Do No Harm: Efficacy of a Single Herbicide Application to Control an Invasive Shrub While Minimizing Collateral Damage to Native Species

Abstract

Control of invasive exotic species in restorations without compromising the native plant community is a challenge. Efficacy of exotic species control needs to consider collateral effects on the associated plant community. We asked (1) if short-term control of a dominant exotic invasive, Lespedeza cuneata in grassland restorations allows establishment of a more diverse native plant community, and (2) if control of the exotic and supplemental seed addition allows establishment of native species. A manipulative experiment tested the effects of herbicide treatments (five triclopyr and fluroxypyr formulations plus an untreated control) and seed addition (and unseeded control) on taxonomic and phylogenetic diversity, and community composition of restored grasslands in three sites over three years. We assessed response of L. cuneata through stem density counts, and response of the plant community through estimates of canopy cover. Herbicide treatments reduced the abundance of the exotic in the first field season leading to a less dispersed community composition compared with untreated controls, with the exotic regaining dominance by the third year. Supplemental seed addition did not provide extra resistance of the native community to reinvasion of the exotic. The communities were phylogenetically over-dispersed, but there was a short-term shift to lower phylogenetic diversity in response to herbicides consistent with a decrease in biotic filtering. Native plant communities in these grassland restorations were resilient to short-term reduction in abundance of a dominant invasive even though it was insufficient to provide an establishment window for native species establishment.

Survival and regeneration ability of clonal common milkweed (Asclepias syriaca L.) after a single herbicide treatment in natural open sand grasslands

“…In contrast to this study, some short-term studies showed that the non-target vegetation was degraded by herbicide application. For example, Gibbson et al 19 showed that the phylogenetic diversity of the community became lower due to single herbicide treatment. Szitár and Török 20 also showed that the single herbicide spraying of common milkweed disturbed the vegetation, and it modified the succession to an earlier initial state.…”

Survival and regeneration ability of clonal common milkweed (Asclepias syriaca L.) after a single herbicide treatment in natural open sand grasslands

“…For example, herbicide treatment can be more efficient when assimilates translocate to the roots in the late summer, as reported in several studies on other invasive clonal plants [110,111]. However, the substances and the treatment's halflife must be considered in protected areas, and a break of at least 1 year between treatments is advisable to allow regeneration of natural vegetation [19,20].…”

“…In the case of established invasive species, the most successful options are eradication or isolation [8][9][10][11][12][13]. Herbicide treatment is one of the most effective ways to control or eradicate invasive plants in large areas [10,[14][15][16][17][18][19]. Nevertheless, the prevention and control measures of invasive species with chemicals are rather arguable whereas their use endangers other species and the ecology and abiotic elements (above and below ground waters, soil and air) in protected areas [18,20,21].…”

“…Nevertheless, the prevention and control measures of invasive species with chemicals are rather arguable whereas their use endangers other species and the ecology and abiotic elements (above and below ground waters, soil and air) in protected areas [18,20,21]. Consequently, herbicides have to be carefully chosen (dosage, types and combination) based on the native species community [16,19,20]. Therefore, the herbicide application must be well planned and localized, the applied chemicals should be safe and effective.…”

“…This knowledge gap also requires not only extensive research but also effective exchange of information and experience [cf. 10,18,19].…”