Invasion, alien control and restoration: Legacy effects linked to folivorous insects and phylopathogenic fungi

Abstract

Invasive alien trees increase native tree stress and may increase attack by herbivores and pathogenic fungi. Alien tree removal should ameliorate such impacts. Here we compared the levels of damage by phylopathogenic fungi and folivorous insects on Brabejum stellatifolium and Metrosideros angustifolia (native trees) and Acacia mearnsii (invasive tree species) among near-pristine, invaded and restored sites. Generally, foliar damage levels were higher at invaded than at near-pristine sites. Damage levels at restored sites were similar, or even higher than those at invaded sites. Decreased native tree species richness did not explain these patterns, as restored sites had native tree species richness levels similar to those of near-pristine sites. Increased host abundance and leaf nitrogen content did not significantly correlate with increased damage in most cases. Therefore, plant species richness recovers following restoration, but native trees still experience increased pressure from folivores and phylopathogenic fungi, which may even exceed levels experienced at invaded sites, thus impacting recovery trajectories.