Saturday, December 9, 2023

Climate change sharpens weed and pest threat

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But report also highlights opportunities for a food-producing nation as crop conditions alter.
AgResearch senior scientist Dr Trevor James says with or without climate change, weeds have proven themselves to be highly adaptable when it comes to spreading beyond their usual habitats.
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At the forefront of the global megatrends coming to bear on New Zealand’s food-producing future is climate change as it starts to impact how and where crops and proteins can be grown.

A report by the Better Border Biosecurity (B3) sector group, which consists of the best minds in border protection and invasive species, also underscores how weeds and diseases are likely to spread further, accompanied by new “alien” pests and diseases enabled by the changing climate. 

But the report also highlights the upside of climate change and how it may enable viable new crops, including sorghum, peanuts and chickpeas. 

Dairying and forestry are tapped to do better under climate change’s impact, while beef and sheep are less favoured.

The study aims to better understand and inform the primary sector on how it can handle the changes, both to prepare for them and to take advantage of the opportunities they may present for a food-producing country at the edge of the South Pacific.

“Biological invasions are already a big concern for NZ with its unique insular ecosystems and being home to one of the highest proportions of threatened indigenous species in the world. Our economy is also very dependent upon our primary sector,” project leader Dr Nicolas Meurisse said.

Climate change is by far the biggest megatrend identified by the report’s authors, with changes in trade routes, international conflict and extreme weather all ultimately leading back to the predictable rising of CO2 levels.

The context of climate change in NZ has lowered rainfall across Northland and the eastern regions of both islands, with production declining in those regions. In contrast, western areas are set to benefit from lower frosts and more water availability.  

The report’s authors project that, based on existing emissions pricing, dairying could increase 9.6% by 2050 while sheep and beef decline by 13% and horticulture remains relatively unchanged. 

However, the authors qualify this, citing market conditions and irrigation that will have a significant effect on actual outcomes.

The report notes that the incidence of non-native species living beyond their native ranges has substantially increased in recent decades, with little sign of slowing, while agriculture and ornamental plant industries have pushed expansion faster.

The hundreds of non-native pest species already in NZ are also only like to increase further over coming decades, and there is a need to understand which are likely to arrive, establish and become harmful.

“Natural environments, such as native forests, may be especially vulnerable to invading biosecurity threats. These could be adversely impacted by the combined effects of biological invasions, climate warming and other human-related pressures,” Meurisse said. 

Dr Trevor James, NZ’s leading weed expert, said while he had not yet read the report, he has mixed feelings about how much climate change contributes to the spread of invasive species, and how much is from weeds’ adaptive ability to move beyond their usual habitat.

“When I think about kikuyu grass, no one thought it would ever move beyond Northland, where it was introduced, but it has got down to Waikato despite there being quite strong frosts, and I have personally seen it in the top of the South Island.”

Far from being a climate change denier, James said invasive species often have a habit of turning up in areas where they are least expected. 

He cited work on the dock weed from Europe and comparisons to where it grows in NZ.

“When they mapped its home zones in Europe, then compared to NZ, they found it did not really match up, it was growing here in areas that were not in its home zone. Sometimes some real curve balls are thrown up by weed species. NZ is a land with many microclimates.”

He suspects insects may be more likely to respond directly to climate change, such as increased levels of black beetle in areas that have warmed over the years.

He believes the greatest future weed threat to NZ is from plants that are already here.

There was a reserve of 25,000-35,000 plants in NZ not yet established outside gardens. 

But James said many experts are anticipating this reservoir of plants will likely be the source for NZ’s next surge in invasive species.

“They could be triggered by climate change, or even a slight change in conditions. We have a programme underway to assess which of these thousands of plants pose the greatest risk.”

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