Species Richness and Floristic Quality Metrics Differ in Their Sensitivity to Lonicera maackii Invasions with Increasing Area

Plant invasions are generally associated with lower biodiversity and ecosystem function, but the impacts of plant invasions on species richness are often scale-dependent. Like species richness, metrics of community structure and quality likely differ in their sensitivity to plant invasions with area. Therefore, depending on the spatial scale of sampling, some metrics are unlikely to capture the impacts of plant invasions. Lonicera maackii is a shrub native to Asia and invasive across the eastern United States. The impact of L. maackii invasion on species richness and two floristic quality assessment (FQA) metrics, floristic quality index (FQI) and mean coefficient of conservatism (mean C), was studied across multiple spatial extents to determine the spatial breadth of the sensitivity of these metrics to plant invasions. We selected 12 forest plots: 6 uninvaded plots (<1% L. maackii cover) and 6 invaded plots (>70% L. maackii cover), which we divided into subplots of 1 m², 62.5 m², 125 m², 250 m², and 500 m². Within each plot, we calculated average plant richness, mean C, and FQI for each spatial extent. Invaded plots displayed lower total richness at smaller spatial scales, with richness within L. maackii-invaded plots recovering to levels found among uninvaded plots at an extent of 62.5 m². Invasion lowered both mean C and FQI at spatial extents ≤125 m². Consequently, invasion impacts on FQA metrics likely manifest themselves at small spatial extents, and comparing invasion impact among management units should be carried out at these scales for proper comparison.