Influence of Chinese Privet (Ligustrum sinense Lour.) on Riparian Forests of the Southern Piedmont: Net Primary

Abstract

The spread of invasive, nonnative vegetation in the Southeast has been identified as a critical concern for the maintenance of ecosystem biodiversity and impacts on the forest industry. One example of such a species is Chinese privet (Ligustrum sinense Lour.), whose rapid expansion in riparian forests of the Southeast has been reported. Unfortunately, there has been minimal research on impacts of this species to forest functions and processes such as net primary productivity (NPP), carbon sequestration and native plant regeneration. Research plots were selected in the Piedmont physiographic province of western Georgia that represented a continuum of understory Chinese privet invasion from 0-100%. Above- and belowground net primary productivity (NPP) and standing crop biomass was estimated. Additionally, leaf, stem, and fine root carbon concentrations were determined to estimate carbon sequestration trends. Lastly, the proportion of native plants in the regeneration forest layer was determined. Each of these forest functions and processes was compared with the proportion of Chinese privet found in the understory. Understory Chinese privet invasion (25-79% of total stems) was accompanied by a significant increase in total NPP and carbon sequestration that was strongly influenced by belowground NPP. The initial increase in total NPP and carbon sequestration was followed by a numerical, but not significant, decrease when >80% of total understory stems were Chinese privet. This trend was likely influenced by the lack of a diverse forest stratum found under dense mid-story Chinese privet. When the understory was composed of 40% Chinese privet, it appeared to suppress native plant regeneration to below 50% of total. This has implications for long-term impacts on the replacement of native canopy trees, NPP, and carbon sequestration. Overall, the results suggest that processes and functions such as net primary productivity and carbon allocation will ultimately be diminished in Southeastern riparian forests invaded by Chinese privet due to the loss of large, native canopy trees that are not replaced due to limited native species regeneration.