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

Abstract

There is a limited understanding about the ecological mechanisms that enable certain plant species to become successful invaders of natural areas. This study was conducted to determine the soil and landscape characteristics that correlate with invasion of Chinese privet (CHP), and to develop a model to predict the probability of CHP invasion in Piedmont forests. A landscape ecosystem classification (LEC) system—based on the percentage of clay in the B horizon, depth to maximum clay (cm), exposure, terrain shape, and aspect (degrees)—was used to determine the soil moisture characteristics of invaded and uninvaded plots. Additional measurements included the cover classes of CHP and other species, litter depth (cm), slope (degrees), overstory basal area (m2 ha−1), and soil chemical properties. CHP invasion was negatively correlated with overstory basal area and slope and positively with litter depth and pH. A stepwise logistic regression model containing these four variables was highly sensitive, with an overall accuracy of 78%. Given the accuracy of this model, we propose that it can be used to calculate the probability of invasion in a given area, provided that some basic, readily obtainable site characteristics are known.

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

“…Loewenstein 2005;Merriam and Feil 2002). Several studies have detected a negative relationship between L. sinense cover and tree density, possibly supporting this hypothesis (Barksdale and Anderson 2015;Hagan et al 2014;Hanula et al 2009;Wilcox and Beck 2007). Additionally, Hagan et al (2014) reported that tree basal area was lower in invaded plots (but recall the earlier discussion on invasion frameworks).…”

“…Several studies have detected a negative relationship between L. sinense cover and tree density, possibly supporting this hypothesis (Barksdale and Anderson 2015;Hagan et al 2014;Hanula et al 2009;Wilcox and Beck 2007). Additionally, Hagan et al (2014) reported that tree basal area was lower in invaded plots (but recall the earlier discussion on invasion frameworks). However, Hanula et al (2009) and Greene and Blossey (2014) found no significant relationship between tree basal area and L. sinense cover, and others have found no significant relationship between L. sinense and overstory and subcanopy tree diversity (Kittel 2001;Wilcox and Beck 2007).…”

“…For instance, Wilcox and Beck (2007) observed that native plant species richness was lower in areas with high L. sinense cover, but was this because L. sinense excluded native species or because areas with lower species diversity may be easier to invade (i.e., the "diversity resistance hypothesis"; Kennedy et al 2002)? In another example, Hagan et al (2014) found that L. sinense was more prevalent in areas with lower overstory basal area, but again is this because L. sinense was more likely to invade sites with those conditions or because L. sinense caused those conditions to develop? Sites with low overstory basal area (possibly due to natural or anthropogenic disturbance) may have more available resources (e.g., sunlight) for L. sinense to take advantage of, increasing the likelihood of it successfully invading (Hagan et al 2014).…”

“…In another example, Hagan et al (2014) found that L. sinense was more prevalent in areas with lower overstory basal area, but again is this because L. sinense was more likely to invade sites with those conditions or because L. sinense caused those conditions to develop? Sites with low overstory basal area (possibly due to natural or anthropogenic disturbance) may have more available resources (e.g., sunlight) for L. sinense to take advantage of, increasing the likelihood of it successfully invading (Hagan et al 2014). On the other hand, if L. sinense outcompetes tree species and leads to the reduction of overstory basal area through reduced regeneration or growth, then L. sinense is acting as a driver.…”

“…In contrast, Brantley (2008) found no detectible relationship between L. sinense and overstory tree growth, and Hudson et al (2014) observed no response in tree growth 5 yr after L. sinense removal. The mixed reports regarding the relationship between tree basal area and L. sinense presence (Greene and Blossey 2014;Hagan et al 2014;Hanula et al 2009) further complicate our understanding of how L. sinense may or may not affect mature trees. More research is needed to determine the potential effect of L. sinense on overstory tree health, stand regeneration, and woody community composition.…”