We chose a rich, mesophytic cove forest in the Coweeta Basin, western North Carolina to evaluate the role of a diverse herbaceous layer in ecosystem function. We hypothesized that the experimental removal of a functional group of species would alter ecosystem processes. In summer 1998, we established 6 replicates of herbaceous removal (HR), 6 organic matter addition (OMA), and 6 controls. For fourteen years (1998-2011), we manually removed all herbs and deciduous shrubs from the HR plots and added organic matter (105 g m-2 fresh weight) to the OMA plots. All tree species were allowed to regenerate and grow. Tree seedlings <5.0 cm height were counted and tree seedlings ≥5.0 cm height were tagged and measured. We measured in situ soil CO2 efflux, in situ soil nitrogen availability, forest floor nutrient release using ion exchange resin sheets, and forest floor mass, carbon and nitrogen.
Results/Conclusions
Acer rubrum seedling recruitment was higher on the HR treatment than the control. Other tree species were less abundant and there were no differences among treatments. Even though soil moisture and temperature were comparable among treatments over time, soil N mineralization was higher on the OMA treatment than on HR and control in 2006 and 2011. As expected, soil CO2 efflux was higher in the summer than spring and winter. Average summer CO2 efflux was 3.51 mmol m-2 s-1 across all treatments in 2011, and it was lowest on the HR treatment after fourteen years of herbaceous removal. No significant differences were found for forest floor mass; however, forest floor Oe + Oa nitrogen was greater in the control than the HR or OMA treatments in some years.