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Biocontrol leads to better ecosystem outcomes than herbicide: A 5-year trial on managing heather

Our 5-year study near Tongariro national Park shows that biocontrol of heather produces overall better ecosystem outcomes compared to herbicide control.

Biocontrol and herbicide were both highly effective at reducing cover by heather, Cullana vulgaris. The heather beetle, Lochmaea suturalis, reduced heather cover by 97%, and herbicide reduced it by 87%. In comparison, heather cover increased by 20% in the absence of any management.

However, the key difference between these two management strategies was revealed when we untangled the complexities of ecosystem response to the removal of heather. Monocots, both indigenous and exotic, increased in both biocontrol and herbicide-treated plots. Yet, dicots responded differently depending on the control method: the non-selective herbicide severely damaged all other dicots, indigenous and exotic alike. Conversely, the species-rich indigenous dicots were the group that benefitted the most following biocontrol. Exotic dicots too increased, thereby leading to some secondary invasion.

Herbicides are widely used for the control of non-native, invasive plants in natural ecosystems despite the risk they pose to non-target biota. However, there is mounting social pressure to use alternative, ‘greener’ approaches to pest management, particularly in New Zealand. Weed biocontrol poses a very low-risk of significant non-target damage and is self-sustaining, making it a safe, cost-effective, long-term management tool. Now we have clearly demonstrated that land managers should prioritise biocontrol over herbicide as a management strategy to optimize ecosystem outcomes.

Further reading

Peterson, PG, Merrett MF, Fowler SV, Barrett DP, Paynter Q. 2020. Comparing biocontrol and herbicide for managing an invasive and non-native plant species: efficacy, non-target effects and secondary invasion. DOI:10.111/1365-2664.13691

Editor’s Choice blog post: https://appliedecologistsblog.com/2020/10/01/editors-choice-5710/

Ngāuruhoe and Tongariro landscape, 2000

Ngāuruhoe and Tongariro landscape, 2000

Ngāuruhoe and Tongariro landscape, 2018, showing a great reduction in heather

Ngāuruhoe and Tongariro landscape, 2018, showing a great reduction in heather