Phenology influences invasion success after removal of invasive Scotch Broom

Torres, A., Morán-López, T., Rodriguez-Cabal, M.A. & Núñez, M.A. (2023) Timing of invasive species removal influences nonnative biotic resistance and trajectories of community reassembly. Journal of Ecology, 111, 2342–2356. DOI10.1111/1365-2745.14168

Summary

The interaction between the timing of management efforts and the phenology of the community being managed can affect the success of any invasive management project. Torres et al. (2023) investigated the link between the phenology of species removal and community assembly post-removal of Scotch Broom (Cytisus scoparius) and Sweetbriar rose (Rosa rubiginosa), both nonnative and potentially invasive in the northeastern US. In both a mesocosm and field experiment, the nonnatives were cut down “early” (spring) and “late” in the growing season. Revegetation of the site after the non-native aboveground biomass was removed was then evaluated looking for patterns among/between the remaining species based on the timing of removal. Only the Cytisus results will be summarized.

As an invasive nitrogen fixer, removal of the aboveground Cytisus biomass early in the season can cause a spike in soil nitrogen making soils more hospitable to nitrophilic species. However, when the Cytisus is removed later in the growing season, the nitrogen released in Cytisus root decomposition was less useful to the non-native species since the non-native species had run their resource intensive life cycle phases earlier in the year. Thus, considering the phenology of the potential invader community is important when conducting a removal project. In both field and mesocosm experiments, removal of the invasive Scotch Broom favored establishment of other non-natives, but the effects were greater when Scotch Broom was removed early in the growing season.

Take home points

Impacts of dominant invasives removed from invaded communities can linger in the soil, which can both impair the recovery of native species while also promoting existing non-natives.

Negative impacts of invasive plant removal can be contingent on the phenology of the remaining species, the timing of removal, and the choice of removal techniques.

Management implications

• Removal of dominant invasives in the spring and summer will free up resources for other plants, and sub-dominant invasives may be able to take advantage of these resources more quickly than native species

• Management actions aimed at restoring native communities could benefit from knowing when invaders are most in need of limited resources.

• Consideration of multifaceted phenological timing to reduce impacts of non-native species is a cost-effective tactic to improve restoration outcomes.

• Differences in phenology between native and invasive species can be used to inform when non-natives are less-likely to colonize post-removal projects.

Keywords: Phenology, Shifting Seasons, Restoration, Scotch Broom