Soil Nitrogen Cycling Following Invasive Shrub Removal

Abstract Invasive plants often alter ecosystem functions and processes, especially soil N cycling. In urban or recently disturbed forest stands, soil N is often more available and may facilitate plant invasion, which in turn increases N mineralization and available N. In eastern United States forests, the shrub Rosa multiflora (“rose”) is the dominant invader, yet potential effects on N cycling are poorly understood. Moreover, invasive plant management can impact soil N cycling by decreasing plant N uptake and disturbing the soil. The objectives of this study were to evaluate N cycling along a gradient of rose invasion and investigate potential changes to N cycling under four different management strategies: 1) do nothing (i.e., the control), 2) invasive plant removal, 3) removal followed by native seed mix addition, 4) removal, native seed mix, and chipped woody stem addition. We selected three forest sites experiencing a low, medium, or high amount of shrub invasion, and measured N cycling in the early (June) and late (September) growing seasons. We found N was immobilized in June and mineralized in September. One year after experimental management strategies were implemented, removal alone had no effect on N cycling compared to control plots, but addition of native seed mix and chipped stems reduced early-season nitrification in our medium invasion site. Our findings suggest that initial N cycling under different amounts of rose invasion and subsequent responses to management are complex, and that N cycling responds differentially to management in the year following invasive plant removal.