Relationships betweenLigustrum sinenseInvasion, Biodiversity, and Development in a Mixed Bottomland Forest

Abstract

AbstractInvasion of closed canopy forests by shade-tolerant alien plants has the potential to modify species composition, stand structure, ecosystem function, and long-term forest development patterns.Ligustrum sinenseis a shade-tolerant alien shrub that has invaded bottomland forests throughout the southeastern United States. This species has received comparatively little attention in the literature despite its potential to drastically alter invaded sites. The overarching goal of our study was to document the relationships betweenLigustrum sinenseinvasion and woody plant biodiversity and development patterns in an intact southeastern U.S. bottomland forest. The forest was dominated byQuercus nigraandLiquidambar styraciflua. Ligustrum sinenseranked fifth in basal area contribution, occurred in 97% of our plots, and represented 95% of all understory stems. Spearman's rho for dominance (based on basal area of stems > 5 cm diameter at breast height [dbh]) ofL. sinenseand woody plant species richness for each plot revealed a significant negative relationship (rs= −0.69, P < 0.01). A similar relationship was revealed betweenL. sinensedensity and woody plant species diversity (rs= −0.78, P < 0.01) and evenness (rs= −0.82, P < 0.01). Spearman's rho forL. sinensedensity and native understory stem density (individuals ≥ 1 m height, < 5 cm dbh) also revealed a significant negative association (rs= −0.48, P < 0.01). Under the current disturbance regime and without active management, we projected the forest would shift to support a stronger component ofL. sinenseand that structure would transition from tree to shrub dominance for sites within the forest.