Invasive alien plants pose major threat to farmland biodiversity
August 03 2021 02:30 AM
Great care must be exercised when setting land parcels aside for biodiversity under the next CAP due to the risks posed by invasive alien species, a field expert has warned.
More than 100 invasive alien species now scourge hedges, waterways, uplands, roadways and some grasslands nationwide, outcompeting all native vegetation in their wake and making soil more vulnerable to erosion.
These species were introduced to Ireland from abroad centuries ago, often for decorative garden purposes.
At EU level, plants like Japanese knotweed, Giant hogweed, Himalayan balsam, Old man’s beard and Rhododendron are seen as “key drivers” of ecosystem collapse and targets have now been set to reverse this decline via CAP reform.
However, Dr William Earle, a dairy farmer and leading invasive alien species specialist with INVAS Biosecurity, urges caution on such action.
“With CAP reform, there is huge opportunity to help with biodiversity on farms, but there is also a possibility that farms might open themselves up to exposure of invasive alien species by putting biodiversity areas aside,” he said. “This could lead to an opportunity for invaders to establish in these new niches, accidentally creating invasive alien species reservoirs.
“Often, it’s best to let native species regenerate naturally because they’ve evolved in an area over time. If different seeds are brought in, it raises the risk of introducing invasive species, particularly if close to a pathway, river or road.”
Dr Earle, who will carry out research on the issue with leading Irish institutions, said farms with watercourses are “particularly vulnerable” to invasion.
“Often it’s accidental introduction — many species travel down rivers and along corridors. Since the development of big machinery, there are huge problems with Japanese knotweed being dug up and moved, fragments the size of a thumbnail will grow again. In summer, it becomes so dominant it kills off all native vegetation, leaving nothing but bare exposed soil behind in winter.”
Giant hogweed generates about 70,000 seeds and harbours “a highly-toxic sap”. “If it gets onto your skin and is exposed to UV light, it creates huge blisters and skin damage can recur. It spreads rapidly on watercourses or in flooding.
“It’s very important that farmers seek advice on how to treat or kill each species, especially near watercourses — it’s not like dealing with general weeds. You must isolate the problem, manage it and make that land usable again. If it’s not dealt with, it will only get worse,” he said.
Teagasc Countryside Management Specialist, Catherine Keena, has seen whole fields “almost covered” in white bindweed and Himalayan balsam taking over rivers and swamps in Special Areas of Conservation (SACs).
“The rivers are really bad — it is serious,” Ms Keena said. Old man’s beard is taking over hedges; on the upland farms, rhododendron and giant rhubarb are a big problem.
“My attitude to a biodiversity plan is before planting a hedge, a margin or bird cover, if you see an invasive alien species, the most important thing is to deal with it. It’s very wrong to spend money doing a hedge, while letting something else run riot.”
Colette O’Flynn of the National Biodiversity Data Centre said there is a yearly increase in the number of invasive alien species sightings. She urged farmers “not to cut, mow, strim or disturb” these plants.
Global Plant Protection News 
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