Rapid impact of Impatiens glandulifera control on above- and belowground invertebrate communities

The annual plant Impatiens glandulifera (Himalayan balsam) is the most widespread invasive non-native weed in the British Isles. Manual control is widely used, but is costly and laborious. Recently, biological control using the rust fungus Puccinia komarovii var. glanduliferae has been trialled. We designed an experiment to assess the impact of these control methods on invertebrate communities in relation to unmanaged and uninvaded habitats, and to determine whether mycorrhizal inoculation aided post-control recovery of these communities. Sixty invaded and twenty uninvaded field soil blocks were transplanted to the experiment site, where a mycorrhizal inoculum was added to half of all blocks. Biological and mechanical control treatments were applied to twenty invaded blocks independently; the twenty remaining invaded blocks were left intact. Above- and belowground invertebrate samples were collected from the blocks at the end of the growing season. Overall, aboveground invertebrate abundance increased with the removal of I. glandulifera, and several groups showed signs of recovery within one growing season. The effect of mechanical control was more variable in belowground invertebrates. Biological control did not affect aboveground invertebrate abundance but resulted in large increases in populations of belowground Collembola. Our experiment demonstrates that mechanical removal of I. glandulifera can cause rapid increases in invertebrate abundance, and that its biological control with P. komarovii var. glanduliferae also has the potential to benefit native invertebrate communities.