The ecological effects of Chinese privet (Ligustrum sinense) invasion: a synthesis

Abstract

Chinese privet (Ligustrum sinense Lour.) is a deciduous to evergreen shrub with an expansive nonnative global range. Control costs are often high, so land managers must carefully consider whether the plant’s potential negative effects warrant active management. To help facilitate this decision-making process, we reviewed and synthesized the literature on the potential ecological effects of L. sinense invasion. We also identified research gaps in need of further study. We found ample evidence of negative relationships between L. sinense invasion and native plant communities. While observational studies are not able to confirm whether L. sinense is driving these relationships, experimental evidence suggests that there is a cause–effect relationship. Of particular concern is the possibility that L. sinense could suppress forest regeneration and cause areas to transition from forest to L. sinense–dominated shrublands. Although this outcome would obviously impact a wide variety of wildlife species, empirical evidence of negative effects of L. sinense on wildlife are limited, and some species may actually benefit from the additional cover and foraging opportunities that L. sinense can provide. Further research on the potential effects of L. sinense invasion on large-scale forest structure and wildlife populations is needed. In areas where L. sinense invasion is a concern, evidence suggests early detection and management can mitigate control costs.

Life After Privet: Plant Community Dynamics in a Forested Wetland Following Removal of the Invasive Ligustrum sinense Lour

“…Ligustrum sinense has been described as a driver or “backseat driver” of vegetative community change, because of its light-exclusionary effects on regeneration (Cash et al 2020). Accordingly, we have seen higher light levels in L. sinese -removal sites, correlating with regeneration of vegetation cover and species richness of native species in the herb-layer, but a concerning advance of the nonnative grass Microstegium vimineum and lack of diverse woody seedling recruitment.…”

“…Ligustrum sinense forms multi-stemmed thickets 1-10 m in height (Singh et al 2015) and spreads vegetatively by root suckers, a common trait in wetland-tolerating woody species (Fischer et al 2021). It flowers in spring and produces a multitude of drupes in fall, which are dispersed by endozoochory or water movement (Cash et al 2020). Seeds germinate immediately without cold-stratification (Wang and Grant 2014).…”

Decadal Patterns of Forest and Pollinator Recovery Following the Eradication of an Invasive Shrub

“…Some of the most problematic species invading forested systems involve trees and shrubs that have become naturalized or invasive across their nonnative range (Fagan and Peart, 2004;Hartman and McCarthy, 2007;Richardson and Rejmánek, 2011). By preventing tree regeneration, for instance, dense thickets formed by certain invasive shrubs have the potential to convert native forests into invasive shrublands (Cash et al, 2020;Lázaro-Lobo et al, 2021;Turner et al, 2022). While the loss of forest cover will be gradual, playing out over many decades as overstory trees die, the invasion of such shrubs will have more immediate effects on other species as well as the ecosystem services they provide.…”

“…Among the most ecologically consequential invasive shrubs in North America and beyond is Ligustrum sinense Lour. (i.e., Chinese privet, hereafter "privet") an Asian species that was intentionally introduced as an ornamental plant to countries throughout the world beginning in the mid nineteenth century (Cash et al, 2020). This semi-evergreen species is now naturalized widely where it often forms a dense midstory layer up to about 10 m in height, especially in riparian forests (Figure 1A).…”

“…For example, Wang et al (2016) estimated that the total area invaded by privet in Alabama and Mississippi will increase from 1.36% to nearly one third of total forest area within the next two decades. Because the survival and growth of native tree seedlings is greatly reduced beneath privet (Greene and Blossey, 2012), and privet quickly fills in gaps created by recently fallen trees (Turner et al, 2022), there are real concerns about the future of forest cover in areas invaded by this shade-tolerant species (Cash et al, 2020).…”