Influence of Chinese Privet (Ligustrum sinense) on Decomposition and Nutrient Availability in Riparian Forests

Abstract

As invasive species become increasingly abundant in forests, their presence may influence a number of key nutrient cycling processes. For example, Chinese privet has become well established in southeastern forests and continues to spread. Two studies, a multisite field investigation and a controlled approach on a single site, were conducted to examine the role of Chinese privet (Ligustrum sinense) on decomposition within riparian forests of the Georgia Piedmont. The field study also investigated the effects of privet presence on soil nitrogen (N) mineralization and microbial carbon and N immobilization. Both studies utilized a litterbag approach to examine how increasing proportions of privet in foliar litter influenced mass loss rates and nutrient dynamics. The field investigation included litterbags with representative proportions of the five dominant species from 16 sites. Litterbags in the controlled study were composed of specific levels of privet litter within bags (0, 10, 20, 30, 40, and 50% Chinese privet) as treatments. The litter quality of four native species was compared to Chinese privet in the controlled study. Both studies showed significant positive relationships between percentage of Chinese privet in litterbags and decomposition rates (2.6-fold rate increase with 30% privet in litterfall). Chinese privet leaf litter had lower lignin and cellulose concentrations, higher N concentrations, lower lignin : N ratios, and narrower C : N ratios than the native species. The positive relationship between mass loss rates and the proportion of Chinese privet in litter indicates that Chinese privet enhances decomposition rates as it becomes more abundant. During summer, N mineralization showed approximately a fivefold increase; during winter, microbial biomass N increased by approximately 30% on sites with the highest levels of privet in the understory. Consequently, C and N dynamics in Piedmont riparian forests were significantly influenced in direct proportion to the amount of privet present in the understory.

Invasion of Eastern Texas Forestlands by Chinese Privet: Efficacy of Alternative Management Strategies

“…For example, Stone (1997) has shown that practicing site preparation procedures such as hand-pulling seedlings and mowing and/or cutting stems larger than 2.5 m can successfully reduce Chinese privet invasion in relatively small areas, such as nature preserves [29]. Chinese privet has been shown to inhibit reproduction and growth of trees through altering the occurrence of arbuscular mycorrhizal fungi in the resident soil [30] and influencing a number of key nutrient cycling processes [31]. In addition, a combination of shading and some allelopathic effect of adult leaf leachate inhibit the growth of other plants under a canopy of Chinese privet and contribute to a reduction in plant diversity after invasion [32].…”

The Role of Soil and Landscape Factors in Chinese Privet (Ligustrum sinense) Invasion in the Appalachian Piedmont

“…It has become widely naturalized in the southeastern United States and is reported to have invaded thousands of acres (Mitchell et al 2011;Ward 2002). It generally has multiple stems and a shrub-like growth form, with heights ranging from 1.5 to 3.6 m (5 to 12 ft), although it occasionally becomes treesized (Greene and Blossey 2011).…”

“…Much of the previous research on CHP has focused on growth characteristics, response to flooding, dispersal rates, impacts on native plants and forest regeneration, and influences on decomposition and nutrient availability (Hanula et al 2009;Merriam and Feil 2002;Mitchell et al 2011;Morris et al 2002). Research in the Piedmont region of the United States has indicated that CHP invasion suppresses herbaceous understory, causing decreases in plant species richness and diversity (Greene and Blossey 2011;Merriam and Feil 2002;Wilcox and Beck 2007).…”

“…Research in the Piedmont region of the United States has indicated that CHP invasion suppresses herbaceous understory, causing decreases in plant species richness and diversity (Greene and Blossey 2011;Merriam and Feil 2002;Wilcox and Beck 2007). CHP litter has a lower C : N ratio than most of the understory vegetation that it displaces, which results in accelerated nutrient mineralization, especially during summer months (Mitchell et al 2011). The rapid rate at which CHP spreads impedes the ability of native pine (Pinus spp.…”

“…Their analyses, however, did not include soils, nor did their study design incorporate within-stand variables such as microsite differences in slope, litter depth, etc. However, studies conducted with other species have indicated that factors such as soil texture, nutrient concentrations, landscape, slope, and terrain shape correlate strongly with invasion (Mitchell et al 2011). Determining how site characteristics such as these are related with CHP invasion could be an important management tool in deterring its spread, prioritizing resources for early detection and control, and maintaining understory and overstory diversity in southeastern forests (Wang and Grant 2012).…”