pathway by which forest management may alter future forest communities, possibly promoting nonnative species such as Rhamnus frangula in the forest understory.