Impacts from invasive plant species and their control on the plant community and belowground ecosystem at Rocky Mountain National Park, USA

We assessed the effects of changes in the plant community and belowground soil ecosystem in a mountain meadow, from the invasion of leafy spurge (Euphorbia esula L.) and Canada thistle (Cirsium arvense L.), and the subsequent management efforts to remove them. Sampling included three paired sites containing areas where herbicides and mechanical means had been employed and which were still dominated by leafy spurge, and areas where herbicides had not been applied and where very little (<0.03%) or no leafy spurge or Canada thistle existed. Plant species diversity, frequency, and percent cover were estimated. Decomposition rates were assessed by use of litterbags placed on the sites and retrieved after 1 year. Vesicular–arbuscular mycorrhizal inoculum potential was used as an index for mutualistic associations. Soil microarthropod densities were used as an index for the detrital food web. Significantly greater (P ≤ 0.05) richness of plant species and significantly higher percent relative cover of herbs, sedges, lichen, moss, and fallen litter was found on non-invasive plots compared to plots with invasive species. Plots where herbicides had been applied, and which still possessed leafy spurge, showed a significantly higher percentage of bare ground. Mycorrhizal inoculum potential did not differ between plots. Overall soil arthropod densities and densities of specific suborders of Acari were significantly lower (P ≤ 0.05) in invasive species plots. There was no significant difference in decomposition rates between non-invasive and invasive plots, but there were site differences in losses of lignin, phosphorus, and trace elements from litter placed on invasive and non-invasive plots. When differences were observed, loss rates were always less in invasive plots. Our results indicate that the establishment of leafy spurge and Canada thistle and the subsequent management practices to control them has altered the plant community structure by facilitating the establishment of other exotic species, which has resulted in a change in the composition and functioning of the belowground community.