Abstract
Invasive non-native woody shrubs pose a major threat to forested ecosystems in many parts of the world and there is an urgent need for research on the restoration and recovery of these areas. We studied patterns of tree growth and regeneration 13 years after the experimental eradication (by chainsaw or mulching machine followed by herbicide treatments) ofLigustrum sinenseLour. (Chinese privet) from riparian forests in Georgia, United States. We also followed the recovery of bee and butterfly populations using sites with no history of privet invasion as a reference. By the end of the study, the basal area of restored plots was 24% greater, on average, than still-invaded control plots. Because tree growth rates did not differ among treatments, this increase is attributable to the 60% increase in the number of regenerating native stems (dominated byAcer negundoL.) following privet removal. The benefits of privet removal on pollinators were immediate and long-lasting with the richness and abundance of bees and butterflies being consistently higher in restored plots than in control plots. The diversity, abundance, and composition of bees in restored and reference (i.e., never invaded) plots were comparable by the end of the study. This was less true for butterflies, however, possibly due to the legacy effects of privet invasion on plant communities. Our results demonstrate the long-term benefits of removing privet on forest regeneration and pollinator communities. Indeed, without such efforts, it is probable that forest cover will gradually thin and ultimately disappear from privet-invaded areas as overstory trees die without replacement.
Highlights
Invasive non-native species are considered one of the biggest threats to biodiversity globally and continue to alter the structure and composition of ecosystems in profound ways
In 2019 we measured a total of 4487 trees and woody shrubs >2.5 cm DBH (Supplementary Table 3)
The restored plots had nearly 60% more stems per ha than the control plots, a significant difference (Figure 3). This difference was driven primarily by trees ≤5 cm in diameter which were nearly four times more abundant in restored than control plots, a significant difference (Z = −2.13, P = 0.03) (Figure 4). This regenerating cohort of trees consisted largely of Acer which accounted for 80% of all stems ≤5 cm in diameter (Figures 1C,D)
Summary
Invasive non-native species are considered one of the biggest threats to biodiversity globally and continue to alter the structure and composition of ecosystems in profound ways. 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). There is an urgent need for research on how to preserve forest cover in such areas while conserving diverse assemblages of native species. This is a major and growing challenge facing land managers worldwide (Richardson and Rejmánek, 2011)
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