Invasion of the alien shrub Prunus laurocerasus in suburban deciduous forests: Effects on native vegetation and soil properties

Most invading alien plants affect native biodiversity and ecosystem functioning. In a field survey, we assessed the impact of the invasive shrub Prunus laurocerasus on the native vegetation and soil properties in suburban deciduous forests in the region of Basel, Switzerland. We installed four pairs of plots in patches of P. laurocerasus and in adjacent not invaded areas in each of twelve forest areas. Native species richness, Shannon-diversity and species composition of the ground vegetation and shrub layer were assessed in each plot. Furthermore, in each plot we measured physical and soil chemical characteristics, enzyme activities and the carbon source utilization pattern of the soil microbial community using Ecoplates™. The maximum age of P. laurocerasus in each plot was determined using tree ring analysis, indicating the time elapsed since the invasive plant has established. A lower native plant species richness in both the ground vegetation and shrub layer was observed in plots with presence of P. laurocerasus. A different species composition of the ground vegetation was also found among plots with and without the invasive shrub. Plots invaded by P. laurocerasus had a lower soil moisture content than control plots. The intensity, diversity and substrate richness of the carbon sources were increased in soil from invaded plots compared to soil in control plots. However, the chemical soil characteristics examined and the activities of enzymes were not influenced by the invasive plant. The effects of P. laurocerasus became more pronounced with the time elapsed since the invasive plant has established. Thus, the removal of young P. laurocerasus individuals would be an appropriate management practice for this invasive shrub species.