Variation in nitrogen mineralization and soil microarthropods among forested stands dominated by exotic, invasive plants

Background/Question/Methods

Invasion and proliferation of exotic plant species has the potential to have long-term impacts on terrestrial and aquatic ecosystems. In order to maintain the integrity and biodiversity of natural ecosystems, restoration efforts must be made to remove invasive species and restore the native plant community. We measured soil nutrient cycling and soil microarthropod density among sites dominated by Rhamnus frangula (glossy buckthorn), Ligustrum sinese (Chinese privet) and Celastrus orbiculatus (oriental bittersweet), three common invasive plants in eastern deciduous forests. Glossy buckthorn and Chinese privet are woody shrub species while oriental bittersweet is a vine that can also form a thick ground cover. Since each species had a clumped, localized distribution, experimental sites dominated by invasive plants were paired with control sites randomly selected within 100 m of the experimental site. Soil characteristics were compared between invasive and control site pairs.

Results/Conclusions

Invasive plants were very dense in experimental sites. Glossy buckthorn ranged from 11-25 stems/m², while Chinese privet ranged from 6-14 stems/m². Density of oriental bittersweet was slightly lower, ranging from 1-4 stems/m², although each site also had significant ground cover. pH was significantly greater under Chinese privet and oriental bittersweet compared to non-invaded control sites. There were no differences in pH between glossy buckthorn and control sites. There were significant differences among invasive and control sites for total C, N and C:N ratio. Total N was significantly greater in non-invaded control sites compared to sites dominated by bittersweet. Both Total C and soil C:N ratio was significantly greater in non-invaded control sites compared to sites containing any of the invasive plants. Both cation exchange capacity and exchangeable potassium were significantly greater in sites dominated by oriental bittersweet. Exchangeable magnesium was significantly greater in sites dominated by Chinese privet. Oribatid mite density was nearly twice as great in non-invaded control sites (14.1 x 10³/m²) compared to sites dominated by invasive plants (7.3 x 10³/m²), but the difference was not significant (p = 0.081).  Data collected in this study will be compared to post-restoration data to determine the effect of removing these invasive species on ecosystem properties.