Allee effects and soil nutrient changes mediated by experimental plantings of a nonindigenous, temperate liana

Liana abundance worldwide has the potential to increase due to elevated atmospheric CO2 concentrations and continued anthropogenic forest disturbance. Temperate forests have relatively low liana diversity compared to tropical forests, and it is believed this discrepancy has allowed nonindigenous lianas to disrupt temperate native communities to a greater degree. Due to their nature as structural parasites upon trees, the influence of lianas on forest systems is disproportionately greater than their modest contributions to aboveground biomass, yet the establishment of lianas into temperate communities has not been well studied. We designed a fully factorial experiment to investigate how density (intraspecific competition) and growth orientation (climbing vs. creeping) would influence growth and biomass allocation in wintercreeper (Euonymus fortunei, Celastraceae) an exotic evergreen liana. We also quantified soil nutrients prior to planting and after 17 months of soil conditioning to determine if wintercreeper influences nutrient availability. We found evidence of Allee effects, in which the highest density treatment yielded significantly greater total biomass (in both roots and shoots), longer stems, and higher specific stem length. Soil analyses indicated that wintercreeper significantly altered soil nutrients, increasing C, N, P, Ca, and Mg over the course of the experiment. These findings support previous studies, which found that wintercreeper tends to grow best in dense monoculture populations. While founder populations may be slow to establish, Allee effects combined with wintercreeper’s ability to modify nutrient cycling may help account for this species’ recent recognition as a serious plant-pest following a century of widespread cultivation.