Waging war on weeds
New Zealand is one of the world’s weediest countries and will only get worse as climate change helps more plants jump the garden fence and colonise the world beyond.
Warming temperatures across New Zealand will help invasive plants flourish in what is already one of the world’s weediest countries.
Lincoln University Professor Philip Hulme says climate change will help more plants to jump the garden fence and colonise the world beyond.
Hulme, of Lincoln’s Bio-Protection Research Centre, was awarded the Hutton Medal by the Royal Society Te Apa¯ rangi at the annual Research Honours Aotearoa dinner, held in Dunedin last night.
The award was for his work on plant invasions, especially why and how exotic plants become invasive weeds.
Hulme told The Press weeds were not just plants growing where they were not wanted, and the problem was only going to worsen due to climate change.
‘‘Weeds are pernicious, persistent and have an ongoing negative impact.
‘‘We have quite a few succulent species which are good in drought conditions but quite restricted at the moment as they can’t deal with frost. But with drier conditions, they will take-off big time.’’
Areas like the Port Hills would be especially susceptible to invasion from these aeonium species, he said.
Although billions of dollars were spent managing pest plants annually, they remained one of New Zealand’s biggest and most difficult environmental issues, and were often resistant to herbicides.
Control efforts could exacerbate the problem by disturbing the soil and spreading seeds and roots. These plants smothered and replaced native flora, affected soil stability and composition and also groundwater, and could heighten fire risk.
The worst weed beyond the garden depended on the ecosystem where you lived, with thistles among the worst for pastoral farmers, Hulme said.
‘‘Old man’s beard and blackberry are problems throughout much of the country and colonise bush fragments where they can swamp the vegetation.
‘‘In the north, kahili ginger and tradescantia are big problems in forest, whereas Darwin’s barberry is a problem in forest in the South Island.
‘‘Open grasslands across the country are beset by species such as broom and gorse. In the South Island high country, wilding pines and lupins are big problems.’’
Lagarosiphon was also a national problem in lakes and rivers, Hulme said, and the worst garden weeds included creeping oxalis, onion weed, periwinkle and ivy.
According to the Royal Society citation, Hulme’s work has focused on how botanic gardens, ornamental nurseries and the pastoral sector have helped plant invasions.
He said it was only a matter of time before more exotic garden plants became escapees and a problem.
Concern about noxious plants was not a recent thing.
‘‘We had noxious-weed lists as early as 1850. Thistles were way up there on that and gorse was recognised quite early on.’’
Australia’s national approach to weed eradication, with a weeds of national significance programme, had been a better approach than New Zealand’s focus on regional control work.
Invasive plants were no respecters of land borders, Hulme said.
‘‘That means they can set major targets across the whole of Australia.’’
Here, regional councils, the Department of Conservation, community groups and private landowners were all dealing with similar issues.
‘‘Much of the work across these organisations is unco-ordinated and too shortterm to have any lasting impact.’’