Editor’s Choice 57:10 – Testing the relative effects of biocontrol and herbicide: finding an evidence-based management decision to control invasive plants

Journal of Applied Ecology’s October Editor’s Choice compares biocontrol and herbicide as approaches to invasive species management. Associate Editor, Rafael D. Zenni introduces the selected article by Paul G. Peterson and colleagues, which explores ‘efficacy, non-target effects and secondary invasion’.

This post is also available in Portuguese here.

In most ecosystems, controlling invasive alien plants is necessary in order to reduce and mitigate the negative impacts of  invasions on native biodiversity and ecosystem services. However, several control methods for managing invasion exist, and choosing the most effective, least damaging and most permanent solution is not a simple task. For instance, biological control is specific to the target invasive species but requires extensive research for a particular invasion before a biocontrol agent is found and released, whereas chemical control tends to be more broadly applicable and can be readily used in many cases but with increased potential of non-target effects. Therefore, to achieve the best possible reduction in invasion with the least possible non-target effects, research comparing  control methods in isolation and in combination is necessary. Highly quality evidence-based information on the pros and cons of each control method are key for managers and applied ecologist working on invasive species management.

Ngaruahoe & Tongariro 2000vs2018 landscape
A before-and-after comparison showing purple flowering invasive heather pre-beetle, and over 99% dead heather and recovering native vegetation (and some replacement weeds such as exotic grasses) in the after photo. The volcanic cone of Mt Ngauruhoe is visible in the background. Photo: Paul Peterson

In their Editor’s Choice article, ‘Comparing biocontrol and herbicide for managing an invasive non‐native plant species: Efficacy, non‐target effects and secondary invasion‘, Paul Peterson and colleagues share the results of a five-year long experiment comparing efficacy, undesirable effects and secondary invasion of both biological and chemical controls on the invasive Calluna vulgaris (common heather). Common heather is a woody shrub, native to Europe, Asia and North Africa that was introduced to New Zealand, where the study took place. It eventually become the worst invasive non‐native plant species in the Tongariro National Park, dominating more than 50,000 ha. Importantly, the control methods evaluated by the researchers were the ones being already used by relevant stakeholders in the area. Consequently, the results can be readily applied by managers.

impact photo
Heather protected from heather beetles in an insecticide treatment plot (edge of the sprayed area superimposed). Photo: Paul Peterson

The research team found that, over time, all treatments (herbicide, biocontrol, and herbicide plus biocontrol) greatly reduced the invasive plant cover, compared to an increased in heather cover when no control was applied. For the results of non-target effects, the herbicide control had a greater impact on native species compared with biological control. While native species cover and richness increased when biocontrol was applied compared to no control, herbicide application (both alone and in combination with biocontrol) reduced some native species cover and richness compared to no control. Furthermore, controlling the invasive plant without a restoration effort resulted in secondary invasions by other alien species in most studied scenarios. Taken together, the results of the study suggest that biological control provides the greatest benefits to native flora, even though chemical control resulted in fewer secondary invasions.

There is no silver bullet for the control of invasive alien plants. The best control results are often obtained through a combination of methods and over a long period of time. Both methods tested in the study, biological control and chemical control, were effective for reducing the invasion of common heather, but were not very effective in avoiding further invasion by other non-native species or in the recovery of native biodiversity. The inclusion of active restoration efforts along with the control of the invasive plants could help achieve both reduction in invasions and increase in native biodiversity. Managers may need to go beyond invasive species control if they want to recover native biodiversity and ecosystem services.

The full Editor’s Choice article, ‘Comparing biocontrol and herbicide for managing an invasive non‐native plant species: Efficacy, non‐target effects and secondary invasion‘ is free to read for a limited time in Journal of Applied Ecology.

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