Invasive Plant Restoration: Soil Nutrient Pools and Enzyme Activity Among Stands Dominated by Exotic, Invasive Plants.

Invasion and proliferation of exotic plant species has the potential to have long-term impacts on terrestrial and aquatic ecosystems. This study describes the results of a restoration effort made to reclaim forested areas 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 bittersweet is a vine that can also form a thick ground cover. 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.  Restoration treatments were designed to reduce the density of invasive plants to less than 10% of pre-treatment levels using primarily mechanical methods.  Prior to restoration treatments, soil properties and soil enzyme activity levels were assessed among sites dominated by invasive and native plants.  Soil organic matter was significantly greater in sites dominated by native plants (4.5%) compared to sites dominated by L. sinese (3.4%) but not R. frangula (3.6%) or C. orbiculatus (3.7%).  Both soil NH₄ and NO₃ content was significantly greater in sites dominated by C. orbiculatus (3.7 and 7.2 mg N/kg soil, respectively and R. frangula (4.6 and 3.9 mg N/kg soil, respectively) compared to control sites dominated by native species (1.9 and 2.7 mg N/kg soil, respectively).  The concentration of extractable P was significantly greater in sites dominated by native species (18.9 mg P/kg soil) compared to sites dominated by both L. sinese (14.4 mg P/kg soil) and R. frangula (9.7 mg P/kg soil).  Activity levels of acid phosphatase, chitinase and phenol oxidase were similar among all sites.